Phased array antenna

Abstract

Provided is a phased array antenna which can be used in the millimeter wave band and whose cost is lower than that of a conventional phased array antenna. The phased array antenna (1) includes: an optical modulator (OM) configured to generate a signal light beam SL by carrying out intensity modulation on a carrier light beam CL by use of a sum signal V.sub.IF+LO(t), the sum signal V.sub.IF+LO(t) being obtained by adding an intermediate frequency signal V.sub.IF(t) and a local signal V.sub.LO(t); and a time delay device (TD) configured to generate delayed signal light beams SL′1, SL′2, . . . and SL′n by imparting time delays Δt1, Δt2, . . . and Δtn to the signal light beam SL. Each feeding circuit (Fi) generates, from a corresponding delayed signal light beam SL′i, a delayed radio frequency signal V.sub.RF(t−Δti) to be supplied to an antenna element (Ai).

Claims

1. A phased array antenna comprising: n (n is an integer of 2 or more) antenna elements A1, A2, . . . and An; a multiplexer configured to generate a sum signal V.sub.IF+LO(t) by adding an intermediate frequency signal V.sub.IF(t) and a local signal V.sub.LO(t): an optical modulator configured to generate a signal light beam SL by carrying out intensity modulation on a carrier light beam CL by use of the sum signal V.sub.IF+LO(t); a time delay device configured to generate delayed signal light beams SL′1, SL′2, . . . and SL′n by imparting time delays Δt1, Δt2, . . . and Δtn to the signal light beam SL; and a feeding circuit group constituted by feeding circuits, each of which is a feeding circuit Fi configured to convert a corresponding delayed signal light beam SL′i into a delayed radio frequency signal V.sub.RF(t−Δti) to be supplied to a corresponding antenna element Ai, each feeding circuit Fi (i=1, 2, . . . n) including: an O/E converter configured to generate a delayed sum signal V.sub.IF+LO(t−Δti) by carrying out O/E conversion on the corresponding delayed signal light beam SL′i; a demultiplexer configured to generate a delayed intermediate frequency signal V.sub.IF(t−Δti) and a delayed local signal V.sub.LO(t−Δti) by demultiplexing the delayed sum signal V.sub.IF+LO(t−Δti); and a mixer configured to generate the delayed radio frequency signal V.sub.RF(t−Δti) by multiplying the delayed intermediate frequency signal V.sub.IF(t−Δti) by the delayed local signal V.sub.LO(t−Δti), wherein each feeding circuit Fi further includes: a mixer configured to generate an intermediate frequency signal V.sub.IF′(t+Δti) by multiplying (a) a radio frequency signal V.sub.RF′(t+Δti) which has been received by use of the corresponding antenna element Ai by (b) the delayed local signal V.sub.LO(t−Δti); a multiplexer configured to generate a sum signal V.sub.IF+LO′(t+Δti) by adding the intermediate frequency signal V.sub.IF′(t+Δti) and the delayed local signal V.sub.LO(t−Δti); an optical modulator configured to generate a signal light beam RSLi by carrying out intensity modulation by use of the sum signal V.sub.IF+LO′(t+Δti); an O/E converter configured to generate a delayed sum signal V.sub.IF+LO′(t) by carrying out O/E conversion on a delayed signal light beam RSL′i, the delayed signal light beam RSL′i being obtained by the time delay device imparting a time delay to the signal light beam RSLi; a demultiplexer configured to generate a delayed intermediate frequency signal V.sub.IF′(t) and a local signal V.sub.LO′(t) by demultiplexing the delayed sum signal V.sub.IF+LO′(t); and a mixer configured to generate a delayed radio frequency signal V.sub.RF′(t) by multiplying the delayed intermediate frequency signal V.sub.IF′(t) by the local signal V.sub.LO′(t).

2. The phased array antenna according to claim 1, further comprising: a light source group constituted by light sources each of which generates a carrier light beam CLi such that each of carrier light beams CL1, CL2, . . . and CLn generated by respective ones of the light sources has a differing wavelength; and a multiplexer configured to generate the carrier light beam CL by multiplexing the carrier light beams CL1, CL2, . . . and CLn; wherein the time delay device includes: an optical waveguide configured to generate a delayed signal light beam SL′ by causing chromatic dispersion of the signal light beam SL; and a wavelength demultiplexer configured to generate the delayed signal light beams SL′1, SL′2, . . . and SL′n by carrying out wavelength demultiplexing on the delayed signal light beam SL′.

3. The phased array antenna according to claim 2, wherein each of the light sources is configured to allow for variation of a wavelength of the carrier light beam CLi generated thereby.

4. The phased array antenna according to claim 2, wherein the optical waveguide is configured to allow for variation of the chromatic dispersion caused to the signal light beam SL.

5. The phased array antenna according to claim 1, further including a light source configured to generate the carrier light beam CL, wherein the time delay device includes: an optical splitter configured to generate signal light beams SL1, SL2, . . . and SLn by splitting the signal light beam SL; and an optical waveguide group constituted by optical waveguides, each optical waveguide being configured to generate a delayed signal light beam SL′i by imparting a time delay Δti to a corresponding signal light beam SLi such that each of time delays Δt1, Δt2, . . . and Δtn imparted by respective ones of the optical waveguides is of a differing length.

6. The phased array antenna according to claim 5, wherein: the light source is configured to allow for variation of a wavelength of the carrier light beam CL generated thereby; and each of the optical waveguides is configured to cause differing chromatic dispersion.

7. The phased array antenna according to claim 5, wherein each of the optical waveguides has a variable optical path length.

8. The phased array antenna according to claim 1, wherein: instead of including the mixer configured to generate the delayed radio frequency signal V.sub.RF(t−Δti) by multiplying the delayed intermediate frequency signal V.sub.IF(t−Δti) by the delayed local signal V.sub.LO(t−Δti), each feeding circuit Fi includes: a multiplier configured to generate a delayed local signal V.sub.LOM(t−Δti) by multiplying a frequency of the delayed local signal V.sub.LO(t−Δti); and a mixer configured to generate the delayed radio frequency signal V.sub.RF(t−Δt) by multiplying the delayed intermediate frequency signal V.sub.IF(t−Δti) by the delayed local signal V.sub.LOM(t−Δti).

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a block diagram illustrating a configuration of a phased array antenna in accordance with Embodiment 1 of the present invention.

(2) FIG. 2 is a block diagram illustrating Specific Example 1 of the phased array antenna illustrated in FIG. 1.

(3) FIG. 3 is a block diagram illustrating Specific Example 2 of the phased array antenna illustrated in FIG. 1.

(4) FIG. 4 is a block diagram illustrating a variation of the phased array antenna illustrated in FIG. 1.

(5) FIG. 5 is a block diagram illustrating a configuration of a phased array antenna in accordance with Embodiment 2 of the present invention.

(6) FIG. 6 is a block diagram illustrating Specific Example 1 of the phased array antenna illustrated in FIG. 5.

(7) FIG. 7 is a block diagram illustrating Specific Example 2 of the phased array antenna illustrated in FIG. 5.

(8) FIG. 8 is a block diagram illustrating a variation of the phased array antenna illustrated in FIG. 5.

(9) FIG. 9 is a block diagram illustrating another variation of the phased array antenna illustrated in FIG. 1.

(10) FIG. 10 is a block diagram illustrating another variation of the phased array antenna illustrated in FIG. 5.

(11) FIG. 11 is a block diagram illustrating a configuration of a conventional phased array antenna.

(12) FIG. 12 is a block diagram illustrating a configuration of a conventional phased array antenna.

(13) FIG. 13 is a block diagram illustrating a configuration of a conventional phased array antenna.

(14) FIG. 14 is a block diagram illustrating a configuration of a phased array antenna in accordance with another aspect of Embodiment 1 of the present invention.

(15) FIG. 15 is a block diagram illustrating a configuration of a phased array antenna in accordance with another aspect of Embodiment 2 of the present invention.

DESCRIPTION OF EMBODIMENTS

Embodiment 1

(16) (Configuration of Phased Array Antenna)

(17) The following description will discuss, with reference to FIG. 1, a phased array antenna 1 in accordance with Embodiment 1 of the present invention. FIG. 1 is a block diagram illustrating a configuration of the phased array antenna 1.

(18) As illustrated in FIG. 1, the phased array antenna 1 is a transmitting antenna which includes: a multiplexer MP; an optical modulator OM; a time delay device TD; a feeding circuit group constituted by n feeding circuits F1, F2, . . . and Fn; and an antenna element group constituted by n antenna elements A1, A2, . . . and An. Note here that n represents any integer not less than 2; FIG. 1 illustrates a configuration where n=4.

(19) The multiplexer MP adds an intermediate frequency signal V.sub.IF(t) and a local signal V.sub.LO(t) so as to generate a sum signal V.sub.IF+LO(t) which equals V.sub.IF(t)+V.sub.LO(t). In a case where the intermediate frequency signal V.sub.IF(t) and the local signal V.sub.LO(t) are expressed as shown in Formula (1) and Formula (2), the sum signal V.sub.IF+LO(t) is expressed as shown in Formula (3). The sum signal V.sub.IF+LO(t) generated by the multiplexer MP is supplied to the optical modulator OM as a data signal.

(20) [Math. 1]
V.sub.IF(t)=V.sub.1 cos(2πf.sub.IF(t+θ.sub.IF))  (1)

(21) [Math. 2]
V.sub.LO(t)=V.sub.0 cos(2πf.sub.LO(t+θ.sub.LO))  (2)

(22) [Math. 3]
V.sub.IF+LO(t)=V.sub.1 cos(2πf.sub.IF(t+θ.sub.IF))+V.sub.0 cos(2πf.sub.LO(t+θ.sub.LO))  (3)

(23) The optical modulator OM generates a signal light beam SL by carrying out intensity modulation on a carrier light beam CL by use of the sum signal V.sub.IF+LO(t). The signal light beam SL generated by the optical modulator OM is supplied to the time delay device TD. In Embodiment 1, a Mach-Zehnder (MZ) modulator is used as the optical modulator OM. A configuration of a light source which generates the carrier light beam CL will be discussed later with reference to another drawing.

(24) The time delay device TD generates delayed signal light beams SL′1, SL′2, . . . and SL′n by imparting time delays Δt1, Δt2, . . . and Δtn to the signal light beam SL. In other words, the time delay device TD generates delayed signal light beams from the signal light beam SL having the sum signal V.sub.IF+LO(t) superimposed thereon. Each of the delayed signal light beams is a delayed signal light beam SL′i having a delayed sum signal V.sub.IF+LO(t−Δti) superimposed thereon. As described later, the time delay Δti imparted to each delayed signal light beam SL′i is set in accordance with the direction of a main beam of radiated electromagnetic waves. Each delayed signal light beam SL′i generated by the time delay device TD is supplied to a corresponding feeding circuit Fi. A configuration of the time delay device TD will be discussed later with reference to another drawing.

(25) Each feeding circuit Fi (i=1, 2, . . . n) converts the corresponding delayed signal light beam SL′i into a delayed radio frequency signal V.sub.RF(t−Δti). The delayed radio frequency signal V.sub.RF(t−Δti) generated by each feeding circuit Fi is supplied to a corresponding antenna element Ai.

(26) As illustrated in FIG. 1, each feeding circuit Fi includes an O/E converter OEi, a demultiplexer DPi, and a mixer MXi. Note that in FIG. 1, reference signs have been provided only for the O/E converter OE1, the demultiplexer DPI, and the mixer MX1 of feeding circuit F1 because each feeding circuit Fi is configurationally identical.

(27) The O/E converter OEi generates a delayed sum signal V.sub.IF+LO(t−Δti) by carrying out O/E conversion (photoelectric conversion) on the delayed signal light beam SL′i. The O/E converter OEi can be, for example, a photodiode. In a case where the sum signal V.sub.IF+LO(t) is expressed as in Formula (3), the delayed sum signal V.sub.IF+LO(t−Δti) is expressed as shown in Formula (4).

(28) [Math. 4]
V.sub.IF+LO(t−Δti)=V.sub.1 cos(2πf.sub.IF(t−Δti+θ.sub.IF))+V.sub.0 cos(2πf.sub.LO(t−Δti+θ.sub.LO))  (4)

(29) The demultiplexer DPi generates a delayed intermediate frequency signal V.sub.IF(t−Δti) and a delayed local signal V.sub.LO(t−Δti) by demultiplexing the delayed sum signal V.sub.IF+LO(t−Δti). In a case where the delayed sum signal V.sub.IF+LO(t−Δti) is expressed as in Formula (4), the delayed intermediate frequency signal V.sub.IF(t−Δti) and the delayed local signal V.sub.LO(t−Δti) are expressed as shown in Formulas (5) and (6), respectively.

(30) [Math. 5]
V.sub.IF(t−Δti)=V.sub.1 cos(2πf.sub.IF(t−Δti+θ.sub.IF))  (5)

(31) [Math. 6]
V.sub.LO(t−Δti)=V.sub.0 cos(2πf.sub.LO(t−Δti+θ.sub.LOm))  (6)

(32) The mixer MXi generates a delayed radio frequency signal V.sub.RF(t−Δti) by multiplying the delayed intermediate frequency signal V.sub.IF(t−Δti) by the delayed local signal V.sub.LO(t−Δti). In a case where the delayed intermediate frequency signal V.sub.IF(t−Δti) and the delayed local signal V.sub.LO(t−Δti) are expressed as shown in Formula (5) and Formula (6), the delayed radio frequency signal V.sub.RF(t−Δti) is expressed as shown in Formula (7).

(33) $\begin{array}{cc}\left[\mathrm{Math}.7\right]& \\ V_{\mathrm{RF}}\left(t-\Delta \mathrm{ti}\right)=A\frac{V_0{V}_1}{2}\cos \left(2\pi \left(f_{\mathrm{LO}}+f_{\mathrm{IF}}\right)\left(t-\Delta \mathrm{ti}+\frac{f_{\mathrm{LO}}{\theta }_{\mathrm{LO}}+f_{\mathrm{IF}}{\theta }_{\mathrm{IF}}}{f_{\mathrm{LO}}+f_{\mathrm{IF}}}\right)\right)& \left(7\right)\end{array}$

(34) The time delay Δti in each delayed signal light beam SL′i can be set in a manner similar to that in a conventional phased array antenna. For example, in a case where the antenna elements A1, A2, . . . and An are arranged in this order along the same straight line, the time delay Δti in each delayed signal light beam SL′i can be set as shown in Formula (8), in accordance with the direction of the main beam of radiated electromagnetic waves. In Formula (8), c represents the speed of light, and di represents a distance between the antenna element A1 and an antenna element Ai. Furthermore, θ is an angle formed by (i) the straight line along which the antenna elements A1, A2, . . . and An are arranged and (ii) an equiphase plane of radiated electromagnetic waves.

(35) $\begin{array}{cc}\left[\mathrm{Math}.8\right]& \\ \Delta \mathrm{ti}=\mathrm{di}\frac{\sin \theta }{c}& \left(8\right)\end{array}$

(36) For example, in a case where an electromagnetic wave in the 60 GHz band (not less than 57 GHz and not more than 66 GHz) is radiated, a distance between adjacent ones of the antenna elements can, for example, be set to ½ of a free space wavelength corresponding to a center frequency of 61.5 GHz, that is, be set to 2.44 mm. In other words, the distance di between the antenna element A1 and the antenna element Ai can be set to 2.44×(i−1) mm. In this configuration, the time delay Δti in each delayed signal light beam SL′i can be set to 5.7×(i−1) ps in order to incline a radiation direction such that the angle θ becomes 45°, the angle θ being formed by (i) the straight line along which the antenna elements A1, A2, . . . and An are arranged and (ii) the equiphase plane of radiated electromagnetic waves.

(37) In a case where an electromagnetic wave in the 70 GHz band (not less than 71 GHz and not more than 76 GHz) is radiated, a distance between adjacent ones of the antenna elements can, for example, be set to ½ of a free space wavelength corresponding to a center frequency of 73.5 GHz, that is, be set to 2.04 mm. In other words, the distance di between the antenna element A1 and the antenna element Ai can be set to 2.04×(i−1) mm. In this configuration, the time delay Δti in each delayed signal light beam SL′i can be set to 4.8×(i−1) ps in order to incline a radiation direction such that the angle θ becomes 45°, the angle θ being formed by (i) the straight line along which the antenna elements A1, A2, . . . and An are arranged and (ii) the equiphase plane of radiated electromagnetic waves.

(38) A first noteworthy point of the phased array antenna 1 is that an amount of time delay in the delayed radio frequency signal V.sub.RF(t−Δti) inputted into each antenna element Ai is not dependent on frequency. As such, with the phased array antenna 1, even if the frequency of radiated electromagnetic waves is changed, the electromagnetic waves can be radiated in a constant direction, without a change in the time delays Δt1, Δt2, . . . and Δtn imparted to the signal light beam SL.

(39) A second noteworthy point of the phased array antenna 1 is that the data signal modulated by the optical modulator OM is the sum signal V.sub.IF+LO(t) obtained by adding the intermediate frequency signal V.sub.IF(t) and the local signal V.sub.LO(t). This sum signal V.sub.IF+LO(t) has a frequency which is lower than that of the radio frequency signal. This makes it possible to provide a phased array antenna employing an easily-obtainable and/or low cost optical modulator, even in a case where the phased array antenna 1 operates in the millimeter wave band (radio frequency in a range from 30 GHz to 300 GHz).

(40) In each feeding circuit Fi, it is also possible to provide, between the demultiplexer DPi and the mixer MXi, a multiplier which multiplies the frequency of the delayed local signal V.sub.LO(t−Δti) (for example, as illustrated in FIG. 14). In such a configuration, a delayed local signal V.sub.LOM(t−Δti) inputted into the mixer MXi is expressed by Formula (9), and the delayed radio frequency signal V.sub.RF(t−Δti) generated by the mixer MXi is expressed by Formula (10). In these formulas, k represents any integer not less than 2, and can be, for example, 2 or 3. Even with such a configuration, the amount of time delay in the delayed radio frequency signal V.sub.RF(t−Δti) is not dependent on frequency.

(41) [Math 9]
i V.sub.LOM(t−Δti)=V.sub.0 cos(2πf.sub.LO(t−Δti+θ.sub.LO)x k)  (9)

(42) $\begin{array}{cc}\left[\mathrm{Math}.10\right]& \\ V_{\mathrm{RF}}\left(t-\Delta \mathrm{ti}\right)=A\frac{V_0{V}_1}{2}\cos \left(2\pi \left({\mathrm{kf}}_{\mathrm{LO}}+f_{\mathrm{IF}}\right)\left(t-\Delta \mathrm{ti}+\frac{{\mathrm{kf}}_{\mathrm{LO}}{\theta }_{\mathrm{LO}}+f_{\mathrm{IF}}{\theta }_{\mathrm{IF}}}{{\mathrm{kf}}_{\mathrm{LO}}+f_{\mathrm{IF}}}\right)\right)& \left(10\right)\end{array}$

Specific Example 1 of Phased Array Antenna

(43) The following description will discuss, with reference to FIG. 2, Specific Example 1 of the phased array antenna 1. FIG. 2 is a block diagram illustrating a configuration of the phased array antenna 1 in accordance with Specific Example 1.

(44) The phased array antenna 1 in accordance with Specific Example 1 includes, as components for generating the carrier light beam CL, (i) a light source group constituted by n light sources LS1, LS2, . . . and LSn, and (ii) an optical multiplexer OMP.

(45) Each light source LSi (i=1, 2, . . . n) generates a carrier light beam CLi. Carrier light beams CL1, CL2, . . . and Cn generated by respective ones of the light sources LS1 through LSn have respective wavelengths λ1, λ2, . . . and λn which differ from each other. The carrier light beam CLi generated by each light source LSi is supplied to the optical multiplexer OMP. Note that in Specific Example 1, a semiconductor laser element is used as each light source LSi.

(46) The optical multiplexer OMP generates the carrier light beam CL by multiplexing the carrier light beams CL1, CL2, . . . and CLn. The carrier light beam CL includes, as its components, the carrier light beams CL1, CL2, . . . and CLn which have wavelengths λ1, λ2, . . . and λn, respectively. The carrier light beam CL generated by the optical multiplexer OMP is supplied to the optical modulator OM.

(47) The time delay device TD of the phased array antenna 1 in accordance with Specific Example 1 includes an optical waveguide OWG and a wavelength demultiplexer WDM.

(48) The optical waveguide OWG is constituted by a chromatic dispersion medium. The optical waveguide OWG generates a delayed signal light beam SL′ by causing chromatic dispersion (time delay dependent on wavelength λ) ΔD(λ) of the signal light beam SL. The signal light beam SL includes, as its components, the signal light beams SL1, SL2, . . . and SLn which have differing wavelengths. The delayed signal light beam SL′ includes, as its components, delayed signal light beams SL′1, SL′2, . . . and SL′n which have differing wavelengths and differing phases. The chromatic dispersion ΔD(λ) caused to the signal light beam SL is set to be an adequate amount so that the signal light beams SL′1, SL′2, . . . and SL′n are imparted with the time delays Δt1, Δt2, . . . and Δtn in accordance with the direction of the main beam of radiated electromagnetic waves. The delayed signal light beam SL′ generated by the optical waveguide OWG is supplied to the wavelength demultiplexer WDM. Note that in Specific Example 1, a single-mode fiber is used as the optical waveguide OWG.

(49) The wavelength demultiplexer WDM generates (extracts) the delayed signal light beams SL′1, SL′2, . . . and SL′n by carrying out wavelength demultiplexing on the delayed signal light beam SL′. Each delayed signal light beam SL′i generated by the wavelength demultiplexer WDM is supplied to a corresponding feeding circuit Fi.

(50) Note that any of the following configurations may be employed to achieve beam scanning in the phased array antenna 1 in accordance with Specific Example 1.

(51) <Configuration 1>

(52) In the phased array antenna 1 in accordance with Specific Example 1, the time delay Δti imparted to the delayed radio frequency signal V.sub.RF(t−Δti) can be changed by changing the wavelength λi of each corresponding carrier light beam CLi. This is because an optical waveguide constituted by a chromatic dispersion medium is used as the optical waveguide OWG.

(53) As such, it is possible to achieve beam scanning by employing a configuration in which (i) each light source LSi allows for variation of the wavelength λi of the carrier light beam CLi generated, and (ii) the wavelength λi of the carrier light beam CLi generated by each light source LSi is controlled in accordance with a desired main beam direction.

(54) <Configuration 2>

(55) Alternatively, in the phased array antenna 1 in accordance with Specific Example 1, the time delay Δti imparted to each delayed radio frequency signal V.sub.RF(t−Δti) can be changed by changing the chromatic dispersion ΔD(λ) caused to the signal light beam SL.

(56) As such, it is possible to achieve beam scanning by employing a configuration in which (i) the optical waveguide OWG allows for variation of the chromatic dispersion ΔD(λ) caused to the signal light beam SL, and (ii) the chromatic dispersion ΔD(λ) that the optical waveguide OWG causes to the signal light beam SL is controlled in accordance with a desired main beam direction.

(57) In order to achieve the phased array antenna 1 in which beam scanning in the 60 GHz band is possible, the phased array antenna 1 can be configured such that, for example, (i) the antenna elements A1, A2, . . . and An are arranged at intervals of 2.4 mm along the same straight line, (ii) the frequency fIF of the intermediate frequency signal V.sub.IF(t) is set to be not less than 22 GHz and not more than 31 GHz, and (iii) the frequency fLO of the local signal V.sub.LO(t) is set to be 35 GHz. In order to achieve a phased array antenna in which beam scanning in the 70 GHz band is possible, the phased array antenna 1 can be configured such that, for example, (i) the antenna elements A1, A2, . . . and An are arranged at intervals of 2.1 mm along the same straight line, (ii) the frequency fIF of the intermediate frequency signal V.sub.IF(t) is set to be not less than 31 GHz and not more than 36 GHz, and (iii) the frequency fLO of the local signal V.sub.LO(t) is set to be 40 GHz. This is because, in a case where the frequency of the data signal is less than or equal to 40 GHz, it is possible to employ, as the optical modulator OM, an MZ modulator which is widely commercially available at the time of the filing of the present application.

Specific Example 2 of Phased Array Antenna

(58) The following description will discuss, with reference to FIG. 3, Specific Example 2 of the phased array antenna 1. FIG. 3 is a block diagram illustrating a configuration of the phased array antenna 1 in accordance with Specific Example 2.

(59) The phased array antenna 1 in accordance with Specific Example 2 includes, as a component for generating the carrier light beam CL, a single light source LS.

(60) The light source LS generates the carrier light beam CL. The carrier light beam CL generated by the light source LS is supplied to the optical modulator OM. Note that in Specific Example 2, a semiconductor laser element is used as the light source LS.

(61) The time delay device TD of the phased array antenna 1 in accordance with Specific Example 2 includes an optical splitter OD and an optical waveguide group constituted by n optical waveguides OWGi. The optical waveguides OWG1, OWG2, . . . and OWGn are optical waveguides which cause differing chromatic dispersion or optical waveguides having variable optical path lengths. Possible examples of optical waveguides which cause differing chromatic dispersion include (i) a combination of single-mode fibers and dispersion compensating fibers and (ii) dispersion-shifted fibers.

(62) The optical splitter OD generates the signal light beams SL1, SL2, . . . and SLn by splitting the signal light beam SL. Each signal light beam SLi generated by the optical splitter OD is supplied to a corresponding optical waveguide OWGi.

(63) Each optical waveguide OWGi generates a delayed signal light beam SL′i by imparting a time delay Δti to a corresponding signal light beam SLi. The lengths of the time delays Δt1, Δt2, . . . and Δtn imparted by the optical waveguides OWG1, OWG2, . . . and OWGn are set in accordance with the direction of the main beam of radiated electromagnetic waves. The delayed signal light beam SL′i generated by each optical waveguide OWGi is supplied to a corresponding feeding circuit Fi. Note that in Specific Example 2, an optical fiber having an optical path length in accordance with the time delay Δti is used as each optical waveguide OWGi.

(64) Note that any of the following configurations may be employed to achieve beam scanning in the phased array antenna 1 in accordance with Specific Example 2.

(65) <Configuration 1>

(66) In a case where the optical waveguides OWG1, OWG2, . . . and OWGn are optical waveguides which cause differing chromatic dispersion (i.e., optical waveguides constituted by respective chromatic dispersion mediums having differing chromatic dispersion values), the time delay Δti imparted to each delayed radio frequency signal V.sub.RF(t−Δti) can be changed by changing the wavelength λ of the carrier light beam CL.

(67) In such a case, it is therefore possible to achieve beam scanning by employing a configuration in which (i) the light source LS allows for variation of the wavelength λ of the carrier light beam CL generated, and (ii) the wavelength λ of the carrier light beam CL generated by the light source LS is controlled in accordance with a desired main beam direction.

(68) <Configuration 2>

(69) In a case where the optical waveguides OWG1, OWG2, . . . and OWGn are optical waveguides having variable optical path lengths, it is possible to change the time delay Δti imparted to each delayed radio frequency signal V.sub.RF(t−Δti) by changing the optical path length of a corresponding optical waveguide OWGi.

(70) In such a case, it is therefore possible to achieve beam scanning by employing a configuration in which (i) each optical waveguide OWGi has a variable optical path length, and (ii) the optical path length of each optical waveguide OWGi is controlled in accordance with a desired main beam direction.

(71) (Variation of Phased Array Antenna)

(72) The following description will discuss, with reference to FIG. 4, a variation of the phased array antenna 1. FIG. 4 is a block diagram illustrating a configuration of the phased array antenna 1 in accordance with the present variation.

(73) The phased array antenna 1 in accordance with the present variation is a transmitting and receiving antenna which is obtained by adding components for reception to the phased array antenna 1 illustrated in the FIG. 1.

(74) As illustrated in FIG. 4, each feeding circuit Fi of the phased array antenna 1 in accordance with the present variation includes, as components for reception, a mixer RMX1i, a multiplexer RMPi, an optical modulator ROMi, an O/E converter ROEi, a demultiplexer RDPi, and a mixer RMX2i. Each feeding circuit Fi also includes a circulator C1i and a circulator C2i, which are components for enabling both transmitting and receiving. The phased array antenna 1 also includes a circulator C3 and a wavelength demultiplexer RWDM, which are components for enabling both transmitting and receiving.

(75) The mixer RMX1i generates an intermediate frequency signal V.sub.IF′(t+Δti) by multiplying a radio frequency signal V.sub.RF′(t+Δti) by the delayed local signal V.sub.LO(t−Δti). Here, the radio frequency signal V.sub.RF′(t+Δti) is a radio frequency signal which has been received by use of a corresponding antenna element Ai. Since the radio frequency signal V.sub.RF′(t) is expressed as shown in Formula (11), and the delayed local signal V.sub.LO(t−Δti) is expressed as shown in Formula (6), the intermediate frequency signal V.sub.IF′(t+Δti) is expressed as shown in Formula (12).

(76) $\begin{array}{cc}\left[\mathrm{Math}.11\right]& \\ V_{\mathrm{RF}}^{\prime }\left(t\right)=A\frac{V_0{V}_1}{2}\cos \left(2\pi \left(f_{\mathrm{LO}}+f_{\mathrm{IF}}\right)\left(t-\Delta \mathrm{ti}\right)\right)& \left(11\right)\\ \left[\mathrm{Math}.12\right]& \\ V_{\mathrm{IF}}^{\prime }\left(t+\Delta \mathrm{ti}\right)=A_1\frac{V_0{V}_1}{2}\cos \left(2\pi f_{\mathrm{IF}}\left(t+\Delta \mathrm{ti}\right)+2\pi f_{\mathrm{LO}}\left(2\Delta \mathrm{ti}-{\theta }_{\mathrm{LO}}\right)\right)& \left(12\right)\end{array}$

(77) The multiplexer RMPi generates a sum signal V.sub.IF+LO′(t+Δti) by adding the intermediate frequency signal V.sub.IF′(t+Δti) and the delayed local signal V.sub.LO(t−Δti). Since the intermediate frequency signal V.sub.IF′(t+Δti) is expressed as shown in Formula (12), and the delayed local signal V.sub.LO(t−Δti) is expressed as shown in Formula (6), the sum signal V.sub.IF+LO′(t+Δti) is expressed as shown in Formula (13).

(78) $\begin{array}{cc}\left[\mathrm{Math}.13\right]& \\ V_{\mathrm{IF}+\mathrm{LO}}^{\prime }\left(t+\Delta \mathrm{ti}\right)=A_1\frac{V_0{V}_2}{2}\cos \left(2\pi f_{\mathrm{IF}}\left(t+\Delta \mathrm{ti}\right)+2\pi f_{\mathrm{LO}}\left(2\Delta \mathrm{ti}-{\theta }_{\mathrm{LO}}\right)\right)+V_0\cos \left(2\pi f_{\mathrm{LO}}\left(t-\Delta \mathrm{ti}+{\theta }_{\mathrm{LO}}\right)\right)& \left(13\right)\end{array}$

(79) The optical modulator ROMi generates a signal light beam RSLi by carrying out intensity modulation on the carrier light beam CLi by use of the sum signal V.sub.IF+LO′(t+Δti). The signal light beam RSLi generated by the optical modulator ROMi is supplied to the time delay device TD. Note that in a case where the configuration of Specific Example 1 illustrated in FIG. 2 is employed, the carrier light beam CLi supplied to each optical modulator ROMi is the carrier light beam generated by a corresponding light source LSi. In a case where the configuration of Specific Example 2 illustrated in FIG. 3 is employed, the carrier light beam CLi supplied to each optical modulator ROMi is the carrier light beam generated by the single light source LS.

(80) The time delay device TD generates a delayed signal light beam RSL′ from signal light beams RSL1, RSL2, . . . and RSLn. In a case where the configuration of Specific Example 1 illustrated in FIG. 2 is employed, the time delay device TD is configured to (1) generate a signal light beam RSL by multiplexing the signal light beams RSL1, RSL2, . . . and RSLn and (2) generate the delayed signal light beam RSL′ by causing chromatic dispersion ΔD(λ) of the signal light beam RSL. In a case where the configuration of Specific Example 2 illustrated in FIG. 3 is employed, the time delay device TD is configured to (1) generate delayed signal light beams RSL′1, RSL′2, . . . and RSL′n by imparting the time delays Δt1, Δt2, . . . and Δtn to the signal light beams RSL1, RSL2, . . . and RSLn, respectively, and (2) generate the delayed signal light beam RSL′ by multiplexing the delayed signal light beams RSL′1, RSL′2, . . . and RSL′n. The delayed signal light beam RSL′ generated by the time delay device TD is supplied to the wavelength demultiplexer RWDM.

(81) The wavelength demultiplexer RWDM generates (extracts) the delayed signal light beams RSL′1, RSL′2, . . . and RSL′n by carrying out wavelength demultiplexing on the delayed signal light beam RLS′. Each delayed signal light beam RSL′i generated by the wavelength demultiplexer RWDM is provided to the O/E converter ROEi of a corresponding feeding circuit Fi.

(82) The O/E converter ROEi generates a delayed sum signal V.sub.IF+LO′(t) by carrying out O/E conversion on the delayed signal light beam RSL′i. Since the sum signal V.sub.IF+LO′(t+Δti) is expressed as shown in Formula (13), the delayed sum signal V.sub.IF+LO′(t) is expressed as shown in Formula (14).

(83) $\begin{array}{cc}\left[\mathrm{Math}.14\right]& \\ V_{{\mathrm{IF}}_{+}\mathrm{LO}}^{\prime }\left(t\right)=A_1\frac{V_0{V}_1}{2}\cos \left(2\pi f_{\mathrm{IF}}t+2\pi f_{\mathrm{LO}}\left(2\Delta \mathrm{ti}-{\theta }_{\mathrm{LO}}\right)\right)+V_0\cos \left(2\pi f_{\mathrm{LO}}\left(t-2\Delta \mathrm{ti}+{\theta }_{\mathrm{LO}}\right)\right)& \left(14\right)\end{array}$

(84) The demultiplexer RDPi generates a delayed intermediate frequency signal V.sub.IF′(t) and a local signal V.sub.LO′(t−2Δti) by demultiplexing the delayed sum signal V.sub.IF+LO′(t). Since the delayed sum signal V.sub.IF+LO′(t) is expressed as shown in Formula (14), the delayed intermediate frequency signal V.sub.IF′(t) and the local signal V.sub.LO′(t−2Δti) are expressed as shown in Formulas (15) and (16), respectively.

(85) $\begin{array}{cc}\left[\mathrm{Math}.15\right]& \\ V_{\mathrm{IF}}^{\prime }\left(t\right)=A_1\frac{V_0{V}_1}{2}\cos \left(2\pi f_{\mathrm{IF}}t+2\pi f_{\mathrm{LO}}\left(2\Delta \mathrm{ti}-{\theta }_{\mathrm{LO}}\right)\right)& \left(15\right)\\ \left[\mathrm{Math}.16\right]& \\ V_{\mathrm{LO}}^{\prime }\left(t-2\Delta \mathrm{ti}\right)=V_0\cos \left(2\pi f_{\mathrm{LO}}\left(t-2\Delta \mathrm{ti}+{\theta }_{\mathrm{LO}}\right)\right)& \left(16\right)\end{array}$

(86) The mixer RMX2i generates a delayed radio frequency signal V.sub.RF′(t) by multiplying the delayed intermediate frequency signal V.sub.IF′(t) by the local signal V.sub.LO′(t−2Δti). Since the delayed intermediate frequency signal V.sub.IF′(t) and the local signal V.sub.LO′(t−2Δti) are expressed as shown in Formulas (15) and (16), respectively, the delayed intermediate frequency signal V.sub.IF′(t) is expressed as shown in Formula (17). The delayed radio frequency signal V.sub.RF′(t) generated by the mixer RMX2i is supplied to the receiving circuit R after being multiplexed with delayed radio frequency signals V.sub.RF′(t) generated by other feeding circuits Fj.

(87) [Math. 17]
V.sub.RF′(t)=V.sub.0 cos(2πf.sub.RFt)  (17)

(88) The circulator C1i is provided between the mixer MXi and the antenna element Ai and is connected to the mixer RMX1i. The circulator C1i supplies, to the antenna element Ai, the delayed radio frequency signal V.sub.RF(t−Δti) outputted from the mixer MXi (operation during transmission). The circulator C1i also supplies, to the mixer RMX1i, the radio frequency signal V.sub.RF′(t+Δti) outputted from the antenna element Ai (operation during reception).

(89) The circulator C2i is provided between the time delay device TD and the O/E converter OEi and is connected to the optical modulator ROMi. The circulator C2i supplies, to the O/E converter OEi, the delayed signal light beam SL′i outputted from the time delay device TD (operation during transmission). The circulator C2i also supplies, to the time delay device TD, the signal light beam RSLi generated by the optical modulator ROMi (operation during reception).

(90) The circulator C3 is provided between the optical modulator OM and the time delay device TD and is connected to the wavelength demultiplexer RWDM. The circulator C3 supplies, to the time delay device TD, the signal light beam SL generated by the optical modulator OM (operation during transmission). The circulator C3 also supplies, to the wavelength demultiplexer RWDM, the delayed signal light beam RSL′ outputted from the time delay device TD (operation during reception).

Embodiment 21

(91) (Configuration of Phased Array Antenna)

(92) The following description will discuss, with reference to FIG. 5, a phased array antenna 2 in accordance with Embodiment 2 of the present invention. FIG. 5 is a block diagram illustrating a configuration of the phased array antenna 2.

(93) As illustrated in FIG. 1, the phased array antenna 2 is a transmitting antenna which includes: an optical modulator OM; a time delay device TD; a feeding circuit group constituted by n feeding circuits F1, F2, . . . and Fn; and an antenna element group constituted by n antenna elements A1, A2, . . . and An. Note here that n represents any integer not less than 2; FIG. 1 illustrates a configuration where n=4.

(94) The optical modulator OM generates a signal light beam SL by carrying out quadrature amplitude modulation on a carrier light beam CL by use of an intermediate frequency signal V.sub.IF(t) and a local signal V.sub.LO(t). The intermediate frequency signal V.sub.IF(t) and the local signal V.sub.LO(t) are, for example, expressed as shown in Formulas (18) and (19), respectively. The signal light beam SL generated by the optical modulator OM is supplied to the time delay device TD. In Embodiment 2, a dual-parallel Mach-Zehnder (DPMZ) modulator is used as the optical modulator OM. A configuration of a light source which generates the carrier light beam CL will be discussed later with reference to another drawing.

(95) [Math. 18]
V.sub.IF(t)=V.sub.1 cos(2πf.sub.RF(t+θ.sub.IF))  (18)

(96) [Math. 19]
V.sub.LO(t)=V.sub.0 cos(2πf.sub.LO(t+θ.sub.LO))  (19)

(97) The time delay device TD generates delayed signal light beams SL′1, SL′2, . . . and SL′n by imparting time delays Δt1, Δt2, . . . and Δtn to the signal light beam SL. In other words, the time delay device TD generates delayed signal light beams from the signal light beam SL, which has the intermediate frequency signal V.sub.IF(t) and the local signal V.sub.LO(t) superimposed thereon as an I signal and a Q signal, respectively. Each of the delayed signal light beams is a delayed signal light beam SL′i which has a delayed intermediate frequency signal V.sub.IF(t−Δti) and a delayed local signal V.sub.LO(t−Δti) superimposed thereon as an I signal and a Q signal, respectively. Similarly to in Embodiment 1, the time delay Δti imparted to each delayed signal light beam SL′i is set in accordance with the direction of a main beam of radiated electromagnetic waves. Each delayed signal light beam SL′i generated by the time delay device TD is supplied to a corresponding feeding circuit Fi. A configuration of the time delay device TD will be discussed later with reference to another drawing.

(98) Each feeding circuit Fi (i=1, 2, . . . n) converts the corresponding delayed signal light beam SL′i into a delayed radio frequency signal V.sub.RF(t−Δti). The delayed radio frequency signal V.sub.RF(t−Δti) generated by each feeding circuit Fi is supplied to a corresponding antenna element Ai.

(99) As illustrated in FIG. 5, each feeding circuit Fi includes an optical demodulator ODMi and a mixer MXi. Note that in FIG. 1, reference signs have been provided only for the optical demodulator ODML the mixer MX1 of feeding circuit F1 because each feeding circuit Fi is configurationally identical.

(100) The optical demodulator ODMi generates the delayed intermediate frequency signal V.sub.IF(t−Δti) and the delayed local signal V.sub.LO(t−Δti) by demodulating the corresponding delayed signal light beam SL′i. Since the intermediate frequency signal V.sub.IF(t) and the local signal V.sub.LO(t) are expressed as shown in Formulas (18) and (19), respectively, the delayed intermediate frequency signal V.sub.IF(t−Δti) and the delayed local signal V.sub.LO(t−Δti) are expressed as shown in Formulas (20) and (21), respectively. In Embodiment 2, a coherent receiver is used as the optical demodulator ODMi.

(101) [Math. 20]
V.sub.IF(t−Δti)=V.sub.1 cos(2πf.sub.IF(t−Δti+θ.sub.IF))  (20)

(102) [Math. 21]
V.sub.LO(t−Δti)=V.sub.0 cos(2πf.sub.LO(t−Δi+θ.sub.LO))  (21)

(103) The mixer MXi generates the delayed radio frequency signal V.sub.RF(t−Δti) by multiplying the delayed intermediate frequency signal V.sub.IF(t−Δti) by the delayed local signal V.sub.LO(t−Δti). In a case where the delayed intermediate frequency signal V.sub.IF(t−Δti) and the delayed local signal V.sub.LO(t−Δti) are expressed as shown in Formula (20) and Formula (21), the delayed radio frequency signal V.sub.RF(t−Δti) is expressed as shown in Formula (22).

(104) $\begin{array}{cc}\left[\mathrm{Math}.22\right]& \\ V_{\mathrm{RF}}\left(t-\Delta \mathrm{ti}\right)=A\frac{V_0{V}_1}{2}\cos \left(2\pi \left(f_{\mathrm{LO}}+f_{\mathrm{IF}}\right)\left(t-\Delta \mathrm{ti}+\frac{f_{\mathrm{LO}}{\theta }_{\mathrm{LO}}+f_{\mathrm{IF}}{\theta }_{\mathrm{IF}}}{f_{\mathrm{LO}}+f_{\mathrm{IF}}}\right)\right)& \left(22\right)\end{array}$

(105) A first noteworthy point of the phased array antenna 2 is that an amount of time delay in the delayed radio frequency signal V.sub.RF(t−Δti) inputted into each antenna element Ai is not dependent on frequency. As such, with the phased array antenna 2, even if the frequency of radiated electromagnetic waves is changed, the electromagnetic waves can be radiated in a constant direction, without a change in the time delays Δt1, Δt2, . . . and Δtn imparted to the signal light beam SL.

(106) A second noteworthy point of the phased array antenna 2 is that the data signals modulated by the optical modulator OM are the intermediate frequency signal V.sub.IF(t) and the local signal V.sub.LO(t), each of which has a frequency lower than that of the radio frequency signal. This makes it possible to provide a phased array antenna employing an easily-obtainable and/or low cost optical modulator, even in a case where the phased array antenna 2 operates in the millimeter wave band (radio frequency in a range from 30 GHz to 300 GHz).

(107) In each feeding circuit Fi, it is also possible to provide, between a demultiplexer DPi and the mixer MXi, a multiplier which multiplies the frequency of the delayed local signal V.sub.LO(t−Δti) (for example, as illustrated in FIG. 15). In such a configuration, a delayed local signal V.sub.LOM(t−Δti) inputted into the mixer MXi is expressed by Formula (23), and the delayed radio frequency signal V.sub.RF(t−Δti) generated by the mixer MXi is expressed by Formula (24). In these formulas, k represents any integer not less than 2, and can be, for example, 2 or 3. Even with such a configuration, the amount of time delay in the delayed radio frequency signal V.sub.RF(t−Δti) is not dependent on frequency.

(108) [Math. 23]
V.sub.LOM(t−Δti)=V.sub.0 cos(2πf.sub.LO(t−Δti+θ.sub.LO)x k)  (23)

(109) $\begin{array}{cc}\left[\mathrm{Math}.24\right]& \\ V_{\mathrm{RF}}\left(t-\Delta \mathrm{ti}\right)=A\frac{V_0{V}_1}{2}\cos \left(2\pi \left(k{f}_{\mathrm{LO}}+f_{\mathrm{IF}}\right)\left(t-\Delta \mathrm{ti}+\frac{{\mathrm{kf}}_{\mathrm{LO}}{\theta }_{\mathrm{LO}}+f_{\mathrm{IF}}{\theta }_{\mathrm{IF}}}{{\mathrm{kf}}_{\mathrm{LO}}+f_{\mathrm{IF}}}\right)\right)& \left(24\right)\end{array}$

Specific Example 1 of Phased Array Antenna 2

(110) The following description will discuss, with reference to FIG. 6, Specific Example 1 of the phased array antenna 2. FIG. 6 is a block diagram illustrating a configuration of the phased array antenna 2 in accordance with Specific Example 1.

(111) The phased array antenna 2 in accordance with Specific Example 1 includes, as components for generating the carrier light beam CL, (i) a light source group constituted by n light sources LS1, LS2, . . . and LSn, and (ii) an optical multiplexer OMP.

(112) Each light source LSi (i=1, 2, . . . n) generates a carrier light beam CLi. Carrier light beams CL1, CL2, . . . and Cn generated by respective ones of the light sources LS1 through LSn have respective wavelengths λ1, λ2, . . . and λn which differ from each other. The carrier light beam CLi generated by each light source LSi is supplied to the optical multiplexer OMP. Note that in Specific Example 1, a semiconductor laser element is used as each light source LSi.

(113) The optical multiplexer OMP generates the carrier light beam CL by multiplexing the carrier light beams CL1, CL2, . . . and CLn. The carrier light beam CL includes, as its components, the carrier light beams CL1, CL2, . . . and CLn which have wavelengths λ1, λ2, . . . and λn, respectively. The carrier light beam CL generated by the optical multiplexer OMP is supplied to the optical modulator OM.

(114) The time delay device TD of the phased array antenna 2 in accordance with Specific Example 1 includes an optical waveguide OWG and a wavelength demultiplexer WDM.

(115) The optical waveguide OWG is constituted by a chromatic dispersion medium. The optical waveguide OWG generates a delayed signal light beam SL′ by causing chromatic dispersion (time delay dependent on wavelength λ) ΔD(λ) of the signal light beam SL. The signal light beam SL includes, as its components, the signal light beams SL1, SL2, . . . and SLn which have differing wavelengths. The delayed signal light beam SL′ includes, as its components, delayed signal light beams SL′1, SL′2, . . . and SL′n which have differing wavelengths and differing phases. The chromatic dispersion ΔD(λ) caused to the signal light beam SL is set to be an adequate amount so that the signal light beams SL′1, SL′2, . . . and SL′n are imparted with the time delays Δt1, Δt2, . . . and Δtn in accordance with the direction of the main beam of radiated electromagnetic waves. The delayed signal light beam SL′ generated by the optical waveguide OWG is supplied to the wavelength demultiplexer WDM. Note that in Specific Example 1, a single-mode fiber is used as the optical waveguide OWG.

(116) The wavelength demultiplexer WDM generates (extracts) the delayed signal light beams SL′1, SL′2, . . . and SL′n by carrying out wavelength demultiplexing on the delayed signal light beam SL′. Each delayed signal light beam SL′i generated by the wavelength demultiplexer WDM is supplied to a corresponding feeding circuit Fi.

(117) Note that any of the following configurations may be employed to achieve beam scanning in the phased array antenna 2 in accordance with Specific Example 1.

(118) <Configuration 1>

(119) In the phased array antenna 2 in accordance with Specific Example 1, the time delay Δt imparted to the delayed radio frequency signal V.sub.RF(t−Δti) can be changed by changing the wavelength λi of each corresponding carrier light beam CLi. This is because an optical waveguide constituted by a chromatic dispersion medium is used as the optical waveguide OWG.

(120) As such, it is possible to achieve beam scanning by employing a configuration in which (i) each light source LSi allows for variation of the wavelength λi of the carrier light beam CLi generated, and (ii) the wavelength λi of the carrier light beam CLi generated by each light source LSi is controlled in accordance with a desired main beam direction.

(121) <Configuration 2>

(122) Alternatively, in the phased array antenna 2 in accordance with Specific Example 1, the time delay Δti imparted to each delayed radio frequency signal V.sub.RF(t−Δti) can be changed by changing the chromatic dispersion ΔD(λ) caused to the signal light beam SL.

(123) As such, it is possible to achieve beam scanning by employing a configuration in which (i) the optical waveguide OWG allows for variation of the chromatic dispersion ΔD(λ) caused to the signal light beam SL, and (ii) the chromatic dispersion ΔD(λ) that the optical waveguide OWG causes to the signal light beam SL is controlled in accordance with a desired main beam direction.

Specific Example 2 of Phased Array Antenna 2

(124) The following description will discuss, with reference to FIG. 7, Specific Example 2 of the phased array antenna 2. FIG. 7 is a block diagram illustrating a configuration of the phased array antenna 2 in accordance with Specific Example 2.

(125) The phased array antenna 2 in accordance with Specific Example 2 includes, as a component for generating the carrier light beam CL, a single light source LS.

(126) The light source LS generates the carrier light beam CL. The carrier light beam CL generated by the light source LS is supplied to the optical modulator OM. Note that in Specific Example 2, a semiconductor laser element is used as the light source LS.

(127) The time delay device TD of the phased array antenna 2 in accordance with Specific Example 2 includes an optical splitter OD and an optical waveguide group constituted by n optical waveguides OWGi. The optical waveguides OWG1, OWG2, . . . and OWGn are optical waveguides which cause differing chromatic dispersion or optical waveguides having variable optical path lengths. Possible examples of optical waveguides which cause differing chromatic dispersion include (i) a combination of single-mode fibers and dispersion compensating fibers and (ii) dispersion-shifted fibers.

(128) The optical splitter OD generates the signal light beams SL1, SL2, . . . and SLn by splitting the signal light beam SL. Each signal light beam SLi generated by the optical splitter OD is supplied to a corresponding optical waveguide OWGi.

(129) Each optical waveguide OWGi generates a delayed signal light beam SL′i by imparting a time delay Δti to a corresponding signal light beam SLi. The lengths of the time delays Δt1, Δt2, . . . and Δtn imparted by the optical waveguides OWG1, OWG2, . . . and OWGn are set in accordance with the direction of the main beam of radiated electromagnetic waves. The delayed signal light beam SL′i generated by each optical waveguide OWGi is supplied to a corresponding feeding circuit Fi. Note that in Specific Example 2, an optical fiber having an optical path length in accordance with the time delay Δti is used as each optical waveguide OWGi.

(130) Note that any of the following configurations may be employed to achieve beam scanning in the phased array antenna 2 in accordance with Specific Example 2.

(131) <Configuration 1>

(132) In a case where the optical waveguides OWG1, OWG2, . . . and OWGn are optical waveguides which cause differing chromatic dispersion (i.e., optical waveguides constituted by respective chromatic dispersion mediums having differing chromatic dispersion values), the time delay Δti imparted to each delayed radio frequency signal V.sub.RF(t−Δti) can be changed by changing the wavelength λ of the carrier light beam CL.

(133) In such a case, it is therefore possible to achieve beam scanning by employing a configuration in which (i) the light source LS allows for variation of the wavelength λ of the carrier light beam CL generated, and (ii) the wavelength λ of the carrier light beam CL generated by the light source LS is controlled in accordance with a desired main beam direction.

(134) <Configuration 2>

(135) In a case where the optical waveguides OWG1, OWG2, . . . and OWGn are optical waveguides having variable optical path lengths, it is possible to change the time delay Δti imparted to each delayed radio frequency signal V.sub.RF(t−Δti) by changing the optical path length of a corresponding optical waveguide OWGi.

(136) In such a case, it is therefore possible to achieve beam scanning by employing a configuration in which (i) each optical waveguide OWGi has a variable optical path length, and (ii) the optical path length of each optical waveguide OWGi is controlled in accordance with a desired main beam direction.

(137) (Variation of Phased Array Antenna 2)

(138) The following description will discuss, with reference to FIG. 8, a variation of the phased array antenna 2. FIG. 8 is a block diagram illustrating a configuration of the phased array antenna 2 in accordance with the present variation.

(139) The phased array antenna 2 in accordance with the present variation is a transmitting and receiving antenna which is obtained by adding components for reception to the phased array antenna 2 illustrated in the FIG. 5.

(140) As illustrated in FIG. 8, each feeding circuit Fi of the phased array antenna 2 in accordance with the present variation includes, as components for reception, a mixer RMX1i, an optical modulator ROMi, an optical demodulator ROMDi, and a mixer RMX2i. Each feeding circuit Fi also includes a circulator C1i and a circulator C2i, which are components for enabling both transmitting and receiving. The phased array antenna 2 also includes a circulator C3 and a wavelength demultiplexer RWDM, which are components for enabling both transmitting and receiving.

(141) The mixer RMX1i generates an intermediate frequency signal V.sub.IF′(t+Δti) by multiplying a radio frequency signal V.sub.RF′(t+Δti) by the delayed local signal V.sub.LO(t−Δti). Here, the radio frequency signal V.sub.RF′(t+Δti) is a radio frequency signal which has been received by use of a corresponding antenna element Ai. Since the radio frequency signal V.sub.RF′(t+Δti) is expressed as shown in Formula (25), and the delayed local signal V.sub.LO(t−Δti) is expressed as shown in Formula (21), the intermediate frequency signal V.sub.IF′(t+Δti) is expressed as shown in Formula (26).

(142) 0$\begin{array}{cc}\left[\mathrm{Math}.25\right]& \\ V_{\mathrm{RF}}^{\prime }\left(t+\Delta \mathrm{ti}\right)=A\frac{V_0{V}_1}{2}\cos \left(2\pi \left(f_{\mathrm{LO}}+f_{\mathrm{IF}}\right)\left(t+\Delta \mathrm{ti}\right)\right)& \left(25\right)\\ \left[\mathrm{Math}.26\right]& \\ V_{\mathrm{IF}}^{\prime }\left(t+\Delta \mathrm{ti}\right)=A_1\frac{V_0{V}_1}{2}\cos \left(2\pi f_{\mathrm{IF}}\left(t+\Delta \mathrm{ti}\right)+2\pi \times 2f_{\mathrm{LO}}\Delta \mathrm{ti}\right)& \left(26\right)\end{array}$

(143) The optical modulator ROMi generates a signal light beam RSL by carrying out quadrature amplitude modulation on a corresponding carrier light beam CLi by use of the intermediate frequency signal V.sub.IF′(t+Δti) and the delayed local signal V.sub.LO(t−Δti). The signal light beam RSLi generated by the optical modulator ROMi is supplied to the time delay device TD. In the present variation, a DPMZ modulator is used as the optical modulator ROMi. In a case where the configuration of Specific Example 1 illustrated in FIG. 6 is employed, the carrier light beam CLi supplied to each optical modulator ROMi is the carrier light beam generated by a corresponding light source LSi. In a case where the configuration of Specific Example 2 illustrated in FIG. 7 is employed, the carrier light beam CLi supplied to each optical modulator ROMi is the carrier light beam generated by the single light source LS.

(144) The time delay device TD generates a delayed signal light beam RSL′ from signal light beams RSL1, RSL2, . . . and RSLn. In a case where the configuration of Specific Example 1 illustrated in FIG. 6 is employed, the time delay device TD is configured to (1) generate a signal light beam RSL by multiplexing the signal light beams RSL1, RSL2, . . . and RSLn and (2) generate the delayed signal light beam RSL′ by causing chromatic dispersion ΔD(λ) of the signal light beam RSL. In a case where the configuration of Specific Example 2 illustrated in FIG. 7 is employed, the time delay device TD is configured to (1) generate delayed signal light beams RSL′1, RSL′2, . . . and RSL′n by imparting the time delays Δt1, Δt2, . . . and Δtn to the signal light beams RSL1, RSL2, . . . and RSLn, respectively, and (2) generate the delayed signal light beam RSL′ by multiplexing the delayed signal light beams RSL′1, RSL′2, . . . and RSL′n. The delayed signal light beam RSL′ generated by the time delay device TD is supplied to the wavelength demultiplexer RWDM.

(145) The wavelength demultiplexer RWDM generates (extracts) the delayed signal light beams RSL′1, RSL′2, . . . and RSL′n by carrying out wavelength demultiplexing on the delayed signal light beam RLS′. Each delayed signal light beam RSL′i generated by the wavelength demultiplexer RWDM is provided to the optical demodulator RODMi of a corresponding feeding circuit Fi.

(146) The optical demodulator RODMi generates a delayed intermediate frequency signal V.sub.IF′(t) and a local signal V.sub.LO′(t−2Δti) by demodulating the delayed signal light beam RSL′i. Since the intermediate frequency signal V.sub.IF′(t+Δti) and the delayed local signal V.sub.LO(t−Δti) are expressed as shown in Formulas (26) and (21), respectively, the delayed intermediate frequency signal V.sub.IF′(t) and the local signal V.sub.LO′(t−2Δti) are expressed as shown in Formulas (27) and (28), respectively. Note that in the present variation, a coherent receiver is used as each optical demodulator RODMi.

(147) $\begin{array}{cc}\left[\mathrm{Math}.27\right]& \\ V_{\mathrm{IF}}^{\prime }\left(t\right)=A\frac{V_0{V}_1}{2}\cos \left(2\pi f_{\mathrm{IF}}t+2\times 2f_{\mathrm{LO}}\Delta \mathrm{ti}\right)& \left(27\right)\\ \left[\mathrm{Math}.28\right]& \\ V_{\mathrm{LO}}^{\prime }\left(t-2\Delta \mathrm{ti}\right)=V_0\cos \left(2\pi f_{\mathrm{LO}}\left(t-2\Delta \mathrm{ti}\right)\right)& \left(28\right)\end{array}$

(148) The mixer RMX2i generates a delayed radio frequency signal V.sub.RF′(t) by multiplying the delayed intermediate frequency signal V.sub.IF′(t) by the local signal V.sub.LO′(t−2Δti). Since the delayed intermediate frequency signal V.sub.IF′(t) and the local signal V.sub.LO′(t−2Δti) are expressed as shown in Formulas (27) and (28), respectively, the delayed radio frequency signal V.sub.RF′(t) is expressed as shown in Formula (29). The delayed radio frequency signal V.sub.RF′(t) generated by the mixer RMX2 is supplied to the receiving circuit R after being multiplexed with delayed radio frequency signals V.sub.RF′(t) generated by other feeding circuits Fj.

(149) $\begin{array}{cc}\left[\mathrm{Math}.29\right]& \\ V_{\mathrm{RF}}^{\prime }\left(t\right)=A_1\frac{V_0^2{V}_1}{2}\cos \left(2\pi f_{\mathrm{RF}}t\right)& \left(29\right)\end{array}$

(150) The circulator C1i is provided between the mixer MXi and the antenna element Ai and is connected to the mixer RMX1i. The circulator C1i supplies, to the antenna element Ai, the delayed radio frequency signal V.sub.RF(t−Δti) outputted from the mixer MXi (operation during transmission). The circulator C1i also supplies, to the mixer RMX1i, the radio frequency signal V.sub.RF′(t+Δti) outputted from the antenna element Ai (operation during reception).

(151) The circulator C2i is provided between the time delay device TD and the optical demodulator ODMi and is connected to the optical modulator ROMi. The circulator C2i supplies, to the optical demodulator ODMi, the delayed signal light beam SL′i outputted from the time delay device TD (operation during transmission). The circulator C2i also supplies, to the time delay device TD, the signal light beam RSLi generated by the optical modulator ROMi (operation during reception).

(152) The circulator C3 is provided between the optical modulator OM and the time delay device TD and is connected to the wavelength demultiplexer RWDM. The circulator C3 supplies, to the time delay device TD, the signal light beam SL generated by the optical modulator OM (operation during transmission). The circulator C3 also supplies, to the wavelength demultiplexer RWDM, the delayed signal light beam RSL′ outputted from the time delay device TD (operation during reception).

Further Variation of Phased Array Antenna in Accordance with Embodiment 1

(153) The following description will discuss, with reference to FIG. 9, a further variation of the phased array antenna 1 in accordance with Embodiment 1. FIG. 9 is a block diagram illustrating a configuration of a phased array antenna 9 in accordance with the present variation.

(154) The phased array antenna 9 in accordance with the present variation is a transmitting and receiving antenna which is similar to the phased array antenna 1 illustrated in FIG. 4.

(155) As illustrated in FIG. 9, the phased array antenna 9 in accordance with this further variation is obtained by replacing the circulator C1i, of the phased array antenna 1 in accordance with the first variation, with a switch Si.

(156) The switch Si is controlled such that, during transmission, the mixer MXi and the antenna element Ai are connected, and the delayed radio frequency signal V.sub.RF(t−Δti) outputted from the mixer MXi is supplied to the antenna element Ai. Furthermore, the switch Si is controlled such that, during reception, the antenna element Ai is connected to the mixer RMX1i, and the radio frequency signal V.sub.RF′(t+Δti) outputted from the antenna element Ai is supplied to the mixer RMX1i.

Further Variation of Phased Array Antenna in Accordance with Embodiment 2

(157) The following description will discuss, with reference to FIG. 10, a further variation of the phased array antenna 2 in accordance with Embodiment 2. FIG. 10 is a block diagram illustrating a configuration of a phased array antenna 10 in accordance with the present variation.

(158) The phased array antenna 10 in accordance with the present variation is a transmitting and receiving antenna which is similar to the phased array antenna 2 illustrated in FIG. 8.

(159) As illustrated in FIG. 10, the phased array antenna 10 in accordance with this further variation is obtained by replacing the circulator C1i, of the phased array antenna 2 in accordance with the first variation, with a switch Si.

(160) The switch Si is controlled such that, during transmission, the mixer MXi and the antenna element Ai are connected, and the delayed radio frequency signal V.sub.RF(t−Δti) outputted from the mixer MXi is supplied to the antenna element Ai. Furthermore, the switch Si is controlled such that, during reception, the antenna element Ai is connected to the mixer RMX1i, and the radio frequency signal V.sub.RF′(t+Δt1) outputted from the antenna element Ai is supplied to the mixer RMX1i.

Recap

(161) A phased array antenna in accordance with one of the above embodiments includes: n (n is an integer of 2 or more) antenna elements A1, A2, . . . and An; a multiplexer configured to generate a sum signal V.sub.IF+LO(t) by adding an intermediate frequency signal V.sub.IF(t) and a local signal V.sub.LO(t); an optical modulator configured to generate a signal light beam SL by carrying out intensity modulation on a carrier light beam CL by use of the sum signal V.sub.IF+LO(t); a time delay device configured to generate delayed signal light beams SL′1, SL′2, . . . and SL′n by imparting time delays Δt1, Δt2, . . . and Δtn to the signal light beam SL; and a feeding circuit group constituted by feeding circuits, each of which is a feeding circuit Fi configured to convert a corresponding delayed signal light beam SL′i into a delayed radio frequency signal V.sub.RF(t−Δti) to be supplied to a corresponding antenna element Ai, each feeding circuit Fi (i×1, 2, . . . n) including: an O/E converter configured to generate a delayed sum signal V.sub.IF+LO(t−Δti) by carrying out O/E conversion on the corresponding delayed signal light beam SL′i; a demultiplexer configured to generate a delayed intermediate frequency signal V.sub.IF(t−Δti) and a delayed local signal V.sub.LO(t−Δti) by demultiplexing the delayed sum signal V.sub.IF+LO(t−Δti); and a mixer configured to generate the delayed radio frequency signal V.sub.RF(t−Δti) by multiplying the delayed intermediate frequency signal V.sub.IF(t−Δti) by the delayed local signal V.sub.LO(t−Δti).

(162) With the above configuration, the time delay of the delayed radio frequency signal V.sub.RF(t−Δti) supplied to each antenna element Ai is not dependent on frequency. As such, with the above configuration, even if the frequency of radiated electromagnetic waves is changed, the electromagnetic waves can be radiated in a constant direction, without a change in the time delays Δt1, Δt2, . . . and Δtn imparted to the signal light beam SL.

(163) Furthermore, with the above configuration, the data signal modulated by the optical modulator is the sum signal V.sub.IF+LO(t) obtained by adding the intermediate frequency signal V.sub.IF(t) and the local signal V.sub.LO(t). This sum signal V.sub.IF+LO(t) has a frequency which is lower than that of a radio frequency signal V.sub.RF(t). The above configuration therefore makes it possible to provide a phased array antenna employing an easily-obtainable and/or low cost O/E converter and optical modulator, even in a case where the phased array antenna operates in the millimeter wave band (radio frequency in a range from 30 GHz to 300 GHz).

(164) A phased array antenna in accordance with another one of the above embodiments includes: n (n is an integer of 2 or more) antenna elements A1, A2, . . . and An; an optical modulator configured to generate a signal light beam SL by carrying out quadrature amplitude modulation on a carrier light beam CL by use of an intermediate frequency signal V.sub.IF(t) and a local signal V.sub.LO(t); a time delay device configured to generate delayed signal light beams SL′1, SL′2, . . . and SL′n by imparting time delays Δt1, Δt2, . . . and Δtn to the signal light beam SL; and a feeding circuit group constituted by feeding circuits, each of which is a feeding circuit Fi configured to convert a corresponding delayed signal light beam SL′i into a delayed radio frequency signal V.sub.RF(t−Δti) to be supplied to a corresponding antenna element Ai, each feeding circuit Fi (i=1, 2, . . . n) including: an optical demodulator configured to generate a delayed intermediate frequency signal V.sub.IF(t−Δti) and a delayed local signal V.sub.LO(t−Δti) by demodulating the corresponding delayed signal light beam SL′i; and a mixer configured to generate the delayed radio frequency signal V.sub.RF(t−Δti) by multiplying the delayed intermediate frequency signal V.sub.IF(t−Δti) by the delayed local signal V.sub.LO(t−Δti).

(165) With the above configuration, the time delay of the delayed radio frequency signal V.sub.RF(t−Δti) supplied to each antenna element Ai is not dependent on frequency. As such, with the above configuration, even if the frequency of radiated electromagnetic waves is changed, the electromagnetic waves can be radiated in a constant direction, without a change in the time delays Δt1, Δt2, . . . and Δtn imparted to the signal light beam SL.

(166) Furthermore, with the above configuration, the data signal modulated by the optical modulator is the sum signal V.sub.IF+LO(t) obtained by adding the intermediate frequency signal V.sub.IF(t) and the local signal V.sub.LO(t). This sum signal V.sub.IF+LO(t) has a frequency which is lower than that of a radio frequency signal V.sub.RF(t). The above configuration therefore makes it possible to provide a phased array antenna employing an easily-obtainable and/or low cost O/E converter and optical modulator, even in a case where the phased array antenna operates in the millimeter wave band (radio frequency in a range from 30 GHz to 300 GHz).

(167) The phased array antenna in accordance with the above embodiments can be preferably arranged such that the phased array antenna further includes: a light source group constituted by light sources each of which generates a carrier light beam CLi such that each of carrier light beams CL1, CL2, . . . and CLn generated by respective ones of the light sources has a differing wavelength; and a multiplexer configured to generate the carrier light beam CL by multiplexing the carrier light beams CL1, CL2, . . . and CLn; and such that the time delay device includes: an optical waveguide configured to generate a delayed signal light beam SL′ by causing chromatic dispersion of the signal light beam SL; and a wavelength demultiplexer configured to generate the delayed signal light beams SL′1, SL′2, . . . and SL′n by carrying out wavelength demultiplexing on the delayed signal light beam SL′.

(168) With the above configuration, only one waveguide is needed for imparting a delay to the signal light beam SL. This makes it possible to provide the phased array antenna at a lower cost.

(169) The phased array antenna in accordance with the above embodiments can be preferably arranged such that each of the light sources is configured to allow for variation of a wavelength of the carrier light beam CLi generated thereby.

(170) With the above configuration, it is possible to achieve beam scanning by controlling the wavelength of the carrier light beam CLi generated by each light source.

(171) The phased array antenna in accordance with the above embodiments can be preferably arranged such that the optical waveguide is configured to allow for variation of the chromatic dispersion caused to the signal light beam SL.

(172) With the above configuration, it is possible to achieve beam scanning by controlling the chromatic dispersion which the optical waveguide causes to the signal light beam.

(173) The phased array antenna in accordance with the above embodiments can be preferably arranged such that the phased array antenna further includes: a light source configured to generate the carrier light beam CL, and such that the time delay device includes: an optical splitter configured to generate signal light beams SL1, SL2, . . . and SLn by splitting the signal light beam SL; and an optical waveguide group constituted by optical waveguides, each optical waveguide being configured to generate a delayed signal light beam SL′i by imparting a time delay Δti to a corresponding signal light beam SLi such that each of time delays Δt1, Δt2, . . . and Δtn imparted by respective ones of the optical waveguides is of a differing length.

(174) With the above configuration, only one light source is needed for generating the carrier light beam CL. This makes it possible to provide the phased array antenna at a lower cost.

(175) The phased array antenna in accordance with the above embodiments can be preferably arranged such that: the light source which generates the carrier light beam CL is configured to allow for variation of a wavelength of the carrier light beam CL generated thereby; and each of the optical waveguides is configured to cause differing chromatic dispersion.

(176) With the above configuration, it is possible to achieve beam scanning by controlling the wavelength of the carrier light beam CL generated by the light source.

(177) The phased array antenna in accordance with the above embodiments can be preferably arranged such that each of the optical waveguides has a variable optical path length.

(178) With the above configuration, it is possible to achieve beam scanning by controlling the time delay Δti imparted by each optical waveguide to a corresponding signal light beam.

(179) The phased array antenna in accordance with the above embodiments can be preferably arranged such that: instead of including the mixer configured to generate the delayed radio frequency signal V.sub.RF(t−Δti) by multiplying the delayed intermediate frequency signal V.sub.IF(t−Δti) by the delayed local signal V.sub.LO(t−Δti), each feeding circuit Fi includes: a multiplier configured to generate a delayed local signal V.sub.LOM(t−Δti) by multiplying a frequency of the delayed local signal V.sub.LO(t−Δti); and a mixer configured to generate the delayed radio frequency signal V.sub.RF(t−Δt) by multiplying the delayed intermediate frequency signal V.sub.IF(t−Δti) by the delayed local signal V.sub.LOM(t−Δti).

(180) With the above configuration as well, the time delay of the delayed radio frequency signal V.sub.RF(t−Δti) supplied to each antenna element Ai is not dependent on frequency. As such, with the above configuration as well, even if the frequency of radiated electromagnetic waves is changed, the electromagnetic waves can be radiated in a constant direction, without a change in the time delays Δt1, Δt2, . . . and Δtn imparted to the signal light beam SL.

(181) The phased array antenna in accordance with the above embodiments can be preferably arranged such that each feeding circuit Fi further includes: a mixer configured to generate an intermediate frequency signal V.sub.IF′(t+Δti) by multiplying (a) a radio frequency signal V.sub.RF′(t+Δti) which has been received by use of the corresponding antenna element Ai by (b) the delayed local signal V.sub.LO(t−Δti); a multiplexer configured to generate a sum signal V.sub.IF+LO′(t+Δti) by adding the intermediate frequency signal V.sub.IF′(t+Δti) and the delayed local signal V.sub.LO(t−Δti);

(182) an optical modulator configured to generate a signal light beam RSLi by carrying out intensity modulation by use of the sum signal V.sub.IF+LO′(t+Δti); an O/E converter configured to generate a delayed sum signal V.sub.IF+LO′(t) by carrying out O/E conversion on a delayed signal light beam RSL′i, the delayed signal light beam RSL′i being obtained by the time delay device imparting a time delay to the signal light beam RSLi; a demultiplexer configured to generate a delayed intermediate frequency signal V.sub.IF′(t) and a local signal V.sub.LO′(t) by demultiplexing the delayed sum signal V.sub.IF+LO′(t); and a mixer configured to generate a delayed radio frequency signal V.sub.RF′(t) by multiplying the delayed intermediate frequency signal V.sub.IF′(t) by the local signal V.sub.LO′(t).

(183) The above configuration makes it possible to provide a transmitting and receiving phased array antenna.

(184) The phased array antenna in accordance with the above embodiments can be preferably arranged such that each feeding circuit Fi further includes: a mixer configured to generate an intermediate frequency signal V.sub.IF′(t+Δti) by multiplying (a) a radio frequency signal V.sub.RF′(t+Δti) which has been received by use of the corresponding antenna element Ai by (b) the delayed local signal V.sub.LO(t−Δti); an optical modulator configured to generate a signal light beam RSLi by carrying out quadrature amplitude modulation by use of the intermediate frequency signal V.sub.IF′(t+Δti) and the delayed local signal V.sub.LO(t−Δti); an optical demodulator configured to generate a delayed intermediate frequency signal V.sub.IF′(t) and a local signal V.sub.LO′(t) by demodulating a delayed signal light beam RSL′i, the delayed signal light beam RSL′i being obtained by the time delay device imparting a time delay to the signal light beam RSLi; and a mixer configured to generate a delayed radio frequency signal V.sub.RF′(t) by multiplying the delayed intermediate frequency signal V.sub.IF′(t) by the local signal V.sub.LO′(t).

(185) The above configuration makes it possible to provide a transmitting and receiving phased array antenna.

ADDITIONAL MATTERS

(186) The present invention is not limited to the description of the embodiments or variations above, but may be altered within the scope of the claims. The present invention also encompasses, in its technical scope, any embodiment derived from an appropriate combination of technical means disclosed in differing embodiments or variations.

REFERENCE SIGNS LIST

(187) 1 and 2 Phased array antenna MP Multiplexer OM Optical modulator TD Time delay device Fi Feeding circuit OEi O/E converter DPi Demultiplexer MXi Mixer