Abstract
An impedance matching method for a low-profile ultra-wideband array antenna is provided. The method includes: connecting an arm of a balanced end of a hyperbolic microstrip balun in series with an open circuit line; directly coupling the open circuit line to a radiator layer; connecting another arm of the balanced end of the hyperbolic microstrip balun to the radiator layer via a metallized via hole, and welding an unbalanced end of the hyperbolic microstrip balun to a coaxial line, so that the coaxial line feeds a power to the antenna via the hyperbolic microstrip balun. In this method, the open circuit line is integrated between the hyperbolic microstrip balun and the radiator layer of the antenna to achieve an impedance matching of the ultra-wideband antenna and to simplify a structure of a matching circuit.
Claims
1. An impedance matching method for a low-profile ultra-wideband array antenna, comprising a hyperbolic microstrip balun, a radiator layer, an open circuit line, and a coaxial line, wherein the method comprises: connecting an arm of a balanced end of the hyperbolic microstrip balun in series with the open circuit line; directly coupling the open circuit line to the radiator layer; connecting an other arm of the balanced end of the hyperbolic microstrip balun to the radiator layer via a metallized via hole; and welding an unbalanced end of the hyperbolic microstrip balun to the coaxial line, so that the coaxial line feeds a power to the antenna via the hyperbolic microstrip balun.
2. The method according to claim 1, wherein the arm of the balanced end of the hyperbolic microstrip balun is connected in series with the open circuit line, and the open circuit line is directly coupled to the radiator layer, to form an impedance matching circuit.
3. The method according to claim 1, wherein the open circuit line and the radiator layer share a same dielectric layer.
4. The method according to claim 3, wherein the open circuit line and the radiator layer are electromagnetically coupled.
5. The method according to claim 1, wherein the hyperbolic microstrip balun has a curvilinear structure.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) FIG. 1 is a schematic diagram of an impedance matching circuit of an ultra-wideband array antenna element according to an embodiment of the present disclosure.
(2) FIG. 2 is a schematic structural diagram of an impedance matching method for an ultra-wideband array antenna according to an embodiment of the present disclosure.
(3) FIG. 3 is a schematic sectional view of an impedance matching unit of an ultra-wideband array antenna according to an embodiment of the present disclosure.
(4) FIG. 4 is a schematic structural diagram of a hyperbolic microstrip balun of the ultra-wideband array antenna according to an embodiment of the present disclosure.
(5) FIG. 5 is a side view of a structure of the hyperbolic microstrip balun of the ultra-wideband array antenna according to an embodiment of the present disclosure.
(6) FIG. 6 is an impedance frequency response diagram of the ultra-wideband array antenna according to an embodiment of the present disclosure.
(7) FIG. 7 is a reactance frequency response diagram of the ultra-wideband antenna element in different matching stages according to an embodiment of the present disclosure.
(8) FIG. 8 is a resistance frequency response diagram of the ultra-wideband antenna element in different matching stages according to an embodiment of the present disclosure.
(9) FIG. 9 is a schematic diagram of voltage standing wave ratio (VSWR) parameters of the ultra-wideband array antenna according to an embodiment of the present disclosure.
(10) FIG. 10 is a 2D radiation pattern of the ultra-wideband array antenna at a frequency of 5 GHz according to an embodiment of the present disclosure.
(11) In the figures, there are: an input impedance; a 50Ω port, which represents a port impedance of 50 Ω; a resistance; a reactance; a radiator, which represents the radiator layer; a open circuit, which represents the open circuit line; and a hyperbolic microstrip balun.
DETAILED DESCRIPTION OF THE EMBODIMENTS
(12) To make the objectives, technical solutions, and advantages of the present disclosure clearer, the present disclosure is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely intended to illustrate the present disclosure and are not intended to limit the present disclosure.
(13) Instead, any substitution, modification, equivalent methods and solutions defined by the claims within the spirit and scope of the present disclosure may be covered by the present disclosure. Further, for better understanding of the present disclosure, some specific details of the present disclosure are described in detail below. Those skilled in the art may fully understand the present disclosure without these specific details.
(14) FIG. 1 is a schematic diagram of an impedance matching circuit of an ultra-wideband antenna element according to an embodiment of the present disclosure. Wherein, Zin is an input impedance of an antenna. Once a structure, a dimensions, and a frequency range of the antenna are determined, the impedance of the antenna may be considered as a fixed load of the circuit. The fixed load usually contains a fixed reactance value and a fixed resistance value. One of the ideas of antenna impedance matching is to first reduce the reactance value to radiate more energy, and then perform a transformation of real impedance. In addition, the antenna is served as a balanced structure, and a coaxial feedline is served as an unbalanced structure. To maintain a consistency of currents on an antenna radiating element, the impedance matching circuit is also used to complete a balance-nonbalance conversion. Therefore, in the impedance matching circuit, the antenna is connected in series with an open circuit line 3 to reduce a reactance value in a band, and then an impedance transformation is achieved via a hyperbolic microstrip balun 5. In addition, due to the special structure of the hyperbolic microstrip balun 5, with a balanced structure 52 at one end and an unbalanced structure 53 at the other end, the hyperbolic microstrip balun 5 can act as a balance-nonbalance converter, that is, act as an impedance transformer 51. Usually, a standard impedance value required by a system is 50Ω.
(15) FIG. 2 to FIG. 5 show a specific implementation of the impedance matching circuit in the ultra-wideband array element according to an embodiment of the present invention, including a dielectric layer 1, and a first circuit layer and a second circuit layer respectively arranged above and below the dielectric layer 1. Wherein, the first circuit layer is a radiator layer 2 of the array antenna. It can be seen that a dipole element, i.e., the impedance matching unit 10, is end-to-end connected at the balanced end to form a tightly coupled arm structure. The second circuit layer is the open circuit line 3 coupled with the radiator layer 2. The open circuit line 3 uses an arm of the dipole as a ground 7, and is directly coupled to the radiator layer 2, sparing the use of the dielectric layer 1. The radiator layer 2 is connected to an arm of the hyperbolic microstrip balun 5 (specifically, an arm of the balanced end 52 of the hyperbolic microstrip balun 5) via a metalized via hole 4 and a metal patch 41. Another arm of the balanced end 52 of the hyperbolic microstrip balun 5 is connected to the open circuit line 3. After a conversion by the hyperbolic microstrip balun 5, an initial end, i.e., the unbalanced end 53 of the hyperbolic microstrip balun 5, is welded to a coaxial line 6. The coaxial line 6 feeds a power to the antenna via the hyperbolic microstrip balun 5. The ground 7 in the middle is used to fix a radiation direction of the array antenna. FIG. 3 is a cross-sectional structure diagram of the impedance matching unit.
(16) FIG. 6 shows impedance distribution of the ultra-wideband array antenna element in its frequency range. It can be seen from FIG. 6 that the ultra-wideband array antenna element has two resonant frequency point in a band range. Because the resonant frequency point in a low band has a large impedance fluctuation and a high reactance value, this resonant frequency point is preferentially set as a resonant frequency point of the open circuit line 3, thereby determining λ/4 of the open circuit line 3.
(17) Theoretical analysis: In embodiments of the present disclosure, λ is a propagation distance of a vibration signal in a medium in a cycle. Generally, λ is related to a frequency and a material of the medium. Generally, a wave speed in the medium meets the following relationship:
(18) where V.sub.p is a speed of a signal in the medium, c is a speed of light, and εr is a total relative permittivity, generally greater than 1, so that the speed of the signal in the medium is smaller than that in vacuum. Then from Vp=fλ, where f is a frequency of the signal, a wavelength λ of the signal in the cycle may be calculated.
(19) Then from Z(−l)=−jZ.sub.0 cot βl, an input impedance formula of the open circuit line 3, it can be known that when a length of the open circuit line 3 is set to λ/4 corresponding to the resonant frequency point, the input impedance is 0, a capacitance characteristic is presented in a low band of the resonant frequency, and an inductance characteristic is presented in a high band of the resonant frequency, which is just the opposite of a reactance characteristic of the antenna, and may be used to reduce the reactance value. Herein, l is a distance between an input end of the open circuit line 3 and an open circuit point, Zo is a characteristic impedance of the open circuit line 3, β is a phase constant, j is a symbol of a complex number, j.sup.2=−1, and β=2π/λ.
(20) FIG. 7 and FIG. 8 are schematic diagrams illustrating impedance changes of the ultra-wideband array antenna in different matching stages according to an embodiment of the present disclosure. It can be seen that when the antenna is connected in series with the open circuit line 3, the reactance value near the first resonant frequency point decreases, while the reactance value near a high frequency of the antenna increases. The resistance of the antenna also decreases after the antenna is connected in series with the open circuit line 3, which is conducive to the subsequent impedance matching. After the hyperbolic microstrip balun 5 is provided, the reactance value is matched to around 0 ohm, and the real part of the resistance is matched to around 50 ohms, basically realizing the impedance matching within the entire bandwidth, reaching 5.0 times the bandwidth.
(21) Referring to FIG. 9 and FIG. 10, in the embodiments of the present disclosure, a VSWR chart and an antenna radiation pattern may be important indicators to measure antenna impedance matching results and to determine whether the balance-nonbalance conversion is achieved. Generally, for a narrowband antenna, an excellent result may be achieved when VSWR<1.5, and requirements are basically met when VSWR<2.0. For the ultra-wideband array antenna, it can be considered as an ideal situation when VSWR<2.0 within a broadband. As shown in FIG. 9, the VSWR after the matching is less than 2.0, basically meeting the impedance change requirement. In addition, a far-field pattern in FIG. 10 looks good without a large distortion, indicating that the matching circuit has achieved the conversion from the unbalanced end 53 to the balanced end 52.
(22) As can be known from the matching circuit diagram, the impedance of the antenna is taken as the fixed load of the matching circuit, and the reactance part in the antenna impedance is taken as stage 1 of the matching circuit. The reactance is reduced by using the characteristic that the reactance near the resonant frequency point is opposite to the reactance of the antenna when the open circuit line 3 is connected in series. And then the impedance transformation is achieved by the hyperbolic microstrip balun 5. In the antenna element, the open circuit line 3 is integrated to the matching circuit without adding the dielectric layer 1, which simplifies the processing and reduces material costs. The hyperbolic microstrip balun 5, consisting of two gradient microstrip lines, may be divided into the balanced end 52 and the unbalanced end 53. The hyperbolic microstrip balun 5 transforms an unbalanced circuit at a feed port of the coaxial line 6 into a balanced circuit at a feed port of the antenna, without adding an external balun to the circuit for the balance-nonbalance conversion. In addition, due to its gradually changing impedance, the hyperbolic microstrip balun 5 may achieve the transformation between any two impedances in the broadband, thereby achieving the impedance matching in the broadband.
(23) The above are merely preferred embodiments of the present disclosure, and are not intended to limit the present disclosure. Any modification, equivalent substitution and improvement without departing from the spirit and principle of the present disclosure shall be included within the protection scope of the present disclosure.
