Abstract
A reconfigurable multi-output antenna (16) is disclosed comprising: one or more radiating elements (12, 14), at least two matching circuits (42, 44, 50, 52) coupled to the or each radiating element (12, 14) via e.g. a splitter (30, 32) or a duplexer; and wherein each matching circuit (42, 44, 50, 52) is associated with a separate port (38, 40, 46, 48) arranged to drive a separate resonant frequency so that the or each radiating element (12, 14) is operable to provide multiple outputs simultaneously. The resonant frequency of each output is independently controllable by each matching circuit, with good isolation with each other port, thereby offering very wide operating frequency range with simultaneous multi-independent output operations. Also described is a multi-output antenna control module for coupling to one or more radiating elements, an antenna structure and an antenna interface module. A reconfigurable multi-output antenna is disclosed comprising: one or more radiating.
Claims
1. A multi-output antenna comprising: a non-resonant radiating element mounted on a chassis including a ground plane, the chassis being configured as a radiating chassis and the non-resonant radiating element being configured to excite multiple resonance modes of the radiating chassis so as to provide multiple outputs; a splitter circuit; and at least first and second matching circuits coupled to the non-resonant radiating element by way of the splitter circuit, the splitter circuit configured to direct higher frequency signals to the first matching circuit and lower frequency signals to the second matching circuit; wherein each matching circuit is associated with a separate port arranged to drive a separate resonant frequency so that the radiating element is operable to provide multiple outputs simultaneously; wherein the at least first and second matching circuits are configured so that the radiating element is operable simultaneously to receive in a first frequency band containing the higher frequency signals via the first matching circuit and in a second frequency band containing the lower frequency signals via the second matching circuit; wherein the at least first and second matching circuits are each independently adjustable by way of at least one variable capacitor provided in each of the first and second matching circuits; and wherein the splitter circuit comprises an inductor and a capacitor each having respective first and second electrical connections, the inductor and capacitor being arranged with the first electrical connections joined at a T-junction, the T-junction connected to the non-resonant radiating element, the second electrical connection of the capacitor connected to the first matching circuit and the second electrical connection of the inductor connected to the second matching circuit, such that the ports are substantially uncorrelated, thereby allowing the first matching circuit to be adjusted so as to tune the signal in the first frequency band without affecting the tuning of the signal in the second frequency band and the second matching circuit to be adjusted so as to tune the signal in the second frequency band without affecting the tuning of the signal in the first frequency band.
2. The multi-output antenna according to claim 1, wherein the splitter circuit serves to divide a single feed port provided for the radiating element into two or more ports.
3. The multi-output antenna according to claim 1, wherein more than two matching circuits and ports are associated with the non-resonant radiating element.
4. The multi-output antenna according to claim 1, a pair of non-resonating radiating elements, each of which is coupled to two matching circuits which are in turn associated with two different ports so that the multi-output antenna is operable to provide up to four outputs simultaneously.
5. The multi-output antenna according to claim 4, wherein the pair of radiating elements are mutually coupled and each has an associated feed port which is split into two separate ports, and wherein each port is provided with a separate impedance-matching circuit configured for independent tuning of one of two distinct outputs associated with each radiating element.
6. The multi-output antenna according to claim 4, wherein a first feed port is provided between a first non-resonant radiating element and a first splitter circuit, and wherein a second feed port is provided between a second non-resonant radiating element and a second splitter circuit.
7. The multi-output antenna according to claim 6, wherein the first feed port is located off-centre with respect to the first radiating element.
8. The multi-output antenna according to claim 6, wherein the second feed port is placed in close proximity to the first feed port.
9. The multi-output antenna according to claim 1, wherein the chassis comprises a substrate having the ground plane formed on a first side thereof.
10. The multi-output antenna according to claim 9, wherein a first radiating element is provided on a second side of the substrate, opposite to the first side, and laterally spaced from the ground plane.
11. The multi-output antenna according to claim 10, wherein the first radiating element is constituted by an L-shaped metal patch, having a planar portion and a portion orthogonal to the ground plane.
12. The multi-output antenna according to claim 11, wherein the orthogonal portion extends from an edge of the planar portion furthest from the ground plane such that the orthogonal portion is spaced from the ground plane by a first gap.
13. The multi-output antenna according to claim 12, wherein a second radiating element is constituted by a planar metal patch, orthogonal to the ground plane.
14. The multi-output antenna according to claim 13, wherein the second radiating element is located between the ground plane and the orthogonal portion of the first radiating element.
15. The multi-output antenna according to claim 1, wherein each port is connected to a control system configured to select an operating state of the associated output.
16. An antenna structure comprising: one or more multi-output antennas; and one or more further antennas; wherein each of the one or more multi-output antennas comprises: a non-resonant radiating element mounted on a chassis including a ground plane, the chassis being configured as a radiating chassis and the non-resonant radiating element being configured to excite multiple resonance modes of the radiating chassis so as to provide multiple outputs; a splitter circuit; and at least first and second matching circuits coupled to the non-resonant radiating element by way of the splitter circuit, the splitter circuit configured to direct higher frequency signals to the first matching circuit and lower frequency signals to the second matching circuit; wherein each matching circuit is associated with a separate port arranged to drive a separate resonant frequency so that the radiating element is operable to provide multiple outputs simultaneously; wherein the at least first and second matching circuits are configured so that the radiating element is operable simultaneously to receive in a first frequency band containing the higher frequency signals via the first matching circuit and in a second frequency band containing the lower frequency signals via the second matching circuit; wherein the at least first and second matching circuits are each independently adjustable by way of at least one variable capacitor provided in each of the first and second matching circuits; and wherein the splitter circuit comprises an inductor and a capacitor each having respective first and second electrical connections, the inductor and capacitor being arranged with the first electrical connections joined at a T-junction, the T-junction connected to the non-resonant radiating element, the second electrical connection of the capacitor connected to the first matching circuit and the second electrical connection of the inductor connected to the second matching circuit, such that the ports are substantially uncorrelated, thereby allowing the first matching circuit to be adjusted so as to tune the signal in the first frequency band without affecting the tuning of the signal in the second frequency band and the second matching circuit to be adjusted so as to tune the signal in the second frequency band without affecting the tuning of the signal in the first frequency band.
17. The antenna structure according to claim 16, wherein the one or more further antennas are constituted by a balanced or an unbalanced antenna that is reconfigurable.
18. The antenna structure according to claim 16, wherein the one or more multi-output antennas comprise a plurality of multi-output antennas, and wherein the one or more further antennas each comprise one of the plurality of multi-output antennas.
19. The antenna structure according to claim 18, wherein a first antenna of the plurality of multi-output antennas is located at a first end of the structure, and wherein a second antenna of the plurality of multi-output antennas is located at a second end of the structure.
20. An antenna interface module for coupling a non-resonant radiating element mounted on a chassis including a groundplane, the chassis being configured as a radiating chassis and the non-resonant radiating element being configured to excite multiple resonance modes of the radiating chassis so as to provide multiple outputs, the antenna interface module comprising: a splitter circuit; and at least first and second matching circuits arranged for coupling to the non-resonant radiating element by way of the splitter circuit, the splitter circuit configured to direct higher frequency signals to the first matching circuit and lower frequency signals to the second matching circuit; wherein each matching circuit is associated with a separate port arranged to drive a separate resonant frequency so that the radiating element is operable to provide multiple outputs simultaneously; wherein the at least first and second matching circuits are configured so that the radiating element, when coupled to the control module, is operable simultaneously to receive in a first frequency band containing the higher frequency signals via the first matching circuit and in a second frequency band containing the lower frequency signals via the second matching circuit; wherein the at least first and second matching circuits are each independently adjustable by way of at least one variable capacitor in each of the first and second matching circuits; and wherein the splitter circuit comprises an inductor and a capacitor each having respective first and second electrical connections, the inductor and capacitor being arranged with the first electrical connections joined at a T-junction, the T-junction for connection to the non-resonant radiating element, the second electrical connection of the capacitor connected to the first matching circuit and the second electrical connection of the inductor connected to the second matching circuit, such that the ports are substantially uncorrelated, thereby allowing the first matching circuit to be adjusted so as to tune the signal in the first frequency band without affecting the tuning of the signal in the second frequency band and the second matching circuit to be adjusted so as to tune the signal in the second frequency band without affecting the tuning of the signal in the first frequency band.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) Certain embodiments of the present invention will now be described with reference to the accompanying drawings in which:
(2) FIG. 1 shows a top perspective view of a pair of coupled radiating elements for an antenna according to an embodiment of the present invention;
(3) FIG. 2 shows a block diagram of the circuitry associated with the radiating elements of FIG. 1;
(4) FIG. 3 shows a circuit diagram corresponding to the antenna structure of FIG. 2;
(5) FIG. 4 shows a graph of return loss against frequency for a first configuration of the circuit shown in FIG. 3, when C.sub.1 is varied from 1 pF to 10 pF while C.sub.2, C.sub.3 and C.sub.4 are fixed at 10 pF;
(6) FIG. 5 shows a graph of return loss against frequency for a second configuration of the circuit shown in FIG. 3, when C.sub.1 is varied from 0.5 pF to 10 pF while C.sub.3 is fixed at 1 pF, and C.sub.2 and C.sub.4 are fixed at 10 pF;
(7) FIG. 6 shows a graph of return loss against frequency for a third configuration of the circuit shown in FIG. 3, when C.sub.2 is varied from 0.2 pF to 10 pF while C.sub.1, C.sub.3 and C.sub.4 are fixed at 10 pF;
(8) FIG. 7 shows a graph of return loss against frequency for a fourth configuration of the circuit shown in FIG. 3, when C.sub.3 is varied from 1 pF to 10 pF while C.sub.1, C.sub.2 and C.sub.4 are fixed at 10 pF;
(9) FIG. 8 shows a graph of return loss against frequency for a fifth configuration of the circuit shown in FIG. 3, when C.sub.3 is varied from 0.3 pF to 10 pF while C.sub.2 is fixed at 1 pF, and C.sub.1 and C.sub.4 are fixed at 10 pF;
(10) FIG. 9 shows a graph of return loss against frequency for a sixth configuration of the circuit shown in FIG. 3, when C.sub.4 is varied from 0.45 pF to 10 pF while C.sub.1, C.sub.2 and C.sub.3 are fixed at 10 pF;
(11) FIG. 10A shows a top view of a fabricated antenna structure according to the block diagram of FIG. 2;
(12) FIG. 10B shows a rear view of a fabricated antenna structure according to the block diagram of FIG. 2;
(13) FIG. 11 shows a simulated graph of return loss against frequency for the multi-output chassis-antenna shown in FIGS. 10A and 10B, when C.sub.1, C.sub.2, C.sub.3 and C.sub.4 are fixed at 10 pF;
(14) FIG. 12 shows a measured graph of return loss against frequency for the multi-output chassis-antenna shown in FIGS. 10A and 10B, when C.sub.1, C.sub.2, C.sub.3 and C.sub.4 are fixed at 10 pF;
(15) FIG. 13 shows a top perspective view of a the structure of a chassis-antenna according to a further embodiment of the invention, having two pairs of coupled radiating elements;
(16) FIG. 14 shows a block diagram of the circuitry associated with the radiating elements of FIG. 13;
(17) FIG. 15 shows a simulated graph of return loss against frequency for the multi-output chassis-antenna shown in FIGS. 13 and 14, when the varactors in each of the matching circuits are fixed at 10 pF;
(18) FIG. 16 shows a top perspective view of an embodiment of the present invention which is similar to that shown in FIG. 1 but wherein only a single, large, radiating element is provided;
(19) FIG. 17 shows a block diagram of the circuitry associated with the radiating element of FIG. 16;
(20) FIG. 18 shows a simulated graph of return loss against frequency for the multi-output chassis-antenna shown in FIGS. 16 and 17, when a first varactor C.sub.1 is varied from 0.22 pF to 10 pF while a second varactor C.sub.2 is fixed at 10 pF;
(21) FIG. 19 shows a simulated graph of return loss against frequency for the multi-output chassis-antenna shown in FIGS. 16 and 17, when the second varactor C.sub.2 is varied from 0.3 pF to 10 pF while the first varactor C.sub.1 is fixed at 10 pF;
(22) FIG. 20 shows a simulated graph of return loss against frequency for the multi-output chassis-antenna shown in FIGS. 1 and 2, when all 4 varactors are fixed at 10 pF;
(23) FIG. 21 shows a top perspective view of an embodiment of the present invention which is similar to that shown in FIG. 16 but wherein a second large, radiating element is provided at the opposite end of the substrate to the single, large, radiating element;
(24) FIG. 22 shows a block diagram of the circuitry associated with each radiating element of FIG. 21;
(25) FIG. 23 shows a simulated graph of return loss against frequency for the multi-output chassis-antenna shown in FIGS. 21 and 22, when all 4 varactors are fixed at 10 pF;
(26) FIG. 24 shows a top perspective view of an embodiment of the present invention which is similar to that shown in FIG. 1 but wherein a second pair of coupled radiating elements is provided at the opposite end of the substrate to the first pair of coupled radiating elements;
(27) FIG. 25 shows a simulated graph of return loss against frequency for the multi-output chassis-antenna shown in FIG. 24, when all 8 varactors are fixed at 10 pF;
(28) FIG. 26 shows a range of different shapes which may constitute the radiating elements in embodiments of the invention;
(29) FIG. 27 shows a top perspective view of an embodiment of the present invention which incorporates an antenna interface module on a first antenna chassis;
(30) FIG. 28 shows an enlarged top perspective view of the antenna interface module of FIG. 27;
(31) FIG. 29 shows an enlarged top perspective view of an alternative antenna interface module to that shown in FIG. 28;
(32) FIG. 30A shows a top perspective view of an embodiment of the present invention which incorporates the antenna interface module of FIG. 28 on a first antenna chassis, which is similar to that shown in FIG. 27;
(33) FIG. 30B shows a top perspective view of an embodiment of the present invention which incorporates the antenna interface module of FIG. 28 on a second antenna chassis, which is different in shape to that shown in FIG. 30A;
(34) FIG. 30C shows a top perspective view of an embodiment of the present invention which incorporates the antenna interface module of FIG. 28 on a third antenna chassis, which is different in shape to that shown in FIGS. 30A and 30B;
(35) FIG. 31 shows a circuit diagram corresponding to the antenna structure of FIG. 17, with 2 additional varactors provided for an associated automatic tuning system;
(36) FIG. 32 shows a block diagram of an automatic tuning system for use with the circuit diagram of FIG. 31;
(37) FIG. 33 shows a circuit diagram corresponding to the antenna structure of FIG. 17, with 4 additional varactors provided for an associated automatic tuning system; and
(38) FIG. 34 shows a block diagram of an automatic tuning system for use with the circuit diagram of FIG. 33.
DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS
(39) With reference to FIG. 1 there is shown a pair 10 of coupled radiating elements 12, 14 for an antenna 16 according to an embodiment of the present invention. The radiating elements 12, 14 are similar to those described in WO2011/048357, are mounted in close proximity to each other and are driven over a PCB ground plane 18. Although, in practice, the radiating elements 12, 14 and ground plane 18 are provided on a substrate, no substrate is shown in FIG. 1 for purposes of clarity.
(40) It should be noted that the antenna 16 is fairly simple in construction and in having the ground plane 18 measuring 10040 mm.sup.2 and the pair 10 of radiating elements 12, 14 occupying a very small volumetric space of 4057 mm.sup.3, the antenna 16 meets the requirements for use in the mobile phone industry.
(41) In this particular embodiment, the first radiating element 12 is constituted by an L-shaped microstrip patch having a planar portion 20, parallel to the ground plane 18, and an orthogonal portion 22, orthogonal to the ground plane 18. It will be understood that the planar portion 20 is provided on the opposite side of the substrate from the ground plane 18, laterally spaced therefrom. The orthogonal portion 22 extends from an edge of the planar portion 20 furthest from the ground plane 18 such that the orthogonal portion 22 is spaced from the ground plane 18 by a so-called first gap 24. In this particular embodiment the first gap 24 is less that 10 mm.
(42) The second radiating element 14 is also constituted by a microstrip patch which, in this case, forms a planar rectangle. The second radiating element 14 is also orientated orthogonally to the ground plane 18 and is located within the first gap 24. Thus, the second radiating element 14 is effectively enclosed on two adjacent sides by the L-shaped first radiating element 12. In the embodiment shown, the second radiating element 14 is just over half of the length of the first radiating element 12 and extends from a side edge of the first radiating element 12. The distance between the ground plane 18 and the second radiating element 14 forms a so-called second gap 26. The distance between the second radiating element 14 and the orthogonal portion 22 of the first radiating element 12 will determine the amount of mutual coupling therebetween and this distance is therefore referred to as the mutual gap 28.
(43) As shown in FIG. 2, each radiating element 12, 14 is connected, respectively, to a first and second splitter circuit 30, 32 via a first and second feed port 34, 36. In this particular embodiment, the first and second feed ports 34, 36 are constituted by wires, however, in other embodiments other feed mechanisms could be employed such as microstrip feed lines or non-direct electromagnetic coupling.
(44) Referring back to FIG. 1, the first feed port 34 extends between the orthogonal portion 22 of the first radiating element 12 and the first splitter circuit 30, which is situated close to the nearest edge of the ground plane 18, and is located approximately one third of the distance along the length of the first radiating element 12. As described above, this is advantageous in that it allows the ground plane 18 and the first radiating element 12 to support many different resonances. The second feed port 36 is located adjacent to the first feed port 34 and connects to the adjacent second splitter circuit 32.
(45) As illustrated in FIG. 2, the first splitter circuit 30 is arranged to divide the one and only first feed port 34 of the first radiating element 12 into a first port 38 and a second port 40. The first port 38 is provided with a first matching circuit 42 and the second port 40 is provided with a second matching circuit 44. Similarly, the second splitter 32 is arranged to divide the one and only second feed port 36 of the second radiating element 14 into a third port 46 and a fourth port 48. The third port 46 is provided with a third matching circuit 50 and the fourth port 48 is provided with a fourth matching circuit 52. Together, the two splitter circuits 30, 32, the four matching circuits 42, 44, 50, 52 and the four ports 38, 40, 46, 48 make up a control module 54 for the multi-output antenna 16. The control module 54 may also comprise control means for driving each of the ports and tuning each of the matching circuits in accordance with system requirements.
(46) FIG. 3 shows a circuit diagram corresponding to the antenna 16 illustrated in FIG. 2. Each splitter circuit 30, 32 comprises a capacitor C.sub.S1, C.sub.S2 and an inductor L.sub.S1, L.sub.S2 connected in parallel and joined at a T-junction into the respective first and second feed ports 34, 36. The capacitor C.sub.S1 of the first splitter circuit 30 has a value of 0.3 pF, capacitor C.sub.S2 of the second splitter circuit 32 has a value of 0.6 pF, and the each inductor L.sub.S1, L.sub.S2 has a value of 1 nH.
(47) The capacitor C.sub.S1 of the first splitter circuit 30 is connected in series with the first matching circuit 42 while the inductor L.sub.S1 of the first splitter circuit 30 is connected in series with the second matching circuit 44. Similarly, the capacitor C.sub.S2 of the second splitter circuit 32 is connected in series with the third matching circuit 50 while the inductor L.sub.S2 of the second splitter circuit 32 is connected in series with the fourth matching circuit 52.
(48) Each matching circuit 42, 44, 50, 52 comprises a first inductor L.sub.M1, L.sub.M2, L.sub.M3, L.sub.M4 connected in parallel with a varactor C.sub.1, C.sub.2, C.sub.3, C.sub.4, which in turn is connected in series with a second inductor L.sub.M5, L.sub.M6, L.sub.M7, L.sub.M8. The first inductors L.sub.M1, L.sub.M2, L.sub.M3, L.sub.M4 are all connected to a ground plane and the values of each the inductor are as follows: L.sub.M1=3.559 nH, L.sub.M2=3.533 nH, L.sub.M3=2.2 nH, L.sub.M4=2.6 nH, L.sub.M5=39 nH, L.sub.M6=48 nH, L.sub.M7=4.4 nH, L.sub.M8=21 nH. The varactors C.sub.1, C.sub.2, C.sub.3, C.sub.4 all have a tuning range of 0.2 pF up 10 pF so as to enable the respective ports 38, 40, 46, 48 to tune their associated output resonances to different frequencies.
(49) It is noted that the first step in the design process of the antenna 16 was to simulate the structure illustrated in FIG. 1. All of the simulations were performed using the transient solver in CST Microwave Studio. The s2p file representing the antenna response was then used as a starting point for designing the matching networks shown in FIG. 3. The values of the components within each of the independent matching circuits were then adjusted in order to optimize the return loss performance of the antenna 16 and the isolation between each port 38, 40, 46, 48. The varactors C.sub.1, C.sub.2, C.sub.3, C.sub.4 were all fixed to 10 pF during this phase of the design process. Furthermore, the values of the components in the splitter circuits 30, 32 were chosen to provide 4 uncorrelated outputs whilst still achieving reasonable efficiency for each port 38, 40, 46, 48.
(50) FIG. 4 shows a graph of simulated return loss against frequency for a first configuration of the circuit shown in FIG. 3, when C.sub.1 is varied from 10 pF to 1 pF while C.sub.2, C.sub.3 and C.sub.4 are fixed at 10 pF. Thus, it can be seen that is possible to move the resonant frequency associated with the first port 38 (Port 1) from 459 MHz to 723 MHz by changing the value of the varactor C.sub.1. The resonant frequencies associated with the second port 40 (Port 2), third port 46 (Port 3) and fourth port 48 (Port 4) are also illustrated in FIG. 4 and it is apparent that only the resonance frequency of Port 3 was slightly affected as the varactor C.sub.1 was varied as the resonance frequencies of other two ports were close to static.
(51) However, it was also noted that the isolation between Port 1 and Port 3 deteriorated (i.e. the coupling increased) as the two resonances became closer together. Consequently, a further simulation was obtained and is shown in FIG. 5 for the case when the varactor C.sub.1 is varied from 10 pF to 0.5 pF while C.sub.3 is fixed at 1 pF and the other two varactors (i.e. C.sub.2 and C.sub.4) were fixed at 10 pF. In this case, the resonance frequency of Port 1 was tuned from 459 MHz to 1038 MHz with good isolation (i.e. below 7 dB) from all other ports, including Port 3.
(52) FIG. 6 shows a graph of simulated return loss against frequency for a third configuration of the circuit shown in FIG. 3 in which C.sub.2 is varied from 10 pF to 0.2 pF while C.sub.1, C.sub.3 and C.sub.4 are fixed at 10 pF. It is therefore possible to move the resonance frequency of Port 2 from 1500 MHz to 2181 MHz with good isolation (i.e. below 7 dB) with all other ports.
(53) Similarly, FIG. 7 shows a graph of simulated return loss against frequency for a fourth configuration of the circuit shown in FIG. 3, in which C.sub.3 is varied from 10 pF to 1 pF while C.sub.1, C.sub.2 and C.sub.4 are fixed at 10 pF. In this case, the resonance frequency of Port 3 is tuned from 843 MHz to 1242 MHz.
(54) FIG. 8 shows the simulated return loss when the varactor C.sub.3 is varied from 10 pF to 0.3 pF while C.sub.2 is fixed at 0.2 pF and the other two varactors (i.e. C.sub.1 and C.sub.4) are fixed at 10 pF. In this instance, the resonance frequency of Port 3 can be tuned from 843 MHz to 1935 MHz with good isolation (i.e. below 7 dB) with all of the other ports.
(55) Lastly, FIG. 9 shows a graph of simulated return loss against frequency for a sixth configuration of the circuit shown in FIG. 3, when C.sub.4 is varied from 10 pF to 0.45 pF while C.sub.1, C.sub.2 and C.sub.3 are fixed at 10 pF. In this way it is possible to move the resonance frequency of Port 4 from 2373 MHz to 2901 MHz with good isolation (i.e. below 7 dB) with all of the other ports.
(56) According to the above simulated results, it is apparent that by tuning the independent matching circuits associated with each port it is possible to alter the operating frequency and bandwidth associated with that port without affecting the resonant frequencies of the other ports.
(57) Table 1 below summaries the efficiency and realised gain of the antenna system with the ideal components simulated (i.e. without parasitic loss) and the results are generally very good, making the antenna an suitable candidate for use as a multi-output chassis antenna for as portable device.
(58) TABLE-US-00002 TABLE 1 Simulated Efficiency and Gain for the multi-output chassis-antenna with ideal circuit components Frequency Radiation Efficiency Total Efficiency Realized Port (MHz) (dB) (dB) Gain (dB) 1 459 2.274 3.665 3.221 2 843 0 0.937 1.021 3 1500 0 0.272 3.691 4 2373 0 0.164 4.631
(59) In order to validate the above, the applicants also simulated an antenna having real components and fabricated and demonstrated a prototype device. The intention was not only to demonstrate the frequency agility of the antenna system, but also its potential for use in a mobile device covering DVB-H, GSM710, GSM850, GSM900, GPS1575, GSM1800, PCS1900, and UMTS2100 simultaneously or for use in a Cognitive Radio system which requires multi-resolution spectrum sensing.
(60) The prototype chassis-antenna 60 is illustrated in FIGS. 10A and 10B and comprises the pair of coupled radiating elements of FIG. 1 connected to the splitter circuits, matching circuits and ports of FIGS. 2 and 3. In this instance, the antenna 60 was fabricated from a microwave substrate 62 (of material known as TLY-3-0450-C5) having a permittivity of 2.33 and a thickness of 1.143 mm, provided with a metal ground plate 64 having a thickness of 0.01778 mm. The coupled radiating elements were supported by a Rohacell foam structure 70, which has a dielectric constant of 1.08 within the operating frequency bands. The electrical components of FIG. 3 were each provided on the substrate 62 and connected to each of the respective ports (Port 1, Port 2, Port 3 and Port 4). Accordingly, the single pair of coupling elements 70 was used to excite four separate resonances in the device.
(61) In the embodiment tested, the varactors C.sub.1, C.sub.2, C.sub.3, C.sub.4 of FIG. 3 were replaced with capacitors having a fixed value of 10 pF for demonstration purposes.
(62) FIG. 11 illustrates the simulated S parameters for the antenna 60, when real components are employed. This shows that the resonance frequencies for the 4 ports are 462 MHz, 876 MHz, 1518 MHz and 2370 MHz, with a return loss of 20.83 dB, 7.462 dB, 26.25 dB and 32.36 dB, respectively. It can also be seen from FIG. 11 that the coupling between each port all occurs below 12 dB.
(63) Table 2 shows the simulated efficiencies and realized gain for the antenna 60 when real components are employed. For example, Port 1 has a realized gain of 9.959 dB at 462 MHz which meets specification requires and the outputs from the other ports also have reasonable efficiency and realized gain.
(64) TABLE-US-00003 TABLE 2 Simulated Efficiency and Gain for the prototype antenna shown in FIG. 10 with real circuit components Frequency Radiation Total Realized Gain Port (MHz) Efficiency (dB) Efficiency (dB) (dB) 1 462 11.35 11.59 9.959 2 876 1.942 3.373 1.422 3 1518 3.252 3.577 0.676 4 2370 0.331 0.465 4.235
(65) FIG. 12 illustrates the measured S parameters for the antenna 60. The measured results show that the resonance frequencies for the 4 ports are 481 MHz, 837 MHz, 1459 MHz and 2711 MHz, with a return loss of 13.25 dB, 11.94 dB, 10.66 dB and 15.83 dB, respectively. FIG. 12 also shows that the coupling between each port is generally below 7 dB except for the coupling between ports 3 and ports 4 (i.e. S43) which is 6.76 dB. In general, the measured results compare well with the simulations and it is believed that any discrepancies are due to manufacturing tolerances (e.g. as a result of additional solder).
(66) It should be clear from the above that by operating with splitter circuits and matching circuits as described, the antenna 60 (with a single pair of coupled radiating elements 70) can provide 4 outputs with independent frequency tunable behaviour and which together can cover a frequency range from 456 MHz to 2946 MHz with a 6 dB return loss across the operating band.
(67) The applicants also propose the use of splitter circuits and matching circuits with more pairs of coupled radiating elements so as to provide even more independently tunable outputs. In order to validate this concept, a chassis-antenna 80 having 2 pairs of coupled radiating elements was simulated. The structure of the radiating elements of the antenna 80 is shown in FIG. 13. The antenna 80 is essentially identical to that described above in relation to FIG. 1 but also comprises a second pair 82 of coupled radiating elements 84, 86. The second pair 82 of coupled radiating elements 84, 86 is identical to the first pair 10 of coupled radiating elements 12, 14 described above but is located adjacent the middle of a side of the substrate. However, it should be noted that the location of the second pair 82 of coupled radiating elements 84, 86 is not limited and can be provided at any position around the substrate. It will also be clear that further pairs of coupled radiating elements (or even further individual radiating elements) may be incorporated into the antenna 80 to further increase the number of outputs.
(68) As illustrated in FIG. 14, each radiating element 12, 14, 84, 86 is connected via a feed line to a splitter circuit 30, 32, 88, 90 and each splitter circuit 30, 32, 88, 90 is in turn connected to two separate matching circuits 42, 44, 50, 52, 92, 94, 96, 98 associated with two separate ports 38, 40, 48, 50, 100, 102, 104, 106. The structure of each of the matching circuits and splitter circuits is identical to that shown in FIG. 3 although the values of each of the components may be different as determined adjusting the values to optimize the return loss performance of the antenna 80 and the isolation between each port.
(69) As shown in FIG. 15, by employing 2 pairs of coupled radiating elements, it is possible to obtain 8 independently tunable outputs (1, 2, 3, 4, 5, 6, 7, 8). The 8 resonance frequencies obtained in this example are 460 MHz, 710 MHz, 1060 MHz, 1460 MHz, 1620 MHz, 1790 MHz, 2090 MHz and 2500 MHz, with a return loss of 8.374 dB, 8.326 dB, 16.96 dB, 15.24 dB, 28.88 dB, 20.7 dB, 17.25 dB and 30.47 dB, respectively. The maximum isolation between the ports in FIG. 15 is 6.42 dB.
(70) FIG. 16 shows a top perspective view of a multi-output antenna 110 which is similar to that shown in FIG. 1 but wherein only a single, large, radiating element 12 is used to excite the resonance in a handset chassis. As before, the radiating element 12 is constituted by an L-shaped microstrip patch having a planar portion 20, parallel to a ground plane 18, and an orthogonal portion 22, orthogonal to the ground plane 18. The planar portion 20 is provided on the opposite side of a substrate (not shown) from the ground plane 18, laterally spaced therefrom. The orthogonal portion 22 extends from an edge of the planar portion 20 furthest from the ground plane 18 such that the orthogonal portion 22 is spaced from the ground plane 18 by a first gap 24. In this particular embodiment the first gap 24 is less that 10 mm.
(71) Unlike in FIG. 1, the antenna 110 has a ground plane 18 measuring 5020 mm.sup.2 and the radiating element 12 occupies a space of 2023.5 mm.sup.3, the antenna 110 is therefore well-suited to use in the mobile phone industry.
(72) As shown in FIG. 17, the single radiating element 12 is connected to a first splitter circuit 30 via a first feed port 34. Referring back to FIG. 16, the first feed port 34 extends between the orthogonal portion 22 of the radiating element 12 and the first splitter circuit 30 (illustrated in FIG. 17), which is situated close to the nearest edge of the ground plane 18, and is located approximately one third of the distance along the length of the radiating element 12.
(73) As illustrated in FIG. 17, the first splitter circuit 30 is arranged to divide the one and only first feed port 34 of the radiating element 12 into a first port 38 and a second port 40. The first port 38 is provided with a first matching circuit 42 and the second port 40 is provided with a second matching circuit 44. Together, the splitter circuit 30, the two matching circuits 42, 44, and the two ports 38, 40 make up a control module 54 for the multi-output antenna 110. As before, the control module 54 may also comprise control means for driving each of the ports and tuning each of the matching circuits in accordance with system requirements. It will be understood that as each port incorporates an independent matching circuit its operating frequency and bandwidth can be altered independently, without affecting other resonance frequencies, such as that controlled via the other port.
(74) Although not shown separately, the circuit structure corresponding to the arrangement of FIG. 17 is as illustrated in FIG. 3 in relation to the large radiating element 12 and comprises a first varactor C.sub.1 and a second varactor C.sub.2.
(75) FIG. 18 shows a simulated graph of return loss against frequency for the multi-output chassis-antenna 110 shown in FIGS. 16 and 17, when the first varactor C.sub.1 is varied from 0.22 pF to 10 pF while the second varactor C.sub.2 is fixed at 10 pF. As illustrated, this set-up allows the resonance frequency of Port 1 to be moved from 900 MHz to 1896 MHz, with good isolation (i.e. below 7 dB) with the Port 2. FIG. 19 shows a simulated graph of return loss against frequency for the multi-output chassis-antenna 110 shown in FIGS. 16 and 17, when the second varactor C.sub.2 is varied from 0.3 pF to 10 pF while the first varactor C.sub.1 is fixed at 10 pF. As illustrated, this allows the resonance frequency of Port 2 to be moved from 2448 MHz to over 3000 MHz, with good isolation (i.e. below 7 dB) with Port 1. Thus, with a single radiating element 12 it is possible to have two independent outputs.
(76) FIG. 20 shows a simulated graph of return loss against frequency for the multi-output chassis-antenna 16 shown in FIGS. 1 and 2, which incorporates a pair of radiating elements 12, 14this time occupying a volumetric space of 2023.5 mm and having a ground plane of size of 5020 mm. In accordance with FIG. 3, four varactors (C.sub.1, C.sub.2, C.sub.3 and C.sub.4) having a tuning range of 0.1 pF to 10 pF were employed. FIG. 20 illustrates the 4 independent outputs associated with each of the four ports, when all four varactors are fixed at 10 pF. The four resonance frequencies are 670 MHz, 1840 MHz, 3600 MHz and 5190 MHz, respectively, with reflection coefficients of 9.608 dB, 12.81 dB, 13.21 dB and 15.04 dB, respectively. The maximum isolation between the ports is 7.253 dB.
(77) FIG. 21 shows a top perspective view of a multi-output antenna 120 which is similar to that shown in FIG. 16 but wherein a second large, radiating element 12 is provided at the opposite end of the handset chassis to the single, large, radiating element 12. The radiating element 12 is constituted by an L-shaped microstrip patch having a planar portion 20, parallel to the ground plane 18, and an orthogonal portion 22, orthogonal to the ground plane 18. The planar portion 20 is provided on the opposite side of a substrate (not shown) from the ground plane 18, laterally spaced therefrom. The orthogonal portion 22 extends from an edge of the planar portion 20 furthest from the ground plane 18 such that the orthogonal portion 22 is spaced from the ground plane 18 by a first gap 24. In this particular embodiment the first gap 24 is less that 10 mm.
(78) As shown in FIG. 22, the radiating element 12 is connected to a first splitter circuit 30 via a first feed port 34 as before and the radiating element 12 is connected to a second splitter circuit 30 via a second feed port 34. Referring back to FIG. 21, the second feed port 34 extends between the orthogonal portion 22 of the radiating element 12 and the second splitter circuit 30 (illustrated in FIG. 17), which is situated close to the farthest edge of the ground plane 18, and is located approximately one third of the distance along the length of the radiating element 12. Thus, the radiating element 12 is fed towards the opposite edge of the ground plane 18 than the radiating element 12.
(79) As illustrated in FIG. 22, the first splitter circuit 30 is arranged to divide the one and only first feed port 34 of the radiating element 12 into a first port 38 and a second port 40 having, respectively, a first matching circuit 42 and a second matching circuit 44, as previously. The second splitter circuit 30 is similarly arranged to divide the one and only second feed port 34 of the radiating element 12 into a third port 38 and a fourth port 40 having, respectively, a third matching circuit 42 and a fourth matching circuit 44.
(80) Although not shown separately, the circuit structure corresponding to the arrangement of FIG. 22 is essentially as illustrated in FIG. 3 wherein the small element is replaced by the radiating element 12 which is uncoupled from the radiating element 12. Thus, four varactors (C.sub.1, C.sub.2, C.sub.3 and C.sub.4) having a tuning range of 0.1 pF to 10 pF are employed.
(81) FIG. 23 shows a simulated graph of return loss against frequency for the multi-output chassis-antenna 120 shown in FIGS. 21 and 22, when all four varactors are fixed at 10 pF. This results in four separate resonance frequencies at 680 MHz, 1430 MHz, 2910 MHz and 4520 MHz, respectively, with reflection coefficients of 9.498 dB, 14.40 dB, 20.19 dB and 26.9 dB, respectively. The maximum isolation shown in FIG. 23 is 10.84 dB. Thus, with two radiating elements 12, 12 it is possible to have four independent outputs.
(82) FIG. 24 shows a top perspective view of a multi-output antenna 130 which is similar to that shown in FIG. 1 but wherein a second pair 10 of coupled radiating elements 12, 14 is provided at the opposite end of the ground plane 18 to the first pair 10 of coupled radiating elements 12, 14. The structure of each pair of coupled radiating elements is identical to that described previously although in this case, the ground plane has a size of 5020 mm and each pair of coupled radiating elements occupies a volumetric space of 2023.5 mm. Furthermore, the matching circuit arrangement is as illustrated in FIG. 14, where eight separate ports are employed to produce eight independent outputs using the four radiating elements 12, 14, 12, 14.
(83) FIG. 25 shows a simulated graph of return loss against frequency for the multi-output chassis-antenna 130 shown in FIG. 24, when all eight varactors (one in each matching circuit) are fixed at 10 pF. The eight different resonance frequencies are 630 MHz, 1170 MHz, 1670 MHz, 2390 MHz, 3090 MHz, 3810 MHz, 4490 MHz and 5340 MHz, respectively, with return losses of 9.612 dB, 6.788 dB, 9.483 dB, 9.857 dB, 10.52 dB, 13.81 dB, 19.53 dB and 15.37 dB, respectively. The maximum isolation shown in FIG. 24 is 8.869 dB.
(84) It will be understood that by varying the value of each varactor in each matching circuit, each output can be tuned over a range of frequencies to cover a large operational envelope. It is also apparent that a single radiating element can be employed with appropriate splitter and matching circuits to provide two outputs with independent frequency tunable behaviour. Similarly, two radiating elements can be employed to provide four outputs and four radiating elements can be employed to provide eight outputs. Other embodiments are also envisaged to produce a desired number of outputs by incorporating a suitable combination of splitter circuits, matching circuits and radiating elements in accordance with the present invention.
(85) FIG. 26 shows a range of different shapes which may constitute the radiating elements used to excite the resonance mode of a substrate (e.g. handset chassis or PCB) in any embodiments of the invention. The shape of the radiating element is not limited to the bracket-shapes described above but can be any shape with any size, i.e. circular 140, rectangular 142, elliptical 144, square 146, triangular 148 or trapezium-shaped 150. It is also noted that the radiating elements may be resonant or, perhaps more often, non-resonant elements.
(86) An aspect of the invention provides for an antenna interface module (AIM) comprising a multi-output antenna as described above and an automatic tuning system (e.g. a universal adaptive tuning system) configured to tune each of the multiple outputs to a target operating frequency. It is proposed that the automatic tuning system may therefore optimise the antenna performance in light of environmental changes and may reduce the effect of a user's hand or body on the operating frequencies. More specifically, the same (universal) antenna interface module may be provided in a number of different devices (e.g. mobile phones) and the automatic tuning system may be employed to compensate for differences in the size and/or shape of each device and, in particular, differences in the size and/or shape of each substrate (e.g. chassis) on which the interface module is mounted.
(87) As described above, the multi-output antenna could be provided with one radiating element configured to provide two outputs, two radiating elements configured to provide four outputs and so on. The resonance frequency of each output would be automatically tuned to the target operating frequency by the automatic tuning system. The AIM could find application in Software Defined systems and Cognitive Radio systems for multi-searching functionality or in any current or future portable devices to optimise the antenna performance during use.
(88) As illustrated previously, the radiating elements may be provided as external components attached to a chassis antenna substrate. Alternatively, the radiating elements may be configured as part of an antenna interface module 160 which is attached to a chassis antenna substrate 162 as illustrated in FIG. 27. In this embodiment, the antenna interface module 160 is mounted on a corner of the rectangular substrate 162 and a rectangular ground plane 164 is provided on the top surface of the substrate 162 terminating in line with the start of the antenna interface module 160.
(89) FIG. 28 shows an enlarged top perspective view of the antenna interface module 160. The antenna interface module 160 is constructed from several layers of printed circuit board (PCB) 166 having a single bracket-shaped non-resonant radiating element 168 comprising a planar rectangular portion 170 printed along one edge of the top layer of PCB 166 and a rectangular orthogonal portion 172 depending from the free long edge of the planar portion 170 and extending downwardly for the depth of the PCB 166. Although not shown, the PCB 166 contains all of the circuit components and microprocessors required for the matching circuits, splitter circuit and automatic tuning system associated with the antenna interface module 160. Such an integrated circuit system could be designed and fabricated by any suitable circuit technologies (i.e. simple single or multi-layered PCB (Printed Circuit Board), LTCC (low temperature co-fired ceramic), HTCC (high temperature co-fired ceramic) etc).
(90) FIG. 29 shows an enlarged top perspective view of an alternative antenna interface module 174. The antenna interface module 174 is essentially identical to that described above in relation to FIG. 28 but further comprises a second non-resonant radiating element 176 to provide two more outputs. As illustrated, the second radiating element 176 is of similar size and shape to the orthogonal portion 172 but is incorporated within the layers of the PCB 166 such that it essentially extends downwardly through the PCB 166 from adjacent the other long edge of the planar portion 170.
(91) FIGS. 30A through 30C show the antenna interface module 160 of FIG. 28 mounted on various different antenna substrates. The first substrate 180 (of FIG. 30A) is essentially similar to that shown in FIG. 27. The second substrate 182 (of FIG. 30B) is narrower and longer than that shown in FIG. 30A. The third substrate 184 (of FIG. 30C) is wider and shorter than that shown in FIG. 30A. In each case, the antenna interface module 160 is mounted on a corner of the rectangular substrate 180, 182, 184 and a rectangular ground plane 186 is provided on the top surface of the substrate terminating in line with the start of the antenna interface module 160. It will be understood that, in use, each of the antenna interface modules 160 will employ its automatic tuning system to compensate for the different shapes of the substrates 180, 182, 184 so as tune the outputs to the desired operating frequencies. Thus, the antenna interface module 160 is suitable for use in devices (i.e mobile handsets) having different size or shapes, therefore constituting a universal antenna interface module.
(92) FIG. 31 shows a circuit diagram 190 corresponding to the antenna structure of FIG. 17, with 2 additional (shunt) varactors C.sub.4 and C.sub.5 provided for an associated automatic tuning system. Thus, the circuit diagram 190 is suitable for use in the antenna interface module 160 and comprises a splitter circuit 192 connected to the single radiating element 168, a first matching circuit 194 connected to Port 1 and a second matching circuit 196 connected to Port 2. The additional varactors C.sub.4 and C.sub.5 are provided between the splitter circuit 192 and each matching circuit 194, 196 and connected to ground. In practice, the value of each of the additional varactors C.sub.4 and C.sub.5 will be controlled by the automatic tuning system as will be described below so as to retune each Port to a desired output frequency. It will be noted that the varactors C.sub.2 and C.sub.3 in each matching circuit 194, 196 are still employed to achieve the wide tuning range of each associated output.
(93) FIG. 32 shows a block diagram of an automatic tuning system 200 for use with the circuit diagram 190 of FIG. 31 in the antenna interface module 160. The automatic tuning system 200 is arranged to monitor a power level of a reflected signal of the target operating frequency at each port (Input RF_1 and Input RF_2) and to adjust a bias voltage of the respective additional varactors C.sub.4 and C.sub.5 so as to minimise the power level of the reflected signal. As illustrated, the automatic tuning system 200 therefore further comprises a directional coupler 202, 204 connected, respectively, to each port, a power detector 206, 208 connected, respectively, to each directional coupler 202, 204, a sampling analogue to digital converter (ADC) 210, 212 connected, respectively, to each power detector 206, 208, a microprocessor 214, 216 connected, respectively, to each ADC 210, 212 and 2 digital to analogue converters (DAC) 218 connected, respectively, to each of the microprocessors 214, 216. Each microprocessor 214, 216 employs an appropriate algorithm which is configured to provide a bias voltage (via the DACs 218) to an associated one of the varactors C.sub.2, C.sub.3, C.sub.4, C.sub.5 in the circuit diagram 190.
(94) FIG. 33 shows a circuit diagram 210 corresponding to the antenna structure of FIG. 31, with a further 2 additional (shunt) varactors C.sub.6 and C.sub.7 provided for an associated automatic tuning system to improve the matching performance of the AIM, offer more flexibility and improve the signal sensitivity in different environments. The circuit diagram 210 is essentially as described in relation to FIG. 31 but with the 2 additional (shunt) varactors C.sub.6 and C.sub.7 connected respectively to an initial shunt inductor L.sub.4 and L.sub.5 in each matching circuit 212, 214 and then connected to the ground. Thus, the single radiating element 168 is provided with two matching circuits 212, 214, each of which comprises three varactors.
(95) FIG. 34 shows a block diagram of an automatic tuning system 220 for use with the circuit diagram 210 of FIG. 33 in the antenna interface module 160. The automatic tuning system 220 is substantially as described above in relation to FIG. 32 but with each microprocessor 222, 224 employing an appropriate algorithm which is configured to provide a bias voltage (via 3 separate DACs 226) to an associated one of the three varactors in each matching circuit 212, 214. Thus, the automatic tuning system 220 comprises 6 DACs 226 in total, connected to the 6 varactors in the circuit diagram of FIG. 33.
(96) According to the above, embodiments of the present invention provide a multi-output tunable antenna which is able to cover existing cellular services such as DVB-H, GSM710, GSM850, GSM900, GPS1575, GSM1800, PCS1900, UMTS2100 and WiFi bands simultaneously. The antenna is also suitable for Cognitive Radio systems which might require a multi-resolution spectrum sensing function. The proposed antenna is therefore an ideal candidate for portable devices which require multi-service access simultaneously, and is particular well suited to applications involving small terminals such as smart phones, laptops and PDAs.
(97) It will be appreciated by persons skilled in the art that various modifications may be made to the above-described embodiments without departing from the scope of the present invention. In particular, features described in relation to one embodiment may be incorporated into other embodiments also.
