GB2427759A

GB2427759A - Antenna element coupled to a differential feed arrangement

Info

Publication number: GB2427759A
Application number: GB0513053A
Authority: GB
Inventors: Terence Edwin Dodgson; Ee Lee; Kin Meng Chan; Peter Gardner; Peter Scott Hall
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 2005-06-27
Filing date: 2005-06-27
Publication date: 2007-01-03
Anticipated expiration: 2025-06-27
Also published as: GB0513053D0; GB2427759B

Abstract

An antenna suitable for mobile communication terminals comprises an antenna element 201 with a feed arrangement comprising a feed line 209 on a substrate with two feed ports 205, 207 wherein the feed structure is not in direct contact with the antenna element 201. The signals to the feed ports 205, 207 may have different phases and may be differential signals. The antenna element 201 may be a microstrip patch, slot or dielectric antenna. The feed ports 205, 207 may be at either end of a feed through line 209 or at the distal ends of collinear lines with a gap between their proximal ends. The feed arrangement may operate as a form of aperture or proximity coupling. The antenna may be a multi-layer structure comprising a ground plate 204 with a coupling aperture 203 which may be arranged between the antenna element 201 and the feed arrangement or the feed arrangement may be located between the ground plate and the antenna element. The coupling aperture 203 may have a rectangular, bowtie, dog-bone or H-shape. The antenna may have a conductive case and the feed structure may be formed on the same substrate or monolithic integrated circuit (MMIC) chip carrier as a transceiver. The antenna may provide a simple, compact and cheap antenna design.

Description

Antenna design The present invention relates to antenna designs suitable

for mobile wireless communications systems. More particularly, but not exclusively, the invention relates to fully integrated compact noncontact antenna designs.

Background

In recent years there is an increasing demand for low cost robust and compact antenna elements in the wireless communications market.

Non-contact coupling methods are considered as advantageous for the use in compact antenna arrays because of its planar structure and thus simple to fabricate. Also, a non-contact coupling is compatible with microstrip circuitry, which is usually used in wireless communications application.

There are two well-established non-contact feeding techniques suitable for coupling electro-magnetic energy from a microstrip circuit to an antenna structure. These techniques are known as aperture coupling and proximity coupling. Aperture coupling has been described in D. M Pozar "A microstrip antenna aperture coupled to a microstrip line ", Electronics Letters, Vol. 21, No. 2, Pg 49-50, Jan 1985 and proximity coupling in S. Vajha, S. N. Prasad "Design and Modelling of Proximity coupled Patch Antenna", 2000 IEEE APS Int'l Symp, 6-8 Nov, pg 43-46.

Referring now to Figure 2, these two techniques will be briefly described.

Figure 2A is a schematic diagram illustrating a single feed non-contact coupling anteima structure, including both an aperture coupled patch antenna and an aperture coupled dielectric resonator antenna (DRA). The structure includes an antenna 101 element and a feed line 107 for providing the antenna with signals. A ground plane 105 is provided in between the antenna element 101 and the feed line 107. The ground plate 105 is provided with an aperture 106 for coupling the signals from the feed line 107 to the antenna element 101. The feed line 107 is provided on the circuit substrate 109, which also includes the transceiver circuit (not shown). The antenna element 101 may for example be a patch antenna 111 provided on an antenna substrate 103, or DRA 113. If a DRA is used the DRA 113 is directly mounted onto the ground plate 105.

Conventional feeding techniques using a microstrip feed line and probe feed are inherently asymmetric. This generates high order modes that produce cross-polarized radiation. Aperture coupling uses a common ground plane between the radiating antenna and the feed line. Ideally this should reduce the level of cross-polarized radiation. As the antenna and radio frequency (RF) circuit are constructed on separate substrates, it allows independent selection of antenna and feed substrate material. The use of a high permittivity material for the RF circuit and a low permittivity material for the antenna allows optimum RF performance for both. Substrate space for both antenna and the RF circuit are also increased. One attractive benefit of the aperture coupling is that no extra component or assembly processes are required; the only requirement is a properly etched aperture in the ground plane between the antenna and the feed line. This coupling method basically removes the need for any via hole.

Figure 2B is a schematic diagram illustrating a single feed non-contact proximity coupling anteima structure, including both a proximity coupled patch antenna and a proximity coupled dielectric resonator antenna (DRA).

The structure includes again an antenna element 101, a ground plane 105 and a feed line 107. However, in this case the feed line is provided on a layer in direct proximity to the antenna element 101, whereas the ground plane 105 is provided on a layer below the feed line 107. In this way the signals are coupled directly from the feed line 107 to the antenna element 101, and no aperture is required. Again, the feed line 107 is provided on the circuit substrate 109, which also includes the transceiver circuit (not shown).

The proximity coupling technique is also shown using a patch antenna 111 mounted to an antenna substrate 103, or a DRA 113. If a DRA is used the DRA 113 is directly mounted onto circuit substrate 109.

For the proximity coupling technique, the feed line is in between the antenna and the ground plane, i.e. provided in between two substrates. Due to this structure involving two substrates the advantages provided are similar to those of the aperture coupling apply to this technique as well. Unlike the aperture coupled patch, the absence of an aperture in the ground plane in a proximity coupled patch produces a lower back radiation performance.

Waterhouse in W. S. T Rowe, R. B Waterhouse "Investigation of Proximity Coupled Antenna Structures ", 2003 IEEE APS Int'l Symp, Vol. 2, 22-2 7, June 2003, pg. 904-907 has shown that varying the width of the patch element has a minimal effect on the operating frequency while offering control of the resonant ioop size. The location of the microstnp line open circuit termination can also influence the position of the resonant loop with minimal impact on other antenna characteristics. Therefore, the results suggest that the patch length can be used to set the antenna frequency of operation and the patch width and open circuit position can be used to maximize the bandwidth performance. It was also highlighted that if the patch substrate was made thinner, an enlarged impedance loop results. However, the effects are reversed for a thicker feed substrate. This suggests that the thickness of the both substrates can also be used to maximize the bandwidth performance.

Referring now to Figure 2C, the transition between the antenna and the transceiver chip is briefly described for the above single feed noncontact coupling antenna structure.

The feed structure 107 is connected to an amplifier 123 and a balun (balanc ed-unbalanced) circuit 121. The two output ports of the balun are then coupled to a balanced differential mixer 125. The mixer 125 is part of the transceiver chip.

In "A differential Active Patch Antenna Element for Array Applications" by T. Brauner et al., IEEE Microwave and wireless components letters, Vol. 13, No. 4, April 2003, a differential aperture-coupled patch antenna array is described. The aperture coupling used in this paper is basically the same technique as the one described above with reference to Figure 2. Two feed lines and thus two aperture feed slots are used for coupling the energy between the feed structure and the antenna in order to achieve the differential effect. The current maximum built for coupling the signals between the antenna element and the feeding structure is generated by an open circuit termination.

It is an aim of the present invention to provide an alternative and improved antenna structure. It is a further aim of the present invention to provide a method and system of spatially coupling differential signals to an antenna structure.

According to one embodiment of the present invention, there is provided an integrated antenna system for use in mobile communication terminals, the antenna comprising: an antenna element and a feed substrate including a feed structure comprising a feed line with a first and a second port, whereby the first port is adapted to be supplied with a first signal having a first phase and the second port is adapted to be supplied with a second signal having a second phase, and wherein the feed structure is not in contact with the antenna element.

In this way the physical connection between the antenna and transceiver circuitry is removed, and differential signals are combined and electromagnetically coupled into a radiator.

The advantages described above of having a non-contact coupling are thus combined with those of having a differentially fed antenna.

The antenna structure is also very much simplified compared the design described by Brauner et al in the paper cited above. As a result of the simplification, a much tighter integrated active antenna implementation as compared to the design proposed by Brauner et al is feasible.

An advantage of such an antenna structure is that it provides for the feeding circuitry to be integrated in a monolithic integrated circuit (MMIC) with no need for an output bond connection.

Also, the systems allows various resonant antennas to be interchanged using the same MMIC to suit different applications. Thus the advantage of reconfiguring the antenna allows the use of a single RF transceiver chip suitable for multiple standards.

A further advantage is that the described structure provides a simple and elegant solution, resulting in a simple to built and thus cost-efficient design.

Preferably, a single feed line is provided.

In this way the current maximum is generated by feeding a single transmission with a differential signal. This will generate a virtual short circuited under the coupling aperture. In this particular embodiment, only one aperture slot is needed.

Preferably, the odd mode is used to generate the current maximum to feed the antenna differentially using a single feed line and a single aperture.

According to another aspect of the present invention, there is provided an antenna system for use in mobile communication terminals, the antenna comprising: an antenna element and a feed substrate including a first and a second port, whereby the feed line is adapted to be differentially fed via the first and second port and wherein the feed structure is not in contact with the antenna element.

According to another aspect of the present invention, there is provided an antenna system for use in mobile communication terminals, the antenna comprising: an antenna element provided on a first layer and a feed substrate including a feed structure provided on a second layer different to said first layer, wherein the feed structure comprises a first and a second port, wherein the feed structure is adapted to be differentially fed via the first and second port and wherein the feed structure is not in contact with the antenna element.

According to another aspect of the present invention, there is provided an antenna system for use in mobile communication terminals, the antenna system comprising: a conducting case; a transceiver circuit provided on a substrate; and an antenna element; wherein the system further comprises an antenna feed structure provided on the transceiver circuit substrate, wherein the feed structure comprises a feed line with a first and a second port, wherein the feed line is adapted to be differentially fed via the first and second port and wherein the feed structure is not in contact with the antenna element.

According to another aspect of the present invention, there is provided an antenna system for use in mobile communication terminals, the antenna system comprising: a conducting case, a transceiver circuit provided on a substrate inside said conducting case, and an antenna element; wherein the system further comprises a feed structure provided on the chip carrier of the transceiver chip comprising a feed line with a first and a second port, wherein the feed line is adapted to be differentially fed via the first and second port and wherein the feed structure is not in contact with the antenna element.

According to another aspect of the present invention, there is provided an antenna system for use in mobile communication terminals, the antenna system comprising: a conducting case, a transceiver circuit provided on a chip, and an antenna element; wherein the feed structure comprises a feed line with a first and a second port provided on the transceiver chip, wherein the feed line is adapted to be differentially fed via the first and second port; and wherein the feed structure is not in contact with the antenna element.

According to yet another aspect of the present invention, there is provided an antenna system for use in mobile communication terminals, the antenna comprising: an antenna element and a feed substrate including a feed line with a first and a second port, whereby the feed line is adapted to be differentially fed via the first and second port and wherein the feed structure is not in contact with the antenna element.

Embodiments of the present invention will now be described, by example only, with reference to the accompanying figures, whereby: Fig. I is a schematic front view of a mobile terminal in which the present invention can be implemented; Fig. 2A is a schematic diagram illustrating a single feed non-contact coupling antenna structure according to the prior art; Fig. 2B is a schematic diagram illustrating a single feed non-contact proximity coupling antenna structure according to the prior art; Fig. 2C is a schematic illustration of the transition between the antenna and the transceiver chip according to the prior art; Fig. 3A is a schematic illustration of the concept of a differential feed aperture coupling method; Fig. 3B is a schematic illustration of a differential feed aperture coupling antenna system according to one embodiment of the present invention; Fig. 3C is a schematic illustration of a differential feed aperture coupling antenna system according to another embodiment of the present invention; Fig. 3D are schematic illustrations of alternative slot shapes for use in differential feed aperture coupling methods; Fig. 4A is a schematic illustration of the concept of a differential feed proximity coupling method; Fig. 4B is a schematic illustration of a differential feed proximity coupling antenna system according to another embodiment of the present invention; Fig. 4C is a schematic illustration of a differential feed proximity coupling antenna system according to another embodiment of the present invention; Fig. 4D is a schematic illustration of an alternative feed structure for use in differential feed proximity coupling methods according to another embodiment of the present invention; Figs. 5A and 5D are schematic illustrations of the concept of a differential feed through-line proximity coupling method; Fig. 5B is a schematic illustration of a differential feed through-line proximity coupling antenna system according to another embodiment of the present invention; Fig. SC is a schematic illustration of a differential feed through-line proximity coupling antenna system according to another embodiment of the present invention; Figs. 6 and 7 illustrate simulation results for antenna systems using a differential feed aperture coupling, a differential feed proximity coupling and a differential feed through- line proximity coupling according to different embodiments of the present invention; Fig. 8A illustrates a schematic outline of a passive differential feed aperture coupling antenna system according to another embodiment of the present invention; Fig. 8B illustrates a schematic outline of an active differential feed aperture coupling antenna system according to another embodiment of the present invention; Fig. 9 illustrates the measured return loss and isolation performance of an antenna system according to another embodiment of the present invention; Fig. 10 illustrates the measured power gain of an amplifier of an antenna system according to another embodiment of the present invention; Fig. 1 1A and B are schematic illustrations of off-chip implementations of two differential feed non-contact coupling integrated antenna systems according to another embodiments of the present invention; Fig. 1 2A is a schematic illustration of an on-carrier implementation of a differential feed non-contact coupling integrated antenna system according to another embodiments of the present invention; Fig. I 2B is a schematic illustration of an on-chip implementation of a differential feed noncontact coupling integrated antenna system according to yet another embodiments of the present invention; Fig. 13A is a schematic illustration of a single feed active push-pull antenna structures architecture according to the prior art; Fig. 1 3B and 1 3C are illustrations of dual feed push-pull integrated active antenna structures for a patch antenna and a resonant slot antenna,

respectively, according to the prior art.

Figure 1 is a schematic illustration of a mobile communication terminal 10. The terminal 10 includes a display 26, microphone 16, speakers 18, a keypad 21, antenna 20 and navigation keys 23.

In the following three methods of spatially coupling differential signals to an antenna structure will be described. In these methods, differential signals are used to generate either a current or fringing field maximum close to the antenna. If the antenna is positioned appropriately close to these current maximumlfringing field, electro-magnetic energy can be efficiently coupled from the transmission line to the antenna. These noncontact differential feed techniques can be applied to the Microstrip Patch, Dielectric Resonator Antenna (DRA), Resonant Slot antenna and other antenna.

Differential feed aperture coupling method.

Referring now to Figure 3A, a simplified concept of a first feeding technique, referred to as differential feed aperture coupling method, will be described. The antenna element 201 is provided with signals via the feeding structure, i.e. a feed line 209. The feeding line 209 includes a first port 205 and a second port 207. The antenna system further comprises a ground plate 204 with a coupling aperture 203. Differential signals are fed into both ends of the feed structure 209, i.e. a first signal with a first phase of 0 degrees is fed to the first port 205, and a second signal with a second phase of 180 degrees is fed into the second port 207. In this way a current maximum is created in the middle of the feed structure, thereby coupling energy through the aperture 203 into the antenna 201.

It is noted that the current maximum is similar to that of the single feed aperture coupled patch in which the current maximum is created by a quarter wave open circuit stub, such as described in Pozar et al. (see above).

Referring now to Figure 3B, an implementation of the differential feed aperture coupling method using a microstrip patch antenna will be described.

The feed structure 209 is applied to a first substrate 211. The arrangement further includes ground plate 204 with a slot aperture 203, and a patch antenna 213 provided on a second substrate 215. The feed line 209 is provided with a first 205 and a second port 207. The patch antenna 214 is a 1.8GHz resonant patch with a size of 36mm by 36mm. Figure 6 illustrates simulation results of this implementation. It can be seen from Figure 6 that a good return loss performance is achieved.

Referring now to Figure 3C, the above described feeding technique is applied to the design of a differential fed aperture coupled dielectric resonator antenna (DRA). It is noted that the method used for this implementation is similar to the single feed aperture coupling method applied to a DRA as described in St. Martin, J.T.H.; Antar, Y.M.M; Kishk, A.A.; Ittipiboon, A.; Cuhaci, M "Dielectric resonator antenna using aperture coupling", Electronics Letters, Volume 26, Issue 24, 22 Nov. 1990 Page(s):2015 - 2016. However, here a feed line 209 applied to substrate 211 is used which again includes a first and a second port (205 and 207), which are fed with differential signals. The arrangement further includes a ground plate 204 with slot aperture 203. The DRA element 217 is situated on top of ground plate 204.

In the above examples, a simple coupling slot has been used to illustrate the differential coupling technique. However, it is appreciated that, similar to the conventional single feed aperture coupled antenna designs as described in Rathi, V., Kumar, G., Ray, K.P "Improved coupling for aperture coupled microstrip antennas ", Antennas and Propagation, IEEE Transactions on Volume 44, Issue 8, Aug. 1996 Page (s):1196 - 1198, other aperture shapes can be used. Referring now to Figure 3D, alternative slot shapes, such as "bowtie", "dogbone", "H-shaped" or "Hour glass" slots are shown.

Differential feed proximity coupling method Referring now to Figure 4A, a simplified concept of a second feeding technique, referred to as differential feed proximity coupling method, will be described. The antenna element 301 is provided with signals via the feeding structure 309. The feeding structure 309 includes a first portion 305 and a first port and a second portion 307 and a second port. Both portions of the feeding line 309 are co-linear and a gap 322 is provided between the two portions 305 and 307. The antenna system further comprises a ground plate 320 situated below the feeding structure 309.

Again, differential signals are fed into both ends of the feed structure 309. In this way a fringing field across the feed gap is generated with the differential signals. This fringing field will enable the electromagnetic energy to couple to the antenna efficiently.

It is noted that the above described proximity coupling method works particularly well with antennas of certain electromagnetic field configuration, such as patch antenna and DRA.

Referring now to Figure 4B, an implementation of the differential feed proximity coupling method using a microstrip patch antenna will be described. The feed structure 309 is applied to a first substrate 311. The arrangement further includes ground plate 320. A patch antenna 313 provided on a second substrate 315. The feed structure 309 is provided with a first 305 and a second port 307. The patch antenna 214 is a 1.9GHz resonant patch with a size of 36mm by 36mm. Figure 6 illustrates simulation results of this and other implementations (see below). The return loss performance is shown as a function of the frequency. It can be seen from Figure 6 that a good return loss performance is achieved.

Referring now to Figure 4C, the above described feeding technique is applied to the design of a differential fed proximity coupled dielectric resonator antenna (DRA). The design is similar to the patch antenna design described above with reference to Figure 4B. However, here the DRA element 317 is situated directly on top of substrate 315 including the feed structure 309.

The simulation results for both antenna systems are also included in Figure 6. It can be seen that a good return loss performance is achievable Figure 7 illustrates simulation results for different differential proximity coupled microstrip patch antennas. The simulated return loss in dB is shown as a function of the gap width normalised to the patch length. Three different patch sizes (26mm x 36mm, 36mm x 36mm and 50mm x 40mm have been simulated. In addition, the results for a single fed proximity coupled antenna patch of the size 50mm x 40mm have been simulated for comparison.

In the case of the differentially fed patch antenna, it is interesting to note that by varying the feeding gap, good return loss performance was observed over a broad range of gap width, as can be seen from Figure 7. This seems to hold true for a variety of different patch sizes. It is also interesting to note that for very small gap sizes, the return loss stays below -10dB regardless of the patch sizes used.

Tuning for the differentially fed proximity coupled patch can be easily achieved by varying the gap width. As can be seen from the Figure 7, the matching performance of the single fed proximity coupled patch is considerably worse compared to the equivalent differential fed design.

In the paper by Waterhouse (see above) it has been suggested that the patch width, open circuit position and the design of both antenna and circuit substrate could be used to improve the return loss performance. In this respect, the differentially fed proximity coupling method is superior. As the return loss of the differentially fed antenna is not sensitive to the gap width, this suggests that antennas with different operating frequencies can be swapped without adversely affecting its performance. In this way, if the operating frequency changes, the antenna can be simply upgraded to the new operating frequency band without any need for the re-design of the antenna and its associated matching circuitry. This will significantly lower the associated design cost and turnover time needed to get the design to market.

It is noted that the feeding gap illustrated in Figures 4A, B and C is only one of many ways that a gap coupled differential feed design can be implemented. Figure 4D illustrates an alternative way of a gap configuration suitable for proximity coupling. It is appreciated that other alternative ways of implementing the proximity coupling can be applied.

The simulated results imply that the differential feeding network has a very broadband performance. This suggests that antennas operating at different frequencies can be swapped without any adverse impact on the matching performance. The advantage offered by the possibility of reconfiguring the antenna allows for example the use of a single multistandard RF transceiver chip.

Differential Feed Throu2h-line Proximity Coupling Method Referring now to Figure 5A, a simplified concept of a further feeding technique, referred to as differential feed through-line proximity coupling method, will be described. The concept of a passive balanced implementation will be shown. The antenna element 413 is provided with signals via the feeding structure 409. The feeding line 409 includes a first port 405 and a second port 407. Again, differential signals are fed into both ends of the feed structure 409. This technique operates similarly to the first technique in which a current maximum is created in the middle of the differential feed line. The difference is that the current maximum couples the energy straight into the antenna element 413. The ground plate 404 is provided with a slot 433 as a coupling structure.

Referring now to Figure 5B, an implementation of the differential feed through-line coupling method using a microstrip patch antenna will be described. Here, a patch antenna 413 is used, and the ground plate 404 is provided with a slot 403 under the feed line 407 as can be seen in figure 5B.

In this particular embodiment, the patch antenna is suspended in air above the feed line. An alternative way is to print the antenna on another substrate and placed it over the feed line similar to the design shown in Figure 4.

Figure 5D illustrates a simplified concept of the through-line proximity coupling method for the use with slot antennas. The feeding structure 409 is analogue to that described above with reference to Fig. 5A. However, the antenna element 431 is provided as a slot antenna 431 in the ground plate 404.

Figure 5C illustrates a possible implementation of the differential feed through-line proximity method. As can be seen from Figure 6, a good return loss performance is also achievable for this antenna coupling structure.

Again, good return loss performance can also be achieved for this implementation, as can be seen from Figure 6.

It is noted that, similar to the aperture slots described above with reference to Figures 3A to D, different shapes of the slots can be used. This applies both to the patch and to the resonant slot antenna structure shown in Figure 5B and 5C.

Integrated Antenna Designs In recent years, increasing demand in the wireless communication market has generated the need for compact and fully integrated radio frequency (RF) front end products. This has led to the development of fully integrated antenna chip modules.

However, due to its small radiation aperture, chip antennas usually suffer from poor antenna performance at low radio frequencies. In order to overcome this limitation, the viable alternative is to couple the electromagnetic energy from the transceiver chip to an externally built antenna.

Two types of antenna integrated circuit (IC) packages have been proposed. In the first instance, the antenna was built on the chip carrier and energy was coupled to it through the use of a single feed proximity coupling (see Song, C. T P. et al Packaging technique for gain enhancements of electrically small antenna designed on gallium arsenide" Electronic Letters, vol. 36, Issue 18, Aug. 31, 2000, pp. 1524-1525) Inthe second example, it was proposed that the chip carrier itself could also be used as the radiator (see Alexander Paviovich Popov et al,"Package Integrated Antenna for circular and linear polarizations", US patent 6879287, 12th1 April 2005). Although in both cases, a compact design has been realized, a much bigger transceiver chip will be needed to meet the antenna real estate requirement. This will inadvertently increase the cost of the IC chip.

Active and Passive Integrated Antenna design Referring now to Figure 13, active antenna implementation as known in the art are briefly described.

In Figure 2C, a first active integrated antenna implementation is shown. The antenna system is similar to the configuration described in S. Vajha, P. Shastry" A Novel Proximity Coupled Patch Antenna for Active Circuit Integration", 2001 IEEE APS Int'l Symp, Vol. 4, 8-13 July, pp 772- 775, which is herewith incorporated by reference. Similarly, the active integrated antenna concept can also be applied to an aperture coupled antenna, as described in Jong Moon Lee, Won Kyu Choi, Cheol Sig Pyo " RF Integrated Aperture Coupled Antenna for Satellite Communication at KUband", 2003 IEEE APS Int'l Symp, Vol.4, 22-27, June, pg 702-705. In the latter case, the active RF circuitry is shielded by the ground plane, spurious radiation from the circuit can thus be minimized.

Apart from the abovementioned single feed active integrated antenna approach, another interesting active antenna uses a push-pull configuration as illustrated in Fig. I 3A. This configuration uses two 180 hybrids on the inputs and outputs of a pair of push-pull amplifiers, as described in Pang Cheng Hsu, Cam Hguyen, Mark Kintis " Uniplanar BroadBand Push-Pull FET Amplifiers" IEEE MTT Transactions, Vol. 45, Issue 12, Dee, pp 2150-2152, which can be fed to a single feed antenna. It is noted that in this particular design, the use of two hybrids requires a big portion of the circuit space and the losses of the hybrids will degrade the amplifiers' performance.

As described in Deal, W.R.; Radisic, V.; Yongxi Qian; Itoh, T "Novel pushpull integrated antenna transmitter front-end" Microwave and Guided Wave Letters, IEEE Volume 8, Issue 11, Nov. 1998 Page(s):405 - 407 and Deal, W. R.; Radisic, V.; Yongxi Qian; Itoh, T "Integrated-antenna push-pull power amplifiers" Microwave Theory and Techniques, IEEE Transactions on Volume 47, Issue 8, Aug. 1999 Page(s):1418 - 1425, the antenna, in addition to acting as a radiator, can also be used as a 0 dB power combiner. Examples of such active integrated antennas are shown in figures 13B and 13C.

In the following examples will be given how the above described noncontact differential feed methods can be implemented. Below, the implementation of a passive and an active antenna design will be described.

The above described antenna coupling techniques can be implemented in a compact integrated antenna design. Figure 8A illustrates an example of an integrated passive antenna using the aperture-fed differential feeding technique described above with reference to Figure 3A, and an active implementation is shown in figure 8B.

Referring now to Figure 8A, the layout of the passive antenna design will be described. It consists of two layers (501 and 503) of substrate. The substrate may for example be made of FR4 material of different heights, such as 1.6mm substrate for the first layer 501 and 0.8mm substrate for the second layer 503. The first layer includes a patch antenna 505, whereas the second layer 503 includes a feeding structure 507 in form of a ring hybrid. The ring hybrid is fabricated on the underside of the second layer substrate 503. The patch antenna 505, for example a 36mm by 36mm square patch antenna, is provided onto the top side of the first substrate 501. The ring hybrid includes a first port 509 and a second port 511 for providing the antenna signals. Here, the signal is fed into the first port 509 of the ring hybrid and the second port 511 is terminated with 50 ohm. The difference ports are directed inwards to join in the middle and to create a short circuit at the centre of the line as explained above. A ground plate 513 is placed in between the first and the second substrate layers 501 and 503. Ground plate 513 includes an aperture 515 for coupling the energy from the feeding structure 507 to the patch antenna 505.

Referring now to Figure 8B, the active implementation will be described. The overall structure of the active antenna element is the same as that of the passive element described above. Figure 8B is a schematic outline of the ring hybrid structure 509 of Figure 8A, but for the active implementation.

Two amplifiers 521 are introduced in the central part of the ring hybrid structure. For the above implementation, two Agilent MGA-83563 amplifier ICs were used in a push-pull configuration. The amplifiers 521 are placed on the difference ports, with the amplifiers' outputs facing each another as shown in figure 8B.

During odd mode excitation, the amplifiers will be in a push-pull configuration creating a current maximum at the short circuit point. In this implementation, the output matching of the amplifiers could be easily achieved by modifying the aperture dimensions. In this case, the aperture's length was increased from 18mm in the passive version to 25mm in the active version to match the load impedance to the amplifiers without the need for any external matching circuit.

Figure 9 shows the measured return loss and isolation performance for the differential fed aperture coupled microstrip patch antenna in the passive configuration. The return loss S 11 and the isolation Si 2 between the feeding port and the sum port are shown as a function of the transmission frequency of the antenna arrangement.

As can be seen from Figure 9, the measured results show good return loss below -20dB at the resonant frequency. The isolation between the feeding port and the sum port is high over a wide bandwidth.

In order to compare the active and passive design, the gain of the active integrated antenna can be approximated by benchmarking its output performance against a similar passive antenna structure. Figure 10 shows the measured output powers of the passive and active antennas. The output power of both the passive and the active antenna structures are shown as a function of the input power. The difference (in dB) between the two measurements can then be used to quantify the gain of the amplifier. As can be seen from Figure 10, the power gain achieved with the implementation as described above is 22dB. Gain compression in the active antenna is apparent for input powers above about 2dBm. The manufacturer's specification gives a 1dB compression point of I 9.7dBm at the output, corresponding to -1.3dBm at the input. Taking account of the 3dB coupling factor and approximately 1dB excess loss in the ring hybrid, we would therefore expect 1dB gain compression to occur at an input power of 2.7dBm, which is consistent with the measured result.

It is noted that with active device integration, matching can be done in the slots for the above described aperture coupling and through-line proximity coupling techniques. The slot can also be used to tailor the harmonic impedances, which optimises the efficiency and linearity (harmonic and intermodulation) for several different class of amplifiers.

Off Chip Implementation As explained above, the trend towards a transceiver chip suitable for multiple standards implies that a multiband antenna or a reconfigurable antenna capable of operating at various distinct frequencies is desirable.

in order to implement an antenna suitable for these requirements, one possibility is to implement the feeding and antenna structures externally to the transceiver IC chip. Such an implementation will be referred to as off chip' antenna in the following. In this way an increased flexibility in design and a reduction in the chip carrier size can be achieved. This will then also result in a reduced cost of the radio frequency transceiver chip.

Referring now to Figure 11, two different integrated antenna systems in an off-chip implementation will be described.

Figures hA and B illustrate a first and a second implementation, respectively. In both cases, the radio frequency front end circuitry is enclosed inside a metal conducting box 601. This results in good electromagnetic shielding of the device.

In both cases the conducting box 601 includes a substrate 603, and provided thereon a transceiver chip 608 and a feed line 602. The feed line 602 is constructed such that it is suitable for a non-contact coupling such as those described above. The conducting box 601 is closed by ground plane 605.

Figure 9 also includes a suitable design for the transceiver chip 608, comprising low noise amplifiers (LNA) 610 and mixers 612.

In the first implementation shown in Figure 11 A, a coupling slot 606 is introduced into the ground plane 605 of the conducting box 601.

Electromagnetic energy is coupled through the slot 606 to an external patch antenna 609 provided to antenna substrate 607. Patch antenna 609 is covered by a radome 611.

In the second implementation shown in Figure 1IB the energy is directly coupled to a slot antenna 604 in ground plane 605.

On Chip or On Carrier Implementation Alternatively to the implementation described above, so-called on- chip' or on carrier' implementations are possible, wherein the differential feeding network for the antenna can be implemented either on the silicon chip or on the chip carrier, respectively.

Referring now to Figure 12, a differential feeding network implementations on chip' and another one on chip carrier' will be described with reference to Figures 12A and 12B, respectively.

In both cases, the radio frequency front end circuitry is enclosed inside a metal conducting box 701. The conducting box 701 includes a circuit substrate 603, and mounted thereon is a transceiver chip carrier 703. The IC chip 708 together with the feed line 702 is mounted on top of the chip carrier.

The transceiver chip carrier 703 is then mounted onto the circuit substrate 603 by conventional soldering techniques. Again, the feed line 702 is constructed such that it is suitable for a non-contact coupling such as those described above. The conducting box 701 is closed by ground plane 705.

The differential feeding structure 702 has been etched onto to the chip carrier 703 together with a coupling slot 706. The electromagnetic energy is then coupled through the aperture slot 706 directly to the patch antenna 709 etched onto the conducting box 701.

Figure 12 also includes a suitable design for the transceiver chip 708, comprising RFCs 716, bias tees 714, RF signal source 718, amplifiers 720, power source 722 and connections to the feed lines 730 of the feeding structure 702 on the chip carrier 703. The differential amplifier 720 of the radio frequency circuitry is directly wire bonded to the differential through line 730.

Referring now to Figure 12B, the on-chip implementation will be described. Here, the differential feeding structure 702 is implemented on the transceiver chip 708 itself. The outline of the antenna structure is similar to the on-carrier implementation described above. However, the transceiver chip here includes the feed lines 740, which provide a gap between the microstrip lines 740 for providing proximity coupling as described above, and the antenna structure 709 has been etched on the conducting box 701.

In this way the electromagnetic energy is coupled directly from the onchip differential amplifiers 720 to the external antenna 709.

Although in the above described embodiments patch antennas, dielectric resonator and slot antennas have been described, it is appreciated that alternatively other antenna design can be used.

It is to be understood that the above describes embodiments are set out by way of example only, and that many variations or modifications are possible within the scope of the appended claims.

Claims

CLAIMS: 1. An antenna system for use in mobile communication terminals,

the antenna comprising: an antenna element and a feed substrate including a feed structure comprising a feed line with a first and a second port, whereby the first port is adapted to be supplied with a first signal having a first phase and the second port is adapted to be supplied with a second signal having a second phase, and wherein the feed structure is not in contact with the antenna element.
2. An antenna as claimed in claim 1, wherein said antenna element is a micro strip patch antenna, a dielectric resonator or a resonant slot antenna.
3. An antenna as claimed in any preceding claim, wherein the antenna is fed differentially.
4. An antenna as claimed in any preceding claim, wherein the feed structure includes a single feed line.
5. An antenna as claimed in any preceding claim, further comprising a ground plate.
6. An antenna as claimed in any preceding claim, wherein the ground plate is situated in between the antenna element and the coupling structure.
7. An antenna as claimed in claim 5, wherein the feed structure is situated in between the antenna element and the ground plate.
8. An antenna as claimed in any preceding claim, wherein the ground plate comprises a coupling aperture for coupling the energy between the antenna element and the feed structure.
9. An antenna as claimed in claim 7, wherein the ground plate includes a single aperture.
10. An antenna as claimed in claim 5, wherein the ground plate comprises the antenna element.
11. An antenna as claimed in claim 10, wherein the antenna element is a slot antenna in the ground plate.
12. An antenna as claimed in any preceding claim, wherein the feed line comprises a first and a second feed line element, wherein the first and second feed line elements are separated by a gap from each other.
13. An antenna as claimed in claim 12, wherein the first and second feed line elements are co-linear.
14. An antenna as claimed in claim 12 or 13, further comprising a ground plate.
15. An antenna as claimed in claim 12, 13 or 14, wherein the feed structure is situated in between the antenna element and the ground plate.
16. An antenna as claimed in any preceding claim, wherein the antenna element is provided on a first layer and the feed structure is provided on a second layer.
17. An antenna as claimed in any preceding claim, further comprising a ground plate on a third layer.
18. An antenna as claimed in claim 8, wherein the coupling aperture is provided in one of the following shapes: rectangular slot, bowtie slot, dog- bone shaped slot, H-shaped slot.
19. An antenna system for use in mobile communication terminals, the antenna comprising: an antenna element and a feed substrate including a first and a second port, whereby the feed line is adapted to be differentially fed via the first and second port and wherein the feed structure is not in contact with the antenna element.
20. An antenna system for use in mobile communication terminals, the antenna comprising: an antenna element provided on a first layer and a feed substrate including a feed structure provided on a second layer different to said first layer, wherein the feed structure comprises a first and a second port, wherein the feed structure is adapted to be differentially fed via the first and second port and wherein the feed structure is not in contact with the anteima element.
21. An antenna according to claim 20, further comprising a ground plate.
22. An antenna according to claim 20 or 21, wherein the ground plate is provided on a third layer
23. An antenna according to claim 20 or 21, wherein said third layer is in between the first and second layer.
24. An antenna according to claim 20, wherein said ground plate is provided on the first layer.
25. An antenna system for use in mobile communication terminals, the antenna system comprising: a conducting case; a transceiver circuit provided on a substrate; and an antenna element; wherein the system further comprises an antenna feed structure provided on the transceiver circuit substrate, wherein the feed structure comprises a feed line with a first and a second port, wherein the feed line is adapted to be differentially fed via the first and second port and wherein the feed structure is not in contact with the antenna element.
26. An antenna system according to claim 25, wherein said antenna element is a slot antenna provided in a ground plane.
27. An antenna system according to claim 25, wherein said antenna element is a patch antenna.
28. An antenna system according to claim 27, wherein said antenna system further comprises a ground plane situated in between the transceiver circuit substrate and the patch antenna..
29. An antenna system according to claim 27 or 28, wherein said ground plane includes an aperture slot.
30. An antenna system for use in mobile communication terminals, the antenna system comprising: a conducting case, a transceiver circuit provided on a substrate inside said conducting case, and an antenna element; wherein the system further comprises a feed structure provided on the chip carrier of the transceiver chip comprising a feed line with a first and a second port, wherein the feed line is adapted to be differentially fed via the first and second port and wherein the feed structure is not in contact with the antenna element.
31. An antenna as claimed in claim 30, wherein the feed structure is etched into the transceiver chip carrier.
32. An antenna as claimed in claim 30, wherein an aperture slot is provided for coupling the signals from the feed structure to the antenna element.
33. An antenna as claimed in claim 30, wherein the aperture slot is etched into the transceiver chip carrier.
34. An antenna as claimed in claim 30, wherein the patch antenna is etched into the ground plate.
35. An antenna system for use in mobile communication terminals, the antenna system comprising: a conducting case, a transceiver circuit provided on a chip, and an antenna element; wherein the feed structure comprises a feed line with a first and a second port provided on the transceiver chip, wherein the feed line is adapted to be differentially fed via the first and second port; and wherein the feed structure is not in contact with the antenna element.
36. An antenna as claimed in claims 35, wherein the feed line comprises a first and a second feed line element separated by a gap.
37. An antenna system for use in mobile communication terminals, the antenna comprising: an antenna element and a feed substrate including a feed line with a first and a second port, whereby the feed line is adapted to be differentially fed via the first and second port and wherein the feed structure is not in contact with the antenna element.