GB2408148A

GB2408148A - Dielectric resonator antenna array

Info

Publication number: GB2408148A
Application number: GB0400154A
Authority: GB
Inventors: Andrew Fox
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-11-13
Filing date: 2004-01-06
Publication date: 2005-05-18
Anticipated expiration: 2024-01-06
Also published as: GB0400154D0; GB2408148B; GB0326503D0

Abstract

A dielectric resonator array comprises a primary resonator (14) and a plurality of parasitic resonators (16, 18, 20, 22), located adjacent to the primary resonator, arranged such that they are operating in a different resonant mode from the primary resonator. The primary resonator may be arranged to be operating in a resonant mode of a higher order than the parasitic resonators. In that case, the parasitic resonators may be operating in their fundamental resonant mode, or in a higher resonant mode. Alternatively, the primary resonator may be arranged to be operating in a resonant mode of a lower order than the parasitic resonators. The device may have an improved performance in terms of an enhanced bandwidth, increased gain for the size of the device, reduced sidelobes, high cross polarization discrimination, and high efficiency, compared with the primary resonator alone.

Description

DIELECTRIC RESONATOR ANTENNA ARRAY

This invention relates to an antenna array, and in particular to an array of dielectric resonator antennas.

Dielectric resonator antennas are known, for use in wireless communications devices.

However, it is recognised that a drawback with dielectric resonator antennas is their relatively narrow operating bandwidth. One known technique for increasing the operating bandwidth of a dielectric resonator antenna is to place a parasitic resonator in close proximity to the primary resonator. In such an arrangement, the primary resonator is excited such that it operates in a selected resonant mode, and the parasitic resonator is designed such that it is excited to operate in the same resonant mode at a frequency which is at the same frequency as, or closely spaced from, the frequency of the primary resonator. This has the effect that, when taken together, the primary resonator and the parasitic resonator form a device which has an increased bandwidth.

According to the present invention, there is provided a dielectric resonator array comprising a primary resonator and a plurality of parasitic resonators, located adjacent to the primary resonator, arranged such that they are operating in a different resonant mode from the primary resonator.

In some preferred embodiments of the invention, the primary resonator is arranged to be operating in a resonant mode of a higher order than the parasitic resonators. In that case, the parasitic resonators may be operating in their fundamental resonant mode, or in a higher resonant mode.

In other preferred embodiments of the invention, the primary resonator is arranged to be operating in a resonant mode of a lower order than the parasitic resonators.

Arrangements in accordance with the invention have the advantage that, depending on the specific embodiment of the invention, the device may have an improved performance in terms of an enhanced bandwidth, increased gain for the size of the device, reduced sidelobes, high cross polarization discrimination, and high efficiency, compared with the primary resonator alone.

For a better understanding of the present invention, and to show how it may be put into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a schematic representation of a resonator array in accordance with the present invention; Figure 2 is a perspective view of the array shown in Figure 1; and Figure 3 is a perspective view of an alternative resonator array in accordance with the present invention.

Figures 1 and 2 show a first embodiment of a dielectric resonator antenna array in accordance with the present invention. Figure 2 is a perspective view showing the arrangement of the resonators in the array, while Figure 1 is a schematic plan view, which is arranged to show the relative positions of the resonators.

The resonator array 10 is mounted on a substrate 12 in a conventional way, and includes a primary resonator 14 and four parasitic resonators 16, 18, 20, 22. An input electrical signal is fed to the primary resonator 14 by means of a feed line 24 and an impedance matching stub 26. This particular method of feeding the electrical signal to the primary resonator via a stripline is not an essential feature of the invention, as any convenient technique may be used. For example, the electrical signal may alternatively be fed to the primary resonator by means of a monopole, or it may be magnetically coupled to the resonator via a slot. It will also be apparent to the person skilled in the art that, although the invention is described with reference to an input electrical signal being fed into the primary resonator, so that the device acts as a transmit antenna, the same arrangement can equally be used as a receive antenna, which receives an input radio frequency signal.

Thus, the device is a reciprocal antenna and, irrespective of whether energy is fed into the system by means of the feed line 24 or from received radio frequency signals, it has the effect of creating sympathetic resonance between the primary and parasitic resonators.

Although, as shown in Figures 1 and 2, the primary resonator 14 and the parasitic resonators 16, 18, 20, 22 are all mounted on the substrate 12, it is possible to reduce the overall size of the substrate by mounting only the primary resonator 14 with the feed line 24 on the substrate 12, while mounting the parasitic resonators separately.

The resonator array 10 is designed for operation at a particular frequency, or in a particular frequency range. For example, the array may be designed for operation at frequencies in the region of 5.8 GHz.

The resonant frequency of the primary resonator 14 is determined by its material properties, specifically its permittivity, and its dimensions. In this case, the primary resonator 14 is a cuboid, having a length L, a width W. and a height h. The dimensions of the primary resonator, and the material from which it is made, are then chosen such that a specific higher order resonant mode occurs at the desired frequency for the antenna system. However, although the illustrated primary resonator is a cuboid, the primary resonator may be any shape which supports the desired resonant mode.

The input electrical can then be fed to the primary resonator 14 at the desired frequency. Thus, the primary resonator 14 resonates in the selected higher order mode at the desired frequency for the antenna system.

In this illustrated embodiment of the invention, the primary resonator 14 is approximately three times as long as an otherwise equivalent resonator, which would operate in its fundamental HEM 11d resonant mode at the desired frequency. Thus, the primary resonator 14 operates in this case in its HEM 13d mode.

In this illustrated embodiment of the invention, there are four parasitic resonators 16, 18, 20, 22, with a first pair of parasitic resonators 16, 20 located on one side of the primary resonator 14 and a second pair of parasitic resonators 18, 22 located on the other side of the primary resonator 14. Two of the parasitic resonators 16, 18 are located at one end of the primary resonator 14 and the other two parasitic resonators 20, 22 are located at the other end of the primary resonator 14.

Each of the four parasitic resonators 16, 18, 20, 22 has a length M, and the same width W and height h as the primary resonator 14, although in other embodiments the width and height may also vary. Similarly, each of the four parasitic resonators 16, 18, 20, 22 is made of the same material as the primary resonator 14, although in other embodiments they may be made from different materials.

In this illustrated embodiment of the invention, the length M is one third of L (that is, M = U3). The effect of this is that the primary resonator 14 operates as an antenna in its HEM 13d mode at the same frequency (the desired frequency mentioned above) as the fundamental HEM 11 d resonant mode of the four parasitic resonators 16,18, 20, 22.

Thus, the radiation transmitted by the primary resonator 14 excites oscillations in each of the four parasitic resonators 16,18,20,22, and the frequency of the signal fed to the primary resonator 14 is approximately equal to the resonant frequency of each of the four parasitic resonators 16,18, 20,22 in their fundamental HEM 11 d mode. This mode of the parasitic resonators is therefore excited, and they also emit radiation at the frequency of the signal fed to the primary resonator 14.

It was mentioned above that the dimensions and the material of the parasitic resonators 16,18, 20, 22 may differ from that described. Provided that the dimensions and materials are chosen such that the parasitic resonators have their resonant frequencies in the respective modes at or very close to the desired frequency, the required effect can still take place.

In this illustrated embodiment of the invention, the end faces 28, 30 of the parasitic resonators 16,18 lie in the same plane as the end face 32 of the primary resonator 14, while the end faces 34, 36 of the other two parasitic resonators 20,22 lie in the same plane as the other end face 38 of the primary resonator 14.

Thus, the lengths of the parasitic resonators 16,18, 20, 22 extend parallel to the length of the primary resonator 14, and the first pair of parasitic resonators 16,20 located on one side of the primary resonator 14 are spaced apart by a distance e, and the second pair of parasitic resonators 18, 22 located on the other side of the primary resonator 14 are also spaced apart by the same distance e.

Locating the parasitic resonators 16,18, 20, 22 at other positions is also possible, and may affect the bandwidth of the antenna structure, and may additionally or alternatively affect the antenna sidelobe performance and/or cause tilting of the far field radiation pattern. To the extent that these changes are desirable in certain situations, then different positions of the parasitic resonators may be advantageous.

Also, the parasitic resonators 16, 18, 20, 22 are spaced from the primary resonator 14 by a distance d. In this illustrated embodiment of the invention, the distance d is equal to the widths W of the parasitic resonators 16, 18, 20, 22 and of the primary resonator 14(thatis,d=W).

Changing the distance d will alter the properties of the antenna system. In particular, changing the distance d will alter the bandwidth of the antenna system, but will also alter other properties. The distance d should therefore be set so that the antenna system has a desired bandwidth.

In addition, it may be desirable in some situations for the parasitic resonators 16, 18, 20, 22 to be spaced at different distances from the primary resonator 14.

In the illustrated embodiment of Figures 1 and 2, there are four parasitic resonators 16, 18, 20, 22 arranged symmetrically with respect to the parasitic resonator 14. This has the result, which is advantageous in some situations, that the resulting far field radiation pattern is also symmetrical. In other situations, it may be advantageous to generate an asymmetrical far field radiation pattern, and this can be achieved by means of an asymmetrical arrangement of parasitic resonators. For example, compared with the illustrated embodiment, the parasitic resonators 16, 18 could be removed, leaving only the parasitic resonators 20, 22 (that is, the parasitic resonators at the same end of the primary resonator as the signal feed point). This has the result that the bandwidth and gain of the antenna system are somewhat reduced, compared with the illustrated embodiment, but that the far field radiation pattern is tilted away from the feed point. Conversely, if the parasitic resonators 20, 22 are removed, leaving only the parasitic resonators 16, 18 (that is, the parasitic resonators at the end of the primary resonator opposite the signal feed point), this again has the result that the bandwidth and gain of the antenna system are somewhat reduced, compared with the illustrated embodiment, but in this case the far field radiation pattern is tilted towards the feed point.

In this illustrated embodiment of the invention, the primary resonator 14 is designed to operate as an antenna in its HEM 1 ad mode at the desired operational frequency of the antenna system, while the parasitic resonators each have a length which is one third of the length of the primary resonator, and so the parasitic resonators operate in their fundamental HEM 11d mode at the same frequency.

In another embodiment of the invention, the primary resonator 14 is designed to operate as an antenna in its HEM 1 Ed mode at the desired frequency of operation of the antenna system, while the parasitic resonators each have a length which is one fifth of the length of the primary resonator, and so the parasitic resonators operate in their fundamental HEM 11d mode at the same frequency.

In yet another embodiment of the invention, the primary resonator 14 is designed to operate as an antenna in its HEM 17d mode at the desired frequency of operation of the antenna system, while the parasitic resonators each have a length which is three sevenths of the length of the primary resonator, and so the parasitic resonators operate in their HEM 1 ad mode at the same frequency.

Other embodiments are also possible. The common factor between the embodiments shown and described so far is that the primary resonator is resonating at a desired frequency in a higher order mode, while the parasitic resonators are resonating at the same desired frequency (or at very nearly the same desired frequency) in a mode, which may be the fundamental mode or may be a higher order mode, but which is in any event a lower order mode than that in which the primary resonator is operating.

Figure 3 shows an antenna system in accordance with the invention, in which this is not the case. A resonator array 110 is mounted on a substrate 112 in a conventional way, and includes a primary resonator 114 and two parasitic resonators 116, 118. An input electrical signal is fed to the primary resonator 114 by means of a feed line 124 and an impedance matching stub 126. This particular method of feeding the electrical signal to the primary resonator via a stripline is not an essential feature of the invention, as any convenient technique may be used. For example, the electrical signal may alternatively be fed to the primary resonator by means of a monopole, or it may be magnetically coupled to the resonator via a slot. It will also be apparent to the person skilled in the art that, although the invention is described with reference to an input electrical signal being fed into the primary resonator, which therefore acts as a transmit antenna, the same arrangement can equally be used as a receive antenna, which receives an input radio frequency signal.

Although, as shown in Figure 3, the primary resonator 114 and the parasitic resonators 116, 118 are all mounted on the substrate 112, it is possible to reduce the overall size of the substrate by mounting only the primary resonator 114 with the feed line 124 on the substrate 112, while mounting the parasitic resonators separately.

The resonator array 110 is designed for operation at a particular frequency, or in a particular frequency range. For example, the array may be designed for operation at frequencies in the region of 5.8 GHz.

In the embodiment of the invention shown in Figure 3, the primary resonator 114 is designed such that it can operate in its fundamental HEM 11d resonant mode at the desired frequency.

In this illustrated embodiment of the invention, there are two parasitic resonators 116, 118, one located on each side of the primary resonator 14.

Each of the parasitic resonators 116, 118 has the same width and height as the primary resonator 114, although in other embodiments the width and height may also vary. Similarly, each of the parasitic resonators 1 16, 1 18 is made of the same material as the primary resonator 114, although in other embodiments they may be made from different materials.

In this illustrated embodiment of the invention, the length of the primary resonator 114 is one third of the length of each of the parasitic resonators 116, 118. The effect of this is that the parasitic resonators 116, 118 resonate in their HEM 13d mode at the same frequency (the desired frequency mentioned above) as the fundamental HEM 11d resonant mode of the primary resonator 114.

Thus, the radiation transmitted by the primary resonator 114 excites oscillations in each of the parasitic resonators 116, 118, and, as the frequency of the signal fed to the primary resonator 114 is approximately equal to the resonant frequency of each of the parasitic resonators 1 16, 118 in their HEM 1 ad mode, this mode of the parasitic resonators is excited, and they also emit radiation at the frequency of the signal fed to the primary resonator 114.

It was mentioned above that the dimensions and the material of the parasitic resonators 116, 118 may differ from that described. Provided that the dimensions and materials are chosen such that the parasitic resonators have their resonant frequencies in the respective modes at or very close to the desired frequency, the required effect can still take place.

The lengths of the parasitic resonators 116, 1 18 extend parallel to the length of the primary resonator 114, and they are spaced from the primary resonator 114 by equal distances. In this illustrated embodiment, this spacing is equal to the widths of the primary resonator 1 14 and parasitic resonators 1 16, 1 18.

Locating the parasitic resonators 1 16, 118 at other positions is also possible, and may affect the bandwidth of the antenna structure, and may additionally or alternatively affect the antenna sidelobe performance and/or cause tilting of the far field radiation pattern. To the extent that these changes are desirable in certain situations, then different positions of the parasitic resonators may be advantageous.

In the illustrated embodiment of the invention, the primary resonator 114 and the parasitic resonators 116, 118 are all made of the same material, and so the differences in their fundamental resonant frequencies arise from their different lengths.

Alternatively, one or both of the parasitic resonators may be made of different materials from the primary resonator, and the different dielectrics will also contribute to the ? required differences in the fundamental resonant frequencies of the resonators.

In this illustrated embodiment of the invention, the primary resonator 114 is designed to operate as an antenna in its HEM 11d mode at the desired operational frequency of the antenna system, while the parasitic resonators each have a length which is three times the length of the primary resonator, and so the parasitic resonators operate in their HEM 13d mode at the same frequency.

In another embodiment of the invention, the primary resonator 114 is designed to operate as an antenna in its HEM 11d mode at the desired frequency of operation of the antenna system, while the parasitic resonators each have a length which is five times that of the primary resonator, and so the parasitic resonators operate in their HEM 15d mode at the same frequency.

In yet another embodiment of the invention, the primary resonator 114 is designed to operate as an antenna in its HEM 13d mode at the desired frequency of operation of the antenna system, while the parasitic resonators each have a length which is 7/3 times that of the primary resonator, and so the parasitic resonators operate in their HEM 17d mode at the same frequency.

Other embodiments are also possible, for example with different numbers of parasitic resonators, in which the primary resonator is resonating at a desired frequency in a lower order mode (which may be its fundamental resonant mode, but may alternatively be a different mode), while the parasitic resonators are resonating at the same desired frequency (or at very nearly the same desired frequency) in a higher order mode than that in which the primary resonator is operating.

Figures 1 and 2, on the one hand, and Figure 3, on the other hand, show antennas formed from a primary resonator and one or more parasitic resonators. Just as it is possible to form an antenna array from multiple conventional antennas, an antenna array can be formed from multiple antennas of the type illustrated and described herein.

UK Patent Application No. 0312829.5 discloses an antenna system in which a resonator is excited by feeding signals into the resonator at two points, with a phase difference between them, such that each of the feed points couple to a desired resonant mode (such as an HEM xyd mode, where x and y can take any desired values) of the resonator. When the phase difference between the input signals is selected appropriately, for example in the range from 140 to 220 , and in particular close to 180 , this has the effect of broadening the bandwidth of the antenna system.

This technique can advantageously be applied to the antenna systems described above. For example, in order to excite the HEM 1 ad mode of the primary resonator 14 in Figures 1 and 2, means may be provided to feed the input electrical signal into the resonator at two feed points, with a phase difference of close to 180 between the signals entering the two feed points. One of the two feed points may be at one end of the primary resonator 14, with the other feed point being one third of the distance along the length of the primary resonator 14. Other higher order resonant modes can be excited in similar ways. The bandwidth enhancement produced by this technique can also be achieved in conjunction with the advantages achieved by means of the use of the parasitic resonators, as described above.

It is known that dielectric resonator antennas can be designed with a socalled perfect electrical conductor (PEC) provided on one end face thereof. The PEC acts as a mirror, and allows the establishment of resonant modes that would typically occur in a longer resonator. For example, placing a PEC on an end face of a resonator can allow the establishment of resonant modes that would typically occur in a resonator which is twice as long. This technique can be used in embodiments of the present invention.

For example, in Figures 1 and 2, the primary resonator 14 can be replaced by a resonator which is half the length of the resonator 14, but which has a PEC on the end face opposite the feed line 24.

The invention has been described herein with reference to antenna systems, comprising a primary antenna and at least one parasitic antenna, in which only the primary antenna is active, while each parasitic antenna is passive. That is, an input signal is fed to the primary antenna alone. However, the invention is also applicable to antenna systems, in which one or more of the parasitic antennas is active. That is, an input electrical signal may be fed to one or more of the parasitic antennas, as well as to the primary antenna. Typically, the input signal is fed to all of the parasitic antennas.

The input electrical signal, which is typically the same as the input electrical signal fed to the primary antenna, then excites a resonance in the parasitic antenna or antennas to which it is fed.

This has the advantage that it can be used to shape the far-field radiation pattern into a desired configuration, while maintaining the advantages mentioned above, such as the bandwidth and the gain of the antenna system.

There are therefore described antenna systems which can provide advantageous performance for use in wireless communication systems.

Claims

1. A dielectric resonator antenna system, comprising a primary resonator, and at least one parasitic resonator, located adjacent to the primary resonator, wherein the primary resonator and the or each parasitic resonator are such that, for an input signal which causes the primary resonator to resonate at a desired frequency in a first resonant mode, the or each parasitic resonator is caused to resonate at the desired frequency in a second resonant mode which is different from the first resonant mode.

2. A dielectric resonator antenna system as claimed in claim 1, wherein the first resonant mode is a higher order mode than the second resonant mode.

3. A dielectric resonator antenna system as claimed in claim 1, wherein the or each parasitic resonator is caused to operate in its fundamental resonant mode.

4. A dielectric resonator antenna system as claimed in claim 1, wherein the second resonant mode is a higher order resonant mode than the fundamental resonant mode, but is a lower order resonant mode than the first resonant mode.

5. A dielectric resonator antenna system as claimed in claim 1, wherein the first resonant mode is a lower order mode than the second resonant mode.

6. A dielectric resonator antenna system as claimed in claim 5, wherein the first resonant mode is the fundamental resonant mode.

7. A dielectric resonator antenna system as claimed in any preceding claim, wherein the primary resonator and the or each parasitic resonator are made of the same material, and have respective lengths which provide the required different fundamental resonant frequencies.

8. A dielectric resonator antenna system as claimed in any preceding claim, comprising a plurality of parasitic resonators.

9. A dielectric resonator antenna system as claimed in claim 8, wherein the parasitic resonators are arranged symmetrically with respect to the primary resonator.

10. A dielectric resonator antenna system as claimed in claim 8, wherein the parasitic resonators are arranged asymmetrically with respect to the primary resonator.

11. A dielectric resonator antenna system as claimed in any preceding claim, wherein the primary resonator and the or each parasitic resonator have the same height.

12. A dielectric resonator antenna system as claimed in any preceding claim, wherein the primary resonator and the or each parasitic resonator have the same 1 0 width.

13. A dielectric resonator antenna system as claimed in claim 12, wherein the or each parasitic resonator is spaced from the primary resonator by a distance which is equal to the widths of the primary resonator and the or each parasitic resonator.

14. A dielectric resonator antenna system as claimed in claim 8, wherein the parasitic resonators are unequally spaced from the primary resonator.

15. A dielectric resonator antenna system as claimed in any preceding claim, comprising means for feeding an input electrical signal to the primary resonator at two feed points, with a predetermined phase difference, the two feed points being selected such that both couple to said first resonant mode of the primary resonator.

16. A dielectric resonator antenna system as claimed in any preceding claim, wherein at least one of said primary resonator and said at least one parasitic resonator comprises a perfect electrical conductor on an end face thereof.

17. A dielectric resonator antenna system as claimed in any preceding claim, wherein the primary resonator and the or each parasitic resonator are mounted on a common substrate.

18. A dielectric resonator antenna system as claimed in any one of claims 1 to 16, wherein the primary resonator is mounted on a substrate, and the or each parasitic resonator is mounted separately.

19. A dielectric resonator antenna system as claimed in any one of claims 1 to 18, comprising means for feeding an input electrical signal to at least one parasitic resonator.

20. A dielectric resonator array, comprising a plurality of dielectric resonator antennas, at least one of the dielectric resonator antennas being in the form of a dielectric resonator antenna system as claimed in any one of claims 1 to 18.

21. A dielectric resonator antenna system, comprising: a primary resonator, having at least one feed point; and at least one parasitic resonator, the primary resonator and the or each parasitic resonator being dimensioned, and made of suitable dielectric materials, such that the primary resonator and the or each parasitic resonator all resonate at a desired frequency, with the primary resonator operating in a different resonant mode from the parasitic resonators.