WO2003098733A2

WO2003098733A2 - Dielectric antenna array feed mechanism

Info

Publication number: WO2003098733A2
Application number: PCT/GB2003/002126
Authority: WO
Inventors: James William Kingsley
Original assignee: Antenova Limited
Priority date: 2002-05-15
Filing date: 2003-05-15
Publication date: 2003-11-27
Also published as: GB0211109D0; WO2003098733A3; GB2389234B; AU2003234006A8; GB2389234A; AU2003234006A1; GB0311180D0

Abstract

There is disclosed an array of m dielectric antennas and a feed mechanism for transferring energy between each dielectric antenna and a single feed point, wherein each dielectric antenna is tuned to an impedance of substantially n ohms, and wherein the feed mechanism connects the dielectric antennas to the single feed point in such a way that the single feed point is matched to an impedance of substantially n/m ohms. By tuning each dielectric antenna to a higher impedance than that of the single feed point, a feed point impedance matched to a predetermined impedance may be provided without requiring lossy and narrow bandwidth components such as quarter-wavelength transmission lines and the like.

Description

DIELECTRIC ANTENNA ARRAY FEED MECHANISM

The present invention relates to a feed mechanism for an array of dielectric antennas, including dielectric resonator antennas (DRAs) and high dielectric antennas (HDAs).

Dielectric resonator antennas and high dielectric antennas are resonant antenna devices that radiate or receive radio waves at a chosen frequency of transmission and reception, as used in for example in mobile telecommunications. In general, a DRA consists of a volume of a dielectric material (the dielectric resonator) disposed on or close to a grounded substrate, with energy being transferred to and from the dielectric material by way of monopole probes inserted into the dielectric material or by way of monopole aperture feeds provided in the grounded substrate (an aperture feed is a discontinuity, generally rectangular in shape, although oval, oblong, trapezoidal or butterfly/bow tie shapes and combinations of these shapes may also be appropriate, provided in the grounded substrate where this is covered by the dielectric material. The aperture feed may be excited by a strip feed in the form of a microstrip transmission line, coplanar waveguide, slotline or the like which is located on a side of the grounded substrate remote from the dielectric material). Direct connection to and excitation by a microstrip transmission line is also possible. Alternatively, dipole probes may be inserted into the dielectric material, in which case a grounded substrate is not required. By providing multiple feeds and exciting these sequentially or in various combinations, a continuously or incrementally steerable beam or beams may be formed, as discussed for example in the present applicant's co-pending US patent application serial number US 09/431,548 and the publication by KTNGSLEY, S.P. and O'KEEFE, S.G., "Beam steering and monopulse processing of probe-fed dielectric resonator antennas", IEE Proceedings - Radar Sonar and Navigation, 146, 3, 121 - 125, 1999, the full contents of which are hereby incorporated into the present application by reference.

The resonant characteristics of a DRA or HDA depend, inter alia, upon the shape and size of the volume of dielectric material and also on the shape, size and position of the feeds thereto. It is to be appreciated that in a DRA or HDA, it is the dielectric material that resonates when excited by the feed. This is to be contrasted with a dielectrically loaded antenna, in which a traditional conductive radiating element is encased in a dielectric material that modifies the resonance characteristics of the radiating element.

DRAs and HDAs may take various forms, a common form having a cylindrical shape which may be fed by a metallic probe within the cylinder. Such a cylindrical resonating medium can be made from several candidate materials including ceramic dielectrics.

Since the first systematic study of dielectric resonator antennas (DRAs) in 1983 [LONG, S.A., McALLISTER, M.W., and SHEN, L.C.: "The Resonant Cylindrical Dielectric Cavity Antenna", IEEE Transactions on Antennas and Propagation, AP-31, 1983, pp 406-412], interest has grown in their radiation patterns because of their high radiation efficiency, good match to most commonly used transmission lines and small physical size [MONGIA, R.K. and BHARTIA, P.: "Dielectric Resonator Antennas - A Review and General Design Relations for Resonant Frequency and Bandwidth", International Journal of Microwave and Milhmetre-Wave Computer- Aided Engineering, 1994, 4, (3), pp 230-247]. A summary of some more recent developments can be found in PETOSA, A., ITTIPIBOON, A., ANTAR, Y.M.M., ROSCOE, D., and CUHACI, M.: "Recent advances in Dielectric-Resonator Antenna Technology", IEEE Antennas and Propagation Magazine, 1998, 40, (3), pp 35 - 48.

A variety of basic shapes have been found to act as good DRA resonator structures when mounted on or close to a ground plane (grounded substrate) and excited by an appropriate method. Perhaps the best known of these geometries are:

Rectangle [McALLISTER, M.W., LONG, S.A. and CONWAY G.L.: "Rectangular Dielectric Resonator Antenna", Electronics Letters, 1983, 19, (6), pp 218-219]. Triangle [ITTIPIBOON, A., MONGIA, R.K., ANTAR, Y.M.M., BHARTIA, P. and CUHACI, M.: "Aperture Fed Rectangular and Triangular Dielectric Resonators for use as Magnetic Dipole Antennas", Electronics Letters, 1993, 29, (23), pp 2001- 2002].

Hemisphere [LEUNG, K.W.: "Simple results for conformal-strip excited hemispherical dielectric resonator antenna", Electronics Letters, 2000, 36, (11)].

Cylinder [LONG, S.A., McALLISTER, M.W., and SHEN, L.C.: "The Resonant Cylindrical Dielectric Cavity Antenna", IEEE Transactions on Antennas and Propagation, AP-31, 1983, pp 406-412].

Half-split cylinder (half a cylinder mounted vertically on a ground plane) [MONGIA, R.K., ITTJJPIBOON, A., ANTAR, Y.M.M., BHARTIA, P. and CUHACI, M: "A Half-Split Cylindrical Dielectric Resonator Antenna Using Slot-Coupling", IEEE Microwave and guided Wave Letters, 1993, Vol. 3, No. 2, pp 38-39].

Some of these antenna designs have also been divided into sectors. For example, a cylindrical DRA can be halved [TAM, M.T.K. and MURCH, R.D.: 'Ηalf volume dielectric resonator antenna designs", Electronics Letters, 1997, 33, (23), pp 1914 - 1916]. However, dividing an antenna in half, or sectorising it further, does not change the basic geometry from cylindrical, rectangular, etc.

High dielectric antennas (HDAs) are similar to DRAs, but instead of having a full ground plane located under the dielectric pellet, HDAs have a smaller ground plane or no ground plane at all. Removal of the ground plane underneath gives a less well- defined resonance and consequently a very much broader bandwidth. HDAs generally radiate as much power in a backward direction as they do in a forward direction, and are therefore less suited than DRAs for constructing antenna arrays, but useful arrays of HDAs may still be formed. Conventional antennas, e.g. patch antennas, dipoles etc. generally have a well- defined impedance for a given geometry. The present applicant has found that DRAs and HDAs do not generally have a well-defined impedance, but may be fed with a wide range of non-reactive impedances, e.g. 100 ohms, 200 ohms etc.

It is known to feed an antenna array with a feed mechanism transferring power from a single feed point (e.g. an input/output connector) and to distribute the power to a plurality of radiating elements (e.g. dipoles, patch antennas, DRAs, HDAs etc.), often with equal phase and amplitude. Generally, where each radiating element has an impedance of, say, 50 ohms, these are combined by way of a feed mechanism to give lower impedances which are then transformed back to 50 ohms by way of quarter wavelength sections of transmission line so as to result in a feed point impedance matched to 50 ohms. A significant disadvantage of this approach is that quarter- wavelength transformer sections of transmission line tend to be both lossy and somewhat narrow in bandwidth.

It is also known that a pair of DRAs can be fed with different phases [HONG, C.S. and HUANG, C-Y.: "Sequentially rotated array of dielectric resonator antennas", Proc. Natl. Sci. Counc. ROC(A), 25, 3, 2001, pp 202-204]. Hong and Huang describe a pair of circularly polarised cylindrical DRAs with a physical phase rotation of the cylinders and a corresponding phase rotation of the feed signal. This mechanism has the advantage of improving the bandwidth of the system, but it does not reduce the complexity, size or loss of the feed mechanism, which are considerations that embodiments of the present invention seek to address.

For the purposes of the present application, the expression "dielectric antenna" is hereby defined as encompassing DRAs and HDAs.

According to a first aspect of the present invention, there is provided an array of m dielectric antennas and a feed mechanism for transferring energy between each dielectric antenna and a single feed point, wherein each dielectric antenna is tuned to an impedance of substantially n ohms, and wherein the feed mechanism connects the dielectric antennas to the single feed point in such a way that the single feed point is matched to an impedance of substantially n/m ohms.

According to a second aspect of the present invention, there is provided a method of feeding an array of m dielectric antennas by way of a feed mechanism connecting each dielectric antenna to a single feed point, wherein each dielectric antenna is tuned to an impedance of substantially n ohms, and wherein the feed mechanism is connected between the dielectric antennas and the single feed point in such a way that the single feed point is matched to an impedance of substantially n/m ohms.

The basis of the present invention lies in the realisation by the present applicant that a DRA or HDA does not typically have a well-defined impedance (in contrast, for example, to a conventional dipole antenna) but can be tuned to or fed with a wide range of non-reactive impedances.

In contrast to the conventional feed mechanisms discussed above, where the impedance of each radiating element is matched to that of the single feed point using quarter-wavelength sections of transmission line, the present invention simply combines m dielectric antennas each with an impedance of n ohms by way of a feed mechanism to a single feed point impedance matched to n/m ohms. For example, two DRAs each tuned to an impedance of 100 ohms may be connected to a single feed point impedance matched to 50 ohms, as may four DRAs each tuned to an impedance of 200 ohms and so forth. It will be appreciated that m is always a positive integer.

By ttining each dielectric antenna to a higher impedance than that of the single feed point, a feed point impedance matched to a predetermined impedance may be provided without requiring lossy and narrow bandwidth components such as quarter- wavelength transmission lines and the like. A further advantage is that the provision of a relatively high impedance feed to each individual dielectric antenna (as opposed to the relatively low impedance of the single feed point where the feeds to/from each dielectric antenna are combined) is that the space required on, say, a printed circuit board (PCB) on which the dielectric antennas and the feed mechanism is provided is thereby reduced. This allows smaller antenna array structures to be built while retaining the performance characteristics of larger conventional array structures.

As a further development, the feed mechanism may be constructed so as to feed one or more pairs of dielectric antennas, each pair being supplied by a feed line that is connected at one end to the single feed point and then splits into two branches so as to connect to each member of a pair of dielectric antennas, wherein one branch includes an additional length of feed line adapted to introduce a 180° phase shift to its associated member of a pair of dielectric antennas. In this way, both members of a pair of dielectric antennas will operate in phase with each other, but with improved bandwidth. In addition, this arrangement allows the length of the feed mechanism to be reduced, thereby helping to reduce losses therein.

The feed mechanism may feed each dielectric antenna by way of a direct connection (e.g. a direct microstrip feed), or by way of probes located within or adjacent to a dielectric resonator portion of the dielectric antenna, or by slot or aperture feeds or any other appropriate mechanism. Where a direct microstrip transmission line network is provided as the feed mechanism, the feed mechanism and the dielectric antennas may all be located on the same side of a dielectric substrate such as a PCB. Alternatively, where a slot or aperture feed mechanism is provided, a transmission line network may be provided on a side of the dielectric substrate opposed to that on which the dielectric antennas are mounted, a conductive ground plane is provided between the transmission line network and the dielectric antennas, and slots or apertures are then formed in the ground plane between the network and the antennas so as to provide slot or aperture feeding. For a better understanding of the present invention and to show how it may be carried into effect, reference shall now be made by way of example to the accompanying drawing, in which:

FIGURE 1 shows a DRA array configured in accordance with an embodiment of the present invention.

Figure 1 shows a feed network designed for a particular application and comprising a four-element array of dielectric resonators 1, 2, 3, 4 fed directly by a microstrip transmission line 5 having two main branches 6, 7 and a single feed point 13. The resonators 1, 2, 3, 4 are each connected to the microstrip transmission line 5 which is provided on one side of a printed circuit board (PCB) 8. An opposed side of the PCB

8 is provided with a conductive ground plane (not shown). The dielectric resonators are fed in pairs 1, 2 and 3, 4, each member of each pair being fed by one of a pair of sub-branches 9, 10 of each main branch 6, 7 of the microstrip transmission line 5.

One sub-branch 9 of each pair of sub-branches 9, 10 includes an additional length of transmission line 11 adapted to introduce a 180° phase shift in the feed signal so that both members of each pair of resonators 1, 2 and 3, 4 resonate in phase with each other.

Each dielectric resonator 1, 2, 3, 4 is tuned to have an impedance of 100 ohms, such that each pair of resonators 1, 2 and 3, 4 may be fed by its associated main branch 6, 7 of the microstrip transmission line 5 at an impedance of 50 ohms. The two main branches 6, 7 (of impedance 50 ohms each) of the microstrip transmission line 5 are in turn combined with a transforming section 12 of characteristic impedance 70.7 ohms to give an impedance of 100 ohms where they join together at the single feed point 13 where the two main branches 6, 7 combine to give a single 50 ohm input/output. The preferred features of the invention are applicable to all aspects of the invention and may be used in any possible combination.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example "comprising" and "comprises", mean "including but not limited to", and are not intended to (and do not) exclude other components, integers, moieties, additives or steps.

Claims

CLAIMS:

1. An array of m dielectric antennas and a feed mechanism for transferring energy between each dielectric antenna and a single feed point, wherein each dielectric antenna is tuned to an impedance of substantially n ohms, and wherein the feed mechanism connects the dielectric antennas to the single feed point in such a way that the single feed point is matched to an impedance of substantially n/m ohms.

2. An array as claimed in claim 1, wherein each dielectric antenna comprises a dielectric pellet.

3. An array as claimed in claim 2, wherein the dielectric pellet is made of a ceramics material.

4. An array as claimed in any preceding claim, wherein the feed mechanism is configured to feed one or more pairs of dielectric antennas, each pair being supplied by a feed line connected at one end to the single feed point and split into first and second branches, the first branch being connected to one of the pair and the second branch being connected to the other of the pair, and wherein the first branch includes an additional length of feed line for introducing a 180° phase shift to its connected dielectric antenna.

5. An array as claimed in claim 2 or any claim depending therefrom, wherein the dielectric pellets are mounted on one side of a dielectric substrate.

6. An array as claimed in claim 5, wherein the dielectric substrate is a printed circuit board.

7. An array as claimed in any preceding claim, wherein the feed mechanism comprises a direct microstrip transmission line network.

8. An array as claimed in claim 7 depending from claim 5 or claim 6, wherein the microstrip transmission line network is provided on the said one side of the dielectric substrate on which the pellets are mounted.

9. An array as claimed in claim 8, wherein a conductive ground plane is provided on a side of the dielectric substrate opposed to the said one side on which the pellets are mounted.

10. An array as claimed in claim 5 or 6, wherein the feed mechanism comprises a transmission line network provided on a side of the dielectric substrate opposed to the said one side on which the pellets are mounted, and wherein a conductive ground plane is interposed between the network and the pellets and provided with slots or apertures under the pellets so as to provide a slot or aperture feeding mechanism.

11. An array as claimed in any preceding claim, wherein the dielectric antennas are dielectric resonator antennas.

12. An array as claimed in any one of claims 1 to 8, wherein the dielectric antennas are high dielectric antennas.

13. An array of dielectric antennas substantially as hereinbefore described with reference to or as shown in the accompanying drawing.