Dielectric resonator antennas are resonant antenna devices that radiate or receive radio waves at a chosen frequency of transmission and reception, as used 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'H'shape,'<->' shape, 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, grounded or ungrounded coplanar transmission line, triplate, 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 may not be 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 KINGSLEY, 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 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, it is the dielectric material that resonates when excited by the feed, this being due to displacement currents generated in the dielectric material. 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, but without displacement currents being generated in the dielectric material and without resonance of the dielectric material.

DRAs may take various forms and can be made from several candidate materials including ceramic dielectrics.

Since the first systematic study of dielectric resonator antennas (DRAs) in 1983 <BR> <BR> [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 Millimetre-Wave Computer- Aided Engineering, 1994,4, (3), pp 230-247]. A summary of some more recent <BR> <BR> developments can be found in PETOSA, A. , ITTIPIBOON, A. , ANTAR, Y. M. M.,<BR> 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) ].<BR> <P>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., ITTIPIBOON, 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.:"Half 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.

The majority of configurations reported to date have used a slab of dielectric material (a dielectric resonator) mounted on a conductive ground plane (a grounded substrate) excited by either a single aperture feed in the ground plane [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] or by a single probe inserted into the dielectric material [McALLISTER, M. W. , LONG, S. A. and CONWAY G. L.:"Rectangular Dielectric Resonator Antenna", Electronics Letters, 1983,19, (6), pp 218-219]. Direct excitation by a transmission line has also been reported by some authors [KRANENBURG, R. A. and LONG, S. A.:"Microstrip Transmission Line Excitation of Dielectric Resonator Antennas", Electronics Letters, 1994,24, (18), pp 1156-1157].

It is known to provide a side-by-side array of conventional (e. g. patch) antennas all on one side of a feed line and to feed the antennas with differently phased signals, although significant electromagnetic coupling occurs between the antennas if they are located close to one another, this coupling causing serious problems in effective and controllable signal generation.

It is also known (for example from UK patent no. 2360134) to provide a side-by-side array of DRAs all on one side of a feed line and to feed the DRAs with differently phased signals.

According to a first aspect of the present invention, there is provided a dielectric resonator antenna comprising at least one pair of dielectric resonator elements arranged in a back-to-back configuration with a feed mechanism provided between the elements and being activatable to excite both elements individually or in combination.

The feed mechanism is used for transferring energy into and out of the dielectric resonator elements, either individually (for example, only one or other of the pair being excited at any given time) or in combination (for example, both of the pair being excited simultaneously, with the same signal or different signals). In operation, at least one of the dielectric resonator elements is caused to resonate when transmitting or receiving a signal. The feed mechanism may be based on probe feeds,

slot feeds, slot feeds with transmission lines and direct microstrip feeds, among others. The present application gives detailed examples of slot feeding, but it will be appreciated that direct microstrip feeding has been extensively tested and found to work well.

The present applicant has found that electromagnetic coupling between adjacent dielectric resonator elements is not a significant problem when the elements are disposed in a back-to-back configuration; that is, oriented such that signals generated by each element during operation being mainly or substantially directed away from the other element. A significant advantage of such a reduction in coupling is that the two elements may be brought very close together or even adjacent to each other, thereby resulting in a compact DRA ideally suited for incorporation into a small communications device such as a mobile telephone or personal digital assistant (PDA). Furthermore, DRAs according to embodiments of the present invention may find application in small base station devices such as micro-and pico-base stations.

They may also find application in Wireless Local Area Network (WLAN) access points, especially those placed in long, narrow environments such as corridors, railway carriages, tunnels, lift shafts etc. In these environments, a central null in the radiation pattern generated by the DRA may prevent excessive fields across a width of the space, but radiates maximally up and down the space.

In a first preferred embodiment of the present invention, there may be provided a pair of back-to-back dielectric resonator elements mounted on or close to a grounded substrate and separated from each other by a feed structure comprising a single feed line embedded in a dielectric lamina (e. g. a printed circuit board (PCB) substrate) or sandwiched between two dielectric laminas (e. g. a pair of PCB substrates). The generally planar feed structure may be disposed substantially perpendicular to the grounded substrate, and may be provided with a conductive surface save for a region on either side of the feed structure following a line of intersection with the grounded substrate along an upperside thereof. The non-conductive regions, together with the feed line, act as slot feeds for each of the dielectric resonator elements, and each of

the dielectric resonator elements may contact the feed structure. The feed structure may extend below the grounded substrate (the conductive surface can help to reduce backlobes generated by each element and thereby help to reduce coupling between the elements on the upperside of the grounded substrate). Using a single fed structure to excite both dielectric resonator elements is simpler and easier to implement than a pair of separate feeds, one to each element, as required by conventional antenna design techniques.

Using a single feed structure as described above with both slots being activated, the dielectric resonators will be fed out of phase with each other (because the resonators are back-to-back, and voltages supplied by a single feed will therefore be in opposite directions on either side of the feed structure), and this causes the DRA as a whole to have a null in a central azimuth direction (e. g. in a direction substantially perpendicular to the grounded substrate between the dielectric resonators, which may in effect be the direction of extension of the feed line).

By electronically or otherwise deactivating one or other of the slot feeds (for example by shorting out a slot feed on one side of the feed structure), it is possible to activate the DRA so as to radiate in directions predominantly away from the side of the feed structure on which the slot feed is deactivated. In this way, three possible beam patterns and null directions may be generated (i. e. with both slot feeds activated, or with only one or the other of the slot feeds activated).

In a second preferred embodiment of the present invention, there may be provided a pair of back-to-back dielectric resonator elements mounted on or close to a grounded substrate and separated from each other by a feed structure comprising a pair of feed lines embedded in a dielectric lamina (e. g. one or more printed circuit board (PCB) substrates) and with a conductive separating layer disposed between the feed lines.

Alternatively, each feed line may be sandwiched between a pair of dielectric laminas (e. g. two PCB substrates bonded together about the feed line), the pairs of laminas then being sandwiched about a conductive separating layer. In either configuration,

the two feed lines need to be separated by a conductive layer so that each feed line only activates its designated slot. In general, the feed lines are substantially parallel and coextensive. As before, outer surfaces of the feed structure are made conductive, at least in regions above the grounded substrate, except for a pair of slots following the line of intersection between the grounded substrate and the feed structure.

By providing two separate and independent feed lines in the feed structure, it is possible to generate a wider variety of beam patterns than with a single feed line.

Furthermore, by selectively activating the feed lines, it is possible to steer a beam from one side to the other of the feed structure without requiring that the slots be selectively shorted out. Yet another advantage is that the two separate feed lines may be activated in antiphase or with any arbitrary phase difference. The introduction of phase delays or differences may be achieved by providing various electronically selectable lengths of feed line embedded in unused sections of the feed structure, among other ways.

By activating only one of the two feed lines, it is possible to generate a beam predominantly in the direction of the activated feed relative to a plane of the substantially laminar feed structure.

By activating both feed lines in phase, it is possible to generate a beam pattern having a null in a central azimuth direction (e. g. in a direction substantially perpendicular to the grounded substrate between the dielectric resonators).

By activating both feed lines in antiphase, it is possible to generate a beam pattern having a main lobe (and hence direction) in a central azimuth direction (e. g. in a direction substantially perpendicular to the grounded substrate between the dielectric resonators).

By activating both feed lines with various different phases, it is possible to generate a beam pattern in which a main lobe or lobes and a null or nulls of the beam pattern can be rotated.

In both of the above embodiments, it is possible to construct a small compound DRA suitable for incorporation into a mobile telephone, PDA or other electronic communications device in which a radiation or beam pattern can be formed with a steerable null (useful for avoiding interference in certain directions) or with a steerable main lobe or lobes (useful for maximising or improving received or transmitted signal strength).

The present applicant has found that a particularly useful shape for the dielectric resonator elements is a quarter split cylindrical shape, i. e. having two substantially planar and quadrilateral surfaces substantially perpendicular to each other, and a curved surface between distal edges of the quadrilateral surfaces. These elements may be excited in an HE1 is resonance mode.

Other shapes of dielectric resonator element may also be used, for example rectangular or oblong elements, or any other suitable shape. In some embodiments, two different shapes of dielectric resonator element are disposed one on either side of the feed structure.

The two dielectric resonator elements and/or their associated feeds need not be tuned or configured so as to resonate at the same frequency. Indeed, by tuning or configuring to two different frequencies (for example by having slots feeds with different sizes or dielectric resonators of different sizes or shapes or made of materials with different relative permittivities), it may be possible to improve overall bandwidth or to allow dual mode/band operation.

With a single, electrically-small resonator element (e. g. a quarter-split cylinder, a rectangle or other shape) on an electrically-small groundplane, it is difficult to

achieve a low backlobe (i. e. low radiation on the side of the groundplane opposed to the side on which the resonator element is mounted). However, low backlobes are often desirable so as, for example, to reduce SAR (specific absorption rate) in a handset antenna or to reduce radiation out of a building due to WLAN access point antennas mounted on an external wall.

However, when a second, similar resonator antenna element is placed back-to-back with a first element and the two elements are fed in antiphase, this can result is a large reduction in the backlobe. The following examples illustrate a suitable slot feeding mechanism. When direct microstrip feeding is used, one feed can be taken up to one element and another feed down to the other element, thus providing a 180° phase shift for antiphase feeding.

There may be provided two back-to-back pairs of dielectric resonator elements, for example quarter-split elements, the pairs being arranged on either side of a groundplane, and with a conductive wall perpendicular to the groundplane dividing each pair, the elements being arranged in the shape of which each element forms a quarter.

According to a second aspect of the present invention, there is provided a dielectric resonator antenna comprising first and second pairs of quarter-split dielectric resonator elements, each resonator element having a first face aligned substantially parallel to a first plane, and a second face aligned substantially parallel to a second plane that is substantially perpendicular to the first plane, wherein there is provided a conductive groundplane in the first plane and a conductive wall in the second plane, wherein the first pair of resonator elements is disposed in a back-to-back configuration on one side of the conductive groundplane with their first faces substantially parallel to the conductive groundplane and their second faces substantially parallel to and contacting the conductive wall, wherein the second pair of resonator elements is disposed in a back-to-back configuration on the other side of the conductive groundplane with their first faces substantially parallel to the

conductive groundplane and their second faces substantially parallel to and contacting the conductive wall, and wherein a feed mechanism is provided for exciting the resonator elements.

Where the feed mechanism is a direct microstrip feedline mechanism (see below), the conductive groundplane preferably has at least one dielectric layer on each side thereof such that the first faces of the resonator elements do not actually contact the ground plane.

Where the feed mechanism is a slot or aperture feed mechanism, the conductive groundplane may be configured as two conductive grounded substrates sandwiching a dielectric layer or layers, in which is embedded or sandwiched one or more microstrip feedlines. The first faces of the elements may contact the conductive grounded substrates. Apertures or slots are provided in the conductive grounded substrates at appropriate positions underneath the resonator elements.

In both of the above alternatives, the feed mechanism is disposed in the plane of the groundplane.

The conductive wall may be made of metal, for example copper, and is preferably grounded or earthed, for example by way of electrical contact with the conductive groundplane. In some embodiments, the conductive wall may comprise a pair of substantially parallel conductive walls with an air gap therebetween or some other dielectric therebetween. It is, however, important to note that the second faces of the resonator elements actually contact the conductive wall.

The conductive groundplane may also be made of metal, such as copper, but in contrast to the conductive wall (in direct microstrip feedline embodiments), may be provided on each side thereof with at least one layer of dielectric material, for example (but not limited to) a plastics material of the type used in the manufacture of printed circuit boards.

The quarter-split dielectric resonator elements may be quarter-split cylinders, quarter- split cuboids (either split corner-to-corner along diagonals to form triangular prisms, or split perpendicular to side faces to form smaller cuboids) or any other appropriate quarter-split shape. The main requirement is that each resonator element has first and second substantially perpendicular faces, preferably but not necessarily of identical or similar shape and/or size. The shapes and/or sizes of the faces may be slightly different in some embodiments to provide improved bandwidth. Indeed, one resonator element of a pair may have a different size or shape than the other resonator element of that pair, and the two pairs of elements need not be identical. This can provide improved bandwidth as discussed hereinbefore.

The feed mechanism may comprise a direct microstrip line feed to each resonator element, in which case a layer of dielectric material is provided on each side of the conductive groundplane, with direct microstrip feedlines being provided on the outer surface of each layer and passing under and contacting the first faces of the resonator elements. A single direct microstrip feedline may feed (by passing under and contacting) both members of a pair of resonator elements, in which case an aperture must be provided in the conductive wall so as to allow the feedline to pass therethrough without electrical contact therewith. Alternatively, each element may be provided with its own feedline. Each pair of resonator elements may be fed in the same way or in different ways. For example, one pair may be fed together by a single feedline, and the other pair may be fed individually by separate feedlines.

Alternatively, the feed mechanism may comprise a slot or aperture feed, in which case the conductive groundplane may be configured as first and second conductive grounded substrates sandwiching at least one layer of dielectric material. One or more microstrip feedlines are embedded or sandwiched in at least one layer of dielectric material so as to pass under the first faces of the resonator elements. A slot or aperture is provided in the first and second conductive grounded substrates underneath the first face of each element. The slot or aperture may be substantially

contiguous with the conductive wall, or may be at some other location beneath the first face. Where each member of a pair of dielectric resonators is provided with its own feed, first and second microstrip feedlines are sandwiched or embedded in the at least one layer of dielectric material, one on each side of the conductive wall, and passing under the first face of the respective member of the pair. Alternatively, a single microstrip feed may serve to feed both members of a pair, in which case it passes under the first faces of both members and an aperture must be provided in the conductive wall so as to allow the feedline to pass therethrough without electrical contact therewith. Each pair of resonator elements may be fed in the same way or in different ways. For example, one pair may be fed together by a single feedline, and the other pair may be fed individually by separate feedlines.

In some embodiments, a combination of direct microstrip feeding and slot or aperture feeding may be applied.

In the second aspect of the present invention, four independent antennas are clustered in a small space. The isolation between the antennas is determined by the size of the conducting walls that separate the elements and the conducting groundplane that separates the pairs. With four antennas offering pattern diversity an even more effective diversity or Multiple Input Multiple Output (MIMO) system can be implemented than is possible with two elements. Alternatively, the antennas can be fed together with different phasing and weightings in order to manipulate the radiation pattern either statically or in real time.

In summary:

1. The purpose of feeding two back-to-back (e. g. quarter-split) elements in phase (so that the elements resonate out of phase with each other) is: a) to cause a sharp null in a forward direction b) to cause a general increase in gain in other directions c) to cause a split beam effect when the DRA as a whole is used on a large groundplane or grounded substrate 2. The purpose of feeding two back-to-back (e. g. quarter-split) elements out of phase (so that the elements resonate in phase with each other) is: a) to cause a main lobe in a forward direction b) to cause a general region of low gain in other directions c) to cause a very low backlobe 3. The purpose of feeding two back-to-back (e. g. quarter-split) elements with other phases is: a) to cause a sharp null in directions other than forward b) to cause a main lobe in other directions 4. The purpose of feeding either the left or right element only is to create a main lobe that is directed to the left or right.

5. The purpose of switching between 1-4 above is to create a compound DRA that has switchable beam diversity so as to reduce interfering signals, to increase a link budget on a communication path, or to reduce the effects of multipath dead zones.

6. Electronically creating continuous phase steering, rather than switching between discrete values, allows the advantages of 5 to be achieved with greater precision.

The features (la-lc) of having a null in the forward direction and strong gain left and right has applications where a long thin region needs to be illuminated. Examples are corridors, railway train carriages, lift shafts, tunnels, etc. In a corridor, for example, a compound DRA could be placed on a ceiling of a corridor and the null in the downward direction would prevent excess radiation illuminating someone standing directly underneath, while still providing strong radiation up and down the length of the corridor.

One application of phase switching between to create an antenna with beam diversity is for Bluetooth (D short-range radio links. Many devices that communicate using the Bluetooth protocol are static devices such as computers and printers. If such devices happen to have destructive multipath over a wide frequency range on the link between them then they will not be able to communicate. However, switching between different beam positions, even in a random fashion, will allow communications to be restored. Similar comments apply to wireless LAN systems such as 802. 11 a/b.

Similarly, beam diversity and null steering have utility in mobile communication handsets, especially when high data rates are used such as with GPRS, EDGE and 3- G systems. The problems caused by interfering signals from other cells operating on the same frequency, or between different systems operating on adjacent frequencies, mean that the required high data rates are unlikely to be achieved without some form of antenna diversity of the types offered by the present invention.

Omnidirectional antenna arrangements: There is often a requirement in modern communication systems for two substantially omnidirectional antennas operating in the same frequency band to be co-located in a small space. For example, some base station systems produce two independent outputs that must both be radiated substantially omnidirectionally. At present, there are two ways of achieving this result:

(a) the two outputs are combined and fed to a single antenna (which is a lossy process); or (b) the two outputs are fed to two separate antennas (that must be widely separated to avoid coupling).

In many base station situations, especially micro-base stations that are located in urban streets, there is not enough room to adopt the two-antenna solution (b) above.

A currently favoured solution is thus to use a power-combiner, for example in the form of a power-combining box, which takes the two outputs designed for two antennas and combines them to produce a single output for one antenna. The disadvantage of the power-combining box is that, even when 100% efficient, it has a loss of 3dB (and in practice the loss can be more than 3. 5dB). In ideal propagation conditions, this would reduce the radius of a micro-cell by about 33%. Therefore, in ideal propagation situations, removing the loss associated with the power-combining box could substantially reduce the number of installations required to cover a specific area. Such a reduction of installations would be a significant benefit, given the high cost of base station apparatus. For the sake of clarity, it is to be noted that the term "cell"describes an area serviced by a standard base station, and a"micro-cell" describes an area serviced by a micro base station. A micro base station is a base station that may fit into a small space and has limited coverage servicing a limited number of users. The power level of a micro base station is typically around 10% of that of a standard, or macro base station.

There are many other applications in communications and radar when there is a requirement for two or more isolated antennas, each having a substantially omnidirectional radiation pattern. An example might be where two mobile communications network operators, operating in the same frequency band, each require a substantially omnidirectional antenna at the same location.

Similarly there are many other applications in communications and radar when there is a requirement for high-gain substantially omnidirectional antennas constructed from two or more (well-isolated) antennas stacked vertically and fed simultaneously by a feed structure such as a corporate or collinear feed network.

It is to be noted that, throughout the present application, the term'isolation' (and 'isolated'and similar terms) are used to refer to the isolation between one substantially omnidirectional element and another one thereabove or therebelow, and not to the isolation between elements of a back-to-back pair, for example.

Conventional technology does not allow two substantially omnidirectional antennas to work well within the confines of a small space. The reasons for this are that: i) Two substantially omnidirectional antennas cannot be put in the same plane (e. g. horizontal plane) within a small space as they will radiate into each other and be closely coupled. ii) Two dipole-like antennas cannot be stacked on top of each other in a small space because they would occupy too much height. Typically, two dipole antennas stacked vertically would be each be a half-wavelength tall and so together would occupy a whole wavelength, even if they were touching. In order to get sufficient isolation between the antennas, a much greater separation would be required.

Furthermore, there are technical problems associated with producing good substantially omnidirectional patterns from vertical arrays of dipoles fitted with feed structures.

It is known to provide a side-by-side array of conventional (e. g. patch) antennas all on one side of a feed line and to feed the antennas with differently phased signals, although significant electromagnetic coupling occurs between the antennas if they are

located close to one another, this coupling causing serious problems in effective and controllable signal generation.

It is also known (for example from UK patent applications nos. 0207052.2, 0205739.6, 0211109.4 and also from PETOSA, A., ITTIPIBOON, A. , ANTAR, Y.<BR> <P>M. M. , ROSCOE, D. , and CUHACI, M.:"Recent Advances in Dielectric-Resonator Antenna Technology", IEEE Antennas and Propagation Magazine, vol 40,1998, pp 35-48) to provide a side-by-side array of DRAs all on one side of a feed line and to feed the DRAs with differently phased signals.

Substantially omnidirectional antenna arrangements may be obtained by way of embodiments of the present invention specifically using back-to-back arrangements of dielectric resonator elements having a half-split configuration.

Each element may be provided with an individual feed mechanism, rather than the elements sharing a feed mechanism. It is, however, to be appreciated that substantially omnidirectional antenna arrangements may also be achieved with a feed mechanism that is shared between a pair of elements.

In the context of the present invention, an individual feed mechanism means a feed mechanism that excites substantially just the element to which it is connected, and not the other. The individual feed mechanisms may be combined upstream of the elements so as to form a general feed mechanism for the pair of elements.

In preferred embodiments, each element is provided with its own direct microstrip feed line as a feed mechanism. Alternatively or in addition, the feed mechanism may be based on probe feeds, slot feeds, slot feeds with transmission lines, among others.

The feed mechanisms may be configured to transfer energy into and out of the dielectric resonator elements in combination. Alternatively or in addition, the feed mechanisms may be configured so as to allow each dielectric resonator element to be excited individually. This may be achieved, for example, by the provision of an

electrical or other switch allowing one or other or both of the individual feed mechanisms to be switched in or out.

Each of the dielectric resonator elements advantageously has a"half-split" configuration. For example, the elements may take the form of half-split cylinders, half-split polygons (e. g. half-split hexagons, octagons and so forth) and other half- split shapes. Other suitable configurations for the dielectric resonator elements include: rectangular, oblong, triangular, pyramidal, or any other conventional shape, all of which may additionally be shaped to modify their electrical behaviour and mechanical profile (an example of shaping is a half-split cylindrical dielectric resonator with its curved surface ground down to lower its vertical profile).

According to a third aspect of the present invention, there is provided a dielectric resonator antenna comprising at least one pair of half-split dielectric resonator elements, each having a generally planar back surface, the pair being arranged in a back-to-back configuration with a feed mechanism provided between the back surfaces.

Embodiments of the present invention are especially suited for restricted-space base station applications that will provide the capability to dispense with a power- combining box and associated losses. One of the main technological requirements for such base station applications is to have two antennas with good input port isolation and contained within a small space.

Embodiments of the present invention may provide two closely spaced, substantially omnidirectional antennas, one above the other, that have an isolation figure of 20dB or more between them. Key performance parameters in preferred embodiments are: EITHER 2 or more input ports with 20dB or more isolation between them OR one input port feeding two or more elements Small vertical size

Wide bandwidth 2dBi or more gain . Substantially omnidirectional radiation pattern in azimuth Substantially identical radiation patterns from the two input ports The present applicant has found that electromagnetic coupling between adjacent dielectric resonator elements is not a significant problem when the elements are disposed in a back-to-back configuration; that is, oriented such that signals generated by each element during operation are mainly or substantially directed away from the other element. A significant advantage of such a reduction in coupling is that the two elements may be brought very close together or even adjacent to each other, thereby resulting in a compact DRA ideally suited for incorporation into communications devices where space is at a premium.

In a third preferred embodiment of the present invention, there is provided a pair of back-to-back dielectric resonator elements mounted on or close to a substrate, on opposite sides thereof with a microstrip feed to each element. The two back-to-back dielectric resonator elements are separated from each other by a grounded substrate comprising a single conducting layer embedded in a dielectric lamina (e. g. a printed circuit board (PCB) substrate) or sandwiched between two dielectric laminas (e. g. a pair of PCB substrates). Preferred variants of this first preferred embodiment may be considered, in effect, to incorporate a 3-layer board structure. The use of a microstrip feed to excite each dielectric resonator element (rather than a single feed structure to excite both dielectric resonator elements) is preferred because it is easier to obtain the desired performance with the direct microstrip feeding mechanism.

Using a pair of microstrips as a feed structure as described above, with both microstrips being activated in-phase, results in the dielectric resonators being fed out of phase with each other because the two feeds are back-to-back. This arrangement creates a null in a vertical plane (e. g. in a direction substantially parallel to the

grounded substrate between the dielectric resonators, which may in effect be the direction of extension of the feed line).

In a fourth preferred embodiment of the present invention, there may be provided a pair of back-to-back dielectric resonator elements mounted on a 5-layer board structure (by 5-layer board structure is meant a structure in which two generally parallel groundplanes are internally separated by a dielectric layer and externally provided on each side with a dielectric layer-additional feedlines and the like may be embedded in or formed on the dielectric layers as required). In this embodiment there may be provided a pair of back-to-back dielectric resonator elements mounted on or close to a substrate with a microstrip feed to each one, and with a grounded substrate on an inner side (for example, sandwiched within the dielectric substrate).

Beyond the grounded substrate, at the centre of the 5-layer board structure, there may be provided a further substrate containing a central feed distribution network such as a corporate or colinear feed network.

In the fourth preferred embodiment, the 5-layer board structure may be implemented as four PCB substrates bonded together. In general, the feed lines should be substantially parallel and coextensive. The central feed distribution network allows all the substantially omnidirectional pairs of back-to-back elements to be fed together so as to achieve a substantially omnidirectional compound antenna with high gain (i. e. the vertical or elevation pattern of the antenna is smaller as a result of using more than one element at once).

In a fifth preferred embodiment of the present invention, there may be provided two pairs of back-to-back half-split dielectric resonator elements of the third or fourth preferred embodiments, each pair having a separate feed mechanism independent of the feed mechanism to the other pair, the pairs being linearly disposed relative to each other such that the two pairs can be operated as independent yet closely-spaced substantially omnidirectional antennas on the same frequency as each other, or on different frequencies.

An arbitrary phase difference may be applied between elements so as electronically to control the vertical or elevation pattern of the antenna. The introduction of phase delays or differences may be achieved by providing various electronically selectable lengths of feed line embedded in unused sections of the feed structure.

Alternatively or in addition, an arbitrary phase difference may be applied between the back-to-back elements so as electronically to switch or otherwise adjust the pattern from a substantially omnidirectional shape in azimuth to a directional shape in azimuth.

The two dielectric resonator elements and/or their associated feeds need not be tuned or configured so as to resonate at the same frequency. Alternatively or in addition, they may be separately electronically tuned to change their resonant frequency. By tuning or configuring to two different frequencies, it may be possible to improve overall bandwidth or to allow dual mode/band operation or to allow the pattern to be switched from substantially omnidirectional in the azimuthal plane to a directional shape.

In summary, the purposes and advantages of feeding two back-to-back half-split elements in phase are: a) To cause a sharp null in the vertical direction b) To create a substantially omnidirectional radiation pattern in the horizontal plane c) To allow two closely-spaced, substantially omnidirectional antennas to be used as independent antennas or as part of a vertical, substantially omnidirectional array 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 drawings, in which:

FIGURE 1 shows a perspective view of a compound DRA of a first embodiment of the present invention; FIGURE 2 shows a vertical cross-section through the DRA of Figure 1; FIGURE 3 shows a simulated radiation pattern in elevation for the DRA of Figures 1 and 2 in which the dielectric resonator elements are driven separately; FIGURE 4a shows a measured radiation pattern in elevation for the DRA of Figures 1 and 2 in which the dielectric resonator elements are driven simultaneously; FIGURE 4b shows a simulated radiation pattern in elevation for the DRA of Figures 1 and 2 in which the dielectric resonator elements are driven simultaneously; FIGURE 5a shows a vertical cross-section through a compound DRA of a second embodiment of the present invention; FIGURE 5b shows an isometric view of the compound DRA of Figure 5a ; FIGURE 5c shows a perspective view of the compound DRA of Figures 5a and 5b ; FIGURE 6 shows a simulated radiation pattern in elevation for the DRA of Figure 5 in which the dielectric resonator elements are driven simultaneously, either in phase or in antiphase; and FIGURE 7 shows a simulated radiation pattern in elevation for the DRA of Figure 5 in'which the dielectric resonator elements are driven simultaneously with various phase differences.

FIGURE 8 is a perspective view of a compound DRA of the second aspect of the invention.

FIGURE 9 is a vertical cross-section through a compound DRA of a third embodiment of the present invention; FIGURE 10 is a vertical cross-section through a compound DRA of a fourth embodiment of the present invention; FIGURE 11 is an expanded cross-section through a substrate for use with the DRA of Figure 10; FIGURE 12 shows a perspective view of a fifth embodiment of the present invention; and FIGURE 13 shows a measured radiation pattern in azimuth for the DRA of Figure 9 in which the pattern can be seen to be substantially omnidirectional.

As shown in Figures 1 and 2, a first embodiment of the invention comprises a compound DRA 1 made up of two quarter-split cylindrical dielectric resonator elements 2,2'arranged back-to-back on one side of a grounded substrate 3. The elements 2,2'are separated by a feed structure 4 comprising a feed line 5 embedded in a laminar dielectric PCB 6, which extends through the grounded substrate 3. On the side of the grounded substrate 3 on which the elements 2,2'are located, the surfaces of the PCB 6 are provided with a conductive layer 7,7'that extends over substantially all of the surfaces except for a slot 8,8'on each side which is located along an intersection between the grounded substrate 3 and the PCB 6. One or other or both of the slots 8,8'may be shorted out by way of an electrical connection (not shown) between its associated conductive layer 7,7'and the grounded substrate 3.

The two resonator elements 2,2'have slightly different radii, element 2'being a little smaller than element 2. This provides an increase in operational bandwidth.

Figure 3 shows a simulated elevation radiation pattern for the DRA 1 of Figures 1 and 2 when disposed with the grounded substrate 3 substantially vertical and with the elements 2,2'located one above the other. By shorting out the upper slot 8, only the lower element 2'is caused to resonate when the feed line 5 is energised, and the elevation beam pattern 9 is obtained. Alternatively, by shorting out the lower slot 8', only the upper element 2 is caused to resonate when the feed line 5 is energised, and the elevation beam pattern 10 is obtained. Each beam pattern 9,10 has a respective main lobe 11,12, the main lobes 11 and 12 being directed generally in opposed directions (i. e. upwardly or downwardly).

Figures 4a and 4b are respectively a measured radiation pattern in elevation and a simulated radiation pattern in elevation for the DRA 1 of Figures 1 and 2 when both elements 2,2'are driven simultaneously with a single phase and thus resonate out of phase with each other. It is to be noted that Figures 4a and 4b are rotated by 90° clockwise with respect to Figure 3 because of the way that data was collected. When both elements 2,2'are driven simultaneously and thus resonate out of phase, a deep null 13 is directed in a forward direction (i. e. between the elements 2,2'away from the grounded substrate 3).

It is to be noted that Figures 3 and 4b are computer simulations obtained by conventional simulation techniques (Ansoft (R) HFSS) rather than actual measured radiation patterns. However, the computer simulation techniques are believed to be valid because the DRA structure is simple and also because of the high degree of similarity between Figures 4a and 4b.

The complexity involved in shorting out one or other of the slots 8,8'can be avoided by way of a second embodiment of the invention illustrated in Figures 5a, 5b and 5c.

As in Figure 1, there is provided a compound DRA 20 made up of two quarter-split cylindrical dielectric resonator elements 2,2'arranged back-to-back on one side of a grounded substrate 3. The elements 2,2'are separated by a feed structure 21

comprising a pair of feed lines 5, 5', each embedded in a laminar dielectric PCB 6, 6', which extend through the grounded substrate 3. On the side of the grounded substrate 3 on which the elements 2,2'are located, external surfaces of the PCBs 6, 6'are provided with a conductive layer 7,7'that extends over substantially all of the surfaces except for a slot 8,8'on each side which is located along an intersection between the grounded substrate 3 and the PCB 6. A conductive layer 7"is also provided between the PCBs 6,6'and their respective feed lines 5, 5'. Each feed line 5, 5'has a separate connector 22,22'for connection to a signal supply (not shown).

Figure 6 shows a simulated elevation radiation pattern for the DRA 20 of Figure 5 when disposed with the grounded substrate 3 substantially vertical and with the elements 2,2'located one above the other. When both feed lines 5,5'are simultaneously driven in phase (thereby causing the elements 2,2'to resonate out of phase with each other), a beam pattern 23 having a deep null 24 in a forward direction is obtained (cf. Figure 3). When both feed lines 5,5'are simultaneously driven in antiphase, a beam pattern 25 having a main lobe 26 (as opposed to a deep null) in a forward direction is obtained. This allows for easy switching between a null and a lobe.

Figure 7 shows a simulated elevation radiation pattern for the DRA 20 of Figure 5 when disposed with the grounded substrate 3 substantially vertical and with the elements 2,2'located one above the other. When both feed lines 5,5'are simultaneously driven with a phase difference of 45°, a beam pattern 27 is obtained.

When the feed lines 5,5'are simultaneously driven with a phase difference of 90°, a beam pattern 28 is obtained, and when driven with a phase difference of 135°, a beam pattern 29 is obtained. The beam patterns 27,28 and 29 show how a null and a main lobe can be electronically steered in elevation by changing the phase difference of the signals supplied to the feeds 5, 5'.

Figure 8 shows an embodiment of the second aspect of the present invention, comprising four quarter-split cylindrical dielectric ceramics resonator elements 100,

100'and 101,101'. Elements 100,100'make up a first back-to-back pair, and elements 101,101'make up a second back-to-back pair. A conductive groundplane 102 is provided on opposite sides with first and second dielectric layers 103,103' (for example PCB dielectric substrates), and is disposed in a first plane. A conductive wall 104, in this example made of copper, is disposed in a second plane substantially parallel to the first, and is in electrical contact with the groundplane 102. The elements 100,100'are disposed in a back-to-back configuration on an upper side of the groundplane 102 above the dielectric layer 103 such that the elements are separated by and each contact the conductive wall 104. The elements 101,101'are disposed in a similar configuration on the lower side of the groundplane 102 beneath the dielectric layer 103'. A first direct microstrip feedline 105 is provided on the dielectric layer 103 so as to pass beneath the elements 100, 100'. An aperture (not shown) is provided in the conductive wall 104 so as to allow the feedline 105 to pass therethrough without electrical contact. A similar feedline 105'is provided on the dielectric layer 103'so as to contact the elements 101,101', also passing through an aperture (not shown) in the conductive wall 104. It will be appreciated that each element 100,100', 101,101'could be provided with its own feedline 105, in which case no aperture is required in the conductive wall 104.

Alternatively, a slot feeding arrangement as shown in Figure 2 could be employed.

The microstrip feedlines 105,105'may be provided with connectors (see, for example, Figures 5,9 and 10) for supplying electrical current and for earthing the groundplane 102 and conductive wall 104 Turning now specifically to omnidirectional antenna arrangements, Figure 9 shows a third preferred embodiment of the present invention comprising a pair of half-split dielectric (ceramics) resonator elements 30,30' (in this case, half-split hexagons) each having a substantially planar back surface 31,31', the pair being arranged in a back-to-back configuration such that the back surfaces 31, 31'face each other. The left hand side of Figure 9 shows physical design details, whereas the right hand side shows a schematic constructional arrangement.

The back surface 31, 31'of each dielectric resonator 30, 30'is provided with a direct microstrip feed line 32,32', in this case made of etched copper. The microstrip feed lines 32,32'are electrically connected to each other by way of a conductive connecting pin 33, and are linked to a connector 34 by way of an input feed 35, also made of etched copper, and a signal pin 38.

As shown best in the depiction on the right hand side of Figure 9, the feed mechanism to the dielectric resonator elements 30,30'is formed as a board comprising two layers 36,36'of a dielectric substrate sandwiching a conductive etched copper groundplane 37 therebetween. The microstrip feed lines 32,32'are formed on the outer surfaces of the dielectric substrate layers 36,36'and the back surfaces 31, 31'of the dielectric resonators 30,30'are respectively mounted over the microstrip feed lines 32,32'. In order to accommodate the connecting pin 33, a hole is provided in the groundplane 37 so that the pin 33 does not electrically contact the groundplane 37. The input feed 35 continues on the outer surface of dielectric substrate layer 36'as an extension of microstrip feed line 32'. The connector 34 is used to supply power to the feed mechanism. An outer, earthed, part of the connector 34 is electrically connected to the central groundplane 37, and a signal pin 38 of the connector 34 is electrically connected to the input feed 35. In embodiments where the signal pin 38 passes through the groundplane 37, the groundplane 37 must include a hole so as to provide clearance for the signal pin 38. It is to be appreciated that the feed mechanism is formed as a solid structure, for example from materials well known for use in manufacturing printed circuit boards.

In operation, power transmitted through the signal pin 38 of the connector 34 and along the input feed 35 to the microstrip feed lines 32,32'is then coupled into the dielectric resonators 30,30', which resonate and thus radiate the power into free space by acting as DRAs. Since both microstrip feed lines 32,32'are fed in phase, the dielectric resonators 30,30'will be excited out of phase with each other due to

their back-to-back configuration, resulting in a null in the resulting radiation pattern in the plane of the feed mechanism.

Figure 10 shows a fourth preferred embodiment of the present invention comprising a pair of half-split dielectric (ceramics) resonator elements 30,30' (in this case, half- split hexagons) each having a substantially planar back surface 31, 31', the pair being arranged in a back-to-back configuration such that the back surfaces 31, 31'face each other. The left hand side of Figure 10 shows physical design details, whereas the right hand side shows a schematic constructional arrangement.

The back surface 31, 31'of each dielectric resonator 30, 30'is provided with a direct microstrip feed line 32,32', in this case made of etched copper. The microstrip feed lines 32,32'are electrically connected to each other by way of a conductive connecting pin 33, and are linked to a connector 34 by way of an input feed 35, also made of etched copper, and a signal pin 38.

As shown best in the depiction on the right hand side of Figure 10 and also in Figure 11, the feed mechanism to the dielectric resonator elements 30, 30'is formed as a board comprising four layers 36,36', 36"and 36"'of dielectric substrate material.

Microstrip feed lines 32,32'are respectively formed from etched copper printed on outer surfaces of substrate layers 36, 36"'where the back surfaces 31,31'of the back surfaces 31, 31'of the dielectric resonators 30,30'are respectively mounted on the outer surfaces of substrate layers 36,36"'. A first conductive etched copper groundplane 37 is sandwiched between layers 36 and 36', and a second conductive etched copper groundplane 37'is sandwiched between layers 36"and 36"'. The groundplane layers 37,37'are substantially solid and continuous except where holes are provided to allow the connecting pin 33 to pass therethrough without electrically contacting the groundplane layers 37,37'. Finally, an etched copper input feed and distribution microstrip line 35 is sandwiched between layers 36'and 36".

The connector 34 is used to supply power to the feed mechanism. An outer, earthed, part of the connector 34 is electrically connected to the groundplanes 37,37', and a signal pin 38 of the connector 34 is electrically connected to the input feed 35. In embodiments where the signal pin 38 passes through the groundplanes 37,37', the groundplanes 37,37'must include a hole so as to provide clearance for the signal pin 38. It is to be appreciated that the feed mechanism is formed as a solid structure, for example from materials well known for use in manufacturing printed circuit boards.

In operation, power transmitted through the signal pin 38 of the connector 34 and along the input feed 35 to the microstrip feed lines 32,32'is then coupled into the dielectric resonators 30,30', which resonate and thus radiate the power into free space by acting as DRAs. Since both microstrip feed lines 32,32'are fed in phase, the dielectric resonators 30,30'will be excited out of phase with each other due to their back-to-back configuration, resulting in a null in the resulting radiation pattern in the plane of the feed mechanism.

Figure 12 shows a fifth embodiment of the present invention in which two back-to- back dielectric resonator pairs 30,30'are mounted so as to sandwich a feed structure between their back surfaces, the two pairs being linearly disposed along a longitudinal extension of the feed structure. Each resonator pair 30,30'is provided with its own feed mechanism indicated generally at 39 and 39', the feed mechanism having the specific structure as described in relation to Figures 10 or 11. This embodiment allows each pair 30,30'of antenna elements to be operated as independent yet closely-spaced substantially omnidirectional dielectric resonator antennas, either on the same frequency, or on different frequencies.

Figure 13 shows a measured radiation pattern in azimuth for the DRA of Figures 9 and 12 in which the pattern can be seen to be substantially omnidirectional, except for a small ripple 40 that is due to the presence of the connector 34.

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.