WO2003098943A1

WO2003098943A1 - Multi-sectored antenna and radio frequency switch therefor

Info

Publication number: WO2003098943A1
Application number: PCT/GB2003/002082
Authority: WO
Inventors: James William Kingsley; Simon Philip Kingsley; Steven Gregory O'keefe; Ray Sirett
Original assignee: Antenova Limited
Priority date: 2002-05-15
Filing date: 2003-05-15
Publication date: 2003-11-27
Also published as: GB0211076D0; AU2003239668A1; GB2388963A; GB0311179D0

Abstract

There is disclosed an antenna array comprising a plurality of sectors in the form of dielectric substrates arranged in a generally cylindrical configuration with antenna elements mounted on outwardly-facing surfaces of the substrates, and an RF switch for selectively activating the antenna sectors individually or in combination. In this way, a beam formed by the antenna array can be steered in direction, and backlobes can be reduced.

Description

MULTI-SECTORED ANTENNA AND RADIO FREQUENCY SWITCH THEREFORE

The present invention relates to an antenna array having a plurality of sectors and also to a Radio Frequency (RF) switch therefor.

The present invention is applicable to both conventional antennas as well as to dielectric resonator antennas (DRAs) and high dielectric antennas (HDAs).

Dielectric resonator antennas (DRAs) 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 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 applicants 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", TEE 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-3I, 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 MilUmetre-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 CON AY G.L.: "Rectangular Dielectric Resonator Antenna", Electronics Letters, 1983, 19, (6), pp 218-219],

Triangle [ITT IBOON, 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., ΓΓTIPIBOON, 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.

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.

For the purposes of the present application, the following terms are hereby defined:

Element - a single radiating element of an antenna. In the example given here, all the elements are individual DRAs, but embodiments of the present invention are applicable to any kind of antenna element.

Sector - a vertical array of elements phased so as to radiate a narrow beam in a particular direction.

Level - All the elements at the same height on the array. For example the bottom level means all the lowest elements of the antenna. There might be one element per sector, or more than one.

Antenna - although strictly speaking each element is an antenna, we use the word in this document to describe the entire structure, i.e. a collection of N sectors forming N beams.

Switch - a device to select which of the N beams will be used at any given time.

Figure 1 shows a multi-sectored antenna and is intended to make the above terminology clear.

According to a first aspect of the present invention, there is provided an antenna array having a plurality of sectors each provided with a plurality of antenna elements, and a radio frequency switch operable to activate the sectors either individually or in predetermined combinations. According to a second aspect of the present invention, there is provided a radio frequency switch for use with an antenna array having a plurality of sectors, the switch being operable to activate the sectors either individually or in predetermined combinations.

The antenna array of the present invention preferably configured as a router antenna array in mobile telecommunications networks and the like, with particular advantages being that is generates narrow, low-backlobe switchable beams (despite the narrow physical width of each sector) and is able to operate in a substantially omnidirectional mode.

In preferred embodiments of the present invention, the antenna array is comprised as a plurality of dielectric substrates, for example printed circuit board substrates (PCBs), each provided with an array of antenna elements on one surface thereof. Each of substrate with its array of antenna elements is a "sector" in the terminology of the present apphcation. The substrates are then arranged in a generally cylindrical configuration about a longitudinal axis with the surfaces bearing the antenna elements all facing outwardly. It is to be noted that "cylindrical configuration" encompasses polygonal cylinders, since the substrates will generally (but need not always be) flat or planar. Typically, the substrates will be rectangular, although other shapes are possible.

Each substrate is provided with a conductive transmission line feed network connecting all of the antenna elements on the substrate to a common feed point, which may be located at one end of the substrate. Where the antenna elements are dielectric resonator pellets as used, for example, in DRAs and HDAs, the transmission line feed network may comprise a microstrip transmission line network printed on the substrate. For direct microstrip feeding, the transmission line network will be formed on the same surface or side of the substrate as the antenna elements and branches of the network will supply each antenna element by direct contact therewith. For slot or aperture feeding, the transmission line network will generally be formed on an opposed surface or side of the substrate (i.e. the side that faces inwardly when the substrates are arranged in a generally cylindrical configuration), and a conductive ground plane is then provided between the transmission line network and the antenna elements, with slots or apertures provided in the ground plane at predetermined locations so as to allow slot or aperture feeding of each antenna element. Where conventional antenna elements are used, the transmission network will be arranged in any appropriate manner known to those of ordinary skill in the art.

Additional SMT (Surface Mount Technology) components such as isolation resistors and the like may also be provided on the dielectric substrates, generally on the same surface as the antenna elements.

hi a particularly preferred embodiment, five dielectric substrates are provided to form a generally pentagonal cylinder arrangement, although three, four, six or more substrates may be provided for some applications.

The antenna elements are arranged on the outer surface of each substrate in a plurality of levels, one above the other along the longitudinal axis of the generally cylindrical configuration of the antenna array. Each level may comprise one or more antenna elements arranged side-by-side on the substrate. Typically, each level will have the same number of antenna elements, and each substrate will have the same number of levels, although other configurations are possible.

The use of DRA antenna elements is particularly preferred, since these may be configured to have a low backlobe. Accordingly, the antenna elements will tend to direct most radiation outwardly from the cylindrical configuration, and any backlobes will tend to be small, thus reducing coupling between antenna elements in different sectors. A further advantage of using DRAs as the antenna elements for a switched array system is that part of the phase shift required by the switching function may be accomplished by appropriate feeding of the element. For example, by feeding a particular DRA element in opposition to the others introduces a 180 degree phase shift, which means that a half wavelength of transmission line can be removed from the feeάVswitching network. Such a reduction in track length reduces both the size and the losses of the RF switching network.

The switch is preferably a low-loss RF switch, and may have the following functionalities:

1. To switch on all N sectors thereby creating a nominally substantially omnidirectional antenna radiation pattern. For the embodiment shown in Figure 1, N = 5 sectors. 2. To switch on a single sector thereby creating a directional antenna pattern with a single main lobe.

3. To switch on n out of N sectors, where n≤N, thereby creating a directional antenna pattern with n main lobes .

4. To combine a sector in use with rearward facing sectors, with appropriate phase and amplitude adjustments, to reduce a radiation backlobe. There is virtually no loss penalty for this feature if the single sector backlobe is initially -15dB or better.

5. To combine a sector in use with side facing sectors, with appropriate phase and amplitude adjustments, so as to reduce radiation sidelobes. There is virtually no loss penalty for this feature if the single sector sidelobe is initially

-15dB or better.

6. When a single element per level per sector is used, the switch can be designed to combine pairs of sectors in order to control a direction of an azimuth beam. Backlobe and sidelobe reduction, described above, can be incorporated into this scheme. 7. It is possible to design in a limited null steering function (over about ±10°) in order to provide a peak rejection capability.

The RF switch may be formed on a dielectric substrate such as a PCB substrate and adapted to fit within the diameter of the generally cylindrical antenna array at a base thereof, near the common feed point of each antenna array substrate. Alternatively, the RF switch substrate may be larger than the diameter of the cylindrical configuration, and the cylindrical configuration may be mounted on top of the switch substrate.

The RF switch includes various electronic components and transmission lines for connection to the common feed point of each antenna array substrate. The electronic components may include RF components such as RF diodes, RF capacitors, printed inductors and the like. The RF transmission lines will generally be printed tracks. Further low frequency electronic components such as logic decoding lines, switching components for the RF diodes, transistors, resistors, capacitors and diodes (preferably low cost diodes). LEDs may be provided as diodes in order to give a visual indication that the RF switch is functioning, but LEDs are relatively expensive and may have a shorter life-span that other types of low cost diode.

In a particularly preferred embodiment, the RF switch substrate is a double-sided PCB substrate with the RF components on one side thereof and the low frequency components on the other side thereof.

The RF switch substrate and the antenna array substrates may be connected to each other by way of soldering or by press-fit connections so as electrically to connect the RF transmission lines of the RF switch to the common feed points of the antenna array substrates. Additional control circuitry, including components such as transistors, low frequency diodes, resistors and capacitors may be mounted on the antenna array substrates in order to reduce the number of connections between the RF switch substrate and the antenna array substrates. A key feature of the RF switch is that its electronics are configured to switch between the various common feed points of the antenna array substrates (the "sectors"), either individually or in various combinations, so as to supply feed signals to or from the various antenna elements. Various predetermined phase shifts may be introduced to the feed signals to the common feed points by switching in or out additional lengths of RF transmission line by way of the diodes, for example PIN (P- trinsic-N) diodes. In this way, the sectors may be activated individually or in combination to achieve the beamforming capabilities enumerated hereinbefore.

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 an antenna array of an embodiment of the present invention;

FIGURE 2 shows how a substantially omnidirectional radiation pattern can be formed using a switch to combine all the elements of a single level of a 5-sector antenna with 3 levels and one element per level;

FIGURE 3 shows a computer simulation of a narrow beam directional radiation pattern formed by combining adjacent elements of a single level of a 5-sector antenna; and

FIGURE 4 shows laboratory measurements of a narrow beam directional radiation pattern.

Figure 1 shows an antenna array of an embodiment of the present invention comprising five sectors. Each sector comprises a rectangular dielectric PCB substrate 1, 1', 1", 1'", 1"", with the substrates being arranged in a pentagonal cylindrical configuration. An outwardly-facing surface 2 of each substrate 1 is provided with dielectric resonator antenna elements 3 made out of quarter-split cylindrical dielectric ceramics material. The antenna elements 3 are arranged in five vertically-stacked levels 4, 4', 4", 4'", 4"", each level having two antenna elements 3. A conductive ground plane 5 is provided at each level, with one rectangular surface of each quarter-split cylindrical antenna element 3 contacting its respective ground plane 5 and the other rectangular surface contacting a microstrip transmission line (not shown) printed on the PCB substrate 1. A further PCB substrate (not visible in Figure I) is located within the pentagonal cylinder at a base part i ereof, this PCB substrate bearing RF switching components and forming an RF switch.

Figure 2 shows how a substantially omnidirectional radiation pattern can be formed using the RF switch to combine all the elements 3 of a single level 4 of a five-sector antenna array with three levels 4, 4', 4" and one element 3 per level. The results in Figure 2 are computer simulations made using an Ansoft® HFSS package, but equivalent results have been demonstrated in the laboratory by the present applicant.

Figure 3 shows a computer simulation of a narrow beam directional radiation pattern formed by combining adjacent elements of a single level of a 5-sector antenna.

Figure 4 shows laboratory measurements of a narrow beam directional radiation pattern formed by combining adjacent elements of a single level from a 5-sector antenna. The antenna gain shown is lower than would be achieved operationally because of the additional loss incurred by a power splitter/combiner used to make the measurements.

The switch may be implemented on single-sided printed circuit board (PCB), but preferably on a double-sided PCB with one side containing RF diodes, RF capacitors, printed inductors and all RF tracks. Low frequency components such as the logic decoding lines and the switching currents for the RF diodes may be located on an opposed side of the PCB. The components may include transistors, resistors, capacitors, and low cost diodes. RF switching integrated circuits may also be used instead, or as well as, RF diodes. Microelectromechanical (MEM) switches may also be used for RF switching.

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 antenna array having a plurality of sectors each provided with a plurality of antenna elements, and a radio frequency switch operable to activate the sectors either individually or in predetermined combinations.

2. An array as claimed in claim 1, wherein each sector comprises a generally planar dielectric substrate and wherein the substrates are arranged around a longitudinal axis in a polygonal cylindrical configuration.

3. An array as claimed in claim 2, wherein the antenna elements are arranged on outwardly-facing surfaces of the substrates.

4. An array as claimed in claim 3, wherein the antenna elements are arranged on each substrate in a plurality of levels along the longitudinal axis.

5. An array as claimed in claim 4, wherein each level includes a plurality of antenna elements.

6. An array as claimed in claim 2 or any claim depending therefrom, wherein a conductive transmission line feed network is provided on each substrate, and wherein the feed network connects each antenna element on a given substrate to a common feed point.

7. An array as claimed in claim 6, wherein the feed network is formed on outwardly-facing surfaces of the substrates.

8. An array as claimed in claim 6, wherein the feed network is formed on inwardly-facing surfaces of the substrates.

9. An array as claimed in any preceding claim, wherein the antenna elements are dielectric resonator antenna elements.

10. An array as claimed in any one of claims 1 to 8, wherein the antenna elements are high dielectric antenna elements.

11. An array as claimed in any one of claims 1 to 8, wherein the antenna elements are monopole antenna elements.

12. An array as claimed in any preceding claim, wherein the array, when energised, forms a substantially omnidirectional beam pattern.

13. An array as claimed in any preceding claim, wherein the array is configured as a routing antenna array for a telecommunications network.

14. An array as claimed in any preceding claim, wherein the radio frequency (RF) switch is comprised as control electronics mounted on a further dielectric substrate.

15. An array as claimed in claim 14 depending ultimately from claim 6, wherein the further dielectric substrate includes RF transmission lines and means for connecting the RF transmission lines to the common feed points of the antenna element substrates.

16. An array as claimed in claim 15, wherein the control electronics include means for switching in and out various lengths of RF transmission line so as to introduce phase shifts to the respective sectors when feeding a signal thereto.

17. An array as claimed in claim.15 or 16, wherein the control electronics include means for selectively activating the sectors, individually or in predetermined combinations.

18. A radio frequency switch for use with an antenna array as claimed in any preceding claim, the switch comprising a dielectric substrate with control electronics mounted thereon, the control electronics being operable to activate the sectors either individually or in predetermined combinations.

19. An antenna array substantially as hereinbefore described with reference to or as shown in the accompanying drawings.

20. A radio frequency switch substantially as hereinbefore described.