GB2390225A

GB2390225A - Radio transceiver antenna arrangement

Info

Publication number: GB2390225A
Application number: GB0215010A
Authority: GB
Inventors: Andrew John Fox; Roy Peter Henderson
Original assignee: Picochip Designs Ltd
Current assignee: Picochip Designs Ltd
Priority date: 2002-06-28
Filing date: 2002-06-28
Publication date: 2003-12-31
Also published as: GB0215010D0; WO2004004065A1; AU2003244765A1

Abstract

An antenna arrangement has a first transmit antenna 12 for transmitting radio signals in a first frequency band and a second receive antenna 14 for receiving radio signals in a second frequency band, and further has a diffraction grating 22 located between the first and second antennas, for attenuating signals transmitted from the first antenna in the first frequency band.

Description

RADIO TRANSCEIVER

This invention relates to a radio transceiver, and in particular to the receive and transmit antennas for use 5 in a transceiver.

In a mobile communications system, for example, in the case of a duplexerless transceiver, it is conventional to provide one transmit antenna, for signals which are 10 being transmitted over the air interface, and one receive antenna, for signals which are being received over the air interface.

It is then necessary to ensure radio frequency 15 isolation between these two antennas, in particular to ensure that the large amplitude transmitted signals are not received by the receive antenna, in which case there is a danger that they will swamp the received signals. One way of achieving this isolation is to use 20 filter circuitry connected to the antennas. Another way of achieving this is to rely on the spatial separation of the two antennas.

Also, in the case of a transceiver for use in the 25 Universal Mobile Telephony System (UMTS), or 3rd Generation mobile communications network, when operating in time division duplex (TDD) mode, the device uses downlink channel estimates relating to the received channel in order to control transmissions on 30 an uplink channel. For the downlink channel estimates to be properly representative of the uplink channel, it is preferable for the receive and transmit antennas to be as close together as possible, and so this

requirement for a large spatial separation is a disadvantage. According to a first aspect of the present invention, 5 there is provided an antenna arrangement, comprising a first transmit antenna for transmitting radio signals in a first frequency band and a second receive antenna for receiving radio signals in a second frequency band, and further comprising a diffraction grating located lO between the first and second antennas, for attenuating signals transmitted from the first antenna in the first frequency band. The antennas are each generally planar, and they are generally coplanar, and the diffraction grating extends out of the plane of the 15 antennas, preferably perpendicular to the plane of the antennas. According to a second aspect of the present invention, there is provided a radio transceiver, including an 20 antenna arrangement according to the first aspect.

For a better understanding of the present invention, and to show how it may be put into effect, reference will now be made, by way of example, to the 25 accompanying drawings, in which: Figure 1 is a perspective view of a transceiver device in accordance with the invention.

30 Figure 2 is a side view of a part of the transceiver device of Figure 1.

Figure 1 shows a transceiver, for example for use in a base station of a mobile communications system. The

discussion herein relates to a Universal Mobile Telephony System (UMTS) base station, but it will be appreciated that the invention relates to any system.

The transceiver is based on a circuit board 10, which 5 contains a first transmit antenna 12 and a second receive antenna 14. As is conventional, each of these antennas comprises a generally planar metallic patch, which is mounted over a corresponding aperture (not shown) in the circuit board 10, such that the transmit 10 antenna 12 and receive antenna 14 are generally coplanar. The electronic components of the transceiver are generally conventional. Thus, the electronic components comprise the various amplifier, filter etc blocks, which are required, in order to process the 15 signals before transmission and after reception by the respective antenna. The electronic components are located on the lower side of the circuit board 10, as it is oriented in Figure l, generally within a region 16 (shown in dashed lines), which occupies one major 20 portion of the circuit board while the antennas 12, 14 occupy another major portion.

The transmit antenna 12 and receive antenna 14 are closely spaced. In one preferred embodiment of the 25 invention, the edge 12a of the transmit antenna 12 and the edge 14a of the receive antenna 14 which are closest together are separated by a distance d which is slightly more than one half of one wavelength at the frequencies of interest. With this close spacing of 30 the transmit antenna 12 and receive antenna 14, any downlink channel estimates made in UMTS TDD (Time Division Duplex) mode will also act as reliable uplink channel estimates. This close spacing is achieved by placing the transmit antenna 12 and receive antenna 14

on adjacent areas of the circuit board 10, and placing the electronic circuitry 16 away from the antennas.

A first feed line 18 is connected between the electronic circuitry 16 and the transmit antenna 12, and a second feed line is connected from the receive antenna 14 to the electronic circuitry 16.

In use, relatively strong radio frequency signals are 10 transmitted from the transmit antenna in a first frequency band, while at the same time relatively weak radio frequency signals are being received at the receive antenna in a second frequency band.

15 Precautions must be taken to ensure that the received signals can be detected in the presence of the transmitted signals and, in this illustrated embodiment of the invention, a diffraction grating 22 is located between the transmit antenna 12 and receive antenna 14.

Figure 2 is a side view of the diffraction grating 22.

The grating includes a first vertical section 24, which is mounted to the circuit board 10, and extends upwards therefrom. The grating further includes a first 25 horizontal section 26 which is connected to the upper end of the first vertical section 24 and extends perpendicular thereto in the direction of the receive antenna 14, a second vertical section 28 which extends vertically upwards from the end of the first horizontal 30 section 26, and a second horizontal section 30 which is connected to the upper end of the second vertical section 28 and extends perpendicular thereto in the direction of the transmit antenna 12.

The first and second horizontal sections 26, 30 and the second vertical section 28 thus define a corrugation which opens towards the transmit antenna 12.

5 The grating 22 has a conductive surface. Thus, it can be made from any conductive material, or with any conductive coating. The conductive material should preferably be somewhat lossy. For example, it may be made of a metallic material or with a metallic coating.

10 It may conveniently be made from copper sheet.

The grating acts in several different ways to reduce the amplitude of the transmitted radio waves reaching the receive antenna. For example, the transmitted 15 radio waves are diffracted from the corners of the sections 24, 26, 28, 30, and are also absorbed by the grating 22.

Thus, although the term diffraction grating is used 20 herein to refer to any structure which has a significant attenuating effect on the transmitted signals which reach the receive antenna, that attenuating effect is not entirely due to diffraction, and may not even be mainly due to diffraction.

In order to maximise the effect of diffraction, the lengths of the sections can be chosen such that there is destructive interference of the transmitted signals in the region of the receive antenna 14. Specifically, 30 the destructive interference can be maximized by tuning the lengths of the sections to the wavelength of the transmitted signals.

However, as mentioned above, this destructive interference is not the only effect of the diffraction grating, and the size of the grating can be chosen such that it produces the required improvement in isolation.

5 For example, choosing a length L; lOmm, it is found that the isolation between the transmit antenna and receive antenna can be improved from about 25dB to about 40dB in the UMTS band, in the case of the arrangement described above.

The grating 22 therefore extends out of the plane in which the patch antennas lie, and in particular extends generally in a plane which is perpendicular to the plane in which the patch antennas lie. Thus, if the 15 patch antennas are horizontal, the diffraction grating extends generally upwards. The shape of the grating can generally be described as corrugated, with the depths of the corrugations lying parallel to a line from the transmit antenna to the receive antenna, and 20 the longitudinal direction of the corrugations lying perpendicular to such a line.

In terms of the degree of attenuation which is provided by the grating, it is generally preferable to provide 25 more corrugations. However, the further that the grating extends out of the plane in which the patch antennas lie, the greater its effect on the radiation pattern in the far field. A grating as shown in Figure

2, made up of four sections 24, 26, 28, 30, has been 30 found to provide a good compromise between these two requirements. Thus, the diffraction grating 22, located between the transmit antenna 12 and the receive antenna 14, greatly

( 7 reduces (for example by 15dB) the power of the transmitted signal received at the receive antenna.

This has the advantage that it becomes possible to reduce or avoid the necessity for filtering circuitry 5 in the receiver front-end circuitry of the transceiver electronic circuitry.

Claims

1. An antenna arrangement, comprising a first generally planar transmit antenna for transmitting 5 radio signals in a first frequency band and a second generally planar receive antenna for receiving radio signals in a second frequency band, the second antenna being generally coplanar with the first antenna, and the antenna arrangement further comprising a lo diffraction grating located between the first and second antennas, and extending out of a plane in which the first antenna and second antenna lie, for attenuating signals transmitted from the first antenna in the first frequency band.

2. An antenna arrangement as claimed in claim 1, wherein the first and second antennas are patch antennas. 20

3. An antenna arrangement as claimed in claim 1 or 2, wherein the diffraction grating has a conductive surface.

4. An antenna arrangement as claimed in claim 1, 2 or 25 3, wherein the first and second antennas extend in a first plane, and the diffraction grating extends in a second plane, the second plane being generally perpendicular to the first plane and generally perpendicular to a line joining the first and second 30 antennas.

5. An antenna arrangement as claimed in any preceding claim, wherein the diffraction grating is a corrugated diffraction grating.

6. An antenna arrangement as claimed in claim 5, wherein the diffraction grating comprises at least one corrugation which opens towards the transmit antenna.

5

7. An antenna arrangement as claimed in claim 1, wherein the first and second antennas are formed in a circuit board, and wherein the grating comprises: a first vertical section, which is mounted to the circuit board and extends perpendicular thereto; 10 a first horizontal section, which is connected to a distal end of the first vertical section and extends perpendicular thereto; a second vertical section, which extends from a distal end of the first horizontal section and 15 perpendicular thereto; and a second horizontal section, which is connected to a distal end of the second vertical section and extends perpendicular thereto.

20

8. An antenna arrangement as claimed in claim 7, wherein the first horizontal section of the grating extends from the first vertical section in the direction of the second receive antenna.

25

9. A transceiver circuit, comprising an antenna arrangement as claimed in any preceding claim.

10. A transceiver circuit as claimed in claim 9, comprising a circuit board, wherein the first transmit 30 antenna and the second receive antenna are adjacent each other on said circuit board with the diffraction grating located between them, and further comprising electronic circuitry mounted on the circuit board away from the antennas.

11. A base station for a mobile communications system, comprising a transceiver circuit as claimed in claim or 10.