GB2299213A

GB2299213A - Antenna array

Info

Publication number: GB2299213A
Application number: GB9505547A
Authority: GB
Inventors: Martin William Shelley; David John Barnett; Neil Williams; Norman Barry Kirkpatrick
Original assignee: ERA Patents Ltd
Current assignee: ERA Patents Ltd
Priority date: 1995-03-20
Filing date: 1995-03-20
Publication date: 1996-09-25
Also published as: GB9505547D0

Abstract

Antenna for high frequency signals formed from a plurality of elements. Each element has a cavity 4 with an electrically conductive inner wall 5, and an electrically conductive probe 7 extending across the cavity. The probes in each of the cavities are coupled together by a transmission line. Each probe may have an enlarged cross-section portion (10, fig 49) within each cavity. Each cavity may include two probes arranged orthogonally to each other.

Description

ANTENNA The present invention relates to an antenna for the reception and/or transmission of high frequency signals.

It is known to form an antenna with an element for the reception and/or transmission of high frequency signals formed as an electrically conductive cavity. High frequency signals can be carried along transmission lines, for example co-axial lines.

According to the present invention, an antenna for the reception and/or transmission of high frequency signals comprises a plurality of elements, each element consisting of a cavity having an electrically conductive inner wall, and an electrically conductive probe extending substantially across each cavity, the probes being connected together by a transmission line.

Preferably, the cavities are formed from a moulded plastics plate having a plurality of apertures, the inner surfaces of which include an electrically conductive layer.

Preferably the probes are integrally formed with the transmission lines as a single plastics moulding with an electrically conductive layer. By moulding the array of cavities and the transmission line from a plastics material, and forming an electrically conductive layer on the inner surfaces of the cavities and on the line, the antenna may be manufactured easily, and more cheaply than forming individual radiating elements which are then connected together. By manufacturing the antenna from a plastics material with a conductive layer, the weight of the antenna is reduced compared to an antenna manufactured from metal. This allows the antenna to be formed integrally with the housing of a receiver or transceiver.

The weight of the antenna can be further reduced by forming additional recesses in the plate. This removes unrequired material which reduces the weight of'the plate, and helps prevent shrinkage of the plate during moulding. The plate may be formed in two parts, with an upper plate and a lower plate having corresponding apertures. In this case, the probes may be sandwiched between the upper and lower plates. This also allows the antenna to be manufactured simply and cheaply.

Where the antenna is formed of two plates, these are advantageously attached to each other by an electrically conductive adhesive. In this way, the conductive inner surfaces of the cavities are electrically connected to each other.

Preferably, the transmission line connecting the probes is a co-axial line. In this case, the inner conductor is connected to the probes, and the outer conductor is connected to the inner conductive layer of the cavities.

The cavities may be of any shape, but it is preferred that they are square to allow them to tessellate, thereby allowing the maximum number of cavities for a given size antenna.

Advantageously, each probe includes an enlarged crosssection portion within each cavity. In this way, the transfer of energy between the cavity and the probe is improved compared to a probe having a regular cross-section along its length.

Where the antenna is to be used for the transmission and/or reception of orthogonally polarised signals, each cavity preferably includes two probes arranged orthogonally to each other. In this case, it is advantageous for the antenna to be formed from three moulded plastics plates, each having corresponding apertures, and arranged in a stack with a first set of probes between the upper and middle plate, and a second set of orthogonally arranged probes between the middle and lower plate.

An example of the present invention will be described in accordance with the accompanying drawings, in which Figure 1 shows an exploded view of an antenna; Figures 2a and 2b show cross-sectional views of a cavity of the antenna of Figure 1; Figure 3 shows a cross-section of a moulded plate including additional recesses; and, Figures 4a and 4b show cross-sectional views of a cavity of an alternative antenna.

The antenna shown in Figure 1 has an upper plate 1, a lower plate 2, and a co-axial line network 3. The upper and lower plates 1,2 are each moulded plastics plates with an array of cavities 4. The inner walls of each of the cavities 4 are coated with an electrically conductive layer 5. The lower surface of the upper plate 1, and the upper surface of the lower plate 2 include grooves 6. The grooves 6 are arranged to receive the co-axial line network 3 sandwiched between the upper and lower plates 1,2.

As shown in Figure 2a, the co-axial line network includes a number of probes 7 which extend across each of the cavities 4 of the antenna. The upper and lower plates 1,2 are joined together with an electrically conductive adhesive 8 which electrically connects each of the electrically conductive layers 5 of the cavities 4.

In use, each of the cavities 4 act as elements for the reception and/or transmission of high frequency signals.

When receiving signals, the energy from each of the cavities 4 is coupled to the output port 9 via the probes 7 of the co-axial line network 3. When transmitting signals, energy is input to the co-axial line network 3 from the input port 9, and is radiated by each of the probes 7 into the cavities 4. In either case, the external coupling via the port 9 may be by any suitable means, for example by a co-axial line network of a waveguide.

The impedance of the junctions of the co-axial transmission line 3 is chosen to minimise unwanted reflections within the co-axial line network 3. This is achieved by modification of the cross-section of the line, and optimising the size of the grooves 6 formed on the plates 1,2. Additionally, dielectric spacers (not shown) may be provided in the grooves 6 to control the impedance of the junctions, and hold the co-axial line network 3 in place.

Figure 3 shows a cross-section through the antenna/ Additional recesses 11 are provided to reduce the weight of the antenna, and to reduce shrinkage during moulding.

As shown in Figures 4a and 4b, the cross-section of the end of each probe 7 can be modified, for example by providing an enlarged cross-sectional portion 10 to improve the coupling between the cavity 4 and the co-axial line network 3.

Although the cavities 4 are shown with a square crosssection, the cavities may be of any other shape, for example rectangular or circular. Similarly, the co-axial line 3 may be formed from any cross-sectional shaped line, for example square or rectangular rather than the circular shape shown.

Claims

1. An antenna for the reception and/or transmission of high frequency signals comprising a plurality of elements, each element consisting of a cavity having an electrically conductive inner wall, and an electrically conductive probe extending substantially across each cavity, the probes being connected together by a transmission line.

2. An antenna according to claim 1, in which the cavities are formed from a moulded plastics plate having a plurality of apertures, the inner surfaces of which include an electrically conductive layer.

3. An antenna according to claim 1 or 2, in which the probes are integrally formed with the transmission lines as a single plastics moulding with an electrically conductive layer.

4. An antenna according to any one of the preceding claims, in which the plate is formed in two parts, with an upper plate and a lower plate having corresponding apertures.

5. An antenna according to claim 4, in which the probes are sandwiched between the upper and lower plates.

6. An antenna according to claim 4 or 5, in which the two plates, are attached to each other by an electrically conductive adhesive.

7. An antenna according to any one of the preceding claims, in which the transmission line connecting the probes is a co-axial line.

8. An antenna according to claim 7, in which the inner conductor is connected to the probes, and the outer conductor is connected to the inner conductive layer of the cavities.

9. An antenna according to any one of the preceding claims, in which the cavities are square to allow them to tessellate.

10. An antenna according to any one of the preceding claims, in which each probe includes an enlarged crosssection portion within each cavity.

11. An antenna according to any one of the preceding claims, in which each cavity includes two probes arranged orthogonally to each other.

12. An antenna according to claim 11, in which the antenna is formed from three moulded plastics plates, each having corresponding apertures, and arranged in a stack with a first set of probes between the upper and middle plate, and a second set of orthogonally arranged probes between the middle and lower plate.

13. An antenna as shown in, or described with respect to any of the accompanying drawings.