GB2077514A - Microwave frequency rotating joint - Google Patents

Abstract

A microwave rotating joint has two parts 10 and 11 which are mutually rotatable. Each part is an annular array of transmitting and receiving elements 12 centred at the same radius about the axis of rotation. The elements 12 of each array are connected to a common line 13 by feeders 14 which provide identical phase change between the line 13 and each element 12 of the array, e.g. the feeders are of the same length. Energy is coupled between parts 10 and 11 across an axial gap between the arrays of elements 12, without any variation in phase or amplitude as the parts rotate. <IMAGE>

Description

SPECIFIC.ATEON Microwave frequency rotating joint The present invention is concerned with microwave frequency rotating joints. In radar apparatus, a rotating joint is commonly used to carry microwave energy to and from a rotating antenna. A known rotating joint is in the form of an annular waveguide centered on the axis of rotation of the antenna and split in two parts in a centrai plane per pendicular to the axis. One ofthe two parts can then rotate with the antenna whilst the other part remains fixed. Microwave energy for transmission by the antenna can be launched into the circular waveguide from the fixed part and coupled out ofthe waveguide from the rotating part for delivery to the antenna.However, this arrangement has the drawback that the phase of the signal passing through the joint varies with rotation of the joint and there can also be amplitude variation problems arising from the generation of standing waves in the annular waveguide. Various other forms of rotating joint are also known but many are liable to suffer from problems of either phase or amplitude variation with rotation.

According to the present invention a microwave frequency rotating joint comprises at least one pair of circularly extending arrays of microwave receiving/transmitting elements, with one array of the pair rotatable relative to the other about their common axis, and bi-directional microwave feeding means associated with each array and arranged for distributing microwave energy from a single source to said array so that the energy emitted by the elements of the array has substantially uniform phase and amplitude about the circle ofthe array and for constructively combining microwave energy received by the elements at a substantially uniform phase and amplitude about the circle of the array, the arrays of the pair being mutually located so that microwave energy emitted by the elements of one array is received by the elements of the other array.

With this arrangementthe phase of energy emitted from one array to the other (across the rotating joint) is constant completely around the circle of the array so that there is no phase variation of the signals passing through the joint with rotation of the joint. The joint can also provide a compact arrangement enabling multi-channel operation in preferred embodiments as will become apparent.

Conveniently, for each said array, the respective signal paths through the feeding means to the receiving/transmitting elements are all of the same length. Preferably also, the receiving/transmitting elements of each array are evenly spaced about the respective circle.

In a preferred arrangement, the arrays of the pair are annular, of the same radius and axially separated by an annular gap, the elements of the array being arranged to emit and receive microwave energy axially across said gap.

In one embodiment, said elements of the pair of arrays are the open ends of lengths of waveguide constituting said feeding means. In another embodiment, said elements of the pair of arrays are the ends of lengths of stripline constituting said feeding means.

In a multi-channel arrangement, two or more said pairs of arrays with associated feeding means are arranged concentrically in a common radial plane.

An example of the present invention will now be described with reference to the accompanying drawings in which: FIGURE 1 shows schematically an embodiment of the present invention and FIGURE 2 shows the two parts of the joint of FIG URE 1 developed in a flat plane to illustrate the distribution of feed paths in the two parts.

Referring to FIGURE 1, the rotating joint comprises first and second parts 10 and 11 each of which has a generally circular outline on a common axis. In use, the parts would be arranged fixed to mutually rotating conponents between which it was desired to transfer microwave energy. For example, the upper part 10 would be associated with a rotatable radar antenna and the lower part 11 associated with the fixed mounting of the antenna. The part 10 would be rotatable relative to the part 11 about their common axis. The parts 10 and 11 are substantially identical to each other and are each bi-directional from the point of view of microwave energy so that microwave energy can pass through the joint in either direction. Each ofthe parts 10 and 11 has an annular array of microwave energy receiving/transmitting elements 12. These elements are represented in FIGURE 1 simply as radial lines.In a practical embodiment, they may be constituted by any known element, such as apertures in waveguides, the open ends of waveguides, radiating horns or dipole elements. In the present example, these elements are distributed spaced evenly about the annulus of the array and they are arranged to emit and receive microwave energy in a direction parallel to the common axis of the parts 10 and 11. Adjacent elements 12 of the array are spaced apart by a distance less than the wavelength of the microwave energy to be coupled by the rotating joint. Thus, the elements 12 correspond to the elements of an array-type antenna except that the usual line of elements in an array antenna is bent round to form the annular array in the present arrangement.

The elements 12 ofthe array of each part 10 and 11 of the rotating joint are connected to a common microwave energy transmission line 13, e.g. waveguide, stripline, coaxial line etc., by feeding means indicated generally by the reference 14. The feuding means 14 in each part 10 and 11 is arranged to provide identical phase change of signals passing between the common transmission line 13 and each one ofthe elements 12 in the array. As a result, energy delivered along the common transmission line 13 to the part 10 ofthe joint energises each of the elements 12 of the part 10 in phase so that the parts 12 operate as a constant phase array.In the described arrangement the elements 12 are equally spaced about the array and the feeding means 14 are also arranged to deliver substantially equal amounts of energy to each element so that the amplitude of energy emitted by the elements 12 about the array is also substantially constant.

The feeding means 14 comprises in the described example a branching arrangement oftransmission lines between the common line 13 and the elements 12 with branches arranged so that the path length from the common line 13to each element 12 isthe same. The transmission lines 15 of the branching arrangement of the feeding means 14 may be constituted by lengths of waveguide orstripline or any other known microwave transmission line. The junctions between lengths of transmission line 15may also be formed in ways known in the art.However, it is important to ensure that the junctions between the various branches ofthe feeding means 14 do not introduce relative phase changes between the elements 12 and also divide the energy between the branches so that each ofthe elements 12 receive equal amounts of energy from the common transmission line 13.

It may be desirable to include matching transformers distributed throughout the branching arrangements of each of the parts 10 and 11 ofthe rotating jointto ensure impedance matching.

FIGURE 2 shows the arrangement of FIGURE 1 but with the parts 10 and 11 developed in a flat plane to illustrate more completely the distribution of branches 15 of transmission line. In the rotating joint, the two parts 10 and 11 are mutually located so that the elements 12 of the two parts are facing each other across a narrow annular gap. The annular arrays 12 of each of the parts 10 and 11 are ofthe same radius. As a result, it can be seen that microwave energy delivered along the common line 13 and distributed amongst the elements 12 of the part 10 is launched across the annular gap between the parts 10 and 11 and received by the elements 12 of the part 11 wherein the energy is constructively recombined in a single transmission line. Since the phase and amplitude of energy launched from the elements 12 of the part 10 is substantially constant about the annulus of the parts, mutual rotation between the two parts should not affect the phase or amplitude of energy transferred through the joint. is can be ltcanbeseenthatthearrangementofthis example of the present invention provides a relatively large central space 16 inside the annuli ofthe elements 12 of the two parts. In a multi-channel rotating joint where two or more separate microwave signals are to be transferred across the joint, one or more further pairs of arrays of receiving/transmitting elements with associated feeding arrangements can be mounted concentrically in the space 16. This can provide an extremely compact multi-channel joint.

Claims (7)

1. A microwave frequency rotating joint compris ing at least one pair of circularly extending arrays of microwave receiving/transmitting elements, with one array of the pair rotatable relative to the other about their common axis, and bi-directional micro wave feeding means associated with each array and arranged for distributing microwave energy from a single source to said array so that the energy emitted by the elements ofthe array has substan tially uniform phase and amplitude about the circle of the array and for constructively combining microwave energy received by the elements at a substantially uniform phase and amplitude about the circle of the array, the arrays of the pair being mutually located so that microwave energy emitted by the elements of one array is received by the elements of the other array wherein for each said arraythe respective signal paths through the feeding means to the receiving/transmitting elements are all of the same length.

2. Ajoint as claimed in claim 1, wherein the receiving/transmitting elements of each array are evenly spaced about the respective circle.

3. A joint as claimed in claim 1 or claim 2, wherein the arrays of the pair are annular, ofthe same radius and axially separated by an annular gap, the elements of the arrays being arranged to emit and receive microwave energy axially across said gap.

4. Ajoint as claimed in any preceding claim, wherein said elements ofthe pair of arrays are the open ends of lengths of waveguide constituting said feeding means.

5. Ajoint as claimed in any of claims 1 to 3, wherein said elements ofthe pair of arrays are the ends of lengths of stripline constituting said feeding means.

6. Ajoint as claimed in any preceding claim and comprising two or more said pairs of arrays with associated feeding means, arranged concentrically in a common radial plane.

7. A microwave frequency rotating joint substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.