GB2254702A

GB2254702A - Antenna radiation pattern measurement

Info

Publication number: GB2254702A
Application number: GB9107690A
Authority: GB
Inventors: Peter Alan Langsford; Leaonard William Gill
Original assignee: GEC Marconi Ltd; Marconi Co Ltd
Current assignee: BAE Systems Electronics Ltd
Priority date: 1991-04-11
Filing date: 1991-04-11
Publication date: 1992-10-14
Anticipated expiration: 2011-04-11
Also published as: GB2254702B; GB9107690D0

Abstract

Apparatus for measuring the radiation pattern of an antenna (1) in a plane (P) comprises a radiation detector (4) and means for moving the detector in an angular direction (A) about an axis (3) at right angles to the plane, and in a radial direction (R) from the axis, as shown along a track (5) on a rotatable arm (2). A telescopic support arm may be used as in Fig 2 (not shown) along with a two-axis track system as in Figs 3, 4 (not shown). <IMAGE>

Description

ANTENNA RADIATION PATTERN MEASUREMENT The invention relates to the measurement of the radiation pattern of an antenna, and more especially to the measurement of the radiation pattern extending in at least one substantially flat plane.

One known measurement apparatus is arranged to move a suitable detector in the plane in the manner of an X-Y plotter using two relatively movable, mutually orthogonal tracks. The apparatus has to have an overall area similar to the portion of the plane being measured which can be of a substantial size.

In one aspect the invention provides apparatus for use in measuring the radiation pattern of an antenna in at least one substantially flat plane, the apparatus comprising a radiation detector and means for moving the detector in an angular direction about an axis at right angles to the plane, and in a radial direction relative to the axis.

Because of the radial and angular movement, the apparatus can be more compact and can be more transportable than the known apparatus.

In one embodiment the means comprises a pivotally mounted arm, the detector being movable along the arm. In another embodiment the means comprises a pivotally mounted arm of variable length, the detector being attached to the arm.

In another aspect the invention provides a method of measuring the radiation pattern of an antenna in at least one substantially flat plane comprising the steps of; obtaining apparatus comprising a radiation detector and means for moving the detector in an angular direction about an axis, and in a radial direction with respect to the axis; arranging the apparatus so that the axis extends at right angles to the one plane, and operating the apparatus to move the detector both angularly and radially relative to the axis to measure the pattern.

In order that the invention may be well understood, various embodiments thereof will now be described by way of example only with reference to the accompanying diagrammatic drawings, in which; Figure 1 is a schematic perspective view of apparatus according to one embodiment of the invention in front of an antenna; Figure 2 is a schematic perspective view of apparatus according to another embodiment of the invention; Figure 3 is a schematic perspective view of a modification to the apparatus shown in Figure 2; and Figure 4 is a top plan view of the apparatus shown in Figure 3.

As shown in Figure 1 an antenna 1 is of the fixed, non-rotatable, variety. An elongate rigid arm 2 is positioned in front of the antenna 1 and is arranged to pivot about an axis 3 at one end of the arm 2. A radiation detector 4 is movable along a track 5 extending along the length of the arm 2. The directions of movement of the detector in an angular and a radial direction are indicated by the arrows A, R respectively. The movements may be performed by stepper or servo motors (not shown) controlled by a computer (not shown). As shown, the detector 4 is capable of being positioned substantially anywhere within the portion of the plane defined by the circle P in Figure 1. In other similar embodiments the angle of movement of the arm may be limited.

It is important that the position of the detector is accurately known each time a measurement is made. There is a danger that if the arm is not sufficiently rigid, flexure or sagging can occur in certain positions of the arm.

In order to provide some compensation for such discrepancies an optical source 6, e.g. a laser, is arranged to shine a beam of light 7 to the intended location of the detector 4. A sensor 8 attached to the detector is arranged to generate a control signal proportional to the error between the actual and intended locations of the detector. The control signal can then be used to operate the appropriate servo or stepper motors to minimise the error. Alternatively, it is envisaged that two lasers could be used each to shine a beam to intercept at the intended location of the detector. An advantage of using such a laser and sensor compensation system is that the apparatus can be made relatively less rigid and more light-weight than would be case if no such system were fitted.In such a case the arm would have to be made sufficiently rigid so that substantially no error in position of the detector would occur due to sagging or flexing of the arm.

The apparatus shown in Figure 2 is generally similar to that shown in Figure 1 except that the arm 2 is of variable length and the detector 4 is fixed to the arm. As shown, the arm 2 comprises several segments 9 telescopically received within one another. Radial movement of the detector is accomplished by relative movement of the segments 9.

The embodiment shown in Figures 3 and 4 is the same as that shown in Figure 2 except that the detector 4 is mounted upon a subsidiary platform 10. The subsidiary platform 10 includes two orthogonally arranged tracks 11, 12. As shown the track 11 is movable in the, as shown, horizontal plane with respect to the track 12 and the detector 4 is movable along the track 11. In this way the detector can be moved to a limited extent in the direction of the arrows Y and Z in a plane which extends at right angles to the plane in which the pattern is being measured, and any error between the intended and actual location of the detector can be accommodated.

Although the invention has been described with reference to the measurement of the pattern from a fixed antenna in a substantially flat plane, the apparatus may be adapted to measure a pattern in a cylindrical plane extending about a rotary antenna by fixing the angular position of the arm and moving the detector in a radial direction, whilst rotating the antenna.

Claims

1. Apparatus for use in measuring the radiation pattern of an antenna in at least one substantially flat plane, the apparatus comprising a radiation detector and means for moving the detector in an angular direction about an axis at right angles to the plane, and in a radial direction relative to the axis.

2. Apparatus according to claim 1, wherein the means comprises a pivotally mounted arm, the detector being movable along the arm.

3. Apparatus according to claim 1 or 2, wherein the means comprises a pivotally mounted arm of variable length, the detector being attached to the arm.

4. Apparatus according to claim 2 or 3, wherein the detector is mounted upon a subsidiary platform such that the detector is movable relative to the arm so as to compensate for any errors between the intended and actual positions of the detector.

5. Apparatus according to any preceding claim further comprising an optical, source and a co-operating sensor for determining the position of the detector.

6. A method of measuring the radiation pattern of an antenna in at least one substantially flat plane comprising the steps of; obtaining apparatus comprising a radiation detector and means for moving the detector in an angular direction about an axis, and in a radial direction relative to the axis; arranging the apparatus so that the axis extends at right angles to the one plane, and operating the apparatus to move the detector both angularly and radially relative to the axis to measure the pattern.

7. Apparatus for use in measuring the radiation pattern of an antenna substantially as described with reference to any one of the accompanying drawings.

8. A method of measuring the radiation pattern of an antenna substantially as described with reference to any one of the accompanying drawings.