GB1598325A

GB1598325A - Direction finding arrangements

Info

Publication number: GB1598325A
Application number: GB3085077A
Authority: GB
Original assignee: Plessey Co Ltd
Current assignee: Plessey Co Ltd
Priority date: 1976-04-28
Filing date: 1976-04-28
Publication date: 1981-09-16

Description

(54) DIRECTION FINDING ARRANGEMENTS (71) We, THE PLESSEY COMPANY LIMITED, a British Company of Vicarage Lane, Ilford, Essex, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to direction finding arrangements and in particular to such arrangements in which two pairs of aerial elements are used to provide directional information in two co-ordinate directions for a signal received by the antenna elements.

According to this invention there is provided a direction finding arrangement comprising two pairs of aerial elements arranged in a non-linear configuration, delay means arranged to be fed with signals derived from the two pairs of aerial elements and to provide two pairs of signals, the signals in each pair having a relationship dependent upon the phase difference between a respective pair of signals fed to the delay means; a multiplexer for multiplexing signals derived from the delay means into a single signal path, a radio receiver for receiving signals fed over the single signal path, a demultiplexer for demultiplexing output signals fed from the receiver into two pairs of output signals. and comparator means for comparing the signals of each pair of output signals to provide signals representative of two co-ordinates of the direction of origination of a signal received by the aerial elements.

Conveniently four aerial elements are provided arranged one at each corner of a rectangle which in a preferred form is a square.

The signals derived from the two further pairs of aerial elements may comprise two further pairs of signals formed by one signal from each of the four aerial elements but it is preferred to interpose a resistor combining network to provide four signals each being formed as a combination of signals from adjacent aerial elements. The combining network may conveniently provide a single combined output and a receiver may be provided to detect identification signals carried by a received signal.

Preferably the delay means comprises two delay units and in a preferred form each delay unit has two inputs, one for each signal of a respective one of the further pairs of signals and two outputs each connected directly to a respective one of the two inputs there being a delay line provided between the two inter-connected input/output pairs.

Preferably the delay line is formed by a length of coaxial cable.

The multiplexing circuit is preferably operable under the control of an oscillator and the de-multiplexor is also preferably driven by the said oscillator via a delay circuit.

Advantageously the signals representative of the two co-ordinates are obtained by subtractively combining pairs of output signals derived from the delay means.

It is advisable to provide a filter to filter each co-ordinate representative signal to remove switching signal breakthrough from the de-multiplexer.

As so far described the two co-ordinate representative signals will be provided in cartesian form and it is preferred to provide a vector calculator for conversion to polar co-ordinates.

It is advantageous to provide vector display means for displaying the polar coordinates.

The vector display may conveniently incorporate a range display for indicating the range of a received signal the range display being advantageously driven by an a.g.c.

output from the radio receiver means.

This invention will now be described further with reference to the accompanying drawings in which: Figure I shows a preferred embodiment of the invention; and Figure 2 shows the resistor combining network of Figure 1 in more detail.

Referring to Figure 1 the direction finding arrangement shown includes four aerial elements Al, A2, A3, and A4 which are assumed to be arranged at the corners of a square (illustrated linearly disposed for convenience), with the elements A1 and A3 being diagonally opposed and similarly the elements A2 and A4.

Signals received by each element A1 to A4 which may be continuous wave or modulated are fed via respective lengths of cable 1 to respective R.F. pre-amplifiers 2. Each pre-amplifier 2 feeds a respective input of a resistor combining network 3 which as will be described in greater detail with reference to Figure 2 of the drawings and has four outputs A,', A2,, A3' and A41 at which appear signal combinations of signals received by adjacent aerial elements.

As will be described in detail later outputs of the four aerial elements A1, A2, A3 and A4 are combined in diagonal pairs to afford an indication, initially in cartesian i.e. X, Y forms and finally in polar form, of the direction of a signal received by the aerial arrangement.

In use it may not be possible physically to arrange that the four aerial elements are in a square configuration and in such a case the co-ordinate signals derived from diagonal pairs of elements will not be effectively perpendicular to one another.

The use of the resistor network providing effectively elements arranged in a diamond configuration corrects for this. In addition even if the aerial elements are arranged in a physical square, the use of the network provides an effective rotation of the coordinate system, which may be useful for some applications. The resistor network will be described in more detail later.

The diagonal outputs A1, and A3, from the resistor network 3 are fed to respective inputs of a delay unit 4 and the outputs A2, and A4, are similarly connected to a delay unit 5.

The delay units 4 and 5 provide output signals representative of the phase difference between input signals fed thereto and this is effected by connecting a respective delay line 6, 7 each typically in the form of a length of coaxial cable between the input signals.

Each delay unit 4, 5 provides a pair of phase representative output signals which are used to derive co-ordinate representative signals.

Output signals from the delay units 4 and 5 are connected to individual inputs of a multiplexor 8 which, under the control of a driving oscillator 9 connects the signals at the individual inputs cyclically to an A.M.

receiver 10.

The output from the receiver is applied to a de-multiplexor 11 which is controlled by the same oscillator 9 via a delay 12 which compensates for the delay through the receiver 10. The de-multiplexor effectively recovers four output signals corresponding to those of the delay units 4 and 5.

The pair of outputs corresponding to the outputs A1, and A3, are subtractively combined in a subtractor 13 and the outputs corresponding to the outputs A2, and A4' are similarly combined in a subtractor 14.

The subtractors 13 and 14 provide outputs 15 which are representative of the X and Y co-ordinates corresponding to the direction of the received signal.

The two outputs 15 are applied to respective filters 16 which remove switching frequency breakthrough from the demultiplexor 11.

The filtered outputs of the filters 16 are fed to a vector calculator 17 which converts the cartesian co-ordinate signals into polar co-ordinates, these then being applied to a display unit 18 which incorporates a vector display 19 for directly displaying the polar co-ordinates of a received signal.

The display unit 18 also incorporates a range display 20 which is driven by the a.g.c.

output of the receiver 10 and provides an indication of the range of a received signal.

In addition to the functions already described, the resistor combining network 3 is arranged to sum all of the signals derived from the aerial elements A1, A2 A3 and A4 and this combined signal is applied to an auxiliary receiver 21 which may be used to detect an identification code carried by a received signal.

Referring to Figure 2 there is shown the resistor combining network 3 in which adjacent ones of the aerial elements A1, A2, A3 and A4 which provide the four inputs to the network 3 have connected therebetween respective pairs of series connected resistors R1.

An output A1, is provided at the junction of the resistors R1 between the elements A1 and A2, an output A2' between two elements A2 and A3, an output A3, between A3 and A4 and an output A3, between A1 and A4.

The outputs A1,, A2,, A3, and A4, correspond to aerial elements arranged in a diamond configuration.

Connected between diagonally opposed elements are pairs of series connected resistors R2 which meet at a common centre point S at which appears a signal equal to the sum of the signals provided by the aerial elements A1, A2, A3 and A4. This sum signal is read as described above.

Whilst a preferred embodiment of this invention has been made variations will be apparent to persons skilled in the art which may be made without departing from the scope of the invention.

WHAT WE CLAIM IS: 1. A direction finding arrangement comprising two pairs of aerial elements arranged in a non-linear configuration, delay means arranged to be fed with signals derived from the two pairs of aerial elements and to provide two pairs of signals, the signals in each pair having a relationship dependent upon the phase difference between a respective pair of signals fed to the delay means; a multiplexer for multiplexing signals derived from the delay means into a single signal path, a radio receiver for receiving signals fed over the single signal path, a demultiplexer for demultiplexing output signals fed from the receiver into two pairs of output signals, and comparator means for comparing the signals of each pair of output signals to provide signals representative of two co-ordinates of the direction of origination of a signal received by the aerial elements.

2. An arrangement as claimed in claim 1 in which four aerial elements are provided arranged one at each corner of a rectangle.

3. An arrangement as claimed in claim 1 in which the rectangle is a square.

4. An arrangement as claimed in any preceding claim in which the signals derived from the two pairs of aerial elements comprise two further pairs of signals formed by one signal from each of the four aerial elements.

5. An arrangement as claimed in any one of claims 1 to 3 in which the signals derived from the two pairs of aerial elements are derived via a resistor combining network to provide four signals each being formed as a combination of signals from adjacent aerial elements.

6. An arrangement as claimed in claim 5 in which the resistor combining network is operative to provide a single combined output signal and an auxiliary receiver is provided to be responsive to the combined output signal to detect identification signals carried by a received signal.

7. An arrangement as claimed in any preceding claim in which the delay means comprises two delay units.

8. An arrangement as claimed in claim 7 in which each delay unit has two inputs, one for each signal of a respective one of the further pairs of signals and two outputs each connected directly to a respective one of the two inputs there being a delay line provided between the two interconnected input/output pairs.

9. An arrangement as claimed in claim 8 in which each delay line is formed by a length of coaxial cable.

10. An arrangement as claimed in any preceding in which the multiplexing circuit is operable under the control of an oscillator.

11. An arrangement as claimed in claim 10 in which the demultiplexor is driven by the said oscillator via a delay circuit.

12. An arrangement as claimed in any preceding claim in which the signals representative of the two co-ordinates are obtained by subtractively combining pairs of output signals derived from the delay means.

13. An arrangement as claimed in any preceding claim in which there is provided a filter to filter each co-ordinate representative signal to remove switching signal breakthrough from the de-multiplexor.

14. An arrangement as claimed in any preceding claim in which there is provided a vector calculator to convert the co-ordinate representative signals to polar co-ordinates.

15. An arrangement as claimed in claim 14 in which there is provided vector display means for displaying the polar co-ordinates.

16. An arrangement as claimed in claim 15 in which the vector display incorporates a range display.

17. An arrangement substantially as herein described with reference to and as illustrated in Figures 1 and 2 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. invention has been made variations will be apparent to persons skilled in the art which may be made without departing from the scope of the invention. WHAT WE CLAIM IS:

1. A direction finding arrangement comprising two pairs of aerial elements arranged in a non-linear configuration, delay means arranged to be fed with signals derived from the two pairs of aerial elements and to provide two pairs of signals, the signals in each pair having a relationship dependent upon the phase difference between a respective pair of signals fed to the delay means; a multiplexer for multiplexing signals derived from the delay means into a single signal path, a radio receiver for receiving signals fed over the single signal path, a demultiplexer for demultiplexing output signals fed from the receiver into two pairs of output signals, and comparator means for comparing the signals of each pair of output signals to provide signals representative of two co-ordinates of the direction of origination of a signal received by the aerial elements.

3. An arrangement as claimed in claim 1 in which the rectangle is a square.