GB2090074A

GB2090074A - Improvements in and relating to hf slip rings

Info

Publication number: GB2090074A
Application number: GB8040199A
Authority: GB
Original assignee: IDM Electronics Ltd
Current assignee: IDM Electronics Ltd
Priority date: 1980-12-16
Filing date: 1980-12-16
Publication date: 1982-06-30
Also published as: EP0082898A1

Description

1

GB 2 090 074 A 1

SPECIFICATION

Improvements in and relating to HF Slip Rings

This invention relates to HF Slip Rings and to a method and means for improving the waveform of 5 output signals from the slip ring.

An object of the present invention is to improve the waveform of output signals from the slip ring by reducing the destructive effect of stub lines on the signal transmission.

10 A further object of the present invention is to improve the frequency bandwidth of the slip ring without correspondingly increasing the slip ring diameter.

For HF rings having a single input and a single 15 output, the stub length is a maximum and where the stub length is greater than

A

t

8

a considerable loss occurs between the amplitude of the input signal and that of the output signal 20 and a still further object of the invention is to obtain more constancy between the amplitude of the input signal and that of the output signal of the slip ring, particularly at those frequencies where virtual cut-off of the signal occurs when the 25 combination of stubs is particularly destructive to signal transmission.

Thus, according to the invention there is provided a high frequency slip ring assembly having a single input and a single output, wherein 30 the normally destructive effect on the amplitude of the input signal by the effect of stubs is reduced by dividing the input signal path at the brush-slip ring interface followed by recombination of the divided signal paths from the interface to produce 35 said single output signal having an amplitude corresponding substantially to the amplitude of the input signal.

The electrical effect of the division of the electrical signal input into a number of branches to 40 the slip ring-brush interface followed by the recombination to a single output, is to divide the slip ring circumference by

A

n where n is the number of sub divisions of the input 45 signal at the slip ring-brush interface. This effect is illustrated by way of example only in the accompanying drawings wherein:

Figure 1 is a diagrammatic representation of a known RF transmission line showing the signal 50 paths when the input and output are displaced by 180°;

Figure 2 is a diagrammatic representation similar to that of Figure 1 but showing the signal paths when the input and output are in phase; 55 Figure 3 is an equivalent circuit network for an RF slip ring of the present invention showing the signal paths when the input and output are displaced by 180°;

Figure 4 is a network similar to that of Figure 3 60 but with the input and output in phase and

Figure 5 is a sectional view through a slip ring assembly of the present invention and where the slip ring circumference is divided by

A

4

65 In the equivalent circuit network of Figure 1, the stub length of each parallel branch is indicated as

7r D 2 '

the characteristic impedance being indicated at Zo 70 and the slip ring impedance through each parallel stub, as ZSR, for a single input displaced 180° from the output.

In Figure 2, the input and output are in phase given open circuit stub lengths of

7t D

75 _

2

as shown. Figure 1 and 2 thus illustrate the two extremes in an RF slip ring during rotation.

Referring to Figure 3, for the best position where the input and output are displaced by 180°, 80 the number of inputs has been increased by initially dividing the initial characteristic impedance Zo into two branches, each of characteristic impedance 2Zo and then subdividing each of the 2Zo characteristic 85 impedance branches into two parallel branches indicated as ZSR. The brush-slip ring interface is shown dotted in Figure 3 and at the output side, each of the two sub-branches of impedance ZSR are recombined to form two branches of 90 impedance 2Zo and combined again to give a single output of impedance Zo. The stub length of each sub-branch is shown as

7t D 4

i.e. half the stub length of that shown in Figure 1. 95 Similarly in Figure 4, the input characteristic impedance Zo is divided into two branches each of impedance 2Zo and sub-divided to give the slip ring impedance ZSR for each stub line. The stub line impedances ZSR are recombined into two 100 branches each of impedance 2Zo and combined again to give an output of impedance Zo. The diagram shown in Figure 4 is for the worst position during rotation where the input and output are in phase. The open circuit stub length 105 of each of the sub-branches of Figure 4 is indicated as

2

GB 2 090 074 A 2

7t D 4'

again half the stub length of that shown for Figure 2.

Thus it is seen that increasing the number of 5 inputs has the effect of reducing the 'electrical diameter' and reduces the open circuit stub length, thereby improving the characteristics of the slip ring by reducing the normally destructive effect of the stubs on the amplitude of the input 10 signal. In Figures 1 and 2 for a single input/single output RF transmission line, the stub length is a maximum. By dividing the stub length by a factor of 4, the effect of the stub on signal amplitude is reduced, the destructive effect of the stub being 15 particularly apparent when the stub length is greater than

A 8

In order for the sub-division to be effective and to operate satisfactorily in practice, the inputs 20 should be matched to the line and must also be symmetrical to produce inputs of equal magnitude and phase.

The maximum number of inputs for the system of the present invention is four, since it is 25 impractical to produce a line impedance of>4Zo.

A typical RF slip ring assembly is shown in Figure 5 and comprises a slip ring housing 1, and high frequency slip ring 2. A single input conductor 3 is divided into two branches 4, 5, and 30 each branch is sub-divided into two further branches 6, 7, 8, 9 at the brush-slip ring interface X, the sub-branches being recombined at Y to ' form two output branches 10,11, combined to form single output 12.

35 It will be appreciated that the invention is susceptible to considerable modification and is not to be deemed limited to the particular features shown by way of example only in the accompanying drawings.

Claims

40 1 • A high frequency slip ring assembly having a single input and a single output, wherein the normally destructive effect on the amplitude of the input signal by the effect of stubs is reduced by dividing the input signal path at the brush-slip ring

45 interface followed by recombination of the divided signal paths from the interface to produce said single output signal having an amplitude corresponding substantially to the amplitude of the input signal.

50
2. A high frequency slip ring assembly as claimed in claim 1 wherein the single input signal path is initially divided into a pair of branches and each branch sub-divided at the slip ring-brush interface, the sub-divided branches being

55 recombined into two branches and further combined at the output to form the single output path.
3. A high frequency slip ring assembly as claimed in claim 1 or 2 wherein the length of each

60 stub is reduced from

7t D to 71 D - 2 4
4. A high frequency slip ring assembly as claimed in claim 1 or 2 wherein the length of each stub is reduced by a factor of 4.

65
5. A high frequency slip ring as claimed in any preceding claim wherein the divided inputs are matched to the line and are symmetrical to produce inputs of equal magnitude and phase.
6. A high frequency slip ring assembly

70 substantially as hereinbefore described and as shown in Figures 3 to 5 of the accompanying drawings.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1982. Published by the Patent Office, 25 Southampton Buildings, London, WC2A 1AY, from which copies may be obtained.