GB2153175A

GB2153175A - Phase shifting devices

Info

Publication number: GB2153175A
Application number: GB08500480A
Authority: GB
Inventors: Anthony Wykeham Jacomb-Hood
Original assignee: General Electric Co PLC
Current assignee: General Electric Co PLC
Priority date: 1984-01-18
Filing date: 1985-01-09
Publication date: 1985-08-14
Also published as: GB8500480D0; GB8401313D0

Abstract

A reflection phase shifting device incorporating a coupling device (1), having an input port (3) and an output port (5). The coupling device has at least one further port (7 or 9) associated with a switching means (11, 13, 15, 17) operable to selectively connect either a first (19 or 21) or a second (23 or 25) impedance to the further port (7 or 9). The insertion loss of the phase shifting device in a circuit is thus arranged to be substantially the same which ever of the impedances (19, 21, 23, 25) is connected. <IMAGE>

Description

SPECIFICATION Phase shifting devices This invention relates to phase shifting devices.

More particularly the invention relates to phase shifting devices of the kind comprising a coupling device having a first port to which an input signal may be applied, a second port from which an output signal may be obtained, and at least one further port associated with a switching means operable to change the impedance presented to said further port.

Such a phase shifting device is hereafter referred to as a reflection phase shifting device.

In such a device the input signal is reflected at the further port back into the coupling device to produce an output signal at the second port. Hence a shift in the phase of the output signal may be obtained by operating the switching means i.e. by changing the impedance presented to the further port.

In known forms of reflection phase shifting device the switching means is effective to connect a reactance to or disconnect said reactance from said further port. As a result known forms of reflection phase shifting device suffer the disadvantage that the insertion loss of the device in a circuit is substantially different with the reactance connected to rather than with the reactance disconnected from the further port. This is due to the fact that the inherent losses in the switching means are only significant in one state.

It is an object of the present invention to provide a reflection phase shifting device wherein this disadvantage is alleviated.

According to the present invention there is provided a phase shifting device of the kind comprising a coupling device having a first port to which an input signal may be applied, a second port from which an output signal may be obtained, and at least one further port associated with a switching means operable to change the impedance presented to the further port, the device being characterised in that it includes first and second impedances of different value, and the switching means is effective to selectively provide a signal path between either the first or the second impedance and the further port.

One reflection phase shifting device in accordance with the invention will now be described, by way of example only, with reference to the accompanying drawing which is a schematic diagram of the device.

Referring to the figure, the device is intended for use over a relatively limited frequency range in the microwave frequency band, and includes a Lange coupler, indicates as 1, having an input port 3, and an output port 5. The coupler 1 has two further ports 7, 9 each port 7, 9 being connected to a parallel arrangement of a p-i-n diode 11 or 1 3 and an oppositely directed. p-i-n diode 15 or 17, the diodes within each pair of diodes 11, 1 3 and 15, 1 7 being substantially identical. Each diode 11, 1 3 is connected in series with an inductor 19, 21 whilst each diode 15, 17 is connected in series with a capacitor 23, 25.

The ends of the inductors 19 21 and the capacitors 23, 25 remote from the respective diodes 11, 13, 15, 1 7 are each connected to a common earth terminal 27. The values of the inductors 19, 21 are equal, as are the values of the capacitors 1 5 and 1 7. In respect of each diode 11, 13, 15, 1 7 there is provided a biassing arrangement (not shown), each arrangement being effective to control the conductivity of the respective diode. The biassing arrangements for the four diodes 11, 13, 15, 1 7 are interconnected such that at any one time either the diodes 11 and 1 3 only or the diodes 1 5 and 1 7 only are conductive.

In use of the device, an input signal is applied to the port 3, a portion of this signal then passing through port 7, a further portion passing through port 9. These signal portions then pass respectively through whichever of the pairs of diodes 11 and 13 or 1 5 and 17 are conductive, to be reflected back at the reactances connected with the conductive diodes. The reflected signals then pass back into the coupler via ports 7, 9 to combine in the coupler 1 and produce an output signal at the port 5 in which the phase shift imposed on the input signal by its traversal and subsequent reflection through either of the ports 7, 9 is in the same sense, the signals reflected back to the port 3 cancelling out due to the form of the coupler.The phase of this output signal is shifted with respect to the phase of the input signal, the magnitude of the phase shift being dependent on the value of the reactances which reflect the signal portions.

Thus two output signals may be obtained from the port 9, having different phase shifts dependent on whether the inductors 19, 21 or the capactitors 23, 1 5 reflected the signal portions.

It will be appreciated that by choosing appropriate on-resistances for the two pairs of diodes 11, 1 3 and 15, 1 7 it is possible to make the insertion loss of the device in an external circuit (not shown) to be much the same, whichever of the pairs of diodes 11, 1 3 and 15, 1 7 is arranged to be conductive.

Furthermore the variation of phase shift through an appreciable frequency range may be made small by choosing the values of the inductors 19, 21 and the capacitors 23, 25 so that, to a first approximation, the variation of phase shift with frequency when the capacitors 23, 25 are providing the reflection is substantially equal to the variation of phase shift with frequency when the inductors 19, 21 are providing the reflection.

For one particular reflection phase shifting device in which the two alternative output signals were required to be 1 80" out of phase with each other, the input signal frequency bandwidth was 8-1 2 GHZ, the ratio of the capacitive impedance in the non-conductive state. to the resistance in the conductive state of the diodes 11,13,15, 17 was 65, the 0 factor of the inductors 19, 21 was 30, and the capacitors 23, 25 were substantially lossless, the maximum difference in insertion loss for the device not including the coupler was found to be 0.15do compared to 1.0 dB in an equivalent prior art device as described above.

It will be appreciated that whilst use of oppositely directed p-i-n diodes can simplify the necessary biassing arrangements, the diodes may all be correspondingly directed.

It will be also appreciated that whilst in the example described herebefore p-i-n diodes are used to switch between the impedances, any other switching means may be used in a reflection phase shifting device in accordance with the invention. One such example of such a switching device is an appropriately biassed field effect transistor.

It will also be appreciated that whilst a Lange coupler is a particularly convenient coupling device in some applications e.g. for use in a monolithic microwave integrated circuit, other coupling devices such as circulators may alternatively be utilised in a device according to the invention. It will be appreciated that such coupling devices may have one or more than two ports providing reflections.

Claims

1. A phase shifting device of the kind comprising a coupling device having a first port to which an input signal may be applied, a second port from which an output signal may be obtained, and at least one further port associated with a switching means operable to change the impedance presented to the further port, the device being characterised in that it includes first and second impedances of different value, and the switching means is effective to selectively provide a signal path between either the first or the second impedance and the further port.

2. A device according to Claim 1 in which the switching means comprises an arrangement of two switching devices each connected between the further port and a respective one of the first and second impedances, the switching devices being arranged such that in operation only one switching device is conductive at any one time.

3. A device according to either of the preceding claims wherein the values of the first and second impedances are such that the variation in phase shift with frequency of the output signal obtained when a signal path is provided to the first impedance is substantially equal to that when a signal path is provided to the second impedance.

4. A device according to any one of the preceding claims in which the first impedance is capacitive and the second impedance is inductive.

5. A device according to any one of Claims 2 to 4 in which each of the switching devices is a diode.

6. A device according to any one of the preceding claims in which the coupling device is a Lange coupler having two said further ports, each of said further ports being associated with a respective switching means, and each of the respective switching means being effective to selectively provide a respective signal path between one of a respective pair of first and second impedances of different values, and the associated further port.

7. A device according to Claim 6 in which the first impedances within each said pair of impedances are of similar values.

8. A device according to Claim 6 or Claim 7 in which the second impedances within each said pair of impedances are of similar values.

9. A phase shifting device substantially as hereinbefore described with reference to the accompanying drawing.