GB1605409A - Improvements in or relating to transponder interrogators - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO TRANSPONDER INTERROGATORS (71) We, THE PLESSEY COMPANY LIMITED, a British Company of Vicarage Lane, llford 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 transponder/interrogators.

According to the present invention a transponder/interrogator system comprises an interrogator defined by a common channel duplex (CCD) transceiver comprising an oscillator which provides a carrier frequency for transmission and which may be capable of being modulated, mixer means to which received signals are fed and which is fed also from said oscillator so as to provide phase quadrature related signals which are fed to a demodulator to facilitate demodulation of received signals and a transponder comprising aerial means tuned to the frequency of the oscillator and having operatively associated with it modulating means.

The oscillator may be adapted to be angle modulated at constant amplitude. The CCD transceiver may be fabricated as described in the specification of our co-pending UK patent application No.10360/76 (Serial No 1577514) to which attention is hereby directed.

In use the transponder would normally be positioned at a location remote from the interrogator the transponder being operative to transmit in response to and contemporaneously with the reception of a signal from the interrogator.

The transponder may be operated without a local power source, the energy for transmission being derived from the received carrier and the modulating source.

CCI) transceivers have the facility of transmitting a high powered carrier whilst contemporaneously receiving a weak signal on substantially the same frequency .When a CCI) transceiver is used, numerous reflections from the trees and buildings etc. are received as a result of the transmitted carrier signal. The nature of the circuitry used in the CCD equipment is such that all of these unmodulated signals are mixed to a d.c. output and then removed by an a.c. coupling. In a system according to the present invention however, one of the reflections (from the aerial means) is modulated and the modulation is recovered by a demodulator in the CCI) transceiver.

The CCI) transceiver may include a mixer adapted to provide phase quadrature related signals fed to a demodulator as described in figure 2 of our G.B. Patent No 1,172,977.

The aerial means may simply be tuned by reason of its dimensions to the frequency of the oscillator and/or it may have operatively associated with it a resonant circuit tuned to the oscillator frequency.

The modulating means may simply comprise a switch or and ON/OFF relay or the like. The aerial may thus be switched from a resonant high efficiency reflector to a non-resonant low efficiency reflector at the switching frequency.

Alternatively the modulating means may comprise a microphone such as a capacitor microphone. Thus a speech waveform may be arranged to modulate the aerial aperture and a passive voice communicator may thereby be realised.

As a further alternative the modulating means may comprise an oscillator. If the signal power at the transponder is high enough, power can be derived form the signal to drive an oscillator such as a CMOS modulating oscillator or code generator. Thus it may be arranged that data corresponding to a particular parameter or parameters such as temperature for example, may be sensed and utilised to control the modulation whereby parameters appertaining at remote locations or to equipment at such locations can be checked or measured from time to time by the interrogator. Thus it will be appreciated that the frequency or phase or amplitude of the oscillator signal may be modulated in accordance with data transmitted.

The demodulator in the interrogator receiver may include an SSB phasing type detector whereby two a.m. sidebands produced due to modulation applied at the transponder are detected separately in the interrogator.

Means may be provided for measuring the phase difference between the sideband outputs, the distance between the transponder and the interrogator being indicated in dependence upon phase difference measured.

Alternatively speed and/or direction of movement of the transponder or interrogator with respect to each other may be indicated in dependence upon the rate of change of phase and the relative direction of phase change between signals received from the transponder.

Some exemplary embodiments of the invention will now be described with reference to the drawings accompanying the Provisional Specification in which: Figure 1 is a block schematic diagram of a transponder; Figure 2 is a block schematic circuit diagram of an alternative transponder; Figure 3 is a circuit block schematic diagram of yet a further kind of transponder, and wherein Figure 4 is a block schematic diagram of a part of a system for receiving sidebands transmitted from a transponder to an interrogator.

Referring now to Figure 1 of the drawings, a transponder simply comprises a dipole 1 the dimensions of which are chosen so that the length corresponds to a quarter wavelength of the frequency to which the oscillator of an CCD transceiver constituting an interrogator is tuned.

The two halves of the dipole are connected across a switch 2 which when operated provides a modulated signal which may be received by the interrogator.

Referring now to Figure 2, a transponder comprises a dipole 3 which is coupled via an input transformer 4 tuned to the carrier frequency provided by the oscillator of a remote CCI) transceiver which constitutes an interrogator. The secondary winding 4a of the input transformer 4 is fed from a capacitor microphone 5 and it will be appreciated that audio signals picked up by the microphone will be effective to modulate the aerial circuit whereby carrier signals transmitted by the interrogator and received by the dipole 3 and reflected back to the interrogator will carry modulation corresponding to the audio signals fed to the microphone 5.

Referring now to Figure 3, the transponder comprises a dipole 6 coupled via a transformer 7 to secondary winding 7a of which is tuned by a variable capacitor 8 to the carrier frequency radiated by the interrogator which is constituted by a remotely located CCI) transceiver. Input signals received by the dipole 6 are fed via a rectifier 9 and a smoothing circuit comprising a capacitor 10 to a CMOS oscillator 11 and output signals from the oscillator are fed via a diode 12 and a capacitor 13 to modulate the aerial circuit which includes the dipole 6 so as to provide a modulated re-transmission signal which can be received by the interrogator.

In the interrogator, the modulated reflected signal may be detected with a well known single sideband phasing type detector as shown in Figure 4 which comprises a wide band 900 phase shift network 12 fed with quadrature components of the incoming signal on line 13, and wherein, the in phase components are fed on line 14 not only to an adder 15, as in a conventional single sideband phasing type detector but also to a subtractor 16, the adder and subtractor being connected to the output of the wide band 90" phase shift network 12. It will therefore be appreciated that individual sideband outputs are provided on lines 17 and 18 by operation of the arrangement as will be well understood by those skilled in the art. The two a.m. sidebands due to the modulation applied at the transponder are detected separately. The output on line 17 corresponds to the upper sideband, and the other output on line 18 corresponds to the lower sideband. Either of these signals can be amplified and are replicas of the original modulation. The relative phase difference between the sideband outputs of the demodulator is dependent upon a phase difference between the CCI) receiver local oscillator and that of the reflected carrier received. In fact the relative phase difference between the two audio outputs changes at twice the rate of the phase difference between the r.f.

signals. This phenomena can therefore be used to obtain an accurate measurement of the distance between the interrogator comprising the CCI) transceiver equipment and the transponder.

The method used to achieve this result is as follows. Relative phase of the audio signals is firstly measured. The frequency of the CCI) equipment local oscillator is then changed by an amount known and the phase difference is re-measured. The distance between the transponder and the interrogator comprising the CCI) equipment is then given by the following equation.

N-F x 208 x 103 metres where o0 equals the change in audio phase and 8F equals the change in r.f. frequency. The rate of change of phase and the relative direction of phase change can be used to determine the speed and direction of any movement of the transponder relative to the interrogator or vice versa.

Apparatus as just before described may be used for a wide variety of equipment including IFF navigation aids in poor visibility, and range measurements for civil engineering etc.

WHAT WE CLAIM IS: 1. A transponder/interrogator system comprising an interrogator defined by a common channel duplex (CCD) transceiver comprising an oscillator which provides the carrier frequency for transmissions and mixer means to which received signals are fed and which is fed also from said oscillator so as to provide phase quadrature related signals which are fed to a demodulator to facilitate demodulation of

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

Claims (17)

**WARNING** start of CLMS field may overlap end of DESC **. Alternatively speed and/or direction of movement of the transponder or interrogator with respect to each other may be indicated in dependence upon the rate of change of phase and the relative direction of phase change between signals received from the transponder. Some exemplary embodiments of the invention will now be described with reference to the drawings accompanying the Provisional Specification in which: Figure 1 is a block schematic diagram of a transponder; Figure 2 is a block schematic circuit diagram of an alternative transponder; Figure 3 is a circuit block schematic diagram of yet a further kind of transponder, and wherein Figure 4 is a block schematic diagram of a part of a system for receiving sidebands transmitted from a transponder to an interrogator. Referring now to Figure 1 of the drawings, a transponder simply comprises a dipole 1 the dimensions of which are chosen so that the length corresponds to a quarter wavelength of the frequency to which the oscillator of an CCD transceiver constituting an interrogator is tuned. The two halves of the dipole are connected across a switch 2 which when operated provides a modulated signal which may be received by the interrogator. Referring now to Figure 2, a transponder comprises a dipole 3 which is coupled via an input transformer 4 tuned to the carrier frequency provided by the oscillator of a remote CCI) transceiver which constitutes an interrogator. The secondary winding 4a of the input transformer 4 is fed from a capacitor microphone 5 and it will be appreciated that audio signals picked up by the microphone will be effective to modulate the aerial circuit whereby carrier signals transmitted by the interrogator and received by the dipole 3 and reflected back to the interrogator will carry modulation corresponding to the audio signals fed to the microphone 5. Referring now to Figure 3, the transponder comprises a dipole 6 coupled via a transformer 7 to secondary winding 7a of which is tuned by a variable capacitor 8 to the carrier frequency radiated by the interrogator which is constituted by a remotely located CCI) transceiver. Input signals received by the dipole 6 are fed via a rectifier 9 and a smoothing circuit comprising a capacitor 10 to a CMOS oscillator 11 and output signals from the oscillator are fed via a diode 12 and a capacitor 13 to modulate the aerial circuit which includes the dipole 6 so as to provide a modulated re-transmission signal which can be received by the interrogator. In the interrogator, the modulated reflected signal may be detected with a well known single sideband phasing type detector as shown in Figure 4 which comprises a wide band 900 phase shift network 12 fed with quadrature components of the incoming signal on line 13, and wherein, the in phase components are fed on line 14 not only to an adder 15, as in a conventional single sideband phasing type detector but also to a subtractor 16, the adder and subtractor being connected to the output of the wide band 90" phase shift network 12. It will therefore be appreciated that individual sideband outputs are provided on lines 17 and 18 by operation of the arrangement as will be well understood by those skilled in the art. The two a.m. sidebands due to the modulation applied at the transponder are detected separately. The output on line 17 corresponds to the upper sideband, and the other output on line 18 corresponds to the lower sideband. Either of these signals can be amplified and are replicas of the original modulation. The relative phase difference between the sideband outputs of the demodulator is dependent upon a phase difference between the CCI) receiver local oscillator and that of the reflected carrier received. In fact the relative phase difference between the two audio outputs changes at twice the rate of the phase difference between the r.f. signals. This phenomena can therefore be used to obtain an accurate measurement of the distance between the interrogator comprising the CCI) transceiver equipment and the transponder. The method used to achieve this result is as follows. Relative phase of the audio signals is firstly measured. The frequency of the CCI) equipment local oscillator is then changed by an amount known and the phase difference is re-measured. The distance between the transponder and the interrogator comprising the CCI) equipment is then given by the following equation. N-F x 208 x 103 metres where o0 equals the change in audio phase and 8F equals the change in r.f. frequency. The rate of change of phase and the relative direction of phase change can be used to determine the speed and direction of any movement of the transponder relative to the interrogator or vice versa. Apparatus as just before described may be used for a wide variety of equipment including IFF navigation aids in poor visibility, and range measurements for civil engineering etc. WHAT WE CLAIM IS:

1. A transponder/interrogator system comprising an interrogator defined by a common channel duplex (CCD) transceiver comprising an oscillator which provides the carrier frequency for transmissions and mixer means to which received signals are fed and which is fed also from said oscillator so as to provide phase quadrature related signals which are fed to a demodulator to facilitate demodulation of

received signals and a transponder comprising aerial means tuned to the frequency of the oscillator and having operatively associated with it modulating means.

2. A transponder/interrogator system as claimed in claim 1, wherein the oscillator is adapted to be angle modulated at constant amplitude.

3. A transponder/interrogator system as claimed in claim 1 or claim 2, wherein energy for transmission from the transponder is derived from a received carrier signal.

4. A transponder/interrogator as claimed in claim 3, wherein the demodulator is of the form described in Figure 2 of our G.B. Patent Specification No 1,172,977.

5. A transponder /interrogator system as claimed in any preceding claim, wherein the aerial means is tuned by reason of its dimensions to the frequency of the oscillator.

6. A transponder/interrogator system as claimed in any of claims 1 to 5, wherein the aerial means is tuned by means of a resonant circuit operatively associated with it to the oscillator frequency.

7. A transponder/interrogator system as claimed in any preceding claim, wherein the modulating means comprises switch means.

8. A transponder/interrogator as claimed in any of claims 1 to 6, wherein the modulating means comprises a microphone.

9. A transponder/interrogator system as claimed in any of claims 1 to 6, wherein the modulating means comprises an oscillator.

10. A transponder/interrogator system as claimed in claim 9, wherein the oscillator is a CMS modulating oscillator or code generator.

11. A transponder/interrogator system as claimed in any preceding claim wherein the demodulator includes an SSB phasing type detector whereby two a.m. sidebands are produced due to modulation applied at the transponder and.

12. A transponder/interrogator system as claimed in claim 11 wherein the demodulator comprises adder means and subtractor means fed with the phase quadrature related signals via a 900 phase shift network to provide the two sidebands.

13. A transponder/interrogator system as claimed in claim 12, wherein means are provided for measuring the phase difference between the sidebands, the distance between the transponder and the interrogator being indicated in dependence upon the phase difference measured.

14. A transponder/interrogator system as claimed in claim 13, wherein speed and/or direction of movement of the transponder or interrogator with respect to each other are indicated in dependence upon the rate of change of phase and the relative direction of phase change between the sideband signals.

15. A transponder/interrogator system as claimed in any preceding claim and wherein the transceiver is as claimed (Serial No 1577514) in any claim of our U.K. Patent Application No.

10360/76 (Serial No. 1577514).

16. A transponder/interrogator system as claimed in claim 1 and substantially as hereinbefore described with reference to Figures 1 or 2 or 3, of the drawings accompanying the Provisional Specification.

17. A transponder/interrogator system as claimed in claim 1 and substantially as hereinbefore described with reference to Figure 4 of the drawings accompanying the Provisional Specification.