WO2009156762A1

WO2009156762A1 - Object identification system and method

Info

Publication number: WO2009156762A1
Application number: PCT/GB2009/050733
Authority: WO
Inventors: Vincent Francis Fusco
Original assignee: The Queen's University Of Belfast
Priority date: 2008-06-25
Filing date: 2009-06-25
Publication date: 2009-12-30
Also published as: GB0811635D0

Abstract

An identification system and method of use thereof is provided, the system (1) comprising at least one transceiver cell (3) comprising an antenna component (7) which receives a part of an incoming signal (11) from an object (13), and a processor which processes the part of the incoming signal to extract identification information of the object, wherein the processor comprises a frequency downconverter/mixer unit comprising a coupler which produces first and second phase quadrature signals, a first mixer which receives the first signal and mixes it with the part of the incoming signal to produce a first output signal comprising object identification information, and a second mixer which receives the second signal and mixes it with the part of the incoming signal to produce a second output signal comprising object identification information, a phase shifter which receives the second output signal and adds a 90 degree phase shift to the signal to produce a phase shifted second output signal comprising the object identification information, a sideband signal filter which receives the first output signal from the frequency downconverter/mixer unit and receives the phase shifted second output signal from the phase shifter, and operates to produce a sideband signal of the part of the incoming signal which comprises the object identification information, and an object identification component which receives the sideband signal from the sideband signal filter, extracts the object identification information therefrom, and uses the object identification information to identify the object.

Description

Object Identification System and Method

The invention relates to an object identification system and method.

There are many fields in which signals are received from objects, such as medical applications and radar. In some cases, the signals will comprise information, e.g. modulated radio waves. If the information can be extracted, it could be used to identify the object from which it is received.

According to a first aspect of the invention there is provided an identification system for receiving an incoming signal from an object, the system comprising at least one transceiver cell comprising an antenna component which receives a part of the incoming signal, and a processor which processes the part of the incoming signal to extract identification information of the object, wherein the processor comprises a frequency downconverter/mixer unit comprising a coupler which produces first and second phase quadrature signals, a first mixer which receives the first signal and mixes it with the part of the incoming signal to produce a first output signal comprising object identification information, and a second mixer which receives the second signal and mixes it with the part of the incoming signal to produce a second output signal comprising object identification information, a phase shifter which receives the second output signal and adds a 90 degree phase shift to the signal to produce a phase shifted second output signal comprising the object identification information, a sideband signal filter which receives the first output signal from the frequency downconverter/mixer unit and receives the phase shifted second output signal from the phase shifter, and operates to produce a sideband signal of the part of the incoming signal which comprises the object identification information, an object identification component which receives the sideband signal from the sideband signal filter, extracts the object identification information therefrom, and uses the object identification information to identify the object.

According to a second aspect of the invention there is provided a method of identifying an object from which an incoming signal is received comprising using at least one transceiver cell comprising an antenna component to receive a part of the incoming signal, using a coupler of a frequency downconverter/mixer unit to produce first and second phase quadrature signals, using a first mixer of the frequency downconverter/mixer unit to receive the first signal and mix it with the part of the incoming signal to produce a first output signal comprising object identification information, using a second mixer of the frequency downconverter/mixer unit to receive the second signal and mix it with the part of the incoming signal to produce a second output signal comprising object identification information, using a phase shifter to receive the second output signal and add a 90 degree phase shift to the signal to produce a phase shifted second output signal comprising the object identification information, using a sideband signal filter to receive the first output signal from the frequency downconverter/mixer unit and receive the phase shifted second output signal from the phase shifter, and operate to produce a sideband signal of the part of the incoming signal which comprises the object identification information, using an object identification component to receive the sideband signal from the sideband signal filter, extract the object identification information therefrom, and use the object identification information to identify the object.

The coupler of the frequency downconverter / mixer unit may comprise a 90 degree hybrid coupler. The coupler may receive a reference signal and may use the reference signal to produce the first and second phase quadrature signals. Each of the first and second mixers may multiply the signal received from the coupler with the part of the incoming signal to produce the first and second output signals comprising object identification information. The first and second output signals may be intermediate frequency (IF) signals. The frequency downconverter / mixer unit may receive a radio frequency (RF) reference signal and an RF incoming signal, and frequency downconvert these signals to produce IF first and second output signals. The use of the mixers in this unit reduces the leakage between an RF incoming signal and IF output signals.

The first and second output signals may comprise object identification information comprising a modulation factor of the part of the incoming signal. The object may backscatter a signal that has modulation, or produce a signal that has modulation, and the modulation factor may have a non-zero value. First and second output signals are then produced. The object may backscatter a signal that has no modulation, or produce a signal that has no modulation, and the modulation factor may have a zero value. No first and second output signals are then produced, and the remainder of the transceiver cell will remain quiescent. The first and second output signals may comprise object identification information comprising an angular frequency of the part of the incoming signal. The sideband signal filter may operate to add the first output signal and the phase shifted second output signal, to produce a lower sideband signal (LSB) which comprises the object identification information. The sideband signal filter may operate to subtract the first output signal and the phase shifted second output signal, to produce an upper sideband signal (USB) which comprises the object identification information. The operation of addition or subtraction of the first and second output signals, ensures that the amplitude of the sideband signal does not depend on the phase, Φ_d , of the received part of the incoming signal.

The object identification component may compare the extracted object identification information with one or more expected object identification information, and if a match is found, determine that the object is a recognised object, and if a match is not found, determine that the object is an unrecognised object.

The object identification component may extract object identification information comprising a modulation factor. The object identification component may compare the extracted modulation factor with one or more expected modulation factors, and if a match is found, determine that the object is a recognised object, and if a match is not found, determine that the object is an unrecognised object. The object identification component may act to read information carried by the modulation factor. The object identification component may extract object identification information comprising an angular frequency. The object identification component may compare the extracted angular frequency with one or more expected angular frequencies, and if a match is found, determine that the object is a recognised object, and if a match is not found, determine that the object is an unrecognised object, from the signal. The identification system may comprise a phase extraction unit. This may receive the first and second output signals from the frequency downconverter/mixer unit. The phase extraction unit may extract phase information from the first output signal, the second output signal, or both of the output signals, and may use this to derive angle of arrival information of the incoming signal, and, from this, the position of the object.

The identification system may send a signal back to the object from which the incoming signal has been received. The identification system may only send signals back to objects which have been identified as recognised objects. The identification system may output a wide field signal, which impinges on the object. The identification system may output a signal directly to the object. The identification system may act as a retrodirective antenna system which outputs a signal directly to the object.

When the identification system outputs a signal directly to the object, it may comprise two or more transceiver cells, each of which receives a part of the incoming signal, produces a phase conjugate output signal, which output signals from the cells combine to form an outgoing signal directed back to the object. Each transceiver cell may comprise an antenna component, a processor, a phase shift system and an IQ modulator.

The processor comprises the components detailed above. The processor may further comprise a tracking phase locked loop (PLL) circuit. The tracking PLL circuit may receive a SB signal from the object identification component, and duplicate the SB signal to produce first and second same- side SB signals. The tracking PLL circuit may receive a LSB signal from the object identification component and duplicate the LSB signal to produce first and second LSB signals. The tracking PLL circuit may receive a USB signal from the object identification component and duplicate the USB signal to produce first and second USB signals. A voltage controlled oscillator portion of the tracking PLL circuit may receive a DC bias signal. The magnitude of the DC bias signal may be varied, to introduce variation in the phase of the SB signals, i.e. to phase modulate the SB signals.

The phase shift system may comprise a first phase element which receives a first SB signal and outputs a SB signal having a first phase, and a second phase element which receives a second SB signal and outputs a SB signal having a second phase which is in quadrature with the first phase. The first and second phase elements may each comprise a feedback amplifier and associated resistors and capacitor. The first phase element may comprise a minus 90 degree phase shifter, and may produce a SB signal having a first phase which has a minus 90 degree phase shift in comparison to the first SB signal. The second phase element may act to pass the second SB signal, without changing its phase, i.e. produce a SB signal having a second phase which has a 0 degree phase shift in comparison to the second SB signal. The SB signal having the first phase and the SB signal having the second phase are phase conjugate signals.

The IQ modulator may comprise an I input port, a Q input port and a phase adjuster, which receives a SB signal having the first phase on the I input port and a SB signal having the second phase on the Q input port, or receives a SB signal having the first phase on the Q input port and a SB signal having the second phase on the I input port, and phase adjusts the SB signals to produce an output signal which is the phase conjugate of the part of the incoming signal. The phase adjuster of the IQ modulator may comprise a 90 degree hybrid coupler, a first mixer and a second mixer. The IQ modulator may further comprise a reference signal input port, and an output port. A reference signal received on the reference signal input port may be input into the 90 degree hybrid coupler. The coupler may produce a first signal which is input into the first mixer and a second signal which is input into the second mixer. The first mixer may receive the first signal from the coupler and the SB signal from the I input port, and act to mix these signals and produce an output signal. The second mixer may receive the second signal from the coupler and the SB signal from the Q input port, and act to mix these signals and produce an output signal. The output signals from the first and second mixers may be combined, and output from the IQ modulator via the output port. The components of the IQ modulator act to phase adjust the SB signals, as necessary, to produce an output signal at the output port which is the phase conjugate of the part of the incoming signal first received from the antenna component of the transceiver cell comprising the IQ modulator.

The first and second SB signals may be lower sideband (LSB) signals. The phase shift system may output a LSB signal having a first phase and a LSB signal having a second phase which is in quadrature with the first phase. The IQ modulator may receive the LSB signal having the first phase on the Q input port and the LSB signal having the second phase on the I input port, and phase adjust the LSB signals to produce an output signal which is the phase conjugate of the part of the incoming signal.

The first and second SB signals may be upper sideband (USB) signals. The phase shift system may output a USB signal having a first phase and a USB signal having a second phase which is in quadrature with the first phase. The IQ modulator may receive the USB signal having the first phase on the I input port and the USB signal having the second phase on the Q input port, and phase adjust the USB signals to produce an output signal which is the phase conjugate of the part of the incoming signal. The first and second SB signals may be LSB signals or USB signals. The phase shift system may receive LSB signals and output a LSB signal having a first phase and a LSB signal having a second phase which is in quadrature with the first phase. The phase shift system may receive USB signals and output a USB signal having a first phase and a USB signal having a second phase which is in quadrature with the first phase. The system may comprise a switching mechanism. The switching mechanism may receive the LSB signal having the first phase and the LSB signal having the second phase and switch the LSB signal having the first phase to the Q input port of the IQ modulator and switch the LSB signal having the second phase to the I input port of the IQ modulator. The switching mechanism may receive the USB signal having the first phase and the USB signal having the second phase and switch the USB signal having the first phase to the I input port of the IQ modulator and switch the USB signal having the second phase to the Q input port of the IQ modulator.

The switching mechanism may comprise a first input port, a second input port, a first switch, a second switch, a first output port and a second output port. The first and second switches may comprise single pole, single throw switches. The first and second switches may comprise a switch lever. The first and second switches may be operable to cause their switch lever to contact either a first switch contact or a second switch contact. Control of the operation of the switches may be achieved using commands sent to the switches via control lines.

The IQ modulator may act to upconvert the frequency of the SB signals which it receives, from IF signals to an RF output signal. The IQ modulator may be used to produce an amplitude modulated, phase conjugate output signal. I, Q bit patterns may be applied to the first and second mixers, in order to switch them on and off, thus amplitude modulating their output signals.

The system may comprise a first LO PLL circuit which inputs a reference signal into the frequency downconverter / mixer unit of the processor. The system may comprise a second LO PLL circuit which inputs a reference signal into the IQ modulator. The first and second LO PLL circuits may be phase synchronised, by receiving a common low frequency input signal and using this to produce their reference signals.

Use of the phase shift system and the IQ modulator (and the switching mechanism when necessary) allows production of an output signal which is very close in frequency to the input signal received by the transceiver cell. Thus the object identification system can use a narrow bandwidth for the incoming and outgoing signals. This results in good signal to noise ratio, good 'rejection' of thermal noise, low power and difficulty for a third party to identify or jam the input or output signals.

An embodiment of the invention will now be described by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic representation of an object identification system according to the invention;

Figure 2 is a schematic representation of the components of one of the transceiver cells of Figure 1 ;

Figure 3 is a schematic representation of a downconvertor/mixer component of the transceiver cell of Figure 2; Figure 4 is a schematic representation of a phase shifter of the transceiver cell of Figure 2;

Figure 5 is a schematic representation of a first configuration of a sideband signal filter of the transceiver cell of Figure 2, configured as a lower sideband signal filter;

Figure 6 is an schematic representation of a second configuration of the sideband signal filter of the transceiver cell of Figure 2, configured as an upper sideband signal filter;

Figure 7 is a schematic representation of an object identification component of the transceiver cell of Figure 2;

Figure 8 is a schematic representation of a phase element of a phase shifter system of the transceiver cell of Figure 2;

Figure 9 is a schematic representation of a switching mechanism of the transceiver cell of Figure 2, and

Figure 10 is a schematic representation of an IQ modulator of the transceiver cell of Figure 2.

Referring to Figure 1 , in this embodiment, the object identification system 1 comprises three transceiver cells 3. The system may then also act as a retrodirective antenna system. It will be appreciated, however, that other numbers of transceiver cells may be provided, for example one transceiver cell may be provided, and the system will then act as an object identification system only. A spacing of approximately 0.3 λ to approximately 0.8λ is provided between the cells (where λ is the wavelength of a signal emitted by the cells). It will be appreciated that other cell spacing may be used. In this embodiment of the antenna system of the invention, the cells are arranged in a linear array. It will be appreciated, however, that the cell layout does not need to be regular, the cells can be arbitrarily positioned with respect to each other.

Each transceiver cell 3 comprises an antenna component 7. Each transceiver cell 3 outputs an output signal from its antenna component 7, which output signals combine to form an outgoing signal 1 1 . The outgoing signal 1 1 can be a wide angle, continuous wave (CW) signal, having a frequency in the radio frequency (RF) range. The outgoing signal may be represented mathematically as 2Rsinω_ct , where R accounts for source power level and path losses. The outgoing signal 1 1 may impinge on an object 13, situated within the range of the signal 1 1. The object 13 may scatter an incoming signal 15 back to the identification system 1 . Additionally or alternatively, the object 13 can be active and can emit an incoming signal 15 to the identification system 1. The incoming signal 15 may be a CW signal, or may comprise some type of modulation. The incoming signal 15 is in the form of a wavefront, and impinges on the array of transceiver cells 3. The antenna component 7 of each transceiver cell 3 detects a part of the incoming signal 15. Each transceiver cell 3 receives a part of the incoming signal at a different time than each other cell. This results in the parts of the incoming signal received by each of the transceiver cells 3 having different phases, Φ_d, shown as

Φ₂ and Φ₃ in Figure 1 . For each transceiver cell 3, the received part of the incoming signal 15 is passed from the antenna component 7 to a processor, etc. of the cell. Here each part of the incoming signal is processed, as follows. The operation of each transceiver cell 3 of the object identification system 1 is now described in detail, with reference to Figures 2 to 10. As shown in Figure 2, the transceiver cell 3 comprises a processor 20, a phase shift system 22, a switching mechanism 24, an IQ modulator 26, a first LO PLL circuit 28 and a second LO PLL circuit 30.

The processor 20 comprises a low noise amplifier 32, a frequency downconverter / mixer unit 34, a phase shifter 35, a sideband signal filter 36, an object identification component 37, a tracking PLL circuit 38, and a phase extraction unit 39.

The low noise amplifier 32 receives the part of the incoming signal from the antenna component 7 of the transceiver cell 3. The amplifier 32 amplifies the part of the incoming signal, and passes the signal to the downconverter / mixer unit 34. The first LO PLL circuit 28 produces a reference signal, which is output to the unit 34. The first LO PLL circuit 28 also outputs the reference signal to the antenna component 7 of the transceiver cell 3. Thus, in this embodiment, the first LO PLL circuit 28 also acts as a source of the output signal initially output by each antenna component 7 of each transceiver cell 3 of the identification system 1.

Referring to Figure 3, the frequency downconverter / mixer unit 34 comprises a 90 degree hybrid coupler 300, a first mixer 302 and a second mixer 304. The reference signal, 2Rsinω_ct, is received by the coupler 300. The coupler 300 uses the reference signal to produce first and second phase quadrature signals, Rsinω_ct and Rcosω_ct. The first signal, Rsinω_ct , is input into the first mixer 302, and the second signal, Rcosω_ct , is input into the second mixer 304. The part of the incoming signal 15 received by the antenna component 7 of the transceiver cell 3, is represented as:

2D (1 + Msinω_mt) sin(ω_ct + Φ_d) This is also input into the mixers 302, 204. M is the modulation factor of the part of the incoming signal, D accounts for the gain and path losses, ω_c is the angular frequency of the outgoing signal 1 1 , and ω_m is the angular frequency of the incoming signal 15. Each mixer multiplies the signal received from the coupler 300 with the part of the incoming signal, to produce first and second output signals. The first output signal of the first mixer 302 is:

Rsinω_ct • D(1 +Msinω_mt)sin(ω_ct + Φ_d)

and the second output signal of the second mixer 304 is

Rcosω_ct • D(1 +Msinω_mt)sin(ω_ct + Φ_d)

After DC and high frequency filtering and after trigonometric equivalence equations are used, the first output signal of the first mixer 302 can be expressed as RDMcosΦ_dsinω_mt and the second output signal of the second mixer 304 can be expressed as RDMsinΦ_dsinω_mt. These output signals are IF signals, i.e. the RF reference signal and the RF incoming signal have been frequency downconverted. The use of the mixers 302, 304 in this arrangement reduces the leakage between the RF incoming signal and the IF output signals. Each output signal is dependent on M, the modulation factor of the part of the incoming signal 15 received from the object 13. If M equals zero, i.e. the object 13 either backscatters a signal that has no modulation, or produces a signal that has no modulation, then no output signals are generated by the unit 34, and the remainder of the transceiver cell 3 will remain quiescent. If M does not equal zero, i.e. the object 13 either backscatters a signal that has modulation, or produces a signal that has modulation, then the first output signal from the first mixer 302 is generated and is output to the sideband signal filter 36, and the second output signal from the second mixer 304 is generated and is output to the phase shifter 35.

Referring to Figure 4, the phase shifter 35 comprises an operational amplifier and associated components. The phase shifter 35 adds a 90 degree phase shift to the signal it receives from the unit 34, and outputs a signal to the sideband signal filter 36, represented by RDMsinΦ_dcosω_mt. The phase shift is obtained by using a combination of the capacitor and the resister to ground. These create a high pass single pole filter, which induces the phase shift between inverting and non-inverting terminals of the operational amplifier. It will be appreciated that the type of operational amplifier and the values of the associated components shown in the figure are examples only, and other types/values may be used.

The sideband signal filter 36 is configurable to provide either a lower sideband signal filter, Figure 5, or an upper sideband signal filter, Figure 6. Referring to Figure 5, the configuration of the lower sideband signal filter comprises an operational amplifier and associated components in the arrangement shown. The amplifier receives a first input signal, RDMcosΦ_dsinω_mt , from the unit 34 on one of its terminals, and a second input signal, RDMsinΦ_dcosω_mt , from the phase shifter 35 on the other of its terminals. The amplifier operates to subtract the first and second input signals to produce an output signal, RDMsin(ω_mt - Φ_d), i.e. a LSB signal. Referring to Figure 6, the configuration of the upper sideband signal filter comprises an operational amplifier and associated components in the arrangement shown. The amplifier receives a first input signal, RDMcosΦ_dsinω_mt, from the unit 34 on its non-inverting terminal, and a second input signal, RDMsinΦ_dcosω_mt, from the phase shifter 35 on the non-inverting terminal. The amplifier operates to add the first and second input signals to produce an output signal RDMsin(ω_mt + Φ_d), i.e. a USB signal. The sideband signal filter 36 thus outputs either a LSB signal or a USB signal, to the object identification component 37. The operation of addition or subtraction of the first and second input signals, ensures that the power of the output signal does not depend on the phase, Φ_d , of the received part of the incoming signal 15. It will again be appreciated that the type of operational amplifier and the values of the associated components shown in Figures 5 and 6 are examples only, and other types/values may be used.

Referring to Figure 7, the object identification component 37 comprises a diode, capacitor and resistor in the arrangement shown. The object identification component 37 receives either a USB or a LSB signal, RDMsin(ω_mt ± Φ_d), which is an amplitude modulated signal. The diode acts to rectify the signal, and the capacitor and resistor together act as a low pass filter which extracts the modulation factor M from the amplitude envelope of the rectified signal.

The extracted modulation factor is compared with one or more expected modulation factors. If the extracted modulation factor matches the or one of the expected modulation factors, then the part of the incoming signal 15 received by the transceiver cell 3 from the object 13 is identified as having been received from a recognised object. If the extracted modulation factor does not match the or one of the expected modulation factors, then the part of the incoming signal 15 received by the transceiver cell 3 from the object 13 is identified as having been received from an unrecognised object. Thus the object identification system 1 can identify an object from which it receives a signal. The object identification system 1 can receive signals from a plurality of objects in the field of its outgoing signal 1 1 , and identify the objects as recognised or not recognised. Additionally or alternatively, the object identification component 37 may extract the incoming signal angular frequency ω_m from the signal which it receives. The extracted angular frequency is compared with one or more expected angular frequencies. If the extracted angular frequency matches the or one of the expected angular frequencies, then the part of the incoming signal 15 received by the transceiver cell 3 from the object 13 is identified as having been received from a recognised object. If the extracted angular frequency does not match the or one of the expected angular frequencies, then the part of the incoming signal 15 received by the transceiver cell 3 from the object 13 is identified as having been received from an unrecognised object. Thus again, the object identification system 1 can identify an object from which it receives a signal. It can be seen that identification of the object which is the source of the incoming signal is automatic.

The object identification component 37 can further act to read information carried by the modulation factor M of the part of the incoming signal 15. The object identification system 1 can decide whether or not to send a signal back to the object 13 from which the incoming signal 15 has been received. The object identification system 1 may decide to only send signals back to objects which have been identified as recognised objects.

When it is decided to send a signal back to the object 13, either the LSB signal, RDMsin(ω_mt - Φ_d), or the USB signal, RDMsin(ω_mt + Φ_d), is output to the tracking PLL circuit 38. Here, the component of the signal, RDM, is set to 1 , to get a LSB or USB signal, sin(ω_ct ± Φ_d). The tracking PLL circuit 38 duplicates the LSB signal or the USB signal, and outputs either two LSB signals or two USB signals. The tracking PLL circuit 38 may also receive a DC bias signal. The magnitude of this DC bias signal may be varied, to introduce variation in the phase of the LSB signals or the USB signals, i.e. to phase modulate the LSB signals or the USB signals. Thus the LSB signals or the USB signals can be made to carry information to the object which has been recognised. The sideband signal filter 36 and the tracking PLL circuit 38 also act to allow recovery of weak LSB or USB signals.

The LSB signals or the USB signals output by the tracking PLL circuit 38, are input into the phase shift system 22. This comprises a first phase element 40 and a second phase element 42, each of which comprises a feedback amplifier and associated components. In this embodiment, the first phase element 40 comprises a minus 90 degree phase shifter, as shown in Figure 8, and adds a minus 90 degree phase shift to the signal it receives. This phase shift is obtained by using a phase lead circuit comprising the capacitor in the feedback loop of the feedback amplifier of the phase element. The second phase element 42 comprises a feedback amplifier and components as shown in Figure 7, with the exception of the capacitor. Therefore no phase shift is introduced, and the second phase element 42 merely passes the signal it receives, without changing its phase. The resistor components of the phase elements are chosen to equalise the amplitudes of the signals output by the elements. It will be appreciated that the type of operational amplifier and the values of the associated components shown in this figure are examples only, and other types/values may be used. The first phase element 40 therefore receives an LSB signal and outputs an LSB signal having a first phase or receives a USB signal and outputs a USB signal having a first phase, and the second phase element 42 receives an LSB signal and outputs an LSB signal having a second phase which is in quadrature with the first phase or receives a USB signal and outputs a USB signal having a second phase which is in quadrature with the first phase. It will be appreciated that other arrangements of the phase elements 40, 42 can be used, for example the first phase element 40 may comprise a 270 degree phase shifter, and add a 270 degree phase shift to the signal it receives, and the second phase element 42 may merely pass the signal it receives, without changing its phase.

The LSB signals or the USB signals are then passed to the switching mechanism 24, as shown in Figure 9. This comprises a first input port 60, a second input port 62, a first single pole, single throw switch 64, a second single pole, single throw switch 66, a first output port 68 and a second output port 70. The first input port 60 is connected to the first element 40 of the phase shift system 22, and the second input port 62 is connected to the second phase element 42 of the phase shift system 22. The first input port 60 is connected to switch contacts 72, 74, as shown. The second input port 62 is connected to switch contacts 76, 78, as shown. The first switch 64 is operable to cause a switch lever to contact either the switch contact 72 or the switch contact 76. The second switch 66 is operable to cause a switch lever to contact either the switch contact 74 or the switch contact 78. Control of the operation of the switches 64, 66 is achieved using commands sent to the switches via control lines a and a.

The switching mechanism 24 receives either LSB signals or USB signals. The switching mechanism 24 receives the LSB signal having the first phase (-90) from the first phase element 40 on the input port 60, and passes this signal to switch contacts 72 and 74. The switching mechanism also receives the LSB signal having the second phase (0) from the second phase element 42, and passes this signal to switch contacts 76 and 78. A control signal is sent to the first switch 64 via control line a, which causes the switch lever of this switch to contact the switch contact 76. A control signal is also sent to the second switch 66 via control line a, which causes the switch lever of this switch to contact the switch contact 74. Thus the LSB signal having the second phase (0) is passed to the first output port 68, and the LSB signal having the first phase (-90) is passed to the second output port 70.

Alternatively, the switching mechanism 24 receives the USB signal having the first phase (-90) from the first phase element 40 on the input port 60, and passes this signal to switch contacts 72 and 74. The switching mechanism also receives the USB signal having the second phase (0) from the second phase element 42, and passes this signal to switch contacts 76 and 78. A control signal is sent to the first switch 64 via control line a, which causes the switch lever of this switch to contact the switch contact 72. A control signal is also sent to the second switch 66 via control line a, which causes the switch lever of this switch to contact the switch contact 78. Thus the USB signal having the second phase (0) is passed to the second output port 70, and the USB signal having the first phase (-90) is passed to the first output port 68.

The signals on the first and second output ports of the switching mechanism 24 are passed to the IQ modulator 26, Figure 10. This comprises an I input port 90, a Q input port 92, a reference signal input port 93, a 90 degree hybrid coupler 94, a first mixer 96, a second mixer 98, and an output port 100. The first output port 68 of the switching mechanism 24 is connected to the I input port 90, and the second output port 70 of the switching mechanism 24 is connected to the Q input port 92. The second LO PLL circuit 30 is connected to the reference signal input port 93.

The IQ modulator 26 receives either LSB signals or USB signals. The IQ modulator 26 receives the LSB signal having the first phase (-90) on the Q input port 92 and receives the LSB signal having the second phase (0) on the I input port 90. The reference signal received on the reference signal input port 93 is input into the 90 degree hybrid coupler 94. The coupler 94 produces a first signal which is input into the first mixer 96 and a second signal which is input into the second mixer 98. The signals are in phase quadrature. The first mixer 96 receives the first signal from the coupler 94 and the LSB signal having the second phase (0) from the I input port 90. The first mixer 96 acts to mix these signals and produces an output signal. The second mixer 98 receives the second signal from the coupler 94 and the LSB signal having the first phase (-90) from the Q input port 92. The second mixer 98 acts to mix these signals and produces an output signal. The output signals from the first and second mixers are combined, and output from the IQ modulator 26 via the output port 100. The components of the IQ modulator 26 act to phase adjust the LSB signals, as necessary, to produce an output signal at the output port 100 which is the phase conjugate of the part of the incoming signal first received from the antenna component 7 of the transceiver cell 3 comprising the IQ modulator 26.

Alternatively, the IQ modulator 26 receives the USB signal having the second phase (0) on the Q input port 92 and receives the USB signal having the first phase (-90) on the I input port 90. The reference signal received on the reference signal input port 93 is again input into the 90 degree hybrid coupler 94. The coupler 94 produces a first signal which is input into the first mixer 96 and a second signal which is input into the second mixer 98. The signals are again in phase quadrature. The first mixer 96 receives the first signal from the coupler 94 and the USB signal having the first phase (-90) from the I input port 90. The first mixer 96 acts to mix these signals and produces an output signal. The second mixer 98 receives the second signal from the coupler 94 and the USB signal having the second phase (0) from the Q input port 92. The second mixer 98 acts to mix these signals and produces an output signal. The output signals from the first and second mixers are combined, and output from the IQ modulator 26 via the output port 100. The components of the IQ modulator 26 act to phase adjust the USB signals, as necessary, to produce an output signal at the output port 100 which is the phase conjugate of the part of the incoming signal first received from the antenna component 7 of the transceiver cell 3 comprising the IQ modulator 26.

The IQ modulator 26 also acts to upconvert the frequency of the LSB signals or USB signals which it receives, from IF signals to an RF output signal. The IQ modulator 26 receives an RF reference signal from the second LO PLL circuit 30. On mixing this with the IF signals received on the I and Q input ports, an RF output signal is obtained.

The IQ modulator 26 may be used to produce an amplitude modulated, phase conjugate output signal. I, Q bit patterns are applied to the first and second mixers, in order to switch them on and off, thus amplitude modulating their output signals.

The first LO PLL circuit 28 and the second LO PLL circuit 30 are phase synchronised, as they receive a common low frequency input signal and use this to produce their reference signals. (This common low frequency input signal is distributed across the array of transceiver cells 3 of the object identification system 1 , and is locally available at the LO PLL circuits of each transceiver cell in the array, for the purposes of signal down/up conversion). The use of phase synchronised LO PLL circuits 28, 30 for providing reference signals for down and up conversion, and for providing the output signal initially output by the antenna component 7 of the cell 3, ensures synchronised phase information in the part of the incoming signal received by the transceiver cell 3 and the output signal output by the transceiver cell 3. The object identification system 1 comprises three transceiver cells 3. Each cell 3 outputs a signal which has an equal, but opposite, phase to that of the part of the incoming signal received by the cell. The output signals are passed to the antenna components 7 of the cells, and are output therefrom. The output signals combine to produce an outgoing signal, which is transmitted by the identification system 1 . As each output signal is the phase conjugate of its part of the incoming signal, wave interference principles will dictate that the outgoing signal will de directed to the object 13, even if its position is not known a priori. Thus the object identification system 1 also acts as a retrodirective antenna system. The object 13 can detect the outgoing signal transmitted by the object identification system using conventional means, and can remove and process any information encoded upon the signal by modulation. The first outgoing signal 1 1 of the object identification system 12 may be a wide field signal. If a signal is received from an object and this is identified as a recognised object, subsequent outgoing signals may be transmitted which get progressively narrower.

The object identification system 1 also comprises a phase extraction unit 39. This receives signals RDMcosΦ_dsinω_mt and RDMsinΦ_dsinω_mt from the frequency downconverter/mixer unit 36. Each of these signals are dependent on the phase, Φ_d , of the part of the incoming signal received by the transceiver cell 3. The phase extraction unit 39 extracts the phase, and uses this to derive angle of arrival information of the incoming signal, and, from this, the position of the object 13.

As the object identification system 1 of this embodiment is retrodirective, it has a high immunity to clutter. Further, the system 1 is able to lock onto the object 13, and then follow movement of the object 13. The architecture of each transceiver cell 3 of this embodiment of the object identification system 1 results in there being no requirement for a local oscillator running at twice the frequency of the incoming signal in order for retrodirective action to occur. This significantly eases the physical local oscillator requirements in practical implementation of the system 1 . Use of the phase shift system 22, the switching mechanism 24 and the IQ modulator 26, in each of the transceiver cells 3, allows production by the IQ modulator 26 of an output signal which is very close in frequency to the part of the incoming signal received by the transceiver cell 3. In conventional upconverter/mixer arrangements, if an output signal is generated which is very close in frequency to a received input signal, sufficient leakage occurs through the upconverter/mixer to destroy the output signal. Using the arrangement described, allows this leakage to be cancelled. Thus the object identification system 1 can use a narrow bandwidth for the input and output signals. This results in good signal to noise ratio, good 'rejection' of thermal noise, low power and difficulty for a third party to identify or jam the input or output signals. If the object 13 is moving, it may move into a position where received signals by each cell might be summed to be zero in a conventional system. In the object identification system 1 as described, the signals are added to always give a maximum signal, and therefore better signal to noise ratio.

In an alternative embodiment of the object identification system of the invention, the sideband signal filter 36 comprises a lower sideband signal filter, and outputs a LSB signal. This is input into the tracking PLL circuit 38 which duplicates it, and outputs two LSB signals. The LSB signals are input into the phase shift system 22. The first phase element 40 of the system 22 receives an LSB signal and outputs an LSB signal having a first (-90) phase, and the second phase element 42 receives an LSB signal and outputs an LSB signal having a second phase (0), which is in quadrature with the first phase. The LSB signals output by the phase shift system 22 are then directly input into the IQ modulator 26, i.e. no switching mechanism 24 is required. The output of the first phase element 40 is directly connected to the Q input port 92 of the IQ modulator 26, and the output of the second phase element 42 is directly connected to the I input port 90 of the IQ modulator 26. The modulator 26 acts on the LSB signals as previously described, to produce an output signal at the output port 100 which is the phase conjugate of the part of the incoming signal first received from the antenna component 7 of the transceiver cell 3 comprising the IQ modulator 26.

In a further embodiment of the identification system of the invention, the sideband signal filter 36 comprises an upper sideband signal filter, and outputs a USB signal. This is input into the tracking PLL circuit 38 which duplicates it, and outputs two USB signals. The USB signals are input into the phase shift system 22. The first phase element 40 of the system 22 receives a USB signal and outputs a USB signal having a first (-90) phase, and the second phase element 42 receives a USB signal and outputs a USB signal having a second phase (0), which is in quadrature with the first phase. The USB signals output by the phase shift system 22 are then directly input into the IQ modulator 26, i.e. again no switching mechanism 24 is required. The output of the first phase element 40 is directly connected to the I input port 90 of the IQ modulator 26, and the output of the second phase element 42 is directly connected to the Q input port 92 of the IQ modulator 26. The modulator 26 acts on the USB signals as previously described, to produce an output signal at the output port 100 which is the phase conjugate of the part of the incoming signal first received from the antenna component 7 of the transceiver cell 3 comprising the IQ modulator 26. In a further embodiment of the object identification system of the invention, the system does not act as a retrodirective antenna system. This object identification system comprises a single transceiver cell, and the transceiver cell comprises an antenna component, a processor, and a LO PLL circuit. The transceiver cell does not comprise a phase shift system, switching mechanism, IQ modulator or a second LO PLL circuit. The processor comprises a low noise amplifier, a frequency downconverter/mixer unit a phase shifter, a sideband signal filter, an object identification component, and a phase extraction unit. Each of the components of the transceiver cell operates substantially as described above. When a signal is received by the transceiver cell, it is processed to identify whether or not it is received from a recognised object. If it is decided to send a signal to the object, the identification system outputs a wide field signal, which will impinge on the object.

The object identification system of the invention may be used to process signals from objects which scatter/emit modulated signals and which are identified as recognised objects. The object identification system may transmit signals to an object (either using a wide field signal or retrodirectively) if the object is a recognised object. The transmitted signals may comprise information to be used by the object.

One embodiment of the object identification system of the invention may be used in a radio therapy/ablation system. The radio therapy/ablation system comprises an object identification system which also operates as a retrodirective antenna system, a target, and a source of radio signals. The target is positioned on an object, such as a tumour, requiring treatment with or ablation by the radio signals. The object identification system is used to transmit a signal towards the target. On receipt of the signal, the target either scatters a modulated signal back towards the object identification system, and/or transmits a modulated signal back towards the object identification system. On receiving the signal from the target, the object identification system processes the signal to determine if the modulation of the signal received from the target is that expected, i.e. if the target is a recognised object. If this is the case, the object identification system locks onto the target's position. The source of radio signals can then direct a beam of radio signals to the target, and the object on which it is positioned, the signals having a frequency suitable selected for the treatment/ablation type required. If the target is designed to only backscatter the signal transmitted by the antenna system, i.e. the target has no receive capacity, the target can be made particularly small, increasing the area of the object which can be treated with the radio signals. If the object, and therefore the target, is moving, this is of limited consequence, as the object identification system is still able to lock onto the target and direct radio signals to the target and object. This allows tumours or defects in areas where movement is likely to occur, e.g. the heart or lungs, to be treated without administering external means for slowing their movement.

The object identification system of the invention may be used to construct an electromagnetic fence. The system is used to send a signal to one or more objects making up the fence. Signals received from the objects are processed and the objects are identified as recognised objects. If an unrecognised object, e.g. a person interposing themselves between the object identification system and a recognised object, sends a signal to the system, the system will identify the person as an unrecognised object, and can raise an alarm. Such a fence is relatively immune to clutter introduced by objects, e.g. trees, which are moving in the far field of the object identification system, and would be considerably less prone to false detection alarms than current systems.

Claims

1 . An identification system for receiving an incoming signal from an object, the system comprising at least one transceiver cell comprising an antenna component which receives a part of the incoming signal, and a processor which processes the part of the incoming signal to extract identification information of the object, wherein the processor comprises a frequency downconverter/mixer unit comprising a coupler which produces first and second phase quadrature signals, a first mixer which receives the first signal and mixes it with the part of the incoming signal to produce a first output signal comprising object identification information, and a second mixer which receives the second signal and mixes it with the part of the incoming signal to produce a second output signal comprising object identification information, a phase shifter which receives the second output signal and adds a 90 degree phase shift to the signal to produce a phase shifted second output signal comprising the object identification information, a sideband signal filter which receives the first output signal from the frequency downconverter/mixer unit and receives the phase shifted second output signal from the phase shifter, and operates to produce a sideband signal of the part of the incoming signal which comprises the object identification information, an object identification component which receives the sideband signal from the sideband signal filter, extracts the object identification information therefrom, and uses the object identification information to identify the object.

2. An identification system according to claim 1 in which the coupler of the frequency downconverter / mixer unit comprises a 90 degree hybrid coupler.

3. An identification system according to claim 1 or claim 2 in which the coupler receives a reference signal and uses the reference signal to produce the first and second phase quadrature signals.

4. An identification system according to any preceding claim in which each of the first and second mixers multiply the signal received from the coupler with the part of the incoming signal to produce the first and second output signals comprising object identification information.

5. An identification system according to claim 2 in which the frequency downconverter / mixer unit receives a radio frequency reference signal and a radio frequency incoming signal, and frequency downconverts these signals to produce intermediate frequency first and second output signals.

6. An identification system according to any preceding claim in which the sideband signal filter operates to add the first output signal and the phase shifted second output signal, to produce a lower sideband signal which comprises the object identification information.

7. An identification system according to any of claims 1 to 5 in which the sideband signal filter operates to subtract the first output signal and the phase shifted second output signal, to produce an upper sideband signal which comprises the object identification information.

8. An identification system according to any preceding claim in which the object identification component compares the extracted object identification information with one or more expected object identification information, and if a match is found, determines that the object is a recognised object, and if a match is not found, determines that the object is an unrecognised object.

9. An identification system according to any preceding claim in which the object identification component extracts object identification information comprising a modulation factor, and compares the extracted modulation factor with one or more expected modulation factors, and if a match is found, determines that the object is a recognised object, and if a match is not found, determines that the object is an unrecognised object.

10. An identification system according to any preceding claim in which the object identification component extracts object identification information comprising an angular frequency, and compares the extracted angular frequency with one or more expected angular frequencies, and if a match is found, determines that the object is a recognised object, and if a match is not found, determines that the object is an unrecognised object, from the signal.

1 1 . An identification system according to any preceding claim in which the identification system comprises a phase extraction unit which receives the first and second output signals from the frequency downconverter/mixer unit, extracts phase information from the first output signal, the second output signal, or both of the output signals, and uses this to derive angle of arrival information of the incoming signal, and, from this, the position of the object.

12. An identification system according to any preceding claim which sends a signal back to the object from which the incoming signal has been received, by outputting a wide field signal which impinges on the object.

13. An identification system according to any preceding claim which sends a signal back to the object from which the incoming signal has been received, by acting as a retrodirective antenna system which outputs a signal directly to the object.

14. A method of identifying an object from which an incoming signal is received comprising using at least one transceiver cell comprising an antenna component to receive a part of the incoming signal, using a coupler of a frequency downconverter/mixer unit to produce first and second phase quadrature signals, using a first mixer of the frequency downconverter/mixer unit to receive the first signal and mix it with the part of the incoming signal to produce a first output signal comprising object identification information, using a second mixer of the frequency downconverter/mixer unit to receive the second signal and mix it with the part of the incoming signal to produce a second output signal comprising object identification information, using a phase shifter to receive the second output signal and add a 90 degree phase shift to the signal to produce a phase shifted second output signal comprising the object identification information, using a sideband signal filter to receive the first output signal from the frequency downconverter/mixer unit and receive the phase shifted second output signal from the phase shifter, and operate to produce a sideband signal of the part of the incoming signal which comprises the object identification information, using an object identification component to receive the sideband signal from the sideband signal filter, extract the object identification information therefrom, and use the object identification information to identify the object.