WO2011102762A1 - Wideband transmitter/receiver arrangement for multifunctional radar and communication - Google Patents
Wideband transmitter/receiver arrangement for multifunctional radar and communication Download PDFInfo
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- WO2011102762A1 WO2011102762A1 PCT/SE2010/050183 SE2010050183W WO2011102762A1 WO 2011102762 A1 WO2011102762 A1 WO 2011102762A1 SE 2010050183 W SE2010050183 W SE 2010050183W WO 2011102762 A1 WO2011102762 A1 WO 2011102762A1
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- signal
- receiver
- isolator
- antenna
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Classifications
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/38—Transceivers, i.e. devices in which transmitter and receiver form a structural unit and in which at least one part is used for functions of transmitting and receiving
- H04B1/40—Circuits
- H04B1/44—Transmit/receive switching
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/003—Transmission of data between radar, sonar or lidar systems and remote stations
- G01S7/006—Transmission of data between radar, sonar or lidar systems and remote stations using shared front-end circuitry, e.g. antennas
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
- G01S13/06—Systems determining position data of a target
- G01S13/08—Systems for measuring distance only
- G01S13/32—Systems for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/88—Radar or analogous systems specially adapted for specific applications
- G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
- G01S13/90—Radar or analogous systems specially adapted for specific applications for mapping or imaging using synthetic aperture techniques, e.g. synthetic aperture radar [SAR] techniques
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
- G01S7/03—Details of HF subsystems specially adapted therefor, e.g. common to transmitter and receiver
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
- G01S7/03—Details of HF subsystems specially adapted therefor, e.g. common to transmitter and receiver
- G01S7/038—Feedthrough nulling circuits
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
- G01S7/40—Means for monitoring or calibrating
- G01S7/4004—Means for monitoring or calibrating of parts of a radar system
- G01S7/4021—Means for monitoring or calibrating of parts of a radar system of receivers
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
- G01S2013/0236—Special technical features
- G01S2013/0272—Multifunction radar
Definitions
- the present invention relates to a wideband multifunctional transmitter and receiver arrangement, preferably for transmitting and receiving at VHF, UHF or in the microwave bands.
- Such an arrangement can simultaneously and in the same frequency band serve as radar, surveillance, and communication system.
- prior art continuous wave CW radar emits a single frequency continuous wave.
- the CW radar can determine the velocity of detected objects.
- linear frequency modulation sawtooth
- a frequency-modulated continuous wave FMCW radar system is provided.
- the frequency modulation of the CW has the advantage that also the distance to a detected object can be determined.
- Such a FMCW radar system is known from US 3,789,398.
- the FMCW radar is mainly motivated by the fact that it minimizes the peak-to-average power ratio for the radar transmit signal. Its applications are thus as whispering radar, used to defeat detection of the radar signal.
- the FMCW radar is however limited to said radar function and lacks any multifunctional capability.
- the FMCW radar exhibits poor signal cohabitation between its radar function and environmental signals. There is thus a need for an improved transmitter/receiver arrangement removing the above mentioned disadvantages.
- the object of the present invention is to provide an inventive wideband transmitter/receiver arrangement for transmitting and receiving
- Said transmitter/receiver arrangement comprises a digital arbitrary waveform generator AWG connected to a transmitter, and wherein said waveform generator is configured to generate an arbitrary waveform within a given bandwidth.
- Said transmitter/receiver arrangement further comprises an antenna arrangement configured to emit a transmitter signal and to receive an incident signal, and a receiver configured to receive a receiver signal.
- Said transmitter/receiver arrangement further comprises an analogue isolator connected to said antenna arrangement, said transmitter, and said receiver.
- Said analogue isolator is adapted to route said transmitter signal from said transmitter to said antenna arrangement, and said incident signal from said antenna arrangement to said receiver, and to isolate said transmitter signal from said receiver signal.
- Said receiver is adapted to cancel any residual transmitter signal in said receiver signal by means of at least one digital model of at least said isolator, said antenna arrangement, and said transmitter.
- said method comprises the steps of generating an arbitrary waveform within a given bandwidth by means of a digital arbitrary waveform generator AWG connected to a transmitter, routing a transmitter signal from said transmitter to an antenna arrangement and an incident signal on said antenna arrangement to a receiver, and isolating said transmitter signal from said receiver signal, by means of an analogue isolator connected to said antenna arrangement, said transmitter, and said receiver, cancelling any residual transmitter signal in said receiver signal by means of at least one digital model of at least said isolator, said antenna arrangement and said transmitter.
- the inventive wideband transmitter/receiver arrangement serves as core for a multifunctional radar, surveillance, and communication system.
- the system is, due to its excellent leakage cancellation, particularly suitable when compact equipment is required, for example on small or medium sized Unmanned Airborne Vehicle UAV applications.
- transmitter/receiver arrangement also leads to reduced weight and volume compared to pulsed radar equipment, and in that transmitter peak power is reduced using CW radar.
- the present invention intends to combine the radar function with other uses of electromagnetic signal reception and transmission.
- a fundamental requirement is that the radar is not pulsed as ordinary radar but operates on a continuous waveform principle, i.e. as the FMCW radar.
- the very idea of the invention is that the waveform must be allowed to be arbitrary and e.g. modulated to serve as a communication signal, whilst still fulfilling its role as radar transmit signal.
- known FMCW radar designs are of little use. Indeed the main challenge of continuous wave radar is to achieve isolation between transmit and receive and the methods to do so in the present invention are very different from those of the FMCW radar.
- the multifunctional capability of the inventive wideband transmitter/receiver arrangement according to the invention includes providing:
- Radar functions providing microwave and/or low frequency Synthetic Aperture Radar SAR.
- Wideband in this concept implies that the system covers bandwidths of at least octave order with a centre frequency anywhere from VHF to well up in the microwave region, i.e. 50 MHz - 5 GHz.
- the inventive transmitter/receiver arrangement provides an improved level of signal cohabitation between the radar function and environmental signals. Improvements are possible both in that the radar will not cause a strong interference to communication, and in that the radar will be robust with respect to the interference caused by communication signals.
- the issue of cohabitation concerns ways to:
- Cohabitation issues tend to become important for a!i radar frequencies as competing uses of the spectrum spreads upwards in frequency to established microwave radar bands. However the issue of cohabitation is particularly crucial for frequencies below about 1 GHz. A large fraction of all
- Narrow band interference can be removed by creating a notch corresponding to the communication band in the range (or "fast time") spectrum.
- this method results in a seriously large degradation of radar data and SAR image quality.
- Better rejection schemes are to use either
- Cancellation as a method of interference mitigation of type 2, is well suited to digitally modulated signals with built in error correction. Cancellation can be applied as and when the radar ground response signal is so weak that decoding and error correction will fully retrieve the interfering signal. This can then again be encoded, subtracted and thereby mitigated in the overall received signal.
- the situation of the radar response signal being weak compared to the interfering signal is what is commonly experienced. It is also the condition for the scheme of transmitter signal adaption to the incoming signal, since this will re-transmit the radar response signal, which must not impair the decoding of the re-transmitted interference signal. A suitable scheme would thus be to adapt transmitter power levels so that the radar response remains a small part of any environmental signal for which one wishes to avoid causing interference.
- the radar according to the invention should fully capture the interfering signals and retransmit these without interruption.
- the radar should operate on a continuous transmit waveform principle, and since the radar is required to have an ability to retransmit any incident signals, it must apart from continuous operation have the added capability of being able to transmit waveforms of arbitrary shape.
- Such radar which is the core of the invention, will be called Arbitrary
- Waveform Continuous Wave AWCW radar An important candidate for application is as a compact and multifunctional sensor onboard UAVs.
- the smallness of the UAVs, for which the invention is consider in particular, is in fact an important enabling factor for the realization of the AWCW radar.
- the radar will operate at short ranges, i.e. with a low transmitter power.
- the concept of transmitting an arbitrary wave is not new.
- arbitrary waveforms are used in the sense pseudo-random noise signal, repeated in a fixed form from pulse to pulse.
- the present invention launches the new concept that the waveform can be entirely non-repetitive for any length of time and in fact be able to continuously copy incident signals, which are retransmitted and used as a part of a total transmit waveform.
- this invention launches the concept that this non-repetitive waveform can be continuously transmitted without interrupts for receiving as in ordinary pulsed radar.
- the arbitrary waveform is suitably generated by an arbitrary waveform generator, which synthesize the waveforms using digital signal processing techniques.
- an AWCW radar device has apart from its applications as radar also the ability to act as a communication link, which is an immediate consequence of its capability to continuously copy incident signals in the transmitted waveform.
- the transmit waveform is arbitrary it can be modulated to convey sensor data information and thus used to downlink these data.
- the AWCW radar operates with continuous reception it can also fulfil a role of performing signal surveillance within the frequency band for which it is designed. This is done in parallel without any requirement on time sharing or otherwise splitting the capability of the radar device between different applications.
- a continuous and arbitrary transmitter signal is a(t) and assume that the received signal is r(t).
- the signal a(t) is assumed to have bandwidth B and is required to have two basic properties: For some pre-se!ected period of time T , it is required that: 1. the signal a(t) spans B with equal power density for any time interval of length T .
- formula (I) provides bandwidth limited range resolution with a given side lobe level, it is seen that if would have been periodic with period T there would have been range ambiguities with a period Hence the absence of such ambiguities is due to said basic property 2.
- the suppression depth of range ambiguities is limited by the time-bandwidth product . Indeed, for optimal waveforms, the
- suppression depth will equal BT for all ranges and times.
- f(R,t) is low pass filtered to a highest slow time frequency ⁇ /T .
- the required slow time bandwidth of f(R,() is set by the SAR Doppler bandwidth.
- the transmitter/receiver arrangement is used in an UAV based SAR radar, this is typically of the order 100 Hz and thus significantly smaller than 1/T .
- f(R,t) will be further low pass filtered to a bandwidth corresponding to the reciprocai of the SAR integration time of possibly several seconds.
- the degree of suppression will depend on whether the transmit signal adapts to the interference or not, as discussed above.
- the interference will be suppressed by (I) just as any noise component added to r ⁇ t).
- the suppression ratio is set partly by the averaging occurring in (1) and partly by the further time averaging f ⁇ R,t) set by the Doppler bandwidth.
- the suppression rate will be 80 dB for interference as well as noise.
- the interference will be substantially stationary in slow radar time.
- the method of interference mitigation is in that case to reduce the bandwidth of the interference within the Doppler spectrum, and notch the interference 2-dimensionally - both in the range and Doppler spectrum.
- the interference is thus effectively removed - not merely suppressed.
- the impact on SAR image quality is small since the amount of data removed by 2-dimensional filtering is small.
- the level of suppression which can be achieved by this methods will add to the cancellation depth obtainable when the transmit signal does not adapt, as described above.
- the overriding concern of AWCW radar is to obtain sufficient isolation between the transmitter and receiver signals.
- the achievable isolation puts a limit on allowable transmitter power level, since the isolation should reduce this level to the receive noise level determined by environmental noise or the receive channel noise.
- the possible isolation diminishes with increased bandwidth, due to e.g. the reduced dynamic range of analogue to digital converters ADCs and digital to analogue converters DACs operating at high sampling rates.
- Narrow band isolation is achievable by analogue cancellation techniques, as is illustrated in FMCW radars.
- For wideband isolation however, as required by the inventive transmitter/receiver arrangement, fully developed means for digital cancellation is required.
- a wideband isolation approach comprising a combined analogue and digital cancellation scheme providing isolation in three logical steps is disclosed:
- transmitter/receiver arrangement which analogue cancellation is required to be highly linear and time stable and thus accurately characterizable by a digital model.
- a first analogue and digital cancellation step which removes any analogue cancellation error with respect to a digital transmitter signal, by making use of that this is accurately known and also that the analogue cancellation system characteristics are accurately known.
- step 3 takes care of such model errors.
- the achievable isolation depends on two conflicting requirements, i.e. A) the ability of the analogue system to achieve a high degree of isolation by itself, and B) the characterizabiiity of the analogue system required for obtaining a high isolation in steps 2 and 3. Characterizability here means that an analogue system may possibly be designed to yield a high degree of isolation but only in such a way that leakage residuals are less linear or less stable in time. Hence the degree of isolation achievable in the digital suppression stages will be limited for such a system. A suitable trade off between analogue and digital cancellation must be found.
- ADC resolution is a lesser concern since signals to be AD- converters are all low level.
- Figure 1 shows the system building blocks of AWCW radar according to the invention
- Figure 2 shows the leakage and noise reduction stages in the receiver according to the invention
- Figure 3 shows an isolator design according to the invention
- Figure 4 shows an antenna arrangement of the isolator of figure 3
- Figure 5A shows a calibration arrangement for determining a digital model of a transmitter according to the invention
- Figure 5B shows a calibration arrangement for determining the
- Figure 5C shows a calibration arrangement for determining a digital model of an isolator and antenna arrangement according to the invention
- Figure 5D shows a calibration arrangement for determining the
- FIG. 1 shows the system building blocks of AWCW radar according to the invention.
- a digital arbitrary waveform generator AWG 1 feeds a transmitter 19 comprising a first digital to analogue converter DAC 2, and a power amplifier 3.
- the signal generated by the AWG 1 is thus converted to an analogue signal, which is amplified in the power amplifier 3.
- the transmitter 19 subsequently feeds a transmitter signal S1 into a RF isolator 4, which serves to control the direction of signal flow.
- the isolator 4 is further connected to an antenna arrangement 5, and to a receiver, such that signals
- isolator (4) is here considered to encompass any type of device capable of routing said signals S1 , S2 and isolating the transmitter signal S1 from entering the receiver, such as isolator, circulator, and power splitter/combiner networks etc.
- a receiver signal S3 from the isolator is fed to a first subtraction unit 10 via a first attenuator 9.
- the receiver signal S3 has at least three terms, viz. (a) any exterior signal S2 incident on the antenna arrangement 5, (b) antenna reflections and (c) isolator leakage.
- a first cancellation signal S4 is generated by feeding the generated waveform signal from the AWG 1 into a digital model 6 of the transmitter 19, then to a first digital model 7 of the isolator 4, the antenna arrangement 5, and a first subtraction unit 10, and then to a second DAC 8. Said first cancellation signal S4 is subsequently fed from the second DAC 8 to the first subtraction unit 10, which is an analogue subtraction unit 10.
- the signal terms (b) and (c) mentioned above are removed in the first subtraction unit 0, insofar the digital model 6 of the transmitter 19 and said first digital model 7 correctly describes the physical behaviour of the transmitter 19, isolator 4, antenna arrangement 5, and first subtraction unit 10, i.e. how accurate they depict the transfer characteristics of said devices 19, 4, 5, 10.
- a discrepancy forming at least transmitter noise is most likely to remain in the signal output of the first subtraction unit 10.
- the intensity of the signal output from the first subtraction unit 10 is significantly reduced compared to the levels of the receiver signal S3 and the first cancellation signal S4 fed to the first subtraction unit 10.
- the low level signal output from the first cancellation unit 10 is fed to a first analogue to digital converter ADC 11 and subsequently to a second subtraction unit 12, which is a digital subtraction unit 12.
- a second cancellation signal S5 is generated by first feeding the output of the digital model 6 of the transmitter 19 to a third DAC 13 whose output signal is fed to a third subtraction unit 15.
- Another input signal to the third subtraction unit 15 is supplied from the output of the transmitter 19, having passed through a second attenuator 14.
- the output signal from the third subtraction unit 15 corresponds therefore to the difference between the digital model 6 of the transmitter 19 and the actual transmitter output, i.e. any transmitter noise not subtracted in the first subtraction unit 10 due to an inaccurate digital model 6 of the transmitter 19, amongst others.
- the signal output of the third subtraction unit 15 will be analogue to digital converted in a second ADC 16 and subsequently fed to a second digital model 17 of the isolator 4, the antenna arrangement 5, and the third subtraction unit 15.
- This signal will thus match the transmitter noise term fed into the second subtraction unit 12 from the first ADC 11.
- the output of the second subtraction unit 12 will correspond to any signal S2 incident on the antenna arrangement 5, apart from the above mentioned errors related to the characterizability limitations discussed above and resolution of the first, second and third digital to analogue converters 2, 8, 13, which also limits the possible level of cancellation in the first and third subtraction units 10, 15.
- the route of the first cancellation signal S4 accurately handles the large amplitude part of the cancellation by omitting analogue to digital conversion. This omission is possible because the large amplitude part of the signal is known.
- the route of the second cancellation signal S5 handles residuals, which are unknown but have small amplitude and thus allow being analogue to digital converted without critical accuracy being lost.
- Signals S1 generated by the transmitter 19 and coupled to the second attenuator 14 and emitted by the antenna arrangement 5, as well as signals S2 received by the antenna arrangement 5 and coupled to the first attenuator 9 are high intensity signals, whereas the signals at the output of the second subtraction unit 12 are just above ADC quantization level, i.e. ADC interior noise level. All other signals in the block diagram of figure 1 are signals with reduced levels not to saturate the first and second ADCs 11 , 16.
- the noise level "kTB” is calculated according to: wherein "kTB " is the noise temperature in watts, k B is the Boltzmann constant (1.381 ⁇ 10 ⁇ 23 J/K, joules per Kelvin), T s is the noise temperature (K), and B n is the noise bandwidth (Hz).
- the internal noise level "kTB " is thus - 73 dBm and the external noise level -63 dBm.
- LSB Local Bit
- FIG. 1 illustrates the leakage and noise reduction stages in the receiver, wherein the Y-axis represents the signal power in dBm and the X-axis illustrates sequential parts of the receiver, e.g.
- the transmitter signal leakage 20 With a 10 dB value for the first attenuator 9, the transmitter signal leakage 20 becomes in parity to the output level of the second DAC 8, whereupon they can cancel in the first subtraction unit 10.
- the transmitter noise leakage 21 at the output of the first attenuator 9 is -20 dBm, which is full scale for the first ADC 11.
- a strong interference signal may also yield -10 dBm at the isolator output and correspond to full scale for the first ADC 1.
- the transmitter signal leakage 20 With a -70 dB accuracy for the DAC resolution and a -50 dB accuracy for the said first digital model 7, the transmitter signal leakage 20 is reduced in the first subtraction unit 10 to -50 dBm.
- the transmitter noise leakage 21 is not reduced from its full scale value, and the external noise 22 is elevated to -70 dBm due to added noise from the second DAC 8.
- the second attenuator 14 must have a value 30 dB to reduce transmitter signal levels to 0 dBm.
- the transmitter signal S1 from the output of the transmitter 19 and the output of the digital model 6 of the transmitter 19 will thus cancel in the third subtraction unit 15, while transmitter noise remains unmitigated and at its value after the second attenuator 14.
- this value is -20 dBm, which also will be full scale for the second ADC 16.
- the transmitter noise will cancel. Cancellation depth will be given by the quantization noise of the first and second ADCs 11, 16 as well as the accuracy of said second digital model 17. Based on the assumed
- this value is -70 dBm.
- the transmitter signal leakage 20 and transmitter noise leakage 21 are further reduced, in fact, the transmitter signal leakage 20 is a replica of the transmit signal delayed by its
- the residual transmitter signal leakage 20 will have a small effect indeed on the reconstructed range reflectivity data f ⁇ R,t).
- the residual transmitter noise leakage 21 becomes suppressed in proportion to the time bandwidth product of the range reconstruction in the same way as any other noise component added to the received signal.
- the AWCW radar principle is best suited to moderate and low transmit power and in particular in application such radars operating below 1 GHz, where the external noise levels are elevated compared to the purely thermal environmental noise.
- the signal extraction unit 18 in order to achieve the required cohabitation and communication capabilities, the signal extraction unit 18 must contain means to extract communication subbands and to transfer and insert these signals in the AWG 1 , as a part of the transmitted waveform. An ability to demodulate the extracted signals is also required in some of the cohabitation and communication modes.
- This part connects the signal extraction unit 18 and the AWG 1 and furthermore contains suitable digital encoding and decoding devices, as well as a system controller guiding the signal extraction in the signal extraction unit 18, the waveform generation in the AWG 1 , and encoding/decoding processes, as required.
- the isolator 4 is a critical part of the AWCW radar design. For one it is difficult to achieve analogue wide band isolation of any significant depth by such a device. Presently isolation value requirements of at least 20 dB are dictated by the assumed -70 dB DAC accuracy.
- Linear wide band isolator systems can be based on signal cancellation.
- Such a cancellation system consists of two channels which in independent ways transmit and receive but which cancel each other as regards transmitter leakage through either channel.
- the challenge is the many degrees of freedom across which the leakage transfer function in the two channels must be similar.
- This number of degrees of freedom is basically set by the delay occurring in the system times the signal bandwidth.
- a circuitry of small extension is normally characterized by short delays and a simple transfer function also in the wide band case.
- the extension of the system itself is typically many wavelengths. Below 1 GHz, the extension of the system may be less than wavelength order. However in this case the extension of the radar platform becomes decisive, since low frequency antennas are never highly directive and will interact with the platform structure to non-negligible extent. It follows that irrespective of frequency the system will have delays of several periods of the frequencies at which the system operates.
- An octave bandwidth system will thus correspond to a transfer function of non-trivial shape.
- a wide band cancellation scheme for aircraft or UAV operation may be carried out, and which is well suited for frequencies below 1 GHz.
- the principle relies on the right left symmetry of the airframe and adopts two cancellation channels, which are symmetric in this sense. The device operates simultaneously to both right and left. The transmitter signal leakages through either of the two channels will be the same and the two leakage signals can thus be brought to cancel each other.
- Figure 3 illustrates the principle.
- first and second 90-degree hybrids 32, 36 are fed via a power splitter 31 to input ports P11 of the first and second 90-degree hybrids 32, 36.
- Said first 90-degree hybrid 32 in turn feeds a first antenna element 34 from a coupled port 2, and a second antenna element 33 from a transmitted port P22.
- Said second 90-degree hybrid 36 in turn feeds a third antenna element 38 from a coupled port P12, and a fourth antenna element 37 from a transmitted port P22.
- the first and second antenna element 34, 33 form a right antenna 42
- the third and fourth antenna element 38, 37 form a left antenna 43.
- the separation between said antenna elements 33, 34, 37, 38 in either antenna 42, 43 is a quarter of a wavelength at the centre frequency.
- each antenna 42, 43 will propagate the transmitter signal S1 along the separation axis between the antenna elements 33, 34, 37, 38, and in the direction of a phase delay generated by the fact that a signal fed to input port P11 of a 90- degree hybrid 32, 36 will be supplied to transmitted port P22 without phase shift, whereas the same signal will be phase shifted 0 -> 90° on its way from input port P1 to the coupled port P 2. Consequently, the direction of the phase delay goes from the coupled port P12 to the transmitted port P22, and the transmitter signal S1 will thus propagate in the direction of the block arrows illustrated in Figure 3.
- FIG 4 shows the antenna arrangement 5 on an airborne vehicle 44, such as an UAV.
- Each antenna 42, 43 is oriented so that the propagation main beam is orthogonal to the airframe centre plane, with the right antenna 42 propagating to the right and the left antenna 43 propagating to the left of the vehicle 44.
- the right and left antennas 42, 43 are located in a right left symmetric fashion with respect to the airframe centre plane.
- Return signals from the left antenna 43 are collected from the isolator port P21 of the second 90-degree hybrid 36 isolated from transmission and fed to a first input port P11 of the 180-degree hybrid 39.
- return signals from the right antenna 42 are collected from the isolator port P21 of the first 90-degree hybrid 32 and fed to a second input port P21 of a 180-degree hybrid 39.
- the 180-degree hybrid 39 further comprises a delta port P12 and a sum port P22.
- the output signal at sum port P22 is proportional to the sum of the signals at the first and second input ports P11 , P21
- the output signal at the delta port P12 is proportional to the difference between the signals at the first and second input ports P11 , P21.
- the first switch 35 is either set to transfer the transmitter signal S1 unaffected in which case the second switch 40 is set to feed the difference signal to the to the radar receiver, or the first switch 35 is set to a 80-degre phase shift in which case the second switch 40 is set to feed the sum signal to the radar receiver. In either case, the second switch 40 feeds the remaining signal out from the 180-degree hybrid 39 into a resistive load 41.
- any coupling between antenna elements 33 -> 34 and 34 -> 33 cancel each other, as do coupling between antenna elements 37 -» 38 and 38 -» 37 at the isolator ports P21 of the first and second 90-degree hybrids 32, 36.
- the couplings going from the antenna elements in one antenna to the other will not cancel. Just as the antenna reflections these will thus contribute to the signal residues at the isolator ports P21 of the 90-degree hybrids 32, 36.
- the antenna elements 33, 34, 37, 38 are typically broad band monopoles or dipoles. They can be vertically or horizontally polarized, in figure 3 they are vertically polarized and mounted underneath the UAV fuselage. A mechanism making the antenna elements foldable or retractable might be required for their protection during starting and landing.
- the omnidirectional property of radiation, created by this type of isolator 4, is acceptable for the applications 2-4 mentioned.
- SAR application 1
- the first and second switch 35, 40 provide this function.
- Switching must occur sufficiently fast with respect to slow time bandwidth of the ground reflectivity.
- a typical switching frequency might be 1 kHz.
- Switching could for instance be made synchronous with the orthogonal frequency-division multiplexing OFDM symbol rate in cohabitation schemes with television OFDM modulation.
- the first subtraction unit 10 is suitably based on a 180-degree hybrid.
- the first subtraction unit 10 is required to achieve a very high degree of cancellation.
- the required levels of cancellation are obtained by a pre-distortion of the transmitter signal S1 , carried out in the digital mode! 6 of the transmitter 19 and said first digital model 7.
- the pre-distortion must account for the non-perfectness of the 180-degree hybrid forming the first subtraction unit 10.
- the third subtraction unit 15 is suitably designed in the same manner of a 180-degree hybrid, and is subjected to similar requirements as the first subtraction unit 10.
- the cancellation step in the second subtraction unit 12 is performed entirely digital.
- Said second digital mode! 17 follows exactly the same principles as the digital model 6 of the transmitter 19, and said first digital model 7, but is acting on transmitter noise.
- All digital models 6, 7, 17 included in the receiver/transmitter arrangement are preferably implemented as digital finite impulse response FIR filter. The characteristics of such filters and the techniques for modelling them are generally known. Those skilled in the art who have the benefit of this description will be able to develop the necessary software to achieve the digital filter required to meet the needs of their particular situation.
- the pre-distortion is determined by the equation
- y ⁇ t is the output signal of the first subtraction unit 10 for any particular frequency .
- the 180-degree hybrid forming the first subtraction unit 10 is characterised by the real, non-negative but frequency dependent
- test signals can be series of impulses, each consisting of a single non-zero sample transmitted by the AWG 1.
- the impulse will spread time by the expected delays in the analogue parts of the system.
- the separation of each impulse in the test signal should be sufficient not to cause ambiguities due to this spreading.
- the length of the calibration series should be chosen so that when responses are coherently added the obtained signals levels are well above the system internal noise.
- the calibration measurement will directly determine the FIR filter coefficients of the digital models 6, 7, 17 representing the analogue system undergoing calibration.
- said first and second digital models 7, 17, as well as the digital model 6 of the transmitter 19 can all be determined.
- a test signal is generated by the AWG 1 and transmitted to the signal extraction unit 18, which can derive the digital model 6 of the transmitter 19 directly.
- the signal extraction unit 18 can derive the digital model 6 of the transmitter 19 directly.
- no transformation of the signal is performed in the second digital model 17.
- the accuracy is limited by the resolution of the second ADC 16, and will be relatively coarse.
- the transmitter 19 needs not to be determined very accurately due to the second subtraction unit 12, which cancels transmitter noise.
- the characteristics of the 180-degree hybrid forming the third subtraction unit 15, and the pre-distortion coefficients required for its role as subtraction unit, are determined.
- the test signal generated by the AWG 1 and applied to the digital model 6 of the transmitter 19 is fed to both input ports, one by one, of the third subtraction unit 15, and subsequently to the signal extraction unit 18, where the characteristics of the 180-degree hybrid forming the third subtraction unit 15 is derived.
- no transformation of the signal is performed in the second digital model 17.
- the characteristics of the isolator 4 and antenna arrangement 5 is determined.
- the different calibration configuration can all be realized by suitable switches inserted to redirect signals as required.
- calibrations are suitable conducted with the AWCW radar system in situ in the radar platform, and with the radar platform located in an environment corresponding to its predetermined field of use, for example airborne in case of a SAR
- the invention is capable of modification in various obvious respects, all without departing from the scope of the appended claims.
- the wideband cancellation scheme might also be realized without said third digital cancellation step where appropriate, if reduced isolation can be tolerated, whereby the digital mode! 6 of the transmitter 19 and said first digital model 7 can be integrated into a single digital model.
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US13/578,804 US9071337B2 (en) | 2010-02-17 | 2010-02-17 | Wideband transmitter/receiver arrangement for multifunctional radar and communication |
PCT/SE2010/050183 WO2011102762A1 (en) | 2010-02-17 | 2010-02-17 | Wideband transmitter/receiver arrangement for multifunctional radar and communication |
ES10846250.8T ES2613056T3 (en) | 2010-02-17 | 2010-02-17 | Broadband transmitter / receiver arrangement for multifunctional radar and communication |
EP10846250.8A EP2537257B1 (en) | 2010-02-17 | 2010-02-17 | Wideband transmitter/receiver arrangement for multifunctional radar and communication |
CN201080064178.2A CN102771055B (en) | 2010-02-17 | 2010-02-17 | For transmitting and receiving electromagnetic wideband transmitter/receiver apparatus and the method for transmitting and receiving wideband electromagnetic ripple |
IL221054A IL221054A (en) | 2010-02-17 | 2012-07-22 | Wideband transmitter/receiver arrangement for multifunctional radar and communication |
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PCT/SE2010/050183 WO2011102762A1 (en) | 2010-02-17 | 2010-02-17 | Wideband transmitter/receiver arrangement for multifunctional radar and communication |
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EP (1) | EP2537257B1 (en) |
CN (1) | CN102771055B (en) |
ES (1) | ES2613056T3 (en) |
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CN108153321A (en) * | 2017-11-21 | 2018-06-12 | 中国人民解放军陆军工程大学 | Method and device for resisting electromagnetic radiation interference of information link of unmanned aerial vehicle |
CN108153321B (en) * | 2017-11-21 | 2020-09-01 | 中国人民解放军陆军工程大学 | Method and device for resisting electromagnetic radiation interference of information link of unmanned aerial vehicle |
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Also Published As
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EP2537257A4 (en) | 2013-07-10 |
ES2613056T3 (en) | 2017-05-22 |
EP2537257B1 (en) | 2016-11-02 |
IL221054A (en) | 2016-09-29 |
US9071337B2 (en) | 2015-06-30 |
CN102771055B (en) | 2015-11-25 |
US20130201050A1 (en) | 2013-08-08 |
CN102771055A (en) | 2012-11-07 |
EP2537257A1 (en) | 2012-12-26 |
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