JP5544737B2 - Radar receiver - Google Patents

Description

  The present invention relates to a radar receiver, and more particularly to a radar receiver capable of preventing saturation of the receiver when the reception level fluctuates greatly within and between reception pulses.

  The radar receiver normally uses STC (Sensitivity Time Control) or AGC (Automatic Gain Control) to prevent saturation of the received signal in the received pulse. In the case of a radar that has a wide reception pulse width and receives it while moving like a radar, the level fluctuation in the reception pulse varies greatly between pulses and between pulses.

  FIG. 5 shows a configuration of a conventional synthetic aperture radar, which includes a radar antenna 21, an input amplifier 22, a mixer circuit 23, a variable attenuator 24, an amplifier 25, a variable attenuator 26, A configuration including an output amplifier 27, a branching device 28, a rectifier 29, and an AGC circuit 30 is shown.

  The radar antenna 21 transmits a high-frequency pulse from a transmission unit (not shown) to the target, and receives a reflected wave from the target. The received wave includes a signal RX SIG in which a transmission pulse is reflected on the ground other than the target and returned. A signal RX SIG in the figure represents a signal received by the radar antenna 21 on the time axis.

  The received wave is amplified by the input amplifier 22 and then frequency-converted by a local oscillation signal from a LO (Local Oscillator) (not shown) by the mixer circuit 23 and output. The mixer output is converted by the variable attenuator 24 into a signal attenuated according to the STC pattern composed of a fixed pattern by the STC ATT signal. The output of the variable attenuator 24 is amplified at a constant amplification level in the amplifier 25, then attenuated in accordance with the AGC ATT signal from the AGC circuit 30 in the second variable attenuator 26, and then amplified in the output amplifier 27. Is output. The output signal of the output amplifier 27 is output through the branching device 28. At this time, a part of the output signal is branched, rectified by the rectifier 29 and converted into a DC signal, and output by the AGC circuit 30. Control the magnitude of the signal.

  The AGC control in the circuit of FIG. 5 is used to reduce the dynamic range of the signal processing unit provided at the receiver output of the synthetic aperture radar. This is because if the signal dynamic range is large, it is necessary to increase the number of bits of the A / D converter that performs signal processing. If the number of bits is large, the amount of data to be processed increases. This is because signal processing such as recording and transmission is subject to great restrictions. In order to reduce such restrictions, it is desirable to reduce the number of bits as much as possible by reducing the dynamic range of the signal.

  That is, there is an appropriate value for the gain value determined from the number of bits of an A / D converter (not shown) used for signal processing. The appropriate gain data is usually about 40 dB in the case of an 8-bit A / D converter. On the other hand, since the receiver usually has a gain of about 60 dB, the A / D converter will be saturated as it is. Therefore, in the case of a radar receiver, averaging is always performed by some method.

  In addition, averaging of the output signal in the conventional radar receiver is performed by making the data averaged to some extent by the STC circuit become the same signal between the received pulses. That is, it is not the averaging in the reception gate but the averaging for each reception pulse, which is performed two-dimensionally. And since the correction was performed with a fixed pattern with respect to the time axis, the output could not be made flat if the pattern deviated from this pattern.

As described above, since the STC used in the conventional radar receiver controls the attenuator using a fixed attenuation pattern in the received pulse, it transmits and receives a wide range of signals while moving like a synthetic aperture radar. In the radar apparatus, the ideal attenuation pattern determined in advance does not match the pattern of the actual received waveform, so that saturation of the received signal in the radar receiver cannot be prevented.
Moreover, in order to memorize | store the waveform in a pulse and to carry out the averaging process for every pulse, a high-speed arithmetic unit is required and it was technically difficult.

  On the other hand, in Patent Document 1, after passing the output signal of the oscillator through the transmission system, the radio wave is radiated from the antenna via the circulator, and the reflected wave reflected from the target is received by the same antenna and received from the circulator. In a radar device that obtains a received signal through a system, an STC (Sensitivity Time Control) variable attenuator is inserted into the receiving system, and the maximum attenuation of this variable attenuator is received even when a maximum level signal is input to the receiving system. By making the value not to saturate and maximizing the attenuation of the variable attenuator during the transmission period to prevent saturation of the reception system due to leakage of the transmission signal, enabling reception immediately after transmission, A radar device is disclosed.

  However, in the technique described in Patent Document 1, it is difficult to control the AGC so as to prevent saturation of the received signal in the receiver in the case of a radar apparatus that transmits and receives a wide range of signals while moving.

  Further, in Patent Document 2, in a synthetic aperture radar device that is mounted on a flying body and acquires data while emitting a transmission radio wave that is linearly frequency-modulated in a direction oblique to the flight direction, the radio wave emitted toward the ground surface The receiving unit that receives the reflected wave is equipped with a received signal amplitude flattening unit that flattens the reflected wave affected by the degree of attitude variation of the flying object according to the content of the fluctuation, and requests the flying object attitude accuracy. A synthetic aperture radar device is disclosed that acquires high quality images without the need.

  However, in the technique described in Patent Document 2, it is difficult to control the AGC so as to prevent saturation of the received signal in the receiver in the case of a radar apparatus that transmits and receives a wide range of signals while moving.

  In Patent Document 3, the power monitor signal detected from the DC component of the received pulse signal output from the variable gain amplifier is input to the variable gain amplifier that increases or decreases the gain of the received pulse signal according to the input data. In the radar receiver automatic gain control circuit for supplying gain setting data for setting the reception pulse signal to an appropriate level, the A / D conversion circuit performs a plurality of timings on the power monitor signal during one reception pulse period. The level is sampled and converted into digital data, and the data obtained during the pulse period is sequentially added by an integrating circuit. The integration circuit sequentially adds the data obtained during the pulse period. The PROM circuit obtains the average power level of the power monitor signal from this added data and generates appropriate gain setting data corresponding to this level, so that the reception level can be set even when the level fluctuation within one reception pulse is severe. A radar receiver automatic gain control circuit that can be set appropriately is disclosed.

  However, in the technique described in Patent Document 3, it is difficult to control the AGC so as to prevent saturation of the received signal in the receiver in the case of a radar apparatus that transmits and receives a wide range of signals while moving.

  In Patent Document 4, a directional coupler that independently detects the reflection level of an aircraft, a sub-reception unit, a target level detection unit, and an STC attenuation amount corresponding to the reflection level for each target can be obtained adaptively. The target STC generator is combined with the conventional STC generator, and the output of these two STC generators is combined so that the target reflection level does not always exceed the saturation level of the receiving system. The STC control unit and the STC circuit for performing the STC processing can be used to apply appropriate STC attenuation only to a target that is saturated because the target reflection level is too high. In a search radar that uses pulse compression and removes clutter by STC by suppressing time side lobes without impairing To suppress the time side lobe caused by exceeding the saturation level of the machine, search radar apparatus is disclosed.

  However, in the technique described in Patent Document 4, it is difficult to control the AGC so as to prevent saturation of the received signal in the receiver in the case of a radar apparatus that transmits and receives a wide range of signals while moving.

JP 2001-174542 A Japanese Patent Laid-Open No. 03-130683 Japanese Patent Laid-Open No. 06-174826 Japanese Patent Application Laid-Open No. 09-068571

  Since the conventional STC controls the attenuator using a fixed attenuation pattern in the received pulse, a radar device that transmits and receives a wide range of signals while moving, like a synthetic aperture radar in which the target changes every moment, There is a problem that it is difficult to control the AGC so as to prevent saturation of the received signal in the receiver.

  The present invention has been made in view of such circumstances, and in the case of a radar device that transmits and receives a wide range of signals while moving, such as a synthetic aperture radar in which a target changes every moment, a received signal in a receiver. The purpose is to make it possible to control the AGC so as to prevent the saturation of the AGC.

To solve the above problems, this invention relates to a radar receiver of the synthetic aperture radar, the radar antenna transmits radio frequency pulses to the target, receiving a reflected pulse from the target, receiving waves of the radar antenna An input amplifier that amplifies the received amplifier, a mixer circuit that frequency-converts the output of the input amplifier and outputs a received pulse signal, a branching device that branches the received pulse signal output from the mixer circuit, and a branching device that branches A rectifier that monitors and detects one of the received pulse signals, an STC circuit that generates an STC pattern based on a DC component of the received pulse signal detected and detected by the rectifier, and the other branched by the branching device a variable attenuator for varying the attenuation in accordance with the STC attenuation control signal corresponding to the received pulse signal to the STC pattern generated by the STC circuit, the variable Together comprising an output amplifier for amplifying and outputting an output signal of 衰器, the STC circuit is sampled at a plurality of timings the DC component of the detected said detected received pulse signal in the received pulse at the rectifier An A / D conversion circuit for converting into digital data, a memory circuit for recording the A / D conversion result in the A / D conversion circuit, and a digital data recorded in the memory circuit for each received pulse An integration circuit that integrates the time constant of the signal, and an integration result in the integration circuit is averaged to generate the STC pattern for setting the received waveform to an appropriate gain that “does not cause saturation” to generate the STC attenuation control signal And an arithmetic circuit for sending to the variable attenuator .

  According to the radar receiver of the present invention, in a radar receiver such as a synthetic aperture radar, saturation of the received signal can be prevented and the dynamic range of the receiving system can be used effectively.

It is a figure which shows the structural example of the radar receiver of this invention. It is a figure explaining operation | movement of the radar receiver shown by FIG. It is a figure which shows the structural example of the STC circuit in the radar receiver of this invention. FIG. 4 is a diagram for explaining the operation of the STC circuit shown in FIG. 3. It is a figure which shows the structure of the conventional radar receiver.

Embodiment 1

  Hereinafter, the case of a synthetic aperture radar will be described as a first embodiment of the radar receiver of the present invention.

  FIG. 1 shows a configuration example of a radar receiver according to the present invention, which includes a radar antenna 1, an input amplifier 2, a mixer circuit 3, a branching device 4, a rectifier 5, an STC circuit 6, A configuration comprising a variable attenuator 7 and an output amplifier 8 is shown.

  The radar antenna 1 transmits a high-frequency pulse from an oscillator (not shown) to a target and receives a reflected pulse from the target. The received wave includes a signal RX SIG in which a transmission pulse is reflected on the ground other than the target and returned. The received wave is amplified by the input amplifier 2 and then frequency-converted by a local oscillation signal from a LO (Local Oscillator) (not shown) by the mixer circuit 3 and output. The mixer output is sent to the variable attenuator 7 via the branching device 4, but a part thereof is branched, rectified by the rectifier 5, and input to the STC circuit 6. The STC circuit 6 generates an STC ATT signal according to the input signal, and controls the attenuation of the variable attenuator 7 to generate an STC pattern from the received waveform. The output amplifier 8 amplifies and outputs the STC pattern.

FIG. 2 illustrates the operation of the radar receiver of the present invention. Hereinafter, a description will be given while comparing with the case of the prior art.
FIG. 2 (a) shows a case where the backscattering coefficient when the radar transmission wave is reflected by the target is uniform in the reception area. Here, the backscattering coefficient indicates the incident angle dependence due to the roughness of the surface when the transmitted wave is reflected by the target, and is a coefficient indicating the degree to which the transmitted wave is reflected by the target and returned. The backscattering coefficient varies depending on the incident angle of the transmission wave and the nature of the target (difference in artifacts, forests, water surface, cultivated land, etc.).
In the case of FIG. 2 (a), since the backscattering coefficient is uniform in the reception area, it is shown that a flat reception level can be obtained by normal STC correction as in the case of the prior art.

  In FIG. 2, (b) shows a case where the backscattering coefficient is not uniform in the reception area, and it is shown that fluctuations in the reception level cannot be corrected by normal STC correction.

  In FIG. 2, (c) explains the operation of the present invention. The STC circuit calculates the STC pattern in real time from the received waveform and reflects it in the received waveform. Therefore, regardless of the state of the observation area. It is shown that a flat reception level can be obtained by performing STC correction with high accuracy.

  In the case of the present invention, since the three-dimensional averaging is performed on the surface, a flat waveform reception level can be obtained. On the other hand, in the prior art, averaging is performed two-dimensionally, and correction is performed on the time axis of a fixed pattern. Therefore, if it deviates from this pattern, the reception level cannot be made flat.

  As described above, the present invention provides a countermeasure against fluctuations in detection information based on a change in a detection target in a radar apparatus, and as in the case of Patent Document 2, a mobile object (flying object) equipped with a radar apparatus. ) Does not take measures against fluctuations in detection information based on changes in attitude.

Furthermore, in the present invention, the received waveform is monitored, and the monitored signal is A / D converted at a plurality of points at regular intervals within the received pulse, recorded in the memory, and the data recorded in the memory is recorded for each received pulse. An average reception waveform is derived by integration for a predetermined time constant, and an STC pattern in the reception pulse is generated using this result, and the STC attenuator is controlled.
Hereinafter, it will be described in detail with reference to the drawings.

  FIG. 3 shows an example of the configuration of the STC circuit in the radar receiver of the present invention, and shows a configuration comprising an A / D conversion circuit 11, a memory circuit 12, an integration circuit 13, and an arithmetic circuit 14. Has been.

  In FIG. 3, an A / D conversion circuit 11 monitors and detects a received pulse signal, samples a detected direct current component at a plurality of timings within one received pulse, and converts it into digital data. The memory circuit 12 records the A / D conversion result in the A / D conversion circuit 11. The integration circuit 13 integrates the digital data recorded in the memory circuit 12 by a predetermined time constant for each sample. The arithmetic circuit 14 averages the integration results in the integration circuit 13 and generates appropriate gain setting data in the received pulse.

  FIG. 4 explains the operation of the STC circuit shown in FIG. 3. The arithmetic circuit shown in FIG. 3 obtains an average power level for each sample timing between received pulses from the integration data of the integration circuit. The figure shows a mode in which appropriate gain data for this averaged power level is set and sent as an STC ATT signal to a variable attenuator.

FIG. 4 (a) shows the power monitor signal for the nth received pulse signal, and the arrow indicates the sample timing of the A / D conversion.
FIG. 4B shows the power monitor signal for the (n + 1) th received pulse signal, and the arrows indicate the A / D conversion sample timing.

FIG. 4 (c) shows a power monitor signal for the (n + x) th received pulse signal, and the arrows indicate the A / D conversion sample timing.
FIG. 4 (d) shows an STC pattern obtained from the calculation result, which is a flat STC pattern that changes in accordance with the level of the power monitor signal with respect to the received pulse, corresponding to the level of the power monitor signal. Is shown to be obtained.

  As described above, in the present invention, the circuit size is reduced by performing the STC pattern generation in the STC circuit and the AGC setting calculation in the signal processing unit by the same arithmetic circuit, and the STC pattern in the STC circuit is reduced. The configuration differs from the case described in Patent Document 2 in which the generation of AGC and the calculation of the AGC setting in the signal processing unit are performed by different means.

Embodiment 2

Next, a second embodiment of the radar receiver of the present invention will be described.
In the second embodiment of the present invention, by setting the number of samples in the received pulse and the number of samples between pulses (time constant) to the optimum value of each radar receiver, not only the synthetic aperture radar, It can also be applied to other mobile radars.

  Specific examples of other mobile radars include real aperture radar. Synthetic aperture radar synthesizes the received waveform for each transmitted pulse and regards it as one pulse signal. However, in the case of actual aperture radar, the received waveform for each transmitted pulse is processed without being synthesized to obtain the average value. Then, an STC pattern is generated.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. Are also included in the present invention.

  The radar receiver of the present invention can be applied to a radar apparatus that acquires data whose reception level changes greatly during movement, such as a synthetic aperture radar.

DESCRIPTION OF SYMBOLS 1 Radar antenna 2 Input amplifier 3 Mixer circuit 4 Branch device 5 Rectifier 6 STC circuit 7 Variable attenuator 8 Output amplifier 11 A / D conversion circuit 12 Memory circuit 13 Integration circuit 14 Operation circuit

Claims (3)

A radar receiver of a synthetic aperture radar, which transmits a high-frequency pulse to a target and receives a reflected pulse from the target, an input amplifier that amplifies the received wave of the radar antenna , and A mixer circuit that converts the output frequency and outputs a reception pulse signal, a branching device that branches the reception pulse signal output from the mixer circuit, and monitor detection of one of the reception pulse signals branched by the branching device A rectifier that generates an STC pattern based on a DC component of the received pulse signal detected and detected by the rectifier, and the other received pulse signal branched by the branch is generated by the STC circuit. a variable attenuator for varying the attenuation amplifies the output signal of the variable attenuator and outputs in accordance with the STC attenuation control signal corresponding to the STC pattern Together comprising a power amplifier,
The STC circuit samples an DC component of the received pulse signal detected and detected by the rectifier at a plurality of timings in the received pulse and converts it into digital data, and the A / D conversion A memory circuit for recording an A / D conversion result in the circuit, an integration circuit for integrating digital data recorded in the memory circuit for a predetermined time constant for each received pulse, and averaging the integration results in the integration circuit And an arithmetic circuit that generates the STC pattern for setting the received waveform to an appropriate gain that does not cause saturation and sends the generated STC pattern as the STC attenuation control signal to the variable attenuator. Radar receiver. Wherein the received wave of the radar antenna, a radar receiver according to claim 1, wherein the transmit pulse is characterized in that it contains a signal that is reflected back to it on the ground other than the target of the radar antenna. Claim 1 or 2 radar receiver wherein said radar receiver is a radar receiver of the real aperture radar.

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