JPH0545194B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a range compression simulation device,
In particular, the present invention relates to a range compression simulation device for performing range compression simulation for evaluating the influence of errors related to chirp characteristics and amplitude/phase characteristics, which are basic signal characteristics in a synthetic aperture radar transmission/reception system, on a range compression waveform.

[Conventional technology]

A synthetic aperture radar that reproduces images of the ground based on data obtained by irradiating the ground to the side in the direction of travel with pulsed radio waves using a side-lucky radar mounted on a mobile platform such as an aircraft or an artificial satellite, and its images. Processing systems are becoming well known these days.

The data acquired by this synthetic aperture radar is two-dimensionally diffused data, and in order to obtain a desired image from it, range and azimuth compression are required to compress the acquired data in the distance and azimuth directions.

Azimuth compression is often performed following range compression. Azimuth information in the case of synthetic aperture radar is contained in the form of changes in Doppler frequency.

In general, range resolution in radar, including synthetic aperture radar, increases as the frequency bandwidth of the transmitted pulse becomes wider. Therefore, one way to obtain high resolution is to use short pulses of high power, but short pulses of high power have problems such as electrostatic damage within the transmitter. In synthetic aperture radar, instead of shortening the pulse width, it is lengthened to increase the average power, and this pulse is chirp modulated (linear FM).
modulation) to widen the frequency bandwidth. When reproducing an image from received data, compression is performed into sharp pulses by applying correlation processing through a dispersion delay line or matsito filter, whose frequency vs. delay time characteristics are opposite to the chirp modulation applied during transmission. The desired resolution can be obtained. This is the basis of range compression processing.

Equation (1) is a relational expression between range resolution δ _r and pulse width τ _p .

δ _r =C·τ _p /2=2.8/π·C/2Δ (1) In equation (1), Δ indicates the frequency bandwidth and C indicates the speed of light.

In a synthetic aperture radar that uses such a chirp modulated signal, the phase and amplitude characteristics in its transmission and reception system directly affect range compression performance.
This becomes clear when considering the influence of phase/amplitude characteristics on frequency versus delay time characteristics in chirp modulation. Further, the chirp modulation signal usually uses a SAW (Surface Acoustic Wave) device, and therefore, differences from the design value based on manufacturing errors of the device itself inevitably affect the range compression performance.

By the way, phase/amplitude characteristic errors are classified into low frequency components, high frequency components, and random components, and the degree of influence on the range compression pulse is also different.

FIG. 4 is a frequency vs. delay time characteristic diagram showing an example of the influence of phase characteristic error or amplitude characteristic error on range compression. FIG. 4 shows an example in which the frequency vs. delay time characteristic of a linear frequency modulated signal, originally shown as the basic characteristic a, changes due to a phase characteristic error or an amplitude characteristic error of the transmitting/receiving system. Note that FIG. 4 is for low frequency components. When the chirp modulation characteristics change in this way, the range compression waveform changes as shown in FIG.

FIG. 5 is a range compression waveform diagram of the data acquired by the transmission signal having the phase characteristic error or amplitude characteristic error of FIG. A pair of paired echoes P1 and P2 appear at temporally symmetrical positions, and the main lobe M spreads. The position T1 of the paired echo P2 is expressed by the following equation (2).

T ₁ = m・T/△ …(2) In equation (2), m is the frequency of the phase error component,
The smaller m is, the closer the paired echoes P1 and P2 are to the main rope M, which deteriorates the range compression processing accuracy.

The chirp characteristic error in the transmission/reception system mentioned above is mainly caused by the chirp modulation characteristic error in the transmitting system or the manufacturing error of the SAW device in the receiving system, and also depends on the temperature conditions.
Accompanied by changes over time. This chirp characteristic error is
This appears as a change in the pulse width of the main lobe M in FIG. Furthermore, phase characteristic errors and amplitude characteristic errors occur when the phase characteristics and amplitude characteristics across the transmitting/receiving system deviate from their expected values, and like the chirp characteristic error, they also depend on temperature conditions and are accompanied by changes over time.
Errors related to the phase characteristics and amplitude characteristics both appear in the form of the generation of paired echoes P1 and P2 with respect to the main lobe M shown in FIG. The degree can be easily determined based on the level etc.

Understanding the above-mentioned phase/amplitude characteristic errors of the entire transmitting and receiving system in a synthetic aperture radar is an essential element in ensuring the resolution that is increasingly required these days.

Conventionally, as a means to evaluate this type of phase/amplitude characteristic error, the receiving system is supplied with a replica or pseudo-received signal equivalent to the transmitted signal with consideration given to the level, and range-compressed data and design values (ideal values) are supplied to the receiving system.
The influence of phase/amplitude characteristic errors is determined through comparative evaluation.

[Problem that the invention seeks to solve]

However, the above-described conventional phase/amplitude characteristic error evaluation includes the following problems.

In other words, conventional evaluation methods are based on simulations that focus on confirming operation, and do not evaluate phase/amplitude characteristic errors that include these chirp characteristics when the transmitter/receiver system is included. Since each receiving system is evaluated individually, there is a drawback that errors with the actual one are unavoidable.

In addition, in conventional methods, most correlators are composed of SAW devices with characteristics opposite to those of the chirp modulator in the transmission system, and the entire evaluation system is centered around such an analog correlator. However, the analog system is grouped together, and therefore has the disadvantage that it is not possible to separate the errors contained in the correlator itself and evaluate only the transmitting and receiving system.

Furthermore, since the target to be evaluated is an analog compressed waveform, evaluation parameters such as the main lobe width, first side lobe width, dynamic range, compression ratio, etc. cannot be directly evaluated with high accuracy, and it is only possible to visually measure the compressed waveform. The disadvantage is that it is limited.

The purpose of the present invention is to eliminate the above-mentioned drawbacks, and to provide a digital evaluation system that incorporates a synthetic aperture radar image processing method for evaluating the influence of phase/amplitude errors in the transmitting and receiving system on range compression waveforms. An object of the present invention is to provide a range compression simulation device that can comprehensively grasp the influence of only the transmitting and receiving system, measure evaluation parameters based on digital evaluation processing, and eliminate the influence of temperature characteristics on these measurement data. .

[Means for solving problems]

The range compression simulation device of the present invention includes:
A range compression simulation device provided with a function equivalent to the range compression of the synthetic aperture radar in order to evaluate the influence of phase and amplitude characteristic errors of the transmitter/receiver, including the chirp modulation characteristics of the synthetic aperture radar transmission signal, on pulse compression performance. The transmitting signal generated by the transmitting device of the synthetic aperture radar is applied to a receiving device as a test signal set at a predetermined input level before or after high-output amplification, and the output of this receiving device is converted into a real part I video signal. and a test signal applying means for generating a Q video signal of the imaginary part, and the synthetic aperture radar that inputs the I video signal and the Q video signal and provides information regarding the temperature state, operation mode, etc. of the transmitting/receiving device. data converting means for adding a telemetry signal and outputting it as general-purpose magnetic tape data in digital format; The phase of the transmitting/receiving device is determined by simulating range compression through a matched filter with opposite frequency vs. delay time characteristics and temperature compensation corresponding to the telemetry signal, and comparing this result with a theoretical simulation value prepared in advance. and range compression evaluation means for evaluating the influence of amplitude characteristic errors on range compression.

〔Example〕

Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention.

The range compression simulation device shown in FIG. 1 includes a calibrator 1, a variable attenuator 2, a data converter 3, and a range compression evaluator 4, and also transmits and receives SAR (Synthetic Aperture Radar). A device 10 and a directional coupler 11 are also shown.

The calibrator 1 and the variable attenuator 2 form a test signal applying means, which generates and applies one of the test signals S1 and S2 to the receiving system 102 of the SAR transmitter/receiver 10.

Of these two test signals S1 and S2, test signal S1 is generated as follows. That is, the calibrator 1 receives the transmission signal from the transmission system 101 for high-output amplification, that is, the transmission signal before being subjected to final power amplification, adds a predetermined attenuation to this, and supplies it to the reception system 102 as a test signal S1. This test signal S1 is the transmission system 1
It is used for the calibration mode test of the entire transmitting and receiving system, which does not include only the final power circuit of 01.

On the other hand, the test signal S2 is received by supplying the transmission output after high output amplification of the transmission system 101 to the variable attenuator 2 via the directional coupler 11, giving a predetermined attenuation and receiving it at the same level as the test signal S1. Series 10
2. The amount of attenuation provided by the calibrator 1 is also variable like the amount of attenuation provided by the variable attenuator 2, and therefore the levels of the test signals S1 and S2 can be arbitrarily set to the same level.

The test signal S2 is used for an observation mode test of the entire transmitting and receiving system including both the transmitting system 101 and the receiving system 102. At this time, this device can be set in a mode that will not cause any problems during testing.

The above-mentioned calibration mode test using test signal S1 and observation mode test using test signal S2 are both carried out, but which evaluation data obtained from these evaluation tests is used depends on the purpose of use. This can be determined arbitrarily.

Now, from the transmitting system 101 to the receiving system 102
I video signals V1 and Q are output from the receiving system 102 by the test signal S1 or S2 applied to the
A video signal VQ is generated. Test signals S1, S2
Both of these are used by changing the level of the chirp modulation type transmission signal S(t) formed in the transmission system 101, and this transmission signal S(t) is expressed as follows (3).
It is shown by the formula.

S(t)=e ^j {〓 ^(t) } =cos {θ(t)} +jsin{θ(t)} =I(t)+jQ(t) ...(3) I video signal VI, Q video signal VQ are each
The real part and imaginary part I of S(t) shown in equation (3)
(t) and the output of the receiving system 102 corresponding to jQ(t). Therefore, such I,Q video signals
A correlator that correlates with VI and VQ and performs range compression has an inverse characteristic represented by S(t) in the following equation (4).

S(t)=e ^-j {〓 ^(t) } =I(t)−jQ(t) …(4) I, Q video signals based on test signals S1 and S2
VI and VE are then supplied to the data converter 3.

FIG. 2 is a block diagram showing details of the data converter shown in FIG. 1.

This data converter 3 forms data conversion means, and includes video amplifiers 31, 32, A/D
converters 33, 34, stretch circuit 35, format circuit 36, high density data recorder 3
7, a CCT (general purpose magnetic tape) converter 38, and the like.

The data converter 3 uses the I-video signal VI and the Q-video signal VQ in either the calibration mode or the observation mode output from the SAR transmitting/receiving device 10 by the test signal applying means using the calibrator 1 and the variable attenuator 2 described above. Compression evaluator 4
In order to enable the evaluation process to be described later, which is performed by
Along with converting to CCT level data rate,
The purpose is to add a telemetry signal transmitted from the synthetic aperture radar in a predetermined data format at the same data rate in parallel with this data rate conversion, and the processing details are as follows.

High data rate and high frequency I-video signal
VI and Q video signals VQ are amplified by video amplifiers 31 and 32, respectively, and then supplied to A/D converters 33 and 34.

A/D converters 33 and 34 each sample the input at a predetermined sampling frequency, quantize it into a predetermined number of bits, and supply this to a stretching circuit 35.

The I video signal V1 and the Q video signal VQ are used before or after high-output amplification of the transmission signal in the transmission system 101 of the SAR transceiver 10,
A predetermined transmit pulse width is provided for each transmit pulse repetition period. However, when the I, Q video signals VI, VQ are used to evaluate the range compression results, the pulse width is expanded as much as possible in order to reduce the data rate.

Since the actual received signal input to the receiving system 102 is also accompanied by pulse stretching, taking these conditions into account, the quantized data output from the A/D converters 33 and 34 is adjusted by the stretching circuit 35 within a range that does not exceed the transmission pulse period. It is output as data stretched to a predetermined length.

The output of stretch circuit 35 is then provided to format circuit 36. Format circuit 36
In addition to rearranging the data received from the stretch circuit 35 into a predetermined data format, in this case, in addition to the necessary synchronization code, data necessary for range compression processing is inserted based on the telemetry signal regarding the SAR transmitter/receiver 10.

The above-mentioned telemetry signal includes so-called H/K (House Keeping,
Among these H/K data D, the temperature data is particularly necessary for correcting the MATCHIT filter. these
The HK data is supplied to the format circuit 36 from a telemetry signal receiver or the like. The output of format circuit 36 is provided to high density data record 37.

The high-density data recorder 37 records high-density output at a high data rate corresponding to the repetition period of the transmission signal provided from the format circuit 36 by parallel writing, etc., and then reads this as serial data at a predetermined low-speed data rate. It is something to put out. This output is provided to a CCT converter 38.

The CCT converter 38 converts the format of the input data into a format recordable on a general-purpose magnetic tape, records it on tape, and supplies it to the range compression evaluator 4.

FIG. 3 is a block diagram showing in detail the range compression evaluator shown in FIG. 1.

The range compression evaluator 4 provides a range compression evaluation means, and evaluates the range compression result by comparing it with a predetermined theoretical simulation value.

The range compression evaluator 4 includes a data distribution circuit 41,
It is configured to include a match filter 42, a range compression circuit 43, an evaluation circuit 44, and the like.

The output data of the data converter 3 is supplied to the data distribution circuit 41, and the video signal data VD and H.K.
The data is divided into data D and distributed to the range compression circuit 43 and the matched filter 42, respectively.

The range compression circuit 43 includes an FFT circuit 431,
FFT circuit 432, multipliers 433, 434, IFFT
It is configured with a circuit 435 and the like, and performs the same range compression processing as the synthetic aperture radar.

The video signal data VD distributed and output from the data distribution circuit 41 is supplied to the FFT circuit 431,
FFT (Fast Fourier Transform) processing is performed to transform the time domain data into frequency domain data, and the data is supplied to a multiplier 434.

Further, the H/K data D distributed and output from the data distribution circuit 41 is used to determine the parameters of the matched filter 42.

The matched filter 42 has an inverse characteristic to the transmission signal expressed by the above-mentioned equation (3). It is configured as a correlator expressed by equation (4), so if the contents of the transmission signal to be range compressed are known, the parameters can be determined. H.K.
The data D provides the conditions for determining the content of this transmission signal, and at this time, the temperature information included in the H/K data D is
2, and sets the matched filter 42 under the same temperature influence as the SAR transmitter/receiver 10. The influence of the Matsushito filter 42 determined in this way is
Unlike when using a SAW device, this can be understood separately from the SAR transmitter/receiver 10. The configuration data of this matched filter 42 is supplied to an FFT circuit 432.

The FFT circuit 432 converts the input data into frequency domain data and supplies it to the multiplier 433.

The multiplier 433 uses a window function W that uses a Taylor function.
Window processing is performed by multiplying ( ) by the matched filter data output from the FFT circuit 432 at a predetermined window time, and the cut-out data is supplied to the multiplier 434 .

The multiplier 434 performs a correlation calculation by multiplying the input video signal data VD and the matched filter data in the frequency domain. This correlation operation is
This is a frequency domain multiplication of the data expressed by equation (3) and the data expressed by equation (4), whose frequency vs. time delay characteristics are inverse. It becomes data.

The output of multiplier 434 is then IFFT
(InverseFFT) circuit 435 and then subjected to inverse Fourier transform to be supplied again to evaluation circuit 44 as time domain data.

The evaluation circuit 44 compares the range compression data provided in this manner with the theoretical simulation value to obtain an evaluation value for each evaluation parameter, including the difference between the ideal range compression waveform and the actual range compression waveform. can be understood.

The evaluation results of the simulation performed in this way are based on errors due to fluctuations in chirp characteristics,
Errors based on phase and amplitude characteristic fluctuations are separated and extracted, and as mentioned above, the main lobe characteristics shown in Figure 5, the presence or absence of paired echoes, and if present, the logical values and actual values of the distance to the main lobe, level, etc. It can be obtained by comparing

The difference from the theoretical simulation value mentioned above is
This is based on the phase and amplitude characteristic errors of the SAR transmitter/receiver 10, and can be grasped separately from the characteristic fluctuations of the MATCHIT filter 42. In addition,
The above-mentioned theoretical simulation values are secured in advance by a method such as obtaining them off-line using a general-purpose computer device.

In this way, by directly supplying the signal generated in the transmitting system 101 to the receiving system 102, it is possible to evaluate the influence of only the SAR transceiver 10 on range compression, and the entire evaluation system is
As with the image processing system, all the processing is done digitally, so it is possible to perform specific evaluation for each evaluation parameter, and it is also possible to eliminate the influence of temperature characteristics.

Furthermore, various examples of application of the above-mentioned evaluation data can be considered.
It is possible to know the effects of changes over time based on the initial operational values, and these evaluation data are also effective as materials for the next design.

Note that in this example, range compression evaluation of the hardware configuration was performed in consideration of operability as an evaluation system, but this could easily be performed by changing to software processing using a general-purpose computer. That is clear.

〔Effect of the invention〕

The range compression simulation device of the present invention includes:
When evaluating the influence of phase/amplitude characteristic errors in the transmitting/receiving system on the range compression waveform, a method of preparing a digital evaluation system that incorporates the image processing method of synthetic aperture radar and supplying the transmitting signal directly to the receiving system is proposed. By preparing for this, it is possible to comprehensively understand the influence of only the transmitter and receiver system, measure evaluation parameters, and eliminate the influence of temperature characteristics on these measurement data, and based on the evaluation data, evaluate changes over time in the transmitter and receiver system. This has the effect of making it possible to understand the effects and provide initial conditions for the next design.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention;
Figure 2 is a detailed block diagram of the data converter shown in Figure 1, Figure 3 is a detailed block diagram of the range compression evaluator shown in Figure 1, and Figure 4 is a phase characteristic error or amplitude characteristic error. FIG. 5 is a frequency vs. delay time characteristic diagram showing an example of the influence on range compression. FIG. 5 is a range compression waveform diagram due to the transmission signal having the phase characteristic error shown in FIG. 1...Calibrator, 2...Variable attenuator, 3...Data converter, 4...Range compression evaluator, 10...SAR
Transmitting/receiving device, 11... Directional coupler, 31, 32...
Video amplifier, 33, 34...A/D converter,
35...Stretch circuit, 36...Format circuit, 37...High density data recorder, 38...CCT
Converter, 41...Data distribution circuit, 42...Matsuchito filter, 43...Range compression circuit, 44...Evaluation circuit, 101...Transmission system, 102...Reception system, D...H・
K data, VI...I video signal, VQ...Q video signal, S1, S2...test signal, VD...video signal data, A...amplitude, T...time, P1, P2...paired echo, M...main lobe,...frequency, T...
Delay time, a...basic characteristics, h...phase error characteristics.

Claims (1)

[Scope of Claims] 1. A function equivalent to range compression of the synthetic aperture radar in order to evaluate the influence of phase and amplitude characteristic errors of the transmitter/receiver, including the chirp modulation characteristics of the transmitted signal of the synthetic aperture radar, on pulse compression performance. A range compression simulation device is provided with a range compression simulation device, which applies a transmitted signal generated by the transmitting device of the synthetic aperture radar to a receiving device as a test signal set at a predetermined level before or after high-output amplification, and calculates the output of the receiving device. A test signal applying means for generating an I video signal as a real part and a Q video signal as an imaginary part, inputting the I video signal and the Q video signal and providing information regarding the temperature state, operating mode, etc. of the transmitting/receiving device. data converting means for adding a telemetry signal of the synthetic aperture radar to which the synthetic aperture radar is applied and outputting the same as general-purpose magnetic tape data in a digital format; The range compression is simulated through a MATCHIT filter which has a frequency vs. delay time characteristic opposite to the chirp modulation characteristic of the signal and has been given temperature compensation corresponding to the telemetry signal, and the results are compared with theoretical simulation values prepared in advance. A range compression simulation device comprising: range compression evaluation means for evaluating the influence of phase and amplitude characteristic errors of the transmitting/receiving device on range compression.