JP7123670B2 - Radar system and signal processing method - Google Patents

Description

Embodiments of the present invention relate to radar systems and signal processing methods.

As an LPI (Low Probability of Intercept) radar that reduces detectability, there is a radar using coding (Non-Patent Document 1). This radar performs SS (Spectrum Spread) modulation within a pulse (Non-Patent Document 2), or performs encoding for each pulse and performs range compression using a reference signal.

In recent years, the performance of receivers that receive radar waves has improved, and the reception band has become wider. Therefore, it is expected that sufficient LPI properties cannot be ensured by simply performing SS modulation within a pulse or between pulses. Therefore, a technique for improving the LPI property is desired.

Yoshida, "Revised Radar Technology", The Institute of Electronics, Information and Communication Engineers, 1996, pp. 278-280 Marubayashi, Nakagawa, Kono, "Spread spectrum communication and its application", Institute of Electronics, Information and Communication Engineers, 1998, pp. 1-18 Merrill I. Skolnik, "Introduction to radar systems," McGRAW-HILL Inc., 1980, pp.428-430 Nishimura, "Communication system design by digital signal processing", CQ Publishing, 2006, pp. 222-226 Yoshida, "Revised Radar Technology", The Institute of Electronics, Information and Communication Engineers, 1996, pp. 87-89

A problem to be solved by the present invention is to provide a radar system and a signal processing method capable of improving LPI properties.

A radar system according to an embodiment includes a transmitter, a first combiner, a reference signal corrector, a correlation calculator, a second combiner, and a range extractor. The transmitter selects one of a plurality of carrier frequencies for each pulse of a first pulse train with a constant pulse interval and a second pulse train with a different pulse interval, and selects one of a plurality of carrier frequencies. A transmission signal obtained by synthesizing a first pulse train using a frequency and a second pulse train using a selected carrier frequency is transmitted from an antenna. A first combiner corrects and combines signals for each pulse of a first pulse train included in a received signal received by an antenna based on a frequency difference between carrier frequencies selected for the first pulse train. do. The reference signal correcting section corrects the second pulse train using the Doppler frequency obtained from the result of synthesis by the first synthesizing section to generate a reference signal. The correlation calculator calculates the correlation between the signal of the second pulse train included in the received signal and the reference signal for each carrier frequency selected for the second pulse train. The second combiner combines the correlations for each carrier frequency calculated by the first correlation calculator. The range extraction unit uses the correlation synthesized by the second synthesis unit to extract the range of the object that reflected the transmission signal.

FIG. 2 is a block diagram showing a configuration example of a transmission device according to the first embodiment; FIG. FIG. 4 is a diagram showing an example of a transmission pulse included in a modulated signal transmitted by a transmission device; 2 is a block diagram showing a configuration example of a receiving device according to the first embodiment; FIG. FIG. 4 is a diagram showing a processing example of acquiring a Doppler frequency used for Doppler correction; FIG. 7 is a diagram showing a processing example of acquiring a target range from a range extraction pulse train; FIG. 4 is a schematic diagram showing synthesis processing performed by a coherent integrator; FIG. 2 is a block diagram showing a configuration example of a transmission device according to a second embodiment; FIG. FIG. 5 is a schematic diagram showing frequency conversion by a frequency converter according to the second embodiment; FIG. 5 is a schematic diagram showing processing performed in a transmission device according to the second embodiment; FIG. 11 is a block diagram showing a configuration example of a receiving device according to the third embodiment; The block diagram which shows the structural example of the radar system in 4th Embodiment.

A radar system and a signal processing method according to embodiments will be described below with reference to the drawings. In the following embodiments, it is assumed that components denoted by the same reference numerals perform similar operations, and duplicate descriptions are omitted as appropriate.

[First embodiment]
A radar system according to a first embodiment comprises a transmitter and a receiver. The transmitting device and the receiving device may be configured as one device. Moreover, each of the transmitting device and the receiving device may be configured as a plurality of devices.

FIG. 1 is a block diagram showing a configuration example of a transmission device according to the first embodiment. The transmitter (transmitter) includes a reference signal generator 1a, a code generator 5, a modulator 6, a pulse controller 7, a frequency converter 8, a high power amplifier 9 and an antenna 10. FIG. The transmitter transmits a transmission signal used for target detection. The reference signal generator 1 a generates a transmission pulse and supplies the generated transmission pulse to the modulator 6 . The code generator 5 supplies a code sequence for each pulse contained in the transmission pulse to the modulator 6 . The modulator 6 modulates each pulse included in the transmission pulse with a code sequence according to the instruction from the pulse control section 7 to generate a modulated signal. The pulse controller 7 controls the pulse width, pulse interval, and pulse amplitude of the transmission pulse generated by the reference signal generator 1a. Also, the pulse control unit 7 controls switching of the code sequence supplied by the code generator 5 .

The frequency converter 8 converts the frequency of the modulated signal generated by the modulator 6 to a high frequency with a carrier frequency according to the control of the pulse controller 7 and supplies the high frequency modulated signal to the high output amplifier 9. . The high-output amplifier 9 amplifies the high-frequency modulated signal and supplies the amplified modulated signal to the antenna 10 as a transmission signal. A transmission signal is sent out from an antenna 10 .

FIG. 2 is a diagram showing an example of a transmission pulse included in a transmission signal transmitted by a transmission device. The transmission pulse generated by the reference signal generator 1a is a combined pulse train obtained by synthesizing the pulse train P1 for Doppler extraction and the pulse train P2 for range extraction. In FIG. 2, the horizontal axis represents time on the fast-time axis, and the vertical axis represents pulse amplitude. The fast-time axis is a time axis defined by time intervals corresponding to sampling timings of an AD (Analog-Digital) converter provided in a receiving device, which will be described later. The reference signal generator 1a may supply the Doppler extraction pulse train P1 and the range extraction pulse train P2 to the modulator 6 without synthesizing them. The Doppler extraction pulse train P1 and the range extraction pulse train P2 may be synthesized after being modulated with a code sequence.

The pulse train P1 for Doppler extraction is a pulse train whose pulse intervals are equal on the time axis. The carrier frequencies assigned to the pulses included in the Doppler extraction pulse train P1 are randomly selected from a plurality of carrier frequencies under the control of the pulse control section 7 . In the example shown in FIG. 2, two carrier frequencies f1 and f2 are shown as carrier frequencies assigned to each pulse of the Doppler extraction pulse train P1. The pulse control unit 7 may select the carrier frequency to be assigned to each pulse from three or more predetermined carrier frequencies, and control the frequency converter 8 according to the selection.

Since the Doppler extraction pulse train P1 is used to extract the Doppler frequency when detecting a target, the pulse control unit 7 controls the code generator 5 so as to keep the code sequence for the Doppler extraction pulse train P1 constant. In the example shown in FIG. 2, the code sequence for the Doppler extraction pulse train P1 is "1". The modulator 6 modulates the Doppler extraction pulse train P 1 generated by the reference signal generator 1 a with the code sequence generated by the code generator 5 . A signal Sig1 representing the Doppler extraction pulse train P1 is represented by Equation (1).

式（１）において、Ａ（ｔｆ）は時間ｔｆにおける振幅を表す。ｔｆはｆａｓｔ－ｔｉｍｅ軸における時間を表す。ＭＯＤ１（ｔｆ）は各パルスに対する符号系列を表す。なお、ＭＯＤ１（ｔｆ）は、上述のように、一定である。ｆｎは、複数のキャリア周波数（ｆ１，ｆ２，…，ｆＮｆ）から選択されるキャリア周波数を表す。

In equation (1), A(tf) represents the amplitude at time tf. tf represents time on the fast-time axis. MOD1(tf) represents the code sequence for each pulse. MOD1(tf) is constant as described above. fn represents a carrier frequency selected from a plurality of carrier frequencies (f1, f2, . . . , fNf).

The range extraction pulse train P2 is a pulse train in which the pulse interval differs for each pulse on the time axis. The pulse control unit 7 controls the reference signal generator 1a so as to change the pulse interval in the range extraction pulse train P2 for each pulse. In the example shown in FIG. 2, the pulse amplitude and pulse width of the range extraction pulse train P2 are constant, but they may be different for each pulse. In this case, the pulse controller 7 controls the reference signal generator 1a so as to change the pulse amplitude and pulse width of the range extraction pulse train P2 for each pulse.

In the example shown in FIG. 2, two carrier frequencies f1 and f2 are shown as carrier frequencies assigned to each pulse of the range extraction pulse train P2. Similar to the carrier frequencies assigned to the Doppler extraction pulse train P1, the pulse controller 7 may randomly select the carrier frequencies assigned to the range extraction pulse train P2 from three or more carrier frequencies. In the example shown in FIG. 2, the code sequence for the range extraction pulse train P2 is randomly selected from "0" and "1". However, a random code such as an M sequence (Non-Patent Documents 3 and 4) may be used as the code sequence for the range extraction pulse train P2. The modulator 6 modulates the range extraction pulse train P2 generated by the reference signal generator 1a with the code sequence generated by the code generator 5. FIG. A signal Sig2 representing the range extraction pulse train P2 is represented by Equation (2).

式（２）において、Ａ（ｔｆ）は時間ｔｆにおける振幅を表す。ｔｆはｆａｓｔ－ｔｉｍｅ軸における時間を表す。ＭＯＤ２（ｔｆ）は各パルスに対する符号系列を表す。なお、ＭＯＤ２（ｔｆ）は、上述のように、パルスごとに選択される。ｆｎは、複数のキャリア周波数（ｆ１，ｆ２，…，ｆＮｆ）から選択されるキャリア周波数を表す。なお、レンジ抽出用パルス列Ｐ２の各パルスに割り当てられる複数のキャリア周波数と、ドップラ抽出用パルス列Ｐ１の各パルスに割り当てられる複数のキャリア周波数とは異なっていてもよい。

In equation (2), A(tf) represents the amplitude at time tf. tf represents time on the fast-time axis. MOD2(tf) represents the code sequence for each pulse. MOD2(tf) is selected for each pulse as described above. fn represents a carrier frequency selected from a plurality of carrier frequencies (f1, f2, . . . , fNf). The plurality of carrier frequencies assigned to each pulse of the range extraction pulse train P2 may be different from the plurality of carrier frequencies assigned to each pulse of the Doppler extraction pulse train P1.

A signal obtained by synthesizing the pulse train P1 for Doppler extraction and the pulse train P2 for range extraction is expressed by Equation (3) by addition for each carrier frequency.

式（３）において、ｔｆはｆａｓｔ－ｔｉｍｅ軸における時間を表す。ｆｎは、キャリア周波数（ｆ１，ｆ２，…，ｆＮｆ）を表す。

In equation (3), tf represents time on the fast-time axis. fn represents carrier frequencies (f1, f2, . . . , fNf).

The transmitting device modulates the pulse train P1 for Doppler extraction and the pulse train P2 for range extraction with a code sequence, converts them into high-frequency signals with a randomly selected carrier frequency, and then transmits a transmission signal obtained by synthesizing them. do. By performing these signal processings, the transmitting device makes the timing and carrier frequency at which pulses appear in the transmission signal irregular, like the composite pulse train shown in FIG. The use of such transmitted signals makes it difficult for devices used in Electronic Support Measures (ESM) to identify pulse specifications, including pulse width, pulse interval and pulse amplitude, and can reduce the likelihood of radar detection. By transmitting a signal obtained by synthesizing the Doppler extraction pulse train P1 and the range extraction pulse train P2, the transmission apparatus can improve the LPI property.

FIG. 3 is a block diagram showing a configuration example of a receiving device according to the first embodiment. A receiver receives at an antenna the high-frequency modulated signal transmitted by the transmitter and including the modulated signal reflected by the target or object. The receiver performs signal processing on the received signal, detects the Doppler frequency when the modulated signal is reflected by the target, and measures the distance (range) to the target. The receiving device includes an antenna 21, a low-noise amplifier 22, a frequency converter 23, a frequency filter 24, an AD converter 25, a Doppler pulse train extraction unit 26, an FFT (Fast Fourier Transform) unit 27, a coherent integration unit 28a (first synthesis unit), Doppler extraction unit 29, range pulse train extraction unit 30, reference signal correction unit 31, correlation calculation unit 32, coherent integration unit 33a (second synthesis unit), range extraction unit 34, and output unit 35.

A received signal received by the antenna 21 is amplified by the low noise amplifier 22 and supplied to the frequency converter 23 . The frequency converter 23 converts the signal supplied from the low noise amplifier 22 to baseband and supplies the baseband signal to the frequency filter 24 . The frequency filter 24 extracts a frequency band signal containing the frequency of the transmission pulse modulated by the code sequence from the baseband signal for each carrier frequency, and supplies the extracted frequency signal to the AD converter 25 . The AD converter 25 converts each frequency signal into a digital signal.

The signal component Sr(fn, tf) of the reflected wave of the transmission signal Sig(fn, tf), which is included in the received signal, is expressed by Equation (4) in consideration of mixing at the carrier frequency. be.

式（４）において、Ｓｉｇｔ（・）はＳｉｇ（ｆｎ，ｔｆ）に対して目標までの距離を含めた関数である。ｃ、Ｒは、光速、目標までの距離である。ｆｎ、ｔｆは、キャリア周波数、ｆａｓｔ－ｔｉｍｅ軸における時間である。

In Equation (4), Sigt(·) is a function including the distance to the target with respect to Sig(fn, tf). c and R are the speed of light and the distance to the target. fn and tf are the carrier frequency and time on the fast-time axis.

A high SN ratio (signal to noise ratio) is required to detect a small target, and a relatively long observation time is required for integration processing to obtain a high SN ratio. Doppler correction for the range extraction pulse train P2 is necessary in order to reduce the loss in the integration process for the range extraction pulse train P2.

FIG. 4 is a diagram illustrating an example of processing for acquiring Doppler frequencies used for Doppler correction. The processing shown in FIG. 4 is performed by the Doppler pulse train extraction unit 26, the FFT unit 27, the coherent integration unit 28a, and the Doppler extraction unit 29. FIG. The Doppler pulse train extraction unit 26 extracts a Doppler extraction pulse train P1 having a known pulse interval from the received pulse trains included in each digital signal output from the AD converter 25 . The Doppler pulse train extraction unit 26 extracts each pulse of the Doppler extraction pulse train P1 by dividing the digital signal by the PRI (Pulse Repetition Interval) of the Doppler extraction pulse train P1. Division of the digital signal is performed for each carrier frequency. A signal Sr1 of the Doppler extraction pulse train P1 to be extracted is represented by Equation (5).

式（５）において、ＤＩＶ［・］はドップラ抽出用パルス列Ｐ１の抽出処理を表す。ｔｓはｓｌｏｗ－ｔｉｍｅ軸の時間を表し、ｔｆはｆａｓｔ－ｔｉｍｅ軸の時間を表す。ｓｌｏｗ－ｔｉｍｅ軸は、ドップラ抽出用パルス列Ｐ１におけるパルス間隔（パルス周波数）に応じた時間間隔で定められる時間軸である。

In equation (5), DIV[·] represents the extraction processing of the pulse train P1 for Doppler extraction. ts represents time on the slow-time axis and tf represents time on the fast-time axis. The slow-time axis is a time axis defined by a time interval corresponding to the pulse interval (pulse frequency) in the Doppler extraction pulse train P1.

The FFT unit 27 performs slow-time axis FFT on the divided digital signal. In the period of the divided digital signal, the time at which the pulse of the pulse train P1 for Doppler extraction appears is almost constant. On the other hand, the times at which the pulses of the range extraction pulse train P2 appear are not constant. Therefore, the range extraction pulse train P2 included in the received pulse train is suppressed by FFT on the slow-time axis. The extraction results for the received pulse train in FIG. 4 are described without the range extraction pulse train P2 for the sake of simplicity.

The FFT unit 27 performs slow-time axis FFT on the fast-time axis range cells as shown in FIG. 4 in order to extract the Doppler frequency. The FFT result Sr1out is represented by Equation (6). The FFT unit 27 performs the calculation represented by Equation (6) for each carrier frequency (fn), and supplies the calculation result for each carrier frequency to the coherent integration unit 28a.

式（６）において、ＦＦＴ［・］はｓｌｏｗ－ｔｉｍｅ軸のＦＦＴ演算を表す。ωｓはｆａｓｔ－ｔｉｍｅ軸のレンジセルごとのドップラ周波数を表す。

In equation (6), FFT[·] represents the FFT operation on the slow-time axis. ωs represents the Doppler frequency for each range cell on the fast-time axis.

The coherent integrator 28a synthesizes the calculation result Sr1out obtained for each carrier frequency. Depending on the center frequency (wavelength) of the carrier frequency, the Doppler frequency fd differs as expressed in Equation (7). When integrating the calculation result on the range-Doppler axis, the coherent integrator 28a synthesizes after correcting the deviation of the Doppler frequency of each carrier frequency.

式（７）において、Ｖは目標との相対速度を表す。λは波長（ｃ／ｆｎ）を表す。

In equation (7), V represents the relative velocity with respect to the target. λ represents the wavelength (c/fn).

Since the Doppler frequency is inversely proportional to the wavelength and proportional to the frequency as shown in equation (7), the coherent integrator 28a corrects the data on the range-Doppler axis for each Doppler frequency. For example, the coherent integrator 28a corrects the data of the carrier frequency f1 so that the data of the other carrier frequencies are aligned.

In addition, the FFT result Sr1out(fn, ωs, tf) for each carrier frequency has an initial phase difference due to the distance to the unknown target and the carrier frequency. In order to reduce the loss in synthesis of the result Sr1out(fn, ωs, tf), it is necessary to correct the phase difference. Since the initial phase difference is unknown, the coherent integrator 28a applies a phase search method to estimate the phase difference. The coherent integrator 28a adds a phase difference to the result Sr1out(fn, ωs, tf) at predetermined steps from 0 to 360 degrees and synthesizes them, and searches for the phase difference that maximizes the synthesis result. When searching for the phase difference, the coherent integrator 28a may suppress small-amplitude noise by applying a search method to signals above a predetermined threshold.

The coherent integrator 28 a supplies the maximum value Sr1max(ωs, tf) of the synthesized results obtained by the search method to the Doppler extractor 29 . The maximum value Sr1max(ωs, tf) is represented by Equation (8). The maximum value Sr1max(.omega.s, tf) is a combined result obtained by aligning the phases of the results Sr1out(fn, .omega.s, tf) obtained for each carrier frequency.

式（８）において、ＳＲＣ［・］は位相探索法を表す。ｆｎは、キャリア周波数（ｆ１，ｆ２，…，ｆＮｆ）を表す。Φｐは、０から３６０度（２π）の所定ステップ間隔の位相（ｐ＝１，２，…，Ｐ）を表す。

In equation (8), SRC[·] represents the phase search method. fn represents carrier frequencies (f1, f2, . . . , fNf). Φp represents a phase (p=1, 2, . . . , P) at a predetermined step interval from 0 to 360 degrees (2π).

When the transmitting device uses Nf carrier frequencies to transmit a transmission pulse, the coherent integrator 28a combines the number of combinations of phases (P×(Nf−1)) given to each carrier frequency, and obtains the combination result. is searched for the maximum value Sr1max(ωs, tf). Alternatively, the coherent integrator 28a selects two from a plurality of carrier frequencies, searches for the phase that maximizes the synthesis result between the selected two carrier frequencies using equation (8), and selects the result. Iterative application of Equation (8) to Sr1out(fn, ωs, tf) for non-existent carrier frequencies may be performed. With this technique, there is a possibility that the number of times of synthesis can be reduced compared to the case of synthesizing the number of combinations (P.times.(Nf-1)).

The Doppler extractor 29 detects a target by CFAR processing (Non-Patent Document 5) on the maximum value Sr1max(ωs, tf) supplied from the coherent integrator 28a, and detects the Doppler frequency fd (ωs=2π·fd) of the detected target. ). A target relative velocity vt is obtained from the extracted Doppler frequency fd and equation (9). The Doppler extraction unit 29 supplies the Doppler frequency fd and the target relative velocity vt to the reference signal correction unit 31 and the output unit 35 .

式（９）において、ｆｄはドップラ周波数であり、λは波長である。

In equation (9), fd is the Doppler frequency and λ is the wavelength.

The case where a plurality of carrier frequencies are used for the Doppler extraction pulse train P1 has been described. However, when the transmitting apparatus uses one carrier frequency for the Doppler extraction pulse train P1, correction of the Doppler frequency between carrier frequencies and combination including search for the initial phase difference are unnecessary.

Next, distance measurement based on the range extraction pulse train P2 in the receiving apparatus will be described. FIG. 5 is a diagram showing an example of processing for acquiring a target range from the range extraction pulse train P2. The processing shown in FIG. 5 is performed by the range pulse train extraction unit 30, the reference signal correction unit 31, the correlation calculation unit 32, the coherent integration unit 33a, and the range extraction unit . In the process of acquiring the target range from the range extraction pulse train P2, as shown in FIG. is extracted.

Since the code sequence used for modulation of the range extraction pulse train P2 differs for each pulse, correlation processing is performed using a reference signal corresponding to the transmitted range extraction pulse train P2. The range extraction pulse train extraction unit 30 extracts the range extraction pulse train P2 from the digital signal output from the AD converter 25 . In order to extract the range extraction pulse train P2, the range pulse train extraction unit 30 performs FFT on the digital signal corresponding to each carrier frequency on the fast-time axis. A frequency-domain signal Sr_fft(fn, ωf) obtained by FFT is represented by Equation (10). The range pulse train extraction unit 30 supplies the signal Sr_fft(fn, ωf) to the correlation calculation unit 32 .

式（１０）において、ＦＦＴ［・］はｆａｓｔ－ｔｉｍｅ軸のＦＦＴ演算を表す。Ｓｒ（ｆｎ，ｔｆ）は受信信号に含まれる送信信号Ｓｉｇ（ｆｎ，ｔｆ）の反射波の信号である。ｔｆは、ｆａｓｔ－ｔｉｍｅ軸における時間を表す。ωｆは、ｆａｓｔ－ｔｉｍｅ軸に対応する周波数を表す。ｆｎは、キャリア周波数（ｆ１，２，…，ｆＮｆ）を表す。

In equation (10), FFT[·] represents the FFT calculation of the fast-time axis. Sr(fn, tf) is a reflected wave signal of the transmission signal Sig(fn, tf) included in the reception signal. tf represents time on the fast-time axis. ωf represents the frequency corresponding to the fast-time axis. fn represents carrier frequencies (f1, 2, . . . , fNf).

The reference signal correction unit 31 generates a reference signal used for correlation processing based on the range extraction pulse train P2 used in the transmitting apparatus, the code sequence corresponding thereto, and the carrier frequency. Based on the target relative velocity vt obtained by the Doppler extraction unit 29, the reference signal correction unit 31 calculates the Doppler frequency for each carrier frequency (fn) assigned to each pulse of the range extraction pulse train P2. The reference signal correction unit 31 corrects the range extraction pulse train P2 transmitted from the transmission device at the calculated Doppler frequency. At this time, the reference signal correction unit 31 performs zero padding to match the data length of the signal Sr(fn, tf) and the signal length of the reference signal. A reference signal ref(fn, tf) is represented by Equation (11).

式（１１）において、［・，・］はデータの連結を表す。ｚｅｒｏ（・）は与えられたパラメータで示される数（Ｎａｌｌ－Ｎ）のゼロ埋めを表す。Ｎａｌｌは信号Ｓｒ（ｆｎ，ｔｆ）のデータ長を表し、Ｎはレンジ抽出用パルス列Ｐ２に基づくデータ長を表す。ｔｆは、ｆａｓｔ－ｔｉｍｅ軸における時間を表す。ｆｄは、相対速度ｖｔから算出されるキャリア周波数（ｆｎ）のドップラ周波数を表す。Ａ（ｔｆ）は、時間ｔｆにおける振幅を表す。ＭＯＤ２（ｆｎ，ｔｆ）は、変調されたレンジ抽出用パルス列Ｐ２を表す。ｆｎは、キャリア周波数（ｆ１，ｆ２，…，ｆＮｆ）を表す。

In Expression (11), [·,·] represents data concatenation. zero(.) represents zero padding of the number (Nall-N) indicated by the given parameter. Nall represents the data length of the signal Sr(fn, tf), and N represents the data length based on the range extraction pulse train P2. tf represents time on the fast-time axis. fd represents the Doppler frequency of the carrier frequency (fn) calculated from the relative velocity vt. A(tf) represents the amplitude at time tf. MOD2(fn, tf) represents the modulated range extraction pulse train P2. fn represents carrier frequencies (f1, f2, . . . , fNf).

式（１２）において、ＦＦＴ［・］はｆａｓｔ－ｔｉｍｅ軸のＦＦＴ演算を表す。ωｆは、ｆａｓｔ－ｔｉｍｅ軸に対応する周波数を表す。 The reference signal correction unit 31 performs FFT on the reference signal ref(fn, tf) to calculate a signal Ref(fn, ωf) in the frequency domain. The reference signal corrector 31 supplies the signal Ref(fn, ωf) represented by Equation (12) to the correlation calculator 32 .

In equation (12), FFT[·] represents the FFT calculation of the fast-time axis. ωf represents the frequency corresponding to the fast-time axis.

The correlation calculator 32 calculates the signal Sr_fft(fn, ωf) (equation (10)) supplied from the range pulse train extractor 30 and the signal Ref(fn, ωf) (equation (10)) supplied from the reference signal corrector 31 . 12) Perform a correlation calculation for ). The correlation calculator 32 calculates the correlation output Sr2(fn, tf) for each carrier frequency by the calculation shown in Equation (13).

式（１３）において、ＩＦＦＴ［・］はｆａｓｔ－ｔｉｍｅ軸のＩＦＦＴ（Inverse Fast Fourier Transform）演算を表す。＊（アスタリスク）は共役演算を表す。

In Equation (13), IFFT[·] represents an IFFT (Inverse Fast Fourier Transform) operation on the fast-time axis. * (asterisk) represents a conjugate operation.

The correlation calculator 32 obtains the correlation output Sr2(fn, tf) on the range (fast-time) axis for each carrier frequency using equation (13). The correlation calculator 32 supplies the correlation output Sr2(fn, tf) for each carrier frequency to the coherent integrator 33a.

In order to coherently combine the correlation outputs Sr2(fn, tf) for each carrier frequency, it is necessary to correct the initial phase. Since the initial phase difference is unknown, the coherent integrator 33a applies a phase search method to estimate the initial phase difference. The coherent integrator 33a adds a phase difference to the correlation output Sr2(fn, tf) at predetermined steps from 0 to 360 degrees and synthesizes them, and searches for the phase difference that maximizes the synthesis result. The coherent integrator 33a supplies the maximum value Sr2max(tf) of the synthesized results obtained by the phase search method to the range extractor . The maximum value Sr2max(tf) is represented by Equation (14).

式（１４）において、ＳＲＣ［・］は、位相探索法を表す。ｆｎは、キャリア周波数（ｆ１，ｆ２，…，ｆＮｆ）を表す。Φｐは、０から３６０度の所定ステップ間隔の位相（ｐ＝１，２，…，Ｐ）を表す。

In Equation (14), SRC[·] represents the phase search method. fn represents carrier frequencies (f1, f2, . . . , fNf). Φp represents a phase (p=1, 2, . . . , P) at a predetermined step interval from 0 to 360 degrees.

FIG. 6 is a schematic diagram showing synthesis processing performed by the coherent integrator 33a. The coherent integrator 33a sequentially performs Doppler frequency correction, initial phase correction, and coherent integration on data on the range-Doppler axis obtained for each carrier frequency (f1, f2, . . . , fNf). The coherent integrator 33a synthesizes data on the range-Doppler axis by these processes. The synthesizing process shown in FIG. 6 shows a case where correction is performed by matching the Doppler frequency of the carrier frequency f1 with the Doppler frequency of another carrier frequency.

As in the case where the coherent integrator 28a searches for the maximum value Sr1max(ωs, tf) of the synthesized result, the coherent integrator 33a selects two from a plurality of carrier frequencies and synthesizes between the two selected carrier frequencies. Searching for the phase that maximizes the result using equation (14), and applying equation (14) to the result and Sr2(fn, tf) of unselected carrier frequencies may be repeated. .

The range extraction unit 34 extracts a target range by performing CFAR processing or the like on the maximum value Sr2max(tf) obtained by synthesizing the correlation outputs Sr2(fn, tf) of each carrier frequency. The range extraction unit 34 supplies the target range to the output unit 35 . The output unit 35 outputs target information obtained by combining the target Doppler frequency fd and relative velocity vt extracted by the Doppler extractor 29 and the target range extracted by the range extractor.

By extracting the Doppler frequency using the pulse train P1 for Doppler extraction and ranging based on the pulse train P2 for range extraction as described above, the receiving apparatus can detect the reflected wave of the transmitted signal whose LPI property is enhanced in the transmitting apparatus. It can observe target range and relative velocity. A radar system that combines the transmitter and receiver in the first embodiment can observe the target range and relative velocity while improving the LPI property.

[Second embodiment]
In the first embodiment, in the transmission device, a method in which the frequency converter 8 switches the carrier frequency assigned to each pulse of the pulse train P1 for Doppler extraction and the pulse train P2 for range extraction according to the control of the pulse control unit 7 is described. explained. In the second embodiment, a method will be described in which the carrier frequency assigned to each pulse is changed randomly while the frequency of signals to be mixed in the frequency conversion to a high frequency in the frequency converter 8 is kept constant.

FIG. 7 is a block diagram showing a configuration example of a transmission device according to the second embodiment. The transmission device includes a wideband signal generator 1, an FFT section 2, a frequency selection section 3, an IFFT section 4, a code generator 5, a modulator 6, a pulse control section 7, a frequency converter 8, a high output amplifier 9 and an antenna 10. Prepare. The transmission apparatus according to the second embodiment includes a broadband signal generator 1, an FFT section 2, a frequency selection section 3, and an IFFT section 4 in place of the reference signal generator 1a. different from

In the frequency converter 8 of the second embodiment, the high-frequency signal to be mixed in the frequency conversion is one wave of frequency F, and the carrier frequencies (f1, f2, , fNf). FIG. 8 is a schematic diagram showing frequency conversion by the frequency converter 8 in the second embodiment. FIG. 8 shows carrier frequencies (f1, f2) assigned to pulses. In the second embodiment, the carrier frequencies (f1, f2) to be selected are obtained in the transmission band by mixing the modulated signals of the pulse train P1 for Doppler extraction and the pulse train P2 for range extraction and the high frequency signal of frequency F. , a modulated signal is generated having power at a frequency corresponding to the carrier frequency. The frequency F of the high frequency signal is determined based on multiple carrier frequencies assigned to each pulse. For example, the center frequency of the transmission band is set to the frequency F of the high frequency signal.

FIG. 9 is a schematic diagram showing processing performed in the transmission device according to the second embodiment. The wideband signal generator 1 generates a wideband signal and supplies the generated wideband signal to the FFT section 2 . As shown in FIG. 9, the wideband signal has the same band as the transmission band W of the high frequency transmission signal and has a predetermined amplitude in this band. The FFT unit 2 performs FFT on the wideband signal. The FFT performed on the wideband signal is performed on the fast-time axis corresponding to the sampling timing of the AD converter 25 provided in the receiver. The frequency domain signal obtained by the FFT is supplied to the frequency selection unit 3 .

The frequency selector 3 divides the supplied frequency domain signal into bands corresponding to carrier frequencies. As shown in FIG. 9, this signal division provides Nf divided bands corresponding to Nf carrier frequencies (f1, f2, . . . , fNf). The frequency selector 3 selects a signal of a divided band corresponding to the carrier frequency assigned by the pulse controller 7 to the pulses of the pulse train P1 for Doppler extraction and the pulses of the pulse train P2 for range extraction. The frequency selection unit 3 synthesizes the selected sub-band signals and supplies them to the IFFT unit 4 . The IFFT unit 4 performs IFFT on the fast-time axis for the combined sub-band signals. The IFFT unit 4 supplies the time domain signal obtained by the IFFT to the modulator 6 . Although FIG. 9 shows an example of processing for selecting sub-bands corresponding to two carrier frequencies, a number of sub-bands corresponding to the number of carrier frequencies assigned to pulses may be selected.

The code generator 5 generates code sequences for the pulses of the Doppler extraction pulse train P1 and the pulses of the range extraction pulse train P2 under the control of the pulse control unit 7, and supplies the generated code sequences to the modulator 6. . The modulator 6 modulates the signal (pulse) supplied from the IFFT unit 4 with the code sequence generated by the code generator 5 to generate a modulated signal, and supplies the modulated signal to the frequency converter 8 . The frequency converter 8 converts the modulated signal into a high frequency signal with a high frequency signal having a frequency F determined according to the transmission band, and supplies the high frequency modulated signal to the high output amplifier 9 . The high-output amplifier 9 amplifies the high-frequency modulated signal and transmits the amplified modulated signal from the antenna 10 as a transmission signal.

A receiver included in the radar system in the second embodiment has the same configuration as the receiver in the first embodiment, and operates in the same manner.

In the transmission device of the second embodiment, since one high-frequency signal is mixed to obtain a high-frequency modulated signal in the frequency converter 8, a signal selected from a plurality of high-frequency signals is used to obtain a desired carrier. As compared with the case of obtaining the frequency, variations occurring in the carrier frequency for each pulse can be suppressed, and the accuracy of the carrier frequency can be improved. In addition, since the transmission device can reduce the number of high-frequency signals that require maintenance of accuracy, maintainability is also improved. A radar system including a transmitter and a receiver according to the second embodiment can accurately estimate the Doppler frequency in the receiver by suppressing variations in the carrier frequency of the transmission signal and improving the accuracy of the carrier frequency. The radar system can reduce loss in coherent integration with respect to the range extraction pulse train P2 by improving the accuracy of estimating the Doppler frequency, and can improve the observation accuracy of the range and relative velocity of the target.

[Third embodiment]
In the first embodiment, the transmitter randomly switches the carrier frequencies (f1, f2, . . . , fNf) assigned to the Doppler extraction pulse train P1 and the range extraction pulse train P2 for each pulse. Then, the receiving apparatus not only corrects the Doppler frequency difference caused by the carrier frequency difference, but also corrects the initial phase difference between the carrier frequencies caused according to the distance from the target. The processing required for correcting the initial phase difference in the receiving device is complicated and may take time. Therefore, in the third embodiment, a configuration for shortening the processing time in the receiving device will be described.

FIG. 10 is a block diagram showing a configuration example of a receiver according to the third embodiment. The receiving device includes an antenna 21, a low-noise amplifier 22, a frequency converter 23, a frequency filter 24, an AD converter 25, a Doppler pulse train extractor 26, an FFT section 27, an amplitude integrator 28b (first synthesizer), a Doppler It comprises an extractor 29 , a range pulse train extractor 30 , a reference signal corrector 31 , a correlation calculator 32 , an amplitude integrator 33 b (second synthesizer), a range extractor 34 and an output unit 35 . The receiving apparatus according to the third embodiment differs from the receiving apparatus according to the first embodiment in that it includes an amplitude integrator 28b and an amplitude integrator 33b instead of the coherent integrator 28a and the coherent integrator 33a. In the receiver according to the third embodiment, the amplitude integrator 28b amplitude-integrates the calculation result Sr1out(fn, ωs, tf) obtained by the equation (6) to acquire the synthesized result, and the amplitude integrator 33b acquires the result of the equation ( 13) Amplitude integration is performed on the correlation output Sr2(fn, tf) obtained in 13) to obtain a synthesis result.

Also in the receiving apparatus according to the third embodiment, when combining the calculation result Sr1out(fn, ωs, tf) and the correlation output Sr2(fn, tf), it is necessary to correct the Doppler frequency difference occurring between the carrier frequencies. . However, since only the amplitude is integrated in the amplitude integration, it is not necessary to correct the phase difference between carrier frequencies with respect to the initial phase that occurs according to the distance to the target. That is, the phase search method is not required for correcting the phase difference between carrier frequencies, and the signal processing in the receiver is simplified. In the receiver according to the third embodiment, the calculation result Sr1out(fn, .omega.s, tf) and the correlation output Sr2(fn, tf) are combined by a simple calculation, so that the processing time can be shortened. Note that the amplitude integration causes not a little loss due to the phase difference, so the receiving apparatus of the third embodiment may be used when the gain of the radar system has a margin. For example, when the signal-to-noise ratio between the Doppler extraction pulse train P1 and the range extraction pulse train P2 in the received signal is equal to or greater than a certain value, the receiver of the third embodiment may be used.

The receiver shown in FIG. 10 has a configuration in which amplitude integration is used for both synthesis of operation results Sr1out(fn, ωs, tf) and synthesis of correlation outputs Sr2(fn, tf). However, amplitude integration may be used for either combination of the calculation result Sr1out(fn, ωs, tf) or combination of the correlation output Sr2(fn, tf). For example, the receiver acquires the Doppler frequency by synthesizing the calculation result Sr1out(fn, ωs, tf) by amplitude integration, and acquires the target range by synthesizing the correlation output Sr2(fn, tf) by coherent integration. may Using a combination of amplitude and coherent integration simplifies receiver processing while maintaining target range accuracy.

A transmitter included in the radar system according to the third embodiment has the same configuration as any of the transmitters according to the first and second embodiments, and operates in the same manner. For example, if the transmitting device in the third embodiment is the same as the transmitting device in the second embodiment, the processing in the receiving device can be simplified while suppressing variations occurring in the carrier frequency and improving the estimation accuracy of the Doppler frequency. can do.

[Fourth embodiment]
FIG. 11 is a block diagram showing a configuration example of a radar system according to the fourth embodiment. A radar system according to the fourth embodiment includes a transmitter, a receiver, and an unwanted wave detector. The radar system according to the fourth embodiment differs from the radar systems according to the first, second and third embodiments in the configuration including the unwanted wave detector. In the radar system according to the fourth embodiment, the unwanted wave detection device determines whether or not the received signal includes unwanted waves that affect target detection of the radar system. The transmitting device and the receiving device switch operations according to the determination result by the unwanted wave detection device.

An unwanted wave detection device according to the fourth embodiment includes an antenna 41 , a low noise amplifier 42 , a frequency converter 43 , an AD converter 44 and an unwanted wave detector 45 . A received signal received by an antenna 41 is amplified by a low noise amplifier 42 and supplied to a frequency converter 43 . The frequency converter 23 converts the signal supplied from the low noise amplifier 22 to baseband and supplies the baseband signal to the AD converter 25 . The AD converter 25 converts the baseband signal into a digital signal. The unwanted wave detector 45 determines whether or not the digital signal has an amplitude greater than a predetermined threshold.

If the digital signal has an amplitude greater than the threshold, the unwanted wave detector 45 determines that there is an unwanted wave. If the digital signal does not have an amplitude greater than the threshold, the unwanted wave detector 45 determines that there is no unwanted wave. The unwanted wave detector 45 outputs the determination result to the transmitter and the receiver. The unwanted wave detector 45 may determine the presence or absence of unwanted waves for each predetermined band within a predetermined frequency range. In this case, the unwanted wave detector may use a different threshold for each band.

The transmission device in the fourth embodiment includes a wideband signal generator 1, an FFT section 2, a frequency selection section 3c, an IFFT section 4, a code generator 5, a modulator 6, a pulse control section 7, a frequency converter 8, a high output An amplifier 9 and an antenna 10 are provided. The transmission apparatus according to the fourth embodiment differs from the transmission apparatus according to the second embodiment in that it has a frequency selection section 3 c instead of the frequency selection section 3 .

The frequency selection unit 3c assigns one carrier frequency to each of the pulse train P1 for Doppler extraction and the pulse train P2 for range extraction, or selects from a plurality of carrier frequencies according to the determination result output from the unwanted wave detection device. Toggle between When it is determined that there is no unwanted wave, the frequency selector 3c allocates one carrier frequency to the pulse train P1 for Doppler extraction and the pulse train P2 for range extraction. When it is determined that there is an unwanted wave, the frequency selector 3c randomly selects a carrier frequency to be assigned to each pulse from a plurality of carrier frequencies, as in the first and second embodiments.

The receiver in the fourth embodiment includes an antenna 21, a low noise amplifier 22, a frequency converter 23, a frequency filter 24c, an AD converter 25, a Doppler pulse train extraction section 26, an FFT section 27, an integration section 28c (first synthesizer), a Doppler extractor 29, a range pulse train extractor 30, a reference signal corrector 31, a correlation calculator 32, an integrator 33c (second synthesizer), a range extractor 34, and an output unit 35. The receiver in the fourth embodiment has a configuration including a frequency filter 24c, an integrator 28c and an integrator 33c instead of the frequency filter 24, the coherent integrator 28a and the coherent integrator 33a. It differs from the receiver in form.

The frequency filter 24c, the integrator 28c, and the integrator 33c switch their operations according to the determination result output from the unwanted wave detection device. When it is determined that there is no unwanted wave, the frequency filter 24c extracts a signal of a frequency band corresponding to one carrier frequency selected by the frequency selection unit 3c, and supplies the extracted frequency signal to the AD converter 25. . When it is determined that there is an unwanted wave, the frequency filter 24c extracts signals in frequency bands corresponding to a plurality of carrier frequencies assigned to each pulse, and supplies the extracted frequency signals to the AD converter 25. .

When it is determined that there is no unwanted wave, only one carrier frequency is assigned to the pulse train P1 for Doppler extraction, so correction of the Doppler frequency difference caused by the frequency difference between a plurality of carrier frequencies becomes unnecessary. In this case, the integrator 28c coherently integrates the result Sr1out(fn, ωs, tf) by omitting the processing of the Doppler frequency correction and the initial phase difference search. The integrator 28 c supplies the synthesis result obtained by coherent integration to the Doppler extractor 29 . Alternatively, when it is determined that there is no unwanted wave, the integrating section 28c may synthesize the result Sr1out(fn, ωs, tf) using amplitude integration instead of coherent integration.

When it is determined that there is an unwanted wave, the integrating section 28c performs the same operation as the coherent integrating section 28a. That is, the integrator 28c performs processing of Doppler frequency correction and initial phase difference search, and supplies the combined result to the Doppler extractor 29 .

Further, when it is determined that there is no unwanted wave, only one carrier frequency is assigned to the pulse train P2 for range extraction, which eliminates the need to search for an initial phase difference between a plurality of carrier frequencies. In this case, the integrator 33c coherently integrates the correlation output Sr2(fn, tf) supplied from the correlation calculator 32 without searching for the initial phase difference. The integrator 33c supplies the synthesis result obtained by coherent integration to the range extractor 34 . Alternatively, if it is determined that there is no unwanted wave, the integrator 33c may synthesize the correlation output Sr2(fn, tf) using amplitude integration instead of coherent integration.

When it is determined that there is an unwanted wave, the integrating section 33c performs the same operation as the coherent integrating section 33a. That is, the integrator 33c supplies the maximum value Sr2max(tf) of the synthesized results obtained by the phase search method to the range extractor .

In the radar system of the fourth embodiment, when it is determined that there is no unwanted wave, the transmitter assigns one carrier frequency to each pulse. Loss at the time of integration (synthesis) due to this is reduced. In this way, by switching the operations of the transmitter and the receiver according to the presence or absence of unwanted waves, it is possible to reduce the processing load on the receiver and the loss during integration more than the LPI property when there is no unwanted wave. Preferentially, ranging and velocity measurements can be performed while ensuring high gain in target detection. The radar system can observe the range and relative velocity of the target while improving the LPI property by randomly selecting the carrier frequency assigned to each pulse when unwanted waves are present.

The operation of setting the carrier frequency to one wave when there is an unwanted wave has been described. However, the operations of the transmitter and the receiver when there are unnecessary waves and the operations of the transmitter and the receiver when there are no unnecessary waves may be exchanged. By setting the carrier frequency to a single wave in the presence of unwanted waves, the radar system reduces loss during integration (synthesis) and prioritizes robust target detection against unwanted waves over LPI characteristics. be possible.

FIG. 11 shows a configuration example in which the radar system includes the unwanted wave detection device and the reception device as different devices. However, the unwanted wave detection device and the reception device may be configured as one device. In this case, the frequency converter 23 may supply the baseband signal to the AD converter 44, and the antenna, low noise amplifier and frequency converter may be shared for observation of the range and relative velocity of the target and detection of unwanted waves. good.

In the fourth embodiment, a configuration example in which a radar system includes a transmission device modified from the transmission device in the second embodiment has been described. However, the radar system may be provided with a transmitter that is similar to the transmitter in the first embodiment. In addition, a configuration example in which the radar system includes a receiver that is modified from the receiver in the first embodiment has been shown. However, a radar system may include the receiver in the second embodiment.

According to at least one embodiment described above, the carrier frequency is selected for each pulse of the Doppler extraction pulse train P1 (first pulse train) and the range extraction pulse train P2 (second pulse train). By having a transmitting device (transmitting section) that transmits a transmission signal obtained by synthesizing the pulse train P1 for Doppler extraction using the carrier frequency and the pulse train P2 for range extraction using the selected carrier frequency, the pulse interval in the transmission signal is reduced. It becomes non-uniform and the frequency of transmitting the pulses is spread out, which can improve the LPI property.

The transmitting device, receiving device, and unwanted wave detecting device in the above embodiments include a CPU (Central Processing Unit), a memory, an auxiliary storage device, etc., which are connected by a bus. Signal processing may be performed. The CPU executes a program stored in the auxiliary storage device to perform part or all of the operation of the transmitter, part or all of the receiver, and part or all of the unwanted wave detection device. and may be performed. In addition, all or part of the operations of the transmitter, receiver, and unwanted wave detector are performed using hardware such as ASIC (Application Specific Integrated Circuit), PLD (Programmable Logic Device), and FPGA (Field Programmable Gate Array). may be implemented. The program may be recorded on a computer-readable recording medium. Computer-readable recording media are portable media such as flexible disks, magneto-optical disks, ROMs and CD-ROMs, and non-temporary storage media such as hard disks built into computer systems. The program may be transmitted over telecommunications lines.

While several embodiments of the invention have been described, these embodiments have been presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, as well as the scope of the invention described in the claims and equivalents thereof.

Reference Signs List 1 broadband signal generator 1a reference signal generator 2 FFT section 3, 3c frequency selection section 4 IFFT section 5 code generator 6 modulator 7 pulse control section 8 Frequency converter 9 High output amplifier 10, 21 Antenna 22 Low noise amplifier 23 Frequency converter 24 Frequency filter 25 AD converter 26 Doppler pulse train extractor 27 FFT section 28a Coherent integrator 28b Amplitude integrator 28c Integrator 29 Doppler extractor 30 Range pulse train extractor 31 Reference signal corrector 32 Correlation calculator 33a Coherent Integration part 33b... Amplitude integration part 33c... Integration part 34... Range extraction part 35... Output part 41... Antenna 42... Low noise amplifier 43... Frequency converter 44... AD converter 45... Unnecessary Wave detector

Claims (8)

One of a plurality of carrier frequencies is selected for each pulse of a first pulse train with a constant pulse interval and a second pulse train with a different pulse interval, and the selected carrier frequency is used. a transmitter that transmits from an antenna a transmission signal obtained by combining the first pulse train and the second pulse train using a selected carrier frequency;
a first synthesis for correcting and synthesizing a signal for each pulse of the first pulse train included in a received signal received by an antenna based on a frequency difference between carrier frequencies selected for the first pulse train; Department and
a reference signal correction unit that corrects the second pulse train to generate a reference signal using the Doppler frequency obtained from the synthesis result of the first synthesis unit;
a correlation calculator that calculates the correlation between the signal of the second pulse train included in the received signal and the reference signal for each carrier frequency selected for the second pulse train;
a second synthesizer that synthesizes the correlation for each carrier frequency calculated by the correlation calculator;
a range extraction unit that extracts a range of an object that reflected the transmission signal using the correlation synthesized by the second synthesis unit;
radar system with The transmitting unit frequency-converts the first pulse train and the second pulse train to carrier frequencies selected for each, using one high-frequency signal determined based on the plurality of carrier frequencies.
A radar system according to claim 1 . The first synthesis unit corrects the phase difference between the carrier frequencies selected for each pulse of the first pulse train, and then coherently integrates and synthesizes the signal for each pulse of the first pulse train.
A radar system according to claim 1 or claim 2. The first synthesizing unit integrates and synthesizes the signal for each pulse of the first pulse train,
A radar system according to claim 1 or claim 2. The second synthesizing unit corrects the phase difference between the carrier frequencies selected for each pulse of the second pulse train, and then coherently integrates and synthesizes the correlation for each carrier frequency calculated by the correlation calculating unit. do,
Radar system according to any one of claims 1 to 4. The second synthesizing unit performs amplitude integration and synthesizes the correlation for each carrier frequency calculated by the correlation calculating unit.
Radar system according to any one of claims 1 to 4. further comprising an unnecessary wave detection unit for determining the presence or absence of unnecessary waves,
The transmitter selects one of the plurality of carrier frequencies for each pulse of the first pulse train and the second pulse train when it is determined that there is an unwanted wave, if so, selecting one carrier frequency for each pulse in the first pulse train and the second pulse train, respectively;
Radar system according to any one of claims 1 to 6. the computer
One of a plurality of carrier frequencies is selected for each pulse of a first pulse train with a constant pulse interval and a second pulse train with a different pulse interval, and the selected carrier frequency is used. a transmission step of transmitting from an antenna a transmission signal obtained by combining the first pulse train and the second pulse train using a selected carrier frequency;
a first synthesis for correcting and synthesizing a signal for each pulse of the first pulse train included in a received signal received by an antenna based on a frequency difference between carrier frequencies selected for the first pulse train; a step;
a reference signal correction step of correcting the second pulse train to generate a reference signal using the Doppler frequency obtained from the synthesis result of the first synthesis step;
a correlation calculation step of calculating the correlation between the signal of the second pulse train included in the received signal and the reference signal for each carrier frequency selected for the second pulse train;
a second synthesizing step of synthesizing the correlation for each carrier frequency calculated by the correlation calculating step;
a range extraction step of extracting a range of an object that reflected the transmission signal using the correlation synthesized by the second synthesis step;
A signal processing method that performs

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