JP7143146B2 - Radar system and its radar signal processing method - Google Patents

Description

This embodiment relates to a radar system and its radar signal processing method.

A conventional radar system uses an array antenna comprising a plurality of sub-arrays and a composite antenna comprising main channel and auxiliary channel antennas. However, in an environment where clutter and unwanted interference waves exist in a wide band, if there is a difference in frequency characteristics between subarrays or between the main channel and the auxiliary channel, the unwanted waves such as clutter and interference waves cannot be sufficiently suppressed. there was a case.

MSN method, SMI method, Kikuma, 'Adaptive signal processing by array antenna', Science and Technology Publishing, pp.67-86 (2004) Sidelobe Canceller, Kikuma, 'Adaptive Signal Processing by Array Antenna', Science and Technology Publishing, pp.17-21 (2004) STAP, Richard Klemm, 'Applications of Space-Time Adaptive Processing', IEE Radar, Sonar and Navigation series 14, p.375-395 (2004) CFAR (Constant False Alarm Rate), Yoshida, 'Revised Radar Technology', The Institute of Electronics, Information and Communication Engineers, pp.87-89 (1996)

As described above, in a conventional radar system, in an environment where unwanted waves such as clutter and interference waves exist in a wide band, if there is a difference in frequency characteristics between sub-arrays or between the main channel and the auxiliary channel, the unwanted waves can be sufficiently removed. There were times when it was impossible to suppress.
This embodiment has been devised in view of the above problems, and aims to provide a radar system and a radar signal processing method thereof that can sufficiently suppress unwanted waves even in an environment where unwanted waves exist in a wide band. .

In order to solve the above problems, the radar system according to the present embodiment divides the antenna aperture of the array antenna into M (M≧1) subarrays, and each subarray converts the reflected signal of the radar wave into the Received under an environment in which unwanted waves exist in a wide band including a band, the signals received by the M subarrays are converted to the frequency axis, and the M subarray received signals converted to the frequency axis are L (L≧1) frequency division, unwanted wave suppression processing is performed using the outputs of the M sub-arrays for each division unit on the frequency axis, and the suppression processing is performed on the L frequencies. It synthesizes signals, converts the synthesized frequency signal to the time axis, and outputs it.

In addition, the radar system according to the present embodiment uses the antenna of the main channel and the antennas of M (M≧1) auxiliary channels to transmit reflected signals of radar waves in an environment in which unwanted waves are present in a wide band including the band of the radar waves. signals received by the respective antennas of the main channel and the auxiliary channel are respectively transformed into the frequency axis, and the received signals of the main channel and the auxiliary channel transformed into the frequency axis are respectively L (L≧1 ) frequencies, and for each division unit on the frequency axis, unwanted waves are suppressed by side lobe cancellation processing using the outputs of the main channel and the auxiliary channel, and L frequencies subjected to the suppression processing are obtained. A frequency signal is synthesized, and the synthesized frequency signal is converted into a time axis and output.

Further, the radar system according to the present embodiment transmits radar waves of N (N≧1) hit pulses, divides the antenna aperture of an array antenna into M (M≧1) subarrays, and transmits the radar wave in each subarray. A wave reflected signal is received in an environment where unnecessary waves exist in a wide band including the band of the radar wave, and the signals received by the M sub-arrays are each converted into a frequency axis, and converted into the frequency axis. Each of the M sub-array received signals is divided into L (L≧1) frequencies, and for each division unit of the frequency axis, the output of the M sub-arrays is used to divide the space-time (slow-time) axis. Unwanted waves are suppressed by STAP (Space Time Adaptive Processing) processing, L frequency signals subjected to the suppression processing are synthesized, and the synthesized frequency signals are converted to the time axis and output.

Further, the radar system according to the present embodiment transmits radar waves of N (N≧1) hit pulses, and radar wave reflected signals from the main channel antenna and M (M≧1) auxiliary channel antennas is received in an environment where unnecessary waves exist in a wide band including the band of the radar wave, the signals received by the antennas of the main channel and the auxiliary channel are respectively converted to the frequency axis, and converted to the frequency axis Each of the received signals of the main channel and the auxiliary channel is divided into L (L≧1) frequencies, and for each division unit of the frequency axis, side lobe cancellation and STAP ( Space Time Adaptive Processing) processing to suppress unnecessary waves, synthesize L frequency signals subjected to the suppression processing, convert the synthesized frequency signals to the time axis, and output them.

1 is a block diagram showing the configuration of a receiver of a radar system according to a first embodiment; FIG. FIG. 2 is a conceptual diagram showing a subarray configuration used for a receiving antenna in the first embodiment; FIG. 4 is a timing chart showing each step of unwanted wave suppression processing in the first embodiment; 1 is a block diagram showing the configuration of an unwanted wave suppressor using subarrays in the first embodiment; FIG. The block diagram which shows the structure of the receiver of the radar system which concerns on 2nd Embodiment. The block diagram which shows the structure of the unwanted wave suppressor in the case of SLC in 2nd Embodiment. The block diagram which shows the structure of the radar system which concerns on 3rd Embodiment. FIG. 11 is a block diagram showing the configuration of an unwanted wave suppressor using transmission/reception sub-arrays in the third embodiment; FIG. 12 is a timing diagram showing N hit pulses output by the transmitter in the third embodiment; The block diagram which shows the structure of the radar system which concerns on 4th Embodiment. FIG. 11 is a block diagram showing the configuration of an unwanted wave suppressor in the case of transmission/reception SLC in the fourth embodiment;

Hereinafter, embodiments will be described with reference to the drawings. A radar system usually includes a transmitting device and a receiving device, and is configured with an antenna for both transmission and reception. Here, it is assumed that the transmitting device is arranged separately from the receiving device. Further, in the following description, a description of a transmitting device that constitutes a radar system will be omitted if there is no characteristic part according to the embodiment. Also, in each embodiment, the same parts are denoted by the same reference numerals, and overlapping descriptions are omitted.

(First embodiment)
A radar system according to a first embodiment will be described with reference to FIGS. 1 to 4. FIG.
FIG. 1 is a block diagram showing the configuration of a receiver for a radar system according to this embodiment. In FIG. 1, 11 to 1M are subarrays obtained by dividing the receiving aperture of the receiving antenna by the array antenna into M systems as shown in FIG. receive waves. The signals received by the subarrays 11 to 1M are frequency-converted to baseband by frequency converters 21 to 2M, respectively, converted to digital signals by AD converters 31 to 3M, and FFT (Fast Fourier Transform) 41 on the fast-time axis. 4M to the frequency axis, and divided into L frequency bands by frequency dividers 51 to 5M, and then sent to the unwanted wave suppressor 6 together.

The unwanted wave suppressor 6 calculates an adaptive weight for each frequency division unit, and performs adaptation in each division system. The results after adaptation are synthesized by a frequency synthesizer 7, converted into a signal on the time axis by an IFFT (inverse fast Fourier transform) 8 on the fast-time axis, and detected by a target detector 9 such as CFAR (Non-Patent Document 4). A target is detected by processing, converted into a predetermined format by an output processor 10, and output.

In the above configuration, unwanted wave suppression processing according to this embodiment will be described with reference to FIGS. 3 and 4. FIG.
First, the received signals of the subarrays 11 to 1M are frequency-converted to baseband and converted to digital signals. Here, as shown in FIG. 3(a), it is assumed that an unwanted wave with a higher level than the target component arrives in the fast-time axis (high rate)-amplitude axis.

The received digital signals of the M systems are each transformed into the frequency axis by the fast-time axis FFT (Fast Fourier Transform) as shown in the following equation, and as shown in FIG. get

次に、図３（ｃ）に示すように周波数帯域をＬ分割する。

Next, the frequency band is divided into L as shown in FIG. 3(c).

次に、図３（ｄ）に示すように、周波数分割単位毎に不要波の抑圧処理を行う。この場合、（２）式で得られた周波数軸の信号を用いて相関処理によりアダプティブウェイト（複素ウェイトＷ_１～Ｗ_Ｍ）を算出する。通常は、時間軸の信号を用いてアダプテーションを行うが、本実施形態では周波数軸のまま行うことに特徴がある。サブアレイを用いた不要波抑圧器６の構成を図４に示す。図４において、６１はＭ系統のサブアレイ受信信号からアダプティブウェイトを算出するウェイト演算器、６２１～６２ＭはそれぞれＭ系統のサブアレイ受信信号に複素ウェイトＷ_１～Ｗ_Ｍを乗算する乗算器、６３は乗算器６２１～６２Ｍの出力を加算処理によって合成する加算器である。

Next, as shown in FIG. 3D, unnecessary wave suppression processing is performed for each frequency division unit. In this case, adaptive weights (complex weights W ₁ to W _M ) are calculated by correlation processing using the frequency-axis signal obtained by equation (2). Normally, adaptation is performed using signals on the time axis, but this embodiment is characterized in that adaptation is performed on the frequency axis as it is. FIG. 4 shows the configuration of the unwanted wave suppressor 6 using subarrays. In FIG. 4, 61 is a weight calculator for calculating adaptive weights from M-system subarray received signals, 621 to 62M are multipliers for multiplying M-system subarray received signals by complex weights W ₁ to W _M , respectively, and 63 is a multiplier. This is an adder that combines the outputs of the units 621 to 62M by addition processing.

Receivers (parts of frequency converter 2i (i=1 to M), AD converter 3i, FFT 4i, and frequency divider 5i in FIG. 1) are converted into digital signals by R1 to RM and divided into L frequency bands. The subarray signal is input to the weight calculator 61 . The weight calculator 61 calculates weights by correlation processing together with unwanted wave suppression outputs, and calculates complex weights W ₁ to W _M of the signals of the respective subarrays 11 to 1M.

For example, when using the steepest descent method by MSN (maximum SNR method), the adaptive weight is given by the following formula (Non-Patent Document 1).

ここで、ステアリングベクトルは、アンテナ配列が１次元の場合は、次式となる。

Here, the steering vector is given by the following formula when the antenna array is one-dimensional.

本実施形態の定式化では、簡単のために１次元配列アンテナの場合としているが、２次元配列のアンテナの場合にも容易に拡張することができる。
（３）式は、反復演算によりアダプティブウェイトを算出する手法であり、ウェイトが最適化されるまでに過渡応答が生じる。これを防ぐためには、ＳＭＩ（Sampled Matrix Inversion； 非特許文献１）の手法がある。また、ＳＭＩでは干渉波の短時間の時間変化に対応できない場合には、例えばＳＭＩで算出したウェイトを（３）式の初期ウェイトＷ(０,ｍ)として、（３）式によるウェイト演算する手法がある。他にも、周波数軸の一部のデータを用いて、（３）式の反復演算により算出したウェイトを初期ウェイトとし、再度、全周波数軸のウェイトを用いて（３）式の演算を行う手法等がある。これらにより、ウェイトの過渡特性による周波数軸分割単位毎の接続部の抑圧性能の劣化を防ぐことができる。

In the formulation of this embodiment, the case of a one-dimensional array antenna is used for simplicity, but it can be easily extended to the case of a two-dimensional array antenna.
Equation (3) is a method of calculating adaptive weights by iterative calculation, and a transient response occurs until the weights are optimized. In order to prevent this, there is a method of SMI (Sampled Matrix Inversion; Non-Patent Document 1). If the SMI cannot cope with short time changes in the interference wave, for example, the weight calculated by the SMI is used as the initial weight W(0,m) of the equation (3), and weight calculation is performed using the equation (3). There is In addition, a weight calculated by iterative calculation of formula (3) using part of the data on the frequency axis is used as the initial weight, and the weight on the entire frequency axis is used again to perform the calculation of formula (3). etc. As a result, it is possible to prevent the deterioration of the suppression performance of the connection part for each frequency axis division unit due to the transient characteristics of the weight.

When the results after the above adaptation are frequency synthesized, the following equation is obtained (see FIG. 3(e)).

続いて、逆フーリエ変換により、時間軸に戻すと次式となる（図３（ｆ）参照）。

Then, by inverse Fourier transform, the following equation is obtained by returning to the time axis (see FIG. 3(f)).

この時間軸の信号は、干渉信号を含まない。このため、ＣＦＡＲ（非特許文献４）等の検出処理（図３（ｇ）参照）を行うことにより、目標を検出することができる。
以上のように、第１の実施形態では、アレイアンテナにおいて、アンテナ開口をＭ（Ｍ≧１）個のサブアレイに分割し、各々のサブアレイ信号をＦＦＴ（高速フーリエ変換）して周波数軸に変換して、周波数軸をＬ（Ｌ≧１）個に分割し、各々の周波数軸分割単位毎に、Ｍ個のサブアレイを用いて不要波抑圧処理をして、周波数帯を合成した後、ＩＦＦＴ（逆高速フーリエ変換）により時間軸に変換して不要波を抑圧する。これにより、広帯域信号を周波数分割して、各周波数分割単位でサブアレイによる不要波の抑圧処理を実行するので、抑圧性能を向上させることができる。

The signal on this time axis does not contain the interfering signal. Therefore, the target can be detected by performing detection processing (see FIG. 3G) such as CFAR (Non-Patent Document 4).
As described above, in the first embodiment, in the array antenna, the antenna aperture is divided into M (M≧1) subarrays, and each subarray signal is FFT (Fast Fourier Transformed) and transformed into the frequency axis. Then, the frequency axis is divided into L (L≧1) pieces, and for each frequency axis division unit, unwanted wave suppression processing is performed using M subarrays, the frequency band is synthesized, and then IFFT (inverse (Fast Fourier transform) to convert to the time axis and suppress unnecessary waves. As a result, the wideband signal is frequency-divided, and unwanted wave suppression processing is performed by subarrays in units of each frequency division, so suppression performance can be improved.

(Second embodiment)
In the first embodiment, a technique for suppressing unnecessary waves by using a sub-array type adaptive array has been described. In this embodiment, a technique for suppressing unwanted waves of SLC (sidelobe canceller) (Non-Patent Document 2) type will be described.
FIG. 5 is a block diagram showing the configuration of a receiver according to the second embodiment. Signals received by the main antenna 1a and the auxiliary antenna 1b are frequency-converted by frequency converters 2a and 2b, respectively, and converted into digital signals by AD converters 3a and 3b. The flow of processing for suppressing unwanted waves using this digital signal is the same as in FIG. The digital signal is transformed into the frequency domain by fast-time axis FFT (Fast Fourier Transform) 4a and 4b. Next, the frequency band is divided into L frequency bands by dividers 5a and 5b, and unnecessary waves are suppressed by an unnecessary wave suppressor 6A based on SLC for each frequency division unit. Thereafter, as in the first embodiment, the results of each band subjected to unwanted wave suppression processing by the frequency synthesizer 7 are synthesized, and converted into a signal on the time axis by an IFFT (Inverse Fast Fourier Transform) 8 on the fast-time axis. be. Using this signal, the target detector 9 detects the target by detection processing such as CFAR (Non-Patent Document 4), and the output processor 10 converts it into a predetermined format and outputs it.

Since the above flow is the same as that of the first embodiment, the formulation of the common part is omitted, and the formulation of the SLC will be described below.
FIG. 6 shows the configuration of the unwanted wave suppressor 6A for SLC. In FIG. 6, each signal of the main channel (antenna) 1a and the auxiliary channels (antennas) 1b1 to 1bM are converted into digital signals by receivers (frequency converter, AD converter, FFT, frequency divider) Ra, Rb1 to RbM. After being converted and divided into the L frequency bands, it is input to the weight calculator 65 via the subtractor 64 . In the weight calculator 65, weights are calculated by correlation processing together with unwanted wave suppression outputs. Multipliers 661 to 66M weight complex weights _W.sub.1 to _W.sub.M of the signals of each subarray and add all the calculation results. It is added by the unit 67 and sent to the subtractor 64 . The subtractor 64 subtracts the weight calculation result obtained by the adder 67 from the signal of the main channel, thereby suppressing and outputting unnecessary waves.

Here, in the above weight calculation, for example, when the steepest descent method is used, the adaptive weight is given by the following formula (Non-Patent Document 2).

ＳＬＣの場合は、主ｃｈを形成するために、第１の実施形態と同様にステアリングベクトルを用いる。補助ｃｈについても、ビーム形成する場合には、補助ｃｈ用のステアリングベクトルを用いる。
第１の実施形態と同様に、（８）式は、反復演算によりアダプティブウェイトを算出する手法であり、ウェイトが最適化されるまでに過渡応答が生じる。これを防ぐためには、ＳＭＩ（Sampled Matrix Inversion；非特許文献１）の手法がある。また、ＳＭＩでは干渉波の短時間の時間変化に対応できない場合には、例えばＳＭＩで算出したウェイトを（８）式の初期ウェイトＷ(0，m，l)として、（８）式によるウェイト演算する手法がある。他にも、周波数軸の一部のデータを用いて、（８）式の反復演算により算出したウェイトを初期ウェイトとして、再度、全周波数軸のウェイトを用いて（８）式の演算を行う手法等がある。これらにより、ウェイトの過渡特性による周波数軸分割単位毎の接続部の抑圧性能の劣化を防ぐことができる。

In the case of SLC, a steering vector is used as in the first embodiment to form the primary channel. Also for the auxiliary channel, the steering vector for the auxiliary channel is used when forming the beam.
As in the first embodiment, Equation (8) is a method of calculating adaptive weights by iterative calculations, and a transient response occurs until the weights are optimized. In order to prevent this, there is a method of SMI (Sampled Matrix Inversion; Non-Patent Document 1). If the SMI cannot cope with the short time change of the interference wave, for example, the weight calculated by the SMI is used as the initial weight W(0, m, l) of the equation (8), and the weight calculation is performed by the equation (8). There is a method to Another method is to perform the calculation of the formula (8) again using the weights of the entire frequency axis, with the weights calculated by the iterative calculation of the formula (8) using partial data on the frequency axis as the initial weights. etc. As a result, it is possible to prevent the deterioration of the suppression performance of the connection part for each frequency axis division unit due to the transient characteristics of the weight.

The processing of the result after adaptation is the same as in formulas (6) and (7) of the first embodiment, and since the signal on the time axis does not include an interference signal, CFAR (Non-Patent Document 4), etc. The target can be detected by the detection process.
As described above, in the second embodiment, in an antenna having a main channel and M auxiliary channels, the main channel and auxiliary channel signals are FFT (Fast Fourier Transformed) and converted to the frequency axis, and the frequency axis is It is divided into L pieces, and for each frequency axis division unit, unnecessary wave suppression processing is performed using M (M≧1) auxiliary channels to synthesize the frequency band, and then IFFT (Inverse Fast Fourier Transform) ) to suppress unnecessary waves by converting to the time axis. That is, the wideband signal is frequency-divided, and unwanted wave suppression processing is performed by a side lobe canceller (SLC, see Non-Patent Document 1) using main channels and auxiliary channels in each frequency division unit. It can improve performance.

(Third embodiment)
In the first and second embodiments, the receiver has been described. In the case of radar equipment, not only clutter but also interference waves are received, so it is necessary to suppress clutter components and interference wave components. STAP (Space-Time Adaptive Processing, Non-Patent Document 3) is known as a method for suppressing such clutter components and interference wave components. A case of adopting this STAP method will be described as a third embodiment.

FIG. 7 is a block diagram showing the configuration of the radar system according to the third embodiment. The system of the transmission device includes a signal generator 111 that generates a transmission pulse signal, a modulator 112 that modulates the transmission pulse signal for pulse compression, a frequency converter 113 that converts the frequency of the transmission pulse signal to the RF band, and an RF band. It is composed of an amplifier 114 for power-amplifying a transmission pulse signal and a transmission antenna 115 for transmitting the power-amplified transmission pulse signal in a designated direction. The transmit antenna 115 is used, for example, as a full antenna aperture and transmits N hit pulses as shown in FIG. It should be noted that the transmitting antenna 115 and the subarrays 11 to 1M as receiving antennas may be shared to serve as antennas for both transmission and reception.

On the other hand, the receiver system divides the reception aperture into subarrays 11 to 1M in the same manner as in the first embodiment shown in FIG. Signals received in each subarray are frequency-converted by frequency converters 21 to 2M, converted into digital signals by AD converters 31 to 3M, and converted into digital signals by fast-time axis FFT (Fast Fourier Transform) 41 to 4M. After being converted and divided into L frequency bands by frequency dividers 51 to 5M, both are sent to unwanted wave suppressor 6B.

FIG. 8 shows the configuration of an unwanted wave suppressor 6B using the transmission/reception subarrays of this embodiment. The flow of unwanted wave suppression processing of this unwanted wave suppressor 6B is basically the same as that shown in FIG. The difference is that the signal on the -time axis (PRI axis) increases to Nch according to the number of transmission hit pulses. In this case, the weight dimension is M×Nch. That is, it is converted into a digital signal by the transmitter/receiver (transmitting device, frequency converter 2i (i=1 to M), AD converter 3i, FFT 4i, frequency divider 5i) TR1 to TRM and divided into L frequency bands. Each sub-array signal is input to the weight calculator 61, distributed to Nch channels, and sent to multipliers 6211 to 62MN. The weight calculator 61 calculates weights by correlation processing together with unwanted wave suppression outputs, and calculates complex weights W ₁₁ to W _MN of the signals of the respective subarrays 11 to 1M. These complex weights are sent to corresponding multipliers 6211 to 62MN and weighted. Adders 631 to 63N add the N-system weighting calculation outputs, and adder 63 adds all the results to output as unwanted wave suppression results. The output is also sent to the weight calculator 61 and used for the next weight calculation.

In the unwanted wave suppressor 6B configured as described above, each subarray signal and CPI signal (N-hit PRI signal) are converted into digital signals by the transceivers TR1 to TRM.

次に、周波数帯域をＬ分割し、fast-timeの周波数分割単位毎に不要波抑圧処理を実行する。

Next, the frequency band is divided into L, and unwanted wave suppression processing is executed for each fast-time frequency division unit.

この信号がウェイト演算器６１に入力される。ウェイト演算器６１では、不要波抑圧出力とともに、相関処理により、ウェイトが演算され、各サブアレイの信号の複素ウェイトＷ_１１～Ｗ_ＭＮが演算される。
例えば、ＭＳＮによる最急降下法を用いる場合は、アダプティブウェイトは次式となる（非特許文献１）。

This signal is input to the weight calculator 61 . The weight calculator 61 calculates weights by correlation processing together with unwanted wave suppression outputs, and calculates complex weights W ₁₁ to W _MN of the signals of each subarray.
For example, when using the steepest descent method by MSN, the adaptive weight is given by the following formula (Non-Patent Document 1).

ステアリングベクトルは、ＳＴＡＰ（Space Time Adaptive Processing;非特許文献３）の空間軸－時間軸（slow-time）におけるメインローブ形成用であり、空間軸が一次元アレイの場合は次式で与えられる。第１の実施形態、第２の実施形態が空間軸のみであるのに対して、本実施形態では空間－時間（slow-time）軸のＳＴＡＰ処理であり、ＰＲＩ（slow-time）軸が増えている点が異なる。

The steering vector is for mainlobe formation in the space axis-time axis (slow-time) of STAP (Space Time Adaptive Processing; Non-Patent Document 3), and is given by the following equation when the space axis is a one-dimensional array. While the first and second embodiments only use the spatial axis, the present embodiment uses STAP processing on the space-time (slow-time) axis, and the PRI (slow-time) axis is increased. The difference is that

なお、本実施形態の定式化では、簡単のために１次元配列アンテナの場合としているが、２次元配列のアンテナの場合にも容易に拡張することができる。
（１１）式は、反復演算によりアダプティブウェイトを算出する手法であり、ウェイトが最適化されるまでに過渡応答が生じる。これを防ぐためには、ＳＭＩ（Sampled Matrix Inversion；非特許文献１）の手法がある。また、ＳＭＩでは干渉波の短時間の時間変化に対応できない場合には、例えばＳＭＩで算出したウェイトを（１１）式の初期ウェイトＷ(0，m，l)として、（１１）式によるウェイト演算する手法がある。他にも、周波数軸の一部のデータを用いて、（１１）式の反復演算により算出したウェイトを初期ウェイトとして、再度、全周波数軸のウェイトを用いて（１１）式の演算を行う手法等がある。これらにより、ウェイトの過渡特性による周波数軸分割単位毎の接続部の抑圧性能の劣化を防ぐことができる。

In the formulation of this embodiment, the case of a one-dimensional array antenna is used for the sake of simplicity, but it can be easily extended to the case of a two-dimensional array antenna.
Equation (11) is a method of calculating adaptive weights by iterative calculation, and a transient response occurs until the weights are optimized. In order to prevent this, there is a method of SMI (Sampled Matrix Inversion; Non-Patent Document 1). If the SMI cannot cope with the short time change of the interference wave, for example, the weight calculated by the SMI is used as the initial weight W(0, m, l) in the equation (11), and the weight calculation is performed by the equation (11). There is a method to In addition, a method of performing the calculation of formula (11) again using the weights of the entire frequency axis, with the weights calculated by the iterative calculation of formula (11) using partial data on the frequency axis as the initial weights. etc. As a result, it is possible to prevent the deterioration of the suppression performance of the connection part for each frequency axis division unit due to the transient characteristics of the weight.

The processing of frequency synthesis of the results after adaptation is the same as in equations (6) and (7) of the first embodiment. ), etc., the target can be detected.
As described above, in the third embodiment, in an array antenna that transmits and receives N (N≧1) pulses, the antenna aperture is divided into M subarrays, and each subarray signal is subjected to FFT on the fast-time axis. Converting to the frequency axis, dividing the frequency axis into L pieces, and suppressing unnecessary waves using CPI (Coherent Pulse Interval) signals of M (M≧1) subarrays for each frequency axis division unit to synthesize the frequency bands, and then convert to the time axis by IFFT (Inverse Fast Fourier Transform) to suppress unwanted waves. In other words, the suppression performance can be improved by frequency-dividing a wideband signal and performing STAP processing (see Non-Patent Document 3) by a subarray for each division unit.

(Fourth embodiment)
In the third embodiment, the case of sub-array type STAP processing in the case of radar equipment has been described. In this embodiment, SLC-type STAP will be described.
FIG. 10 is a block diagram showing the configuration of the radar system according to the fourth embodiment. In FIG. 10, the transmitting apparatus is the same as in the third embodiment shown in FIG. 7, and the transmitting antenna 115 is used, for example, as an antenna full aperture and transmits N hit pulses as shown in FIG.

On the other hand, the receiver system uses a main antenna 1a and an auxiliary antenna 1b, as in the second embodiment shown in FIG. Signals received by the main antenna 1a and the auxiliary antenna 1b are frequency-converted by frequency converters 2a and 2b, and converted into digital signals by AD converters 3a and 3b. The flow of processing for suppressing unnecessary waves using this digital signal is the same as in the case of FIG. The differences from the third embodiment are formulated below.

FIG. 11 shows the configuration of the unwanted wave suppressor 6B using main channels and auxiliary channels. This embodiment differs from the second embodiment in which only Mch signals on the spatial axis are processed, but Nch signals on the slow-time axis (PRI axis) are increased. The weight dimension is M×Nch.

The main channel signals, auxiliary channel signals and CPI signals (N-hit PRI signals) are converted into digital signals by the transmitters/receivers TR1 to TRM and input to the weight calculator 65 . The weight calculator 65 calculates weights by correlation processing together with the unwanted wave suppression signals output from the subtractors 641 to 64N, and calculates complex weights W ₁₁ to W _MN of the signals of each subarray. These complex weights are sent to corresponding multipliers 6611 to 66MN and weighted. Adders 671 to 67N add the N-system weighting calculation outputs, and adder 67 adds all the results, which are sent to subtractors 641 to 64N for unnecessary wave suppression processing.

In this case, for example, when using the steepest descent method by MSN, the adaptive weight is given by the following formula (Non-Patent Document 2).

ＳＬＣの場合は、主ｃｈを形成するために、第３の実施形態の（１２）式、（１３）式と同様に、空間軸と時間軸を組み合わせたステアリングベクトルを用いる。補助ｃｈについても、ビーム形成する場合には、補助ｃｈ用のステアリングベクトルを用いる。

In the case of SLC, a steering vector combining the spatial axis and the time axis is used to form the main channel, as in the equations (12) and (13) of the third embodiment. Also for the auxiliary channel, the steering vector for the auxiliary channel is used when forming the beam.

As in the first embodiment, Equation (14) is a method of calculating adaptive weights by iterative calculation, and a transient response occurs until the weights are optimized. In order to prevent this, there is a method of SMI (Sampled Matrix Inversion; Non-Patent Document 1). If the SMI cannot cope with the short time change of the interference wave, for example, the weight calculated by the SMI is used as the initial weight W(0, m, l) of the equation (14), and the weight calculation by the equation (14) is performed. There is a method to In addition, a method of calculating equation (14) again using weights on all frequency axes, with weights calculated by iterative calculation of equation (14) using partial data on the frequency axis as initial weights. etc. As a result, it is possible to prevent the deterioration of the suppression performance of the connection part for each frequency axis division unit due to the transient characteristics of the weight.

The processing of frequency synthesis of the result after adaptation is the same as the equations (6) and (7) of the first embodiment, and since the signal on the time axis does not include an interference signal, CFAR (non-patent document The target can be detected by performing the detection process such as 4).
As described above, in the fourth embodiment, in an array antenna that transmits and receives N (N≧1) pulses, in an antenna having a main channel and M (M≧1) auxiliary channels, the main channel and auxiliary channel signals is converted to the frequency axis by FFT, the frequency axis is divided into L (L ≥ 1) pieces, and unnecessary wave suppression processing is performed using M auxiliary channel CPI signals for each frequency axis division unit to synthesize the frequency bands, and then convert to the time axis by IFFT (Inverse Fast Fourier Transform) to suppress unwanted waves. That is, the suppression performance can be improved by frequency-dividing the wideband signal and performing STAP processing by SLC using the main channel and the auxiliary channel in each division unit.

It should be noted that the present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying constituent elements without departing from the gist of the present invention at the implementation stage. Further, various inventions can be formed by appropriate combinations of the plurality of constituent elements disclosed in the above embodiments. For example, some components may be omitted from all components shown in the embodiments. Furthermore, components across different embodiments may be combined as appropriate.

11 to 1M... subarray, 1a... main channel antenna, 1b1 to 1bM... auxiliary channel antenna, 21 to 2M, 2a, 2b... frequency converter, 31 to 3M, 3a, 3b... AD converter, 41 to 4M, 4a, 4b... fast-time axis FFT, 51 to 5M, 5a, 5b... frequency divider, 6, 6A, 6B... unwanted wave suppressor, 61... weight calculator, 621 to 62M... multiplier, 63, 631 to 63N... Adders 64, 641 to 64N... Subtractors 65... Weight calculators 661 to 66M, 6611 to 66MN... Multipliers 67, 671 to 67N... Adders 7... Frequency synthesizers 8... Fast-time axes IFFT, 9: target detector, 10: output processor, R1 to RM: receiver, TR1 to TRM: transmitter/receiver.

Claims (8)

an antenna that divides an antenna aperture of an array antenna into M (M≧1) subarrays, and receives reflected signals of radar waves in each subarray in an environment where unnecessary waves exist in a wide band including the band of the radar waves ;
frequency axis transformation means for transforming the signals received by the M sub-arrays into a frequency axis;
frequency dividing means for dividing each of the M sub-array received signals converted to the frequency axis into L (L≧1) frequencies;
unwanted wave suppression means for performing unwanted wave suppression processing using the outputs of the M sub-arrays for each division unit of the frequency axis;
Synthesizing means for synthesizing the signals of L frequencies subjected to the suppression processing;
and a time axis conversion means for converting the synthesized frequency signal into a time axis and outputting the signal. An antenna for a main channel and M (M≧1) antennas for auxiliary channels, wherein reflected signals of radar waves are generated by the antennas for the main channel and the antennas for the auxiliary channels, and unwanted waves are generated in a wide band including the band of the radar waves. an antenna receiving in the environment present ;
frequency axis transforming means for transforming the signals received by the respective antennas of the main channel and the auxiliary channel into frequency axes;
frequency division means for dividing the received signals of the main channel and the auxiliary channel converted on the frequency axis into L (L≧1) frequencies, respectively;
unwanted wave suppressing means for performing unwanted wave suppression processing by side lobe cancellation processing using the outputs of the main channel and the auxiliary channel for each division unit of the frequency axis;
Synthesizing means for synthesizing the signals of L frequencies subjected to the suppression processing;
and a time axis conversion means for converting the synthesized frequency signal into a time axis and outputting the signal. a transmitter that transmits radar waves of N (N≧1) hit pulses;
An antenna that divides the antenna aperture of an array antenna into M (M≧1) subarrays, and receives the reflected signal of the radar wave in each subarray under an environment in which unnecessary waves exist in a wide band including the band of the radar wave. ,
frequency axis transformation means for transforming the signals received by the M sub-arrays into a frequency axis;
frequency dividing means for dividing each of the M sub-array received signals converted to the frequency axis into L (L≧1) frequencies;
unwanted wave suppression means for performing unwanted wave suppression processing by STAP (Space Time Adaptive Processing) processing on the space-time (slow-time) axis using the outputs of the M subarrays for each division unit of the frequency axis; ,
Synthesizing means for synthesizing the signals of L frequencies subjected to the suppression processing;
and a time axis conversion means for converting the synthesized frequency signal into a time axis and outputting the signal. a transmitter that transmits radar waves of N (N≧1) hit pulses;
An antenna for a main channel and M (M≧1) antennas for auxiliary channels, wherein reflected signals of radar waves are generated by the antennas for the main channel and the antennas for the auxiliary channels, and unwanted waves are generated in a wide band including the band of the radar waves. an antenna receiving in the environment present ;
frequency axis transforming means for transforming the signals received by the respective antennas of the main channel and the auxiliary channel into frequency axes;
frequency division means for dividing the received signals of the main channel and the auxiliary channel converted on the frequency axis into L (L≧1) frequencies, respectively;
unwanted wave suppression means for performing unwanted wave suppression processing by sidelobe cancellation and STAP (Space Time Adaptive Processing) processing using the outputs of the main channel and the auxiliary channel for each division unit of the frequency axis;
Synthesizing means for synthesizing the signals of L frequencies subjected to the suppression processing;
and a time axis conversion means for converting the synthesized frequency signal into a time axis and outputting the signal. The antenna aperture of the array antenna is divided into M (M≧1) subarrays, and each subarray receives the reflected signal of the radar wave in an environment where unnecessary waves exist in a wide band including the band of the radar wave ,
transforming the signals received by the M sub-arrays into a frequency domain;
dividing each of the M sub-array received signals converted to the frequency axis into L (L≧1) frequencies;
performing unwanted wave suppression processing using the outputs of the M sub-arrays for each division unit of the frequency axis;
Synthesizing the signals of L frequencies subjected to the suppression processing,
A radar signal processing method for a radar system that converts the synthesized frequency signal into a time axis and outputs the signal. Receive reflected signals of radar waves with the main channel antenna and M (M≧1) auxiliary channel antennas in an environment where unnecessary waves exist in a wide band including the radar wave band ;
converting the signals received by the respective antennas of the main channel and the auxiliary channel into frequency axes;
dividing the received signals of the main channel and the auxiliary channel converted to the frequency axis into L (L≧1) frequencies, respectively;
performing unwanted wave suppression processing by side lobe cancellation processing using the outputs of the main channel and the auxiliary channel for each division unit of the frequency axis;
Synthesizing the signals of L frequencies subjected to the suppression processing,
A radar signal processing method for a radar system that converts the synthesized frequency signal into a time axis and outputs the signal. Send radar waves of N (N≧1) hit pulses,
An antenna aperture of an array antenna is divided into M (M≧1) subarrays, and each subarray receives the reflected signal of the radar wave in an environment where unnecessary waves exist in a wide band including the band of the radar wave ,
transforming the signals received by the M sub-arrays into a frequency domain;
dividing each of the M sub-array received signals converted to the frequency axis into L (L≧1) frequencies;
performing unwanted wave suppression processing by STAP (Space Time Adaptive Processing) processing on the space-time (slow-time) axis using the outputs of the M sub-arrays for each division unit of the frequency axis;
Synthesizing the signals of L frequencies subjected to the suppression processing,
A radar signal processing method for a radar system that converts the synthesized frequency signal into a time axis and outputs the signal. Send radar waves of N (N≧1) hit pulses,
receiving reflected signals of radar waves with a main channel antenna and M (M≧1) auxiliary channel antennas in an environment in which unnecessary waves exist in a wide band including the radar wave band ;
converting the signals received by the respective antennas of the main channel and the auxiliary channel into frequency axes;
dividing the received signals of the main channel and the auxiliary channel converted to the frequency axis into L (L≧1) frequencies, respectively;
performing unwanted wave suppression processing by side lobe cancellation and STAP (Space Time Adaptive Processing) processing using the outputs of the main channel and the auxiliary channel for each division unit of the frequency axis;
Synthesizing the signals of L frequencies subjected to the suppression processing,
A radar signal processing method for a radar system that converts the synthesized frequency signal into a time axis and outputs the signal.

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