JP5618494B2 - Radar equipment - Google Patents

Description

  The present invention relates to a radar apparatus having a function of suppressing clutter components contained in a received signal.

  A general pulse radar radiates a pulsed radio wave into space, extracts a reflected wave from a target, and performs distance measurement. In addition to the reflected wave component from the target, the received signal of the antenna also includes a reflected wave component from an unnecessary object called clutter. Such clutter interferes with the target detection process. Therefore, in the conventional radar system of the search system, as a clutter removal means for suppressing the clutter, an MTI (Moving Target Indicators) that removes the clutter component caused by the reflected wave from the stationary object from the reception processing signal. ) Is used (see, for example, Patent Document 1).

This MTI is a type that suppresses only the clutter by utilizing the fact that the Doppler frequency is generated in the reflected wave from the moving target but the Doppler frequency is not generated in the clutter which is the reflected wave from the ground or the building. It is a filter. Specifically, the MTI intensively suppresses clutter having a Doppler frequency of around 0 by subtracting the reception processing signal delayed by one pulse from the reception processing signal of each range bin. In general, an MTI whose transfer function is represented by 1-z ^-1 is called a single erasure unit, and an MTI whose transfer function is represented by (1-z ^-1 ) ^M is a multiple erasure unit. (Where M> 1).

Japanese Patent Publication No.58-55474

  Here, the MTI calculation processing can be regarded as a filter that operates using a pulse repetition period as a sampling interval. The filter amplitude characteristic of the MTI is a characteristic in which the filter blocking region is repeated for each pulse repetition frequency PRF (Pulse Repetition Frequency).

  Search-type radars are often operated at a relatively low PRF because they aim to correctly measure the distance to the target. That is, a relatively low PRF is equivalent to a relatively narrow range (-PRF / 2 to PRF / 2) in which the target Doppler frequency can be measured correctly. However, in such a setting, if the target moves at a high speed, the Doppler frequency is generated, but the Doppler frequency is included in the MTI blocking region, and the target signal is attenuated. The probability that a blind phenomenon will occur increases.

  Therefore, in the conventional radar apparatus, when the MTI performs the clutter suppression process, a blind phenomenon occurs depending on the target moving speed. As a result, there is a problem that the target signal is attenuated by the MTI and the target detection becomes difficult.

  The present invention has been made to solve the above-described problems, and can reduce the target blind speed region associated with the clutter suppression processing of the clutter removal means, and can perform target detection more reliably. The purpose is to obtain.

The radar apparatus according to the present invention transmits an input pulse signal as a transmission signal to an external space, receives an reflected wave of the transmission signal from the external space as a reception signal, and a plurality of the pulses having different transmission frequencies. A transmission signal processing means for generating a signal and inputting the generated plurality of pulse signals to the antenna in a time division manner; and the reception signal of the antenna for each transmission frequency of the pulse signal corresponding to the reception signal. Receiving signal processing means for converting into a receiving processing signal for internal processing and converting it into a plurality of receiving processing signals, and for each of the plurality of receiving processing signals from the receiving signal processing means, a reflected wave from a stationary object Clutter removal means for removing the resulting clutter component in order to detect the moving target, and before the clutter component removal by the clutter removal means It is determined whether or not a plurality of reception processing signals include a target signal indicating a target of distance measurement, and the reception processing signals including the target signal among the plurality of reception processing signals are measured signal And a target distance measuring means for measuring a distance to the target based on a measurement target signal from the frequency selecting means, and the frequency selecting means includes the plurality of reception processing signals. When it is confirmed that there are a plurality of the reception processing signals that include the target signal, each of the plurality of reception processing signals that includes the target signal is selected as the measurement target signal, The measurement target signal from the frequency selection means is held until transmission / reception of the plurality of pulse signals is completed, and when there are a plurality of measurement target signals, Calculating a correlation matrix related to a matrix obtained by arranging a number of the measurement target signals in a column direction, calculating an eigenvector corresponding to the maximum eigenvalue of the calculated correlation matrix, and determining the plurality of measurement target signals as maximum signal-to-noise A frequency maximum ratio synthesizing unit for synthesizing with a ratio; and the target distance measuring unit replaces the measurement target signal from the frequency selecting unit with the plurality of measurement target signals synthesized by the frequency maximum ratio synthesizing unit. Based on this, the distance to the target is measured.

  According to the radar apparatus of the present invention, a plurality of pulse signals having different transmission frequencies are input to the antenna in a time division manner by the transmission signal processing means, and the reception processing signal containing the target signal is measured by the frequency selection means. Therefore, even if the reception processing signal for some transmission frequencies among the plurality of transmission frequencies is affected by the blind phenomenon of the clutter removal means, Since the reception processing signal can avoid the influence of the blind phenomenon of the clutter removal means, the target blind speed region generated when the clutter suppression processing is performed by MTI can be reduced, and the target detection is performed more reliably. be able to.

1 is a block diagram showing a radar apparatus according to Embodiment 1 of the present invention. It is explanatory drawing for demonstrating the transmission timing of a pulse wave. It is a graph for demonstrating the change of the gain of MTI with respect to a target signal. It is a block diagram which shows the radar apparatus by Embodiment 2 of this invention. FIG. 5 is a block diagram specifically showing an internal configuration of a frequency maximum ratio combining unit in FIG. 4. It is a block diagram which shows the radar apparatus by Embodiment 3 of this invention. It is a block diagram which shows the radar apparatus by Embodiment 4 of this invention. It is a block diagram which shows the radar apparatus by Embodiment 5 of this invention. It is a block diagram which shows the radar apparatus by Embodiment 6 of this invention.

Embodiments of the present invention will be described below with reference to the drawings.
Embodiment 1 FIG.
FIG. 1 is a block diagram showing a radar apparatus according to Embodiment 1 of the present invention. In FIG. 1, the receiver 5 is shown as RX, the A / D converter 6 is shown as A / D, and the MTI processing means 7 is shown as MTI (the same applies to other block diagrams).
In FIG. 1, a radar apparatus includes an antenna (transmission / reception antenna) 1, a circulator 2, a transmitter 3, a frequency switching means 4, a receiver 5, an A / D converter 6, an MTI processing means 7 as a clutter removal means, and a frequency selection. Means 8 and target distance measuring means 9 are provided.

  The antenna 1 is composed of a single antenna element. The antenna 1 transmits the input pulse signal to the external space as a transmission signal, and receives a reflected wave from the external space of the pulse signal as a reception signal. The circulator 2 (transmission / reception switching device) is electrically connected to the antenna 1, the transmitter 3, and the receiver 5. The circulator 2 electrically connects the transmitter 3 and the antenna 1 during radio wave transmission (pulse transmission), and receives the receiver 5 and the antenna 1 during radio wave reception (pulse reception). Is electrically connected.

  The transmitter 3 generates pulse signals (transmission pulse train signals) having a plurality of different transmission frequencies. The frequency switching means 4 sends a switching signal for switching a plurality of transmission frequencies to the transmitter 3 at regular time intervals. The transmitter 3 switches a plurality of transmission frequencies by time division according to the switching signal from the frequency switching means 4 and sends a pulse signal to the antenna 1. The transmitter 3 and the frequency switching means 4 constitute transmission signal processing means.

  The receiver 5 detects the phase of the received signal in the RF band received by the antenna 1 and converts it into a baseband received signal for internal processing for each transmission frequency of the pulse signal corresponding to the received signal. The A / D converter 6 performs A / D conversion on the reception processing signal from the receiver 5. The receiver 5 and the A / D converter 6 constitute reception signal processing means.

  The MTI processing means 7 removes the clutter component caused by the reflected wave from the stationary object contained in the reception processing signal from the A / D converter 6. The frequency selection unit 8 performs peak detection processing or threshold detection processing on the reception processing signal after the clutter component removal by the MTI processing unit 7, and whether or not a target signal indicating a distance measurement target is included. Discriminate (simple detection). Note that the frequency selection unit 8 can determine that the target signal is included in the reception processing signal if the signal component extracted by the peak detection processing or the threshold detection processing does not spread in the distance direction. Then, the frequency selection unit 8 sets the reception processing signal including the target signal as the measurement target signal.

  The target distance measuring means 9 performs target detection processing (detailed detection) such as CFAR (Constant False Alarm Rate) and distance measurement processing based on the measurement target signal from the frequency selection means 8, Measure the distance to the target.

  Here, the radar apparatus can be configured by a computer (not shown) having an arithmetic processing unit (CPU), a storage unit (ROM, RAM, hard disk, etc.) and a signal input / output unit. The functions of the transmitter 3, frequency switching means 4, receiver 5, A / D converter 6, MTI processing means 7, frequency selection means 8 and target distance measurement means 9 are realized in the computer storage unit of the radar apparatus. A program is stored for this purpose.

Next, the operation of the radar apparatus according to the first embodiment will be described. Here, a case where radio waves are transmitted by switching the _three transmission frequencies f _{1 to} f ₃ will be described. FIG. 2 is an explanatory diagram for explaining the transmission timing of the pulse radio wave. As shown in FIG. 2, first, the transmitter 3 transmits a pulse signal having a transmission frequency f ₁ to the antenna 1 for a preset time, and the pulse signal having the transmission frequency f ₁ is transmitted and received by radio waves.

Next, the transmitter 3 sequentially switches the transmission frequency of the pulse signal to f ₂ and f ₃ in a time division manner. Then, similarly to the case of the transmission frequency f ₁ , pulse signals of the transmission frequencies f ₂ and f ₃ are transmitted and received by radio waves. The reflected waves of the radio waves radiated at the respective transmission frequencies are received by the antenna 1 and then phase-detected by the receiver 5 to become reception processing signals. The reception processing signal after phase detection is converted into a digital signal by the A / D converter 6 and sent to the MTI processing means 7.

  Here, generally, the clutter component caused by the reflected wave from the stationary object is suppressed by the MTI. Further, in the search system radar, since the target moving speed is generally unknown information, the Doppler frequency of the target signal is also unknown information. Therefore, as long as the MTI process is performed, it is difficult to completely avoid the phenomenon that the target signal is attenuated.

但し、λ：送信電波の波長 ｆ：送信周波数 ｃ：電波伝搬速度 The amplitude characteristic of MTI is uniquely determined once the PRF is determined. On the other hand, the Doppler frequency fd of the target signal is expressed by the following equation (1). That is, it can be seen that if the transmission frequency changes, the Doppler frequency changes even if the target speed v is constant.

Where λ: wavelength of the transmission radio wave f: transmission frequency c: radio wave propagation speed

The change in the Doppler frequency as shown in the equation (1) is relatively small in principle even if the transmission frequency is switched for a target whose moving speed is extremely slow. For this reason, the change in MTI gain is also relatively small. However, if the target moves at a high speed to some extent, the change in the Doppler frequency is relatively large. Therefore, a target that could not be detected at the transmission frequency f ₁ may be detected at the transmission frequency f ₂ .

  Therefore, in the radar apparatus according to the first embodiment, the probability that the target signal is attenuated by the MTI processing means 7 is reduced by using the change of the Doppler frequency as shown in the above equation (1). The amplitude characteristic of the MTI processing means 7 is determined by the order of the MTI processing means 7 (how many erasures it is) and the PRF. That is, even when the order of the MTI processing means 7 and the PRF are fixed, the target moving speed is constant, and the positional relationship with the radar apparatus does not change, the Doppler frequency changes if the transmission frequency is different. Thereby, the target attenuation amount in the MTI processing means 7 changes.

Therefore, the frequency selection unit 8 first performs peak detection or threshold detection processing on each of the output signals of the MTI processing unit 7 at the transmission frequencies f _{1 to} f ₃ to perform simple target detection. . Next, if the extracted signal component does not spread in the distance direction, the frequency selection means 8 can determine that it is a target signal candidate. Thereby, the reception processing signal from which such a signal has been extracted is selected.

In the example shown in FIG. 2, target detection is possible at the transmission frequencies f ₁ and f ₃ , and target detection is not possible at the transmission frequency f _2. Therefore, the reception processing signals corresponding to the transmission frequencies f ₁ and f ₃ are The frequency selection means 8 selects the measurement target signal. The frequency selection unit 8 selects a reception processing signal having a high reflection intensity as a measurement target signal from reception processing signals corresponding to the transmission frequencies f ₁ and f ₃ . In addition, the frequency selection means 8 may select the reception processing signal corresponding to the reflected wave previously received by the antenna 1 among the reception processing signals corresponding to the transmission frequencies f ₁ and f ₃ as the measurement target signal. it can.

  Here, if the order of the MTI processing means 7 and the PRF are determined in advance, the MTI gain for a target having a moving speed in a specific range is always ensured by adjusting the frequency difference between a plurality of transmission frequencies to be switched. Can do.

Next, a change in the MTI gain of the radar apparatus according to the first embodiment will be described in comparison with a conventional radar apparatus. FIG. 3 is an explanatory diagram for explaining a change in the MTI gain of the radar apparatus of FIG. In the example illustrated in FIG. 3, a plurality of transmission frequencies to be switched are set to f _{1 to} f ₃ . Wherein the calculation example, based on the transmission frequency _{f 1, f 2 = 1.1 ×} f 1, f 3 = 1.2 × f 1 and is ^{_{changed, PRF = f 1/10 6}} , MTI processing means In this example, 7 is a double eraser.

Also, the horizontal axis in FIG. 3 represents the target speed, and the vertical axis in FIG. 3 represents the MTI gain. Further, in FIG. 3, a change in MTI gain of the radar apparatus according to the first embodiment is indicated by a solid line, and a change in MTI gain of a conventional radar apparatus (using only the transmission frequency f ₁ ) is indicated by a broken line. In FIG. 3, when the MTI gain is less than 0, it means that the target signal is attenuated. Furthermore, FIG. 3 shows the decibel value of the MTI gain with respect to the target signal when the target moving speed is changed from 300 m / s to 700 m / s.

  First, in the conventional radar apparatus, as shown by arrows A1 to A3 in FIG. 3, there are many target speeds at which the gain is greatly deteriorated, and it can be seen that a blind phenomenon occurs. On the other hand, in the radar apparatus according to the first embodiment, a gain of 5 dB or more can always be secured, and it can be seen that the target signal is not attenuated within the assumed target speed range (the entire region on the horizontal axis in FIG. 3).

  FIG. 3 shows an example in which the target speed range is 300 m / s to 700 m / s. However, in the calculation, an MTI gain of 0 dB or more is ensured even when the target speed range is 120 m / s to 1200 m / s. It has been confirmed that an MTI gain of 0 dB or more can be secured over a wider range than the example shown in FIG.

  According to the radar apparatus of the first embodiment as described above, a plurality of pulse signals having different transmission frequencies are input to the antenna 1 by the transmitter 3 in a time division manner, and the reception processing signal including the target signal is the frequency. The signal is selected as a measurement target signal by the selection means 8. Then, the measurement target signal is sent to the target distance measuring means 9. With this configuration, even when reception processing signals for some transmission frequencies among a plurality of transmission frequencies are affected by the blind phenomenon of the MTI processing means 7, the other transmission frequencies of the plurality of transmission frequencies are Since the reception processing signal can avoid the influence of the blind phenomenon of the MTI processing means 7, the target blind speed region generated when the MTI processing means 7 performs the clutter suppression processing can be reduced. The target distance can be calculated more accurately than in the apparatus.

  In the first embodiment, the example using three transmission frequencies has been described as shown in FIG. However, the present invention is not limited to this example, and two or more transmission frequencies may be used.

Embodiment 2. FIG.
In the radar apparatus of the first embodiment, in order to avoid the target signal from being attenuated by the MTI processing means 7, the transmission frequency is switched in a time-sharing manner to perform radio wave transmission. Therefore, compared with a radar having a fixed transmission frequency, The total number of pulse hits decreases. As a result, in the radar apparatus according to the first embodiment, the possibility that the target signal is present but disappears by the MTI processing unit 7 is reduced, but the S / N (signal to noise ratio) when the target is detected is reduced. ) Is inevitable. On the other hand, in the radar apparatus according to the second embodiment of the present invention, the frequency maximum ratio combining means 20 is used in order to improve the S / N degradation in the first embodiment.

  FIG. 4 is a block diagram showing a radar apparatus according to Embodiment 2 of the present invention. In FIG. 4, the radar apparatus according to the second embodiment further includes frequency maximum ratio combining means 20 in addition to the configuration of the radar apparatus according to the first embodiment. The frequency selection means (multiple frequency selection means) 8 according to the second embodiment selects one or more types of necessary reception processing signals from reception processing signals corresponding to a plurality of transmission frequencies. The frequency maximum ratio combining unit 20 performs frequency maximum ratio combining processing (processing of each function shown in FIG. 5), and when receiving a plurality of types of reception processing signals from the frequency selection unit 8, the plurality of types of reception processing signals. Is synthesized.

  Next, the frequency maximum ratio combining means 20 will be specifically described. FIG. 5 is a block diagram specifically showing the internal configuration of the frequency maximum ratio combining means 20 of FIG. In FIG. 5, the maximum frequency ratio combining means 20 includes a combined load calculating means (frequency maximum ratio combined load calculating means) 21 for calculating a load vector corresponding to the maximum eigenvalue, and a plurality of multipliers 22A to 22M (M multiplications). Device 22: M is an integer of 2 or more) and an adder 23.

Next, the operation of the radar apparatus according to the second embodiment will be described. First, when the number of pulse hits is NH and a pulse signal is transmitted by switching the transmission frequency from f _{1 to} f _N for each pulse hit number NH, the reception processing signal after the clutter removal by the MTI processing means 7 is xf _i. (N, r) (where i = 1 to NH).

The frequency selection unit 8 performs threshold detection on the reception processing signal xf _i (n, r) subjected to MTI processing. And the frequency selection means 8 selects the reception processing signal of the range bin in which a target signal candidate exists among several reception processing signals. Now, in the range bin number R, when the reception processing signals corresponding to the transmission frequencies f ₁ , f ₃ , and f ₅ are selected as the measurement target signals by the frequency selection unit 8, these measurement target signals are set as vectors Xf and the following It is defined as equation (2).

但し、添字のＨは複素共役転置を表す。 In the frequency maximum ratio combining unit 20, in order to obtain the spatial maximum ratio combined load using this vector Xf, the combined load calculating unit 21 calculates a correlation matrix R related to the vector Xf based on the following equation (3). The correlation matrix R is a correlation matrix related to a matrix obtained by arranging a plurality of measurement target signals in the column direction.

However, the subscript H represents complex conjugate transposition.

The combined load calculation means 21 calculates an eigenvector W corresponding to the maximum eigenvalue of the correlation matrix R, that is, a load vector W of the frequency maximum ratio combination, and calculates the calculated load vector W (W _{1 to} W _M ). The data is sent to the multiplier 22 (22A to 22M). The multiplier 22 multiplies the plurality of measurement target signals from the frequency selection unit 8 and the load vector W.

Then, the adder 23 adds the outputs of the multipliers 22 as shown in the following equation (4), thereby synthesizing the measurement target signal with the maximum S / N (maximum signal-to-noise ratio). The output signal X _FMRC (r) is calculated.

  Here, the frequency maximum ratio combining unit 20 holds the measurement target signal from the frequency selection unit 8 until transmission / reception of a plurality of pulse signals is completed. Then, the frequency maximum ratio combining unit 20 causes the adder 23 to execute the processing in response to the completion of transmission / reception of a plurality of pulse signals.

The combined output signal X _FMRC (r) calculated by the adder 23 is sent to the target distance measuring means 9. Then, the target distance measuring means 9 detects the target by performing threshold processing in the distance direction (range bin direction) using the combined output signal X _FMRC (r), and calculates the target distance. Other configurations and operations are the same as those in the first embodiment.

  According to the radar apparatus of the second embodiment as described above, the frequency maximum ratio combining unit 20 calculates the eigenvector corresponding to the maximum eigenvalue, and combines a plurality of measurement target signals with the maximum signal-to-noise ratio. With this configuration, the S / N can be improved as compared with that of the first embodiment, and a more accurate distance measurement is possible.

Embodiment 3 FIG.
In the radar apparatus of the second embodiment, the S / N is improved by the frequency maximum ratio combining means 20. Here, when the target target moving speed is relatively high, the target Doppler frequency is also relatively high, and the change in MTI gain due to switching of the transmission frequency is relatively large. Thereby, even if the frequency difference between the transmission frequencies is relatively small, the effect can be easily obtained.

  Here, the maximum ratio combining process according to the second embodiment is ideally equivalent to coherent integration in which the phases of signals are aligned and added. However, in the frequency maximum ratio combining process in which signals are combined between a plurality of transmission frequencies, the S / N improvement effect may decrease as the Doppler frequency difference of the target signal between the plurality of transmission frequencies increases. . On the other hand, in the radar apparatus according to Embodiment 3 of the present invention, a pulse Doppler filter (hereinafter referred to as PDF: Pulse Doppler Filter) 30 is used in order to cope with the case where the influence of the Doppler frequency of the target signal is relatively large. It is done.

  FIG. 6 is a block diagram showing a radar apparatus according to Embodiment 3 of the present invention. In FIG. 6, the radar apparatus according to the third embodiment further includes a PDF 30 as frequency component separation means in addition to the configuration of the radar apparatus according to the second embodiment. The PDF 30 receives the reception processing signal vector Xf from the MTI processing means 7 shown in the previous equation (2), and performs a discrete Fourier transform on the reception processing signal vector Xf in the pulse hit direction. Here, assuming that the number of discrete Fourier transform points is NF, the output signal vector XF for the reception processing signal of PDF 30 is expressed by the following equation (5).

従って、ＰＤＦ３０は、ＭＴＩ処理手段７からの複数の受信処理信号のそれぞれに対して、離散フーリエ変換を行って周波数成分を算出し、その算出した周波数成分を複数の受信処理信号のそれぞれから分離する。

Accordingly, the PDF 30 performs a discrete Fourier transform on each of the plurality of reception processing signals from the MTI processing means 7 to calculate a frequency component, and separates the calculated frequency component from each of the plurality of reception processing signals. .

但し、この例では、全ての送信周波数でそれぞれ異なる周波数チャンネルにピークが検出されたものとする。 The frequency selection unit 8 according to the third embodiment performs peak detection on the output signal vector XF shown in Expression (5). For example, if the frequency selection means 8 detects the peaks at the frequencies f ₁ , f ₃ , and f ₅ , the complex signal of the frequency channel is rearranged as in the following equation (6), and the vector XF _s And

However, in this example, it is assumed that peaks are detected in different frequency channels at all transmission frequencies.

The frequency maximum ratio combining means 20, to determine the frequency maximum ratio combined load using this vector XF _s, calculated on the basis of the correlation matrix R _s related vector XF _s in the following equation (7).

他の構成及び動作は、実施の形態２と同様である。 Next, the frequency maximum ratio combining means 20 (multiplier 22 in FIG. 5) performs the eigenvector W _s corresponding to the maximum eigenvalue of the correlation matrix R _s in Expression (7), that is, the load vector W _{s of the} frequency maximum ratio combination. And the vector XF _s is performed as in the following equation (8).

Other configurations and operations are the same as those in the second embodiment.

  According to the radar apparatus of the third embodiment as described above, the PDF 30 performs discrete Fourier transform on each of the plurality of reception processing signals from the MTI processing means 7 to calculate the frequency component, and the calculated frequency The component is separated from each of the plurality of reception processing signals. With this configuration, the S / N can be improved even when the influence of the Doppler frequency of the target signal is relatively large.

Embodiment 4 FIG.
In the radar device according to the second embodiment, the antenna 1 constituted by a single antenna element is used. On the other hand, in the radar apparatus according to the fourth embodiment of the present invention, an array antenna constituted by a plurality of antenna elements 41A to 41M (M antenna elements: M is an integer of 2 or more) instead of antenna 1. 40 is used. Further, in the fourth embodiment, a space / frequency maximum ratio combining unit 47 is used instead of the frequency maximum ratio combining unit 20 in the second embodiment.

FIG. 7 is a block diagram showing a radar apparatus according to Embodiment 4 of the present invention. Note that f ₁ , f ₂ , and f _{N in} the upper left of FIG. 7 indicate that transmission frequencies are switched in a time division manner, and radio waves are transmitted and received with transmission signals of the respective transmission frequencies (FIGS. 8 and 9). The same applies to. In FIG. 7, the array antenna 40 when receiving the reflected wave corresponding to the transmission frequency f ₂ is indicated by a broken line, and the array antenna 40 when receiving the reflected wave corresponding to the transmission frequency f _N is shown. This is indicated by a dashed line (the same applies to FIGS. 8 and 9).

  In FIG. 7, the radar apparatus of the fourth embodiment includes a transmitter (not shown), a circulator (not shown), frequency switching means (not shown), and M array antennas 40 as a whole. Antenna elements 41A-41M, M phase shifters 42A-42M for directing the antenna beam in a desired direction, M receivers 43A-43M, and M A / D conversion processing means 44A- 44M, M MTI processing means 45A to 45M, frequency selection means (multiple frequency selection means) 46, spatial / frequency maximum ratio synthesis means 47 for spatial synthesis with a maximum signal-to-noise ratio, and target distance Measuring means 48.

  Here, the configuration and operation of the transmitter, circulator, frequency switching means, receivers 43A to 43M, A / D conversion processing means 44A to 44M, MTI processing means 45A to 45M and frequency selection means 46 according to the fourth embodiment. The configuration and operation of the radar apparatus of the first and second embodiments are the same.

Next, the operation of the radar apparatus according to the fourth embodiment will be described. Here, a case where radio wave transmission / reception is performed at the transmission frequency f ₁ will be described. The transmission signal having the transmission frequency f ₁ transmitted from the array antenna 40 is reflected by the target and is incident on the array antenna 40 to become a reception signal. The phase shifter 42 performs a beam steering operation for directing the reception beam in the same direction as the transmission direction.

Here, the received signal at each of the antenna elements 41A to 41M at the transmission frequency f ₁ is x _{m, 1} (m = 1, 2,..., M), and the transmission frequency is switched to perform pulse transmission at f _n . X _{m, n} (m = 1, 2,..., M) is a received signal at each of the antenna elements 41A to 41M. In this case, when the reception processing signal to the space / frequency maximum ratio combining unit 47 is expressed as a vector, the following equation (9) is obtained.

但し、添字のＨは複素共役転置を表す。 The space / frequency maximum ratio combining means 47 uses the data matrix shown in the previous equation (9) to calculate the correlation matrix R _sf for Z using the following equation (10) in order to calculate the space / frequency maximum ratio combined load. Calculated by

However, the subscript H represents complex conjugate transposition.

他の動作は、実施の形態２と同様である。 Further, the space / frequency maximum ratio combining means 47 calculates an eigenvector W corresponding to the maximum eigenvalue of the correlation matrix R _sf , that is, a load vector W for frequency maximum ratio combining. Then, similarly to the radar apparatus of the second embodiment, the space / frequency maximum ratio combining unit 47 performs the calculation of the following equation (11), thereby spatially combining the output signal with the maximum S / N. X _SFMRC (r) can be obtained.

Other operations are the same as those in the second embodiment.

  According to the radar apparatus of the fourth embodiment as described above, a plurality of reception processing signals based on a plurality of reception signals of the array antenna 40 are spatially / maximumly S / N and spatially generated by the space / frequency maximum ratio combining means 47. Synthesized. With this configuration, the same effect as in the second embodiment can be obtained, the amount of information used for distance measurement can be increased, and the accuracy of distance measurement can be further improved.

Embodiment 5. FIG.
FIG. 8 is a block diagram showing a radar apparatus according to Embodiment 5 of the present invention. In FIG. 8, the configuration of the radar apparatus of the fifth embodiment is obtained by adding PDF 50A to 50M equivalent to the PDF 30 of the third embodiment to the configuration of the radar apparatus of the fourth embodiment. The configuration of the radar apparatus according to the fifth embodiment other than PDF 50A to 50M is the same as that of the radar apparatus according to the fourth embodiment.

但し、ｍはアンテナ素子番号である。 Next, the operation of the radar apparatus according to the fifth embodiment will be described. The reception processing signals subjected to MTI processing by the MTI processing means 45A to 45M are subjected to pulse Doppler processing by the PDF 50 corresponding to the respective antenna elements 41A to 41M. The output signal vector of the PDF 50 is XF _m (m = 1, 2,..., M) shown in the following equation (12).

Here, m is an antenna element number.

他の動作は、実施の形態３，４と同様である。 The frequency selection means 46 of the fifth embodiment performs the peak detection on XF _m shown in Formula (12). For example, when the frequency selection unit 46 detects the frequencies f ₁ and f ₅ in the antenna elements 41A to 41M, the frequency selection unit 46 rearranges the complex signals of the frequency channels as shown in the following equation (13). Let it be a vector XF _s .

Other operations are the same as those in the third and fourth embodiments.

  According to the radar apparatus of the fifth embodiment as described above, the PDF 50A to 50M equivalent to the PDF 30 of the third embodiment are added to the configuration of the radar apparatus of the third embodiment, so that the third and fourth embodiments. The same effect can be obtained.

Embodiment 6 FIG.
In the radar apparatus according to the sixth embodiment of the present invention, the plurality of antenna elements of the array antenna 40 in the radar apparatus according to the fifth embodiment are grouped as a plurality of subarrays 60A to 60M. FIG. 9 is a block diagram showing a radar apparatus according to Embodiment 6 of the present invention. In FIG. 9, each of the plurality of subarrays 60 </ b> A to 60 </ b> M includes a plurality of antenna elements 61, a plurality of phase shifters 62, and a combiner 63.

Next, the operation of the radar apparatus according to the sixth embodiment will be described. Here, the case of performing pulse transmission and reception at the transmission frequency f _n. The transmission pulse having the frequency f _n transmitted from the array antenna 40 is reflected from the target and is also incident on the array antenna 40 to become a reception signal x _{m, n} (n = 1, 2,..., N). Note that the number of array elements is M, the number of subarrays is MS, and the number of elements in the subarray is MM.

The phase shifter 62 performs a beam steering operation for directing the reception beam in the same direction as the transmission direction. Here, assuming that the steering vector is B (θ), the synthesizer 63 uses Y _{m, n} (m = 1, 2,..., MS) shown in the following equation (15) as an output signal of the subarray 60. can get.

Here, taking the case where the array antenna 40 is a linear array as an example, the steering vector B (θ) can be expressed by the following equation (16).

The receiver according to the sixth embodiment uses the reception signal of the array antenna 40, that is, the output signal Ym _{, n} of the subarray 60 shown in Expression (16), for each transmission frequency of the pulse signal corresponding to the output signal, and the subarray. Every 60, it is converted into a reception processing signal. Then, by using the reception processing signal after the MTI processing as an input signal of the frequency selection means 46, the subsequent operation can be the same as that of the radar apparatus of the fifth embodiment.

  According to the radar apparatus of the sixth embodiment as described above, the plurality of antenna elements 61 are grouped as subarrays. With this configuration, even when the number of antenna elements increases, calculation processing can be performed in units of subarrays (group units), thereby suppressing an increase in the amount of calculations. In addition, the same effect as that of the fifth embodiment (third and fourth embodiments) can be obtained.

  In the sixth embodiment, the PDF 50 is used in the radar device. However, the PDF 50 may be omitted as in the radar device in the fourth embodiment.

  DESCRIPTION OF SYMBOLS 1 Antenna, 3 Transmitter, 4,46 Frequency switching means, 5, 43A-43M Receiver, 7, 45A-45M MTI processing means (clutter removal means), 8 Frequency selection means, 9, 48 Target distance measurement means, 20 Frequency maximum ratio combining means, 40 array antenna, 41A to 41M, 61 antenna element, 47 space / frequency maximum ratio combining means, 60A to 60M subarray.

Claims (4)

An antenna that receives an input pulse signal as a transmission signal to an external space and receives a reflected wave from the external space of the transmission signal as a reception signal;
Transmission signal processing means for generating a plurality of pulse signals of different transmission frequencies, and inputting the generated pulse signals to the antenna in a time-sharing manner;
A reception signal processing means for converting the reception signal of the antenna into a reception processing signal for internal processing for each transmission frequency of the pulse signal corresponding to the reception signal, and obtaining a plurality of reception processing signals;
Clutter removal means for removing a clutter component caused by a reflected wave from a stationary object for each of the plurality of reception processing signals from the reception signal processing means in order to detect a moving target;
It is determined whether or not the plurality of reception processing signals after the clutter component removal by the clutter removal means includes a target signal indicating a target of distance measurement, and the target signal is included among the plurality of reception processing signals. Frequency selection means for selecting the received processed signal as a measurement target signal;
A target distance measuring means for measuring a distance to the target based on a measurement target signal from the frequency selecting means,
When the frequency selection means confirms that there are a plurality of reception processing signals that include the target signal among the plurality of reception processing signals, the plurality of receptions that include the target signal. Select each of the processed signals as the measurement target signal,
The measurement target signal from the frequency selection unit is held until transmission / reception of the plurality of pulse signals is completed, and when there are a plurality of measurement target signals, the plurality of measurement target signals are arranged in a column direction. A frequency maximum ratio combining unit that calculates a correlation matrix for the matrix obtained by arranging, calculates an eigenvector corresponding to the calculated maximum eigenvalue of the correlation matrix, and combines the plurality of measurement target signals with a maximum signal-to-noise ratio; In addition,
The target distance measuring unit measures a distance to the target based on the plurality of measurement target signals synthesized by the frequency maximum ratio synthesis unit instead of the measurement target signal from the frequency selection unit. A characteristic radar device. For each of the plurality of reception processing signals after the clutter component removal by the clutter removal means, a frequency component is calculated by performing discrete Fourier transform, and the calculated frequency component is separated from each of the plurality of reception processing signals A component separation means,
The frequency selection unit determines whether the target signal is included in each of the plurality of reception processing signals whose frequency components have been separated by the frequency component separation unit, and among the plurality of reception processing signals The radar apparatus according to claim 1, wherein the reception processing signal including the target signal is selected as the measurement target signal. The antenna is an array antenna composed of a plurality of antenna elements,
The radar apparatus according to claim 1, wherein the maximum frequency ratio combining unit spatially combines the plurality of measurement target signals with a maximum signal-to-noise ratio. The plurality of antenna elements are each grouped as a plurality of subarrays,
The reception signal processing means converts the reception signal of the array antenna into the reception processing signal for each transmission frequency of the pulse signal corresponding to the reception signal and for each sub-array. 3. The radar device according to 3.

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