JP5606097B2 - Passive radar device - Google Patents

Description

  The present invention relates to a passive radar device having a function of improving the resolution of a Doppler frequency by taking a long observation time.

  Passive radar uses a transmission radio wave from an existing radio wave source such as a broadcasting station, and the path length between a signal (direct wave) that arrives directly from the radio wave source and a signal that is scattered by the target (scattered wave) This is a method for measuring the difference and the Doppler frequency shift of the scattered wave signal (see FIG. 1).

  As a radio wave source of this passive radar, an artificial satellite of the Global Navigation Satellite System (GNSS) is being studied in addition to a television or radio broadcasting station. In addition, passive radars are attracting attention as a method that contributes to power saving and radio resource saving because they do not emit radio waves themselves. For example, Non-Patent Document 1 systematically summarizes the conventional development results related to passive radar and the advantages and disadvantages of passive radar.

  By the way, the broadcasting wave of terrestrial digital television broadcasting that has started operation in recent years has a flat frequency characteristic within an occupied bandwidth and a relatively small separation width between channels. For this reason, a plurality of channels can be combined and regarded as a wideband signal. If such a broadcast wave is used, it is possible to observe the target with high resolution even using a passive radar. Furthermore, by ensuring a long observation time, it is expected that even a passive radar can generate a radar image corresponding to an inverse synthetic aperture radar (ISAR) image.

  Moreover, as a prior art regarding target radar image generation using a passive radar, for example, there are those shown in Non-Patent Document 2 and Non-Patent Document 3. Non-Patent Document 2 discloses a technique for improving the resolution by taking a very wide observation angle with respect to a target during observation on the premise that the band of a broadcast wave signal is not so wide. Non-Patent Document 3 discloses a technique for generating a high-quality inverse synthetic aperture radar image on the assumption that the target motion is accurately known.

  In addition to these, examples of prior art related to the present invention include those shown in Patent Documents 1 and 2 and Non-Patent Document 4.

Japanese Patent No. 2938728 Japanese Patent No. 4046422

N.J. Willis and H.D. Griffiths, “Advances in Bistatic Radar,” Scitech publishing Inc., 2007 M. Cetin and A.D. Lanterman, “Region-Enhanced Passive Radar Imaging,” IEE Proceedings. Radar, Sonar and Navigation, Vol.152, No.3, pp.185--194, Jun. 2005 Y. Wu, D.C. Munson, Jr, “Wide-angle ISAR passive imaging using smoothed pseudo Wigner-Ville distribution,” Proc. IEEE Radar Conf., 2001. pp.363--368, May, 2001 D.R. Wehner, “High Resolution Radar Second Edition,” Artech House, Inc. 1995

  As described above, the radar image generation method using passive radar has been studied as shown in Non-Patent Document 2 and Non-Patent Document 3. However, in the case of the non-patent document 2, it is actually difficult to prepare such observation conditions. In the case of Non-Patent Document 3, it is generally difficult to actually know the movement of the target to be observed accurately. Therefore, the non-patent documents 2 and 3 are considered to be difficult to be practically operated, and are impractical.

  In particular, a passive radar receives a direct wave from a transmitting station (broadcasting station) and a scattered wave in which a radio wave transmitted from the transmitting station is scattered by a target (target), and calculates a correlation between two received signals. Based on this, the delay time difference and the Doppler frequency shift are observed. This delay time estimation accuracy (ie, distance resolution) is determined by the band of the signal transmitted from the transmitting station, and Doppler frequency shift estimation accuracy (Doppler frequency resolution) is determined by the observation time. For this reason, in the conventional passive radar device, in order to generate a target high-resolution radar image, it is necessary to observe continuously at a high sampling frequency for a long time.

  As a result, in a conventional passive radar device, a receiver (reception processing unit) continuously receives scattered waves and direct waves over the entire observation time, and performs a reception process for each of the series of scattered waves and direct waves. After that, the correlation calculation of the two received signals was performed. Therefore, since the correlation calculation processing is performed after the reception processing of each of the series of scattered waves and direct waves is completed, there is a problem that the entire processing time becomes long.

  The present invention has been made to solve the above-described problems, can reduce the overall processing time, and is a practical method for high-resolution radar images by inverse synthetic aperture radar using passive radar. It is an object to obtain a passive radar device that can be generated by

A passive radar device according to the present invention is capable of receiving a direct wave that is a radio wave that is emitted from a radio wave source and directly arrives from the radio wave source, and a plurality of scattered waves that are obtained by scattering radio waves from the radio wave source by a target. Antenna, a reception processing unit connected to the plurality of antennas and performing reception processing on each of the direct wave and the scattered wave received by the plurality of antennas, and the direct wave signal received from the reception processing unit And the scattered wave signal are sequentially divided into a plurality of segments for each predetermined unit time, and a cross-correlation between the direct wave signal and the scattered wave signal is obtained for each segment, thereby obtaining a high-resolution profile. A range compression unit for generating a history of the high resolution profile for the history of the high resolution profile generated by the range compression unit Range migration compensation unit that compensates for range migration, which is a phenomenon in which a target signal representing the target on the history of the profile moves in the range direction due to movement of the target, and range migration obtained by the range migration compensation unit A phase compensation unit that compensates for a phenomenon in which the phase of the target signal changes due to the movement of the target with respect to the compensated signal, and a signal after the phase compensation obtained by the phase compensation unit is reversed in the time direction. A cross-range compression unit that improves the resolution in the cross-range direction by performing Fourier transform, and the reception processing unit determines the operation timing of the reception processing for the direct wave and the scattered wave according to the distance to be observed. It is something to shift .

  According to the passive radar device of the present invention, the range compression unit sequentially divides the direct wave signal and the scattered wave signal into a plurality of segments for each predetermined unit time, and the direct wave signal for each segment. Since the history of the high-resolution profile is generated by calculating the cross-correlation between the signal and the scattered wave signal, the overall processing time can be shortened by enabling the correlation calculation processing on a segment basis. A high-resolution radar image can be generated by a practical method using inverse synthetic aperture radar.

It is a conceptual diagram which shows the passive radar apparatus by Embodiment 1 of this invention. It is a block diagram which shows the passive radar apparatus main body of FIG. It is explanatory drawing for demonstrating the reception process of a general passive radar apparatus. It is explanatory drawing for demonstrating the reception process of the direct wave reception process part of FIG. 2, and a scattered wave reception process part. It is a conceptual diagram which shows the range history before and behind the process by the range migration compensation part of FIG. It is a block diagram which shows the range migration compensation part of FIG. It is a block diagram which shows the phase compensation part of FIG. It is a block diagram which shows the passive radar apparatus by Embodiment 2 of this invention. It is a conceptual diagram which shows the segment division | segmentation process by the pulse division | segmentation type range compression part of FIG. It is a conceptual diagram which shows the signal before and behind the process by the Doppler frequency cell corresponding | compatible inclination compensation part of FIG. It is a block diagram which shows the range migration compensation part corresponding to the Doppler frequency cell of FIG. It is a conceptual diagram which shows the signal before and behind the process by the range migration compensation part corresponding to the Doppler frequency cell of FIG. It is a conceptual diagram for demonstrating the phenomenon in which a target signal straddles several Doppler frequency cells. It is a block diagram which shows a part of passive radar apparatus by Embodiment 3 of this invention.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.
Embodiment 1 FIG.
FIG. 1 is a conceptual diagram showing a passive radar device according to Embodiment 1 of the present invention. In FIG. 1, the observation geometry is shown together with the passive radar device.
In FIG. 1, 1 is a transmitting station (broadcasting station) as a radio wave source, 2 is a direct wave receiving antenna, 3 is a scattered wave receiving antenna, 10 is a passive radar apparatus body, and 100 is A target (target: for example, an aircraft). Hereinafter, the generic names of the antennas 2 and 3 and the passive radar apparatus body 10 are also referred to as “receiving station 4”.

  The direct wave receiving antenna 2 is arranged so as to be directed to the transmitting station 1. Further, the direct wave receiving antenna 2 can receive a direct wave that is a radio wave transmitted from the transmitting station 1 and directly reaching. The scattered wave receiving antenna 3 is arranged so as to be directed to an observation region where the target 100 exists. The scattered wave receiving antenna 3 can receive a scattered wave obtained by scattering a radio wave transmitted from the transmitting station 1 by the target 100.

It is assumed that the transmitting station 1 continuously transmits (broadcasts) a signal having a carrier frequency f _c and a signal band B. The passive radar apparatus body 10 amplifies signals received by the direct wave receiving antenna 2 and the scattered wave receiving antenna 3 and takes out a signal in a desired band through a bandpass filter. Thereafter, the passive radar apparatus body 10 down-converts these signals and samples them. That is, a series of processing from amplification to sampling is reception processing.

  Here, various parameters shown in FIG. 1 are defined as follows.

Further, the distances r _s and r _r between each of the transmission station 1 and the reception station 4 and the target 100 and the distance r _d between the transmission station 1 and the passive radar apparatus body 10 are expressed by the following equation (2). Is defined as follows.

  FIG. 2 is a block diagram showing the passive radar apparatus body 10 of FIG. In FIG. 2, the passive radar apparatus body 10 includes a direct wave reception processing unit (direct wave receiver) 11, a scattered wave reception processing unit (scattered wave receiver) 12, a range compression unit 13, a clutter suppression unit 14, and range migration compensation. Section 15, phase compensation section 16, cross-range compression section 17, and display section 18.

  Here, the passive radar apparatus body 10 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 storage unit of the computer of the passive radar apparatus body 10 includes a direct wave reception processing unit 11, a scattered wave reception processing unit 12, a range compression unit 13, a clutter suppression unit 14, range migration compensation units 15 and 16, and a cross range compression unit 17. A program for realizing the above functions is stored. The direct wave reception processing unit 11 and the scattered wave reception processing unit 12 may be configured by combining circuit elements such as an oscillator and a mixer, or may be configured by combining circuit elements and arithmetic processing using a program. .

FIG. 3 is an explanatory diagram for explaining a reception process of a general passive radar device. FIG. 4 is an explanatory diagram for explaining the reception processing of the direct wave reception processing unit 11 and the scattered wave reception processing unit 12 of FIG. 3 and 4 is a time axis. In a general passive radar device, as shown in FIG. 3, reception processing of direct waves and scattered waves is performed continuously from observation time t _start to t _end (over the entire observation time).

On the other hand, the direct wave reception processing unit 11 and the scattered wave reception processing unit 12 of the first embodiment intermittently (that is, at intermittent timing) for the direct wave and the scattered wave, respectively, as shown in FIG. ) Receive processing. In this case, the direct wave reception processing unit 11 and the scattered wave reception processing unit 12 repeat T ₀ [sec] reception N times at intervals of Δt [sec].

Hereinafter, in accordance with the term of pulse Doppler radar, in this specification, one reception process of T ₀ [sec] is referred to as “pulse”, and T ₀ which is the reception processing time is described as “pulse width”. Further, Δt is assumed to be “pulse repetition interval (PRI)”, and time T _C = NΔt required for observation of N hits for coherent processing is assumed to be “observation time”.

Subsequently, in order to explain the operations of the range compressor 13 and the subsequent processing blocks, the direct wave from the transmission station 1 and the signal of the scattered wave from the target are formulated. Now, the transmission wave from the transmitting station 1 because a narrow-band signal of the center frequency f _c, can represent direct wave from the transmission station 1 at the location of the receiving station 4 by the following equation (3).

Here, a (t) is the complex amplitude of the transmission signal, and τ _d is the propagation delay time of the direct wave. In the passive radar, since the transmission signal is unknown, it is appropriate to treat a (t) as a random process. In the following, wide-sense stationarity (WSS) is assumed. On the other hand, since both the transmitting and receiving stations 1 and 4 are assumed to be fixed stations, τ _d is a constant.

When the target moves, the propagation delay time of the scattered wave is time-varying. However, when the pulse width T ₀ is sufficiently short, the propagation delay time between them can be considered as a first order approximation.

  Based on this relationship, the received signal of the scattered wave can be approximately expressed as the following equation (6).

However, it is assumed here that the target is composed of one scattering point. Α is a ratio of amplitude due to the difference in attenuation caused by the difference in propagation length. further,

Is the Doppler frequency at time t _n . Also, here, the rate of change of propagation delay time compared to the complex amplitude band

Is sufficiently small, the term of the complex amplitude a (t) is regarded as being constant at τ _sn0 between the pulse width T ₀ and the pulse width T ₀ .

When the observed geometry is expressed as shown in FIG. 1, the delay times τ _d and τ _{sn0 of} the direct wave and the scattered wave and the Doppler frequency f _dn of the scattered wave are expressed by the following equations (7) to (7) to It is obtained as in (9).

Here, for the derivation of the equation (9), the relationship of time differentiation of r _s (t) in the following equation (11) is used (the same applies to r _r (t)).

From equation (4) and (6), down-converted signal using a sinusoidal signal of local frequency _f l _{= f c -Δf} c, the following equation (12) is represented by (13).

However, τ _n = τ _{sn0 −τ d} is a delay time difference between the direct wave and the scattered wave. Φ is the initial phase of the local oscillator. Note that the last equation of Expression (13) represents the scattered wave signal using the direct wave signal.

The range compressor 13 performs range compression by executing a cross-correlation process using the following equation (14) for each pulse. Hereinafter, in this specification, the cross-correlation function χ _n (τ) obtained by the range compression by the range compression unit 13 will be described as a “range profile” (high resolution profile).

In addition, the range compression unit 13 sends the range profile χ _n (τ) (n = 0, 1,..., N−1) to the subsequent-stage clutter suppression unit 14. Hereinafter, in this specification, one group (one set) of the range profiles for these N pulses will be described as a “range history” (high resolution profile history).

Substituting equation (13) into equation (14), it can be seen that the range profile χ _n (τ) when one scattering point exists as a target is expressed by the following equation (15).

As for a (t), it is assumed that a broad sense of stationarity (WSS) is established, so the expected value R _a (τ) of the autocorrelation function is expressed by the following equation (16).

Then, the expected value of the range profile χ _n (τ) is next expressed by Expression (17).

In this equation (18), the term of the sinc function is a term representing a loss of correlation with the direct wave generated because the scattered wave is subjected to Doppler shift due to the movement of the target 100, but the pulse width T ₀ is If it is relatively short, this loss can be ignored and the above approximation holds. Further, from the term (T ₀ −τ), it can be confirmed that the pulse width T ₀ needs to be sufficiently long with respect to the assumed delay time difference.

Here, the operation timings of the reception processing of the direct wave reception processing unit 11 and the scattered wave reception processing unit 12 are shifted, and the operation timing of the reception processing of the scattered wave reception processing unit 12 is changed to that of the reception processing of the direct wave reception processing unit 11. by delaying for an operating timing, without widening the pulse width T _0, it is possible to observe the distance. For example, if the operation timing of the scattered wave reception processing unit 12 is delayed by τ _n , the target signal can be integrated without loss. Actually, since the target position is unknown, it is desirable to provide a delay time determined by the distance to the center of the desired observation area.

From the equation (17), the expected value E {χ _n (τ)} of the range profile has a peak at the target delay time difference τ = τ _n (that is, expressed by the following relational expression).

  Further, the value of the complex amplitude at this peak is expressed by the following equation (19).

From this equation (19), it can be confirmed that the phase (expected value) at the peak of the nth range profile is represented by 2π (f _c −Δf _c ) τ _n .

Next, the clutter suppression unit 14 executes a process of subtracting the average of the pulse direction in the range history χ _n (τ) (n = 0, 1,..., N−1) from each range profile, thereby obtaining the background. Suppresses reflection signals (clutter) from stationary objects. Note that the processing of the clutter suppression unit 14 is formulated as the following equation (20).

For a reflected wave signal from a stationary object, the delay time difference does not change for each pulse. That is, it has not undergone a Doppler frequency shift. This is because in Equation (19), if the target is fixed (fixed), it is constant at τ = τ _n , so that it can be confirmed that the signal phase is constant regardless of the pulse number n. In the equation (20), the clutter suppression unit 14 extracts a signal having a Doppler frequency of zero by calculating an average of the N pulse range profiles, and subtracts the extracted signal from each range profile to obtain the Doppler frequency. Suppresses a zero signal. Thereby, the reflection signal (namely, clutter) from the stationary object in the background can be suppressed.

  Here, for the range migration compensation unit 15, the phase compensation unit 16, and the cross range compression unit 17, for example, known inverse synthetic aperture radar processing as shown in Non-Patent Document 4, Patent Document 1, and Patent Document 2 is performed. Applicable. For this reason, in this specification, the description about the detail of the process of each process block 7-9 is abbreviate | omitted, and it demonstrates centering on the content regarding the input / output signal in each process block 7-9.

  The range migration compensation unit 15 executes range migration compensation processing to compensate for range migration, which is a phenomenon in which the target signal moves in the range direction on the range history. FIG. 5 is a conceptual diagram showing a range history before and after processing by the range migration compensation unit 15 of FIG. In FIG. 5, a thick triple line represents a target signal. 5A shows a range history after range compression and before range migration processing, and FIG. 5B shows a range history after range compression and after range migration processing. Further, in the example of FIG. 5, the movement target is approaching the transmitting station 1 and the receiving station 4.

  The range migration compensation unit 15 causes the target signal to appear in the same range in the range history based on the first step of estimating the range migration movement amount and the estimated range migration movement amount. A two-step process is performed with the second step for compensating for the range migration.

  FIG. 6 is a block diagram showing the range migration compensation unit 15 of FIG. FIG. 6 is a block diagram in the case of being configured in accordance with, for example, the method described in the prior art column of Patent Document 2. In addition, although you may comprise according to the content described in the claim of patent document 2, in order to promote an understanding about the outline | summary of a process, it is adding description based on the method as described in a prior art. Is preferred.

  In FIG. 6, the range migration compensation unit 15 includes an amplitude maximum range bin detection unit 15a, a smoothing unit (first smoothing unit) 15b, and a range compensation unit 15c. The maximum amplitude range bin detection means 15a detects the range bin having the maximum amplitude for each pulse of the range history. Range migration is smooth because the pulse repetition period is short enough for the target motion. However, the position of the range bin detected by each pulse often varies due to the influence of noise and interference.

  The smoothing means 15b smoothes the range bin position detected by the maximum amplitude range bin detection means 15a by a method such as applying a curve by the least square method, and the smoothed range migration estimated value is obtained. To derive. The range compensation unit 15c moves the range profile for each pulse in the range direction based on the estimated value of the range migration movement amount derived by the smoothing unit 15b, so that the target signals in the range history are aligned in the same range bin. To compensate.

  The phase compensation unit 16 performs a process of estimating and compensating for the phase change amount at the target reference point. FIG. 7 is a block diagram showing the phase compensation unit 16 of FIG. FIG. 7 is a block diagram in the case where the phase compensation unit 16 is configured according to the method described in the section of the prior art in Patent Document 2, for example. In addition, although you may comprise according to the content described in the claim of patent document 2, in order to promote an understanding about the outline | summary of a process, it is adding description based on the method as described in a prior art. Is preferred.

  In FIG. 7, the phase compensation unit 16 includes a target range bin determining unit 16a, a short-time FFT unit 16b (Fast Fourier Transform), an amplitude maximum frequency detecting unit 16c, a smoothing unit (second smoothing unit) 16d, A phase compensation amount calculation unit 16e and a phase compensation amount multiplication unit 16f are provided.

  The attention range bin determination means 16a calculates the average power in each range of the range profile after the range compensation. Further, the target range bin determining unit 16a sets the range bin that maximizes the calculated average power value as the target range bin, and sends the received signal sequence of the range bin to the subsequent short-time FFT unit 16b.

  The short-time FFT unit 16b performs short-time FFT on the received signal sequence in the target range bin. This makes it possible to observe the time change of the Doppler frequency of the signal in the target range bin. Hereinafter, in this specification, the processing result of the short-time FFT unit 16b will be described as “Doppler history in the target range bin”.

  The amplitude maximum frequency detection means 16c detects the Doppler frequency cell having the maximum Doppler frequency with respect to the Doppler history in the target range bin. Similar to range migration, the change of the Doppler frequency is generally smooth, but the position of the Doppler frequency cell detected in each pulse often varies due to the influence of noise, interference, and the like. Therefore, the smoothing unit 16d uses the least square method for the position of the Doppler frequency cell detected by the maximum amplitude frequency detecting unit 16c, similarly to the smoothing process of the smoothing unit 15b in the range migration compensation unit 15. Then, smoothing is performed by a method such as fitting a curve, and an estimated value of a smooth Doppler frequency change is derived.

  The phase compensation amount calculating means 16e calculates an estimated value of the change amount of the signal phase based on the estimated value of the Doppler frequency change derived by the smoothing means 16d. The phase compensation amount multiplying unit 16f multiplies the signal by a phase component so as to cancel out this phase change based on the estimated value of the change amount of the signal phase calculated by the phase compensation amount calculating unit 16e.

  The cross range compression unit 17 improves the resolution in the cross range direction by performing Fourier transform on the output signal of the phase compensation unit 16 in the pulse direction. Then, the output signal of the cross range compression unit 17 is displayed on the display unit 18 as a radar image. The processing of the cross range compression unit 17 (cross range compression processing) is essentially processing for obtaining a Doppler frequency difference. As described in Non-Patent Document 4, etc., the cross-range axis of the inverse synthetic aperture radar is the axis of the Doppler frequency difference. This also applies to the inverse synthetic aperture radar processing by the passive radar device. It is the same.

  As described above, according to the first embodiment, the direct wave reception processing unit 11 and the scattered wave reception processing unit 12 perform reception processing intermittently. At the same time, the range compression unit 13 obtains a cross history of a direct wave signal and a scattered wave signal for each pulse, thereby generating a range history that is a group of N pulse range profiles. With this configuration, correlation processing can be performed in units of pulses, so that the overall processing time can be shortened, and high-resolution radar images can be generated by a practical method using inverse synthetic aperture radar using passive radar. .

  Here, in the conventional passive radar device, since it is necessary to observe continuously at a high sampling frequency for a long time, the amount of received data is enormous. On the other hand, in the first embodiment, the direct wave reception processing unit 11 and the scattered wave reception processing unit 12 perform reception processing intermittently. Therefore, even when continuously observing at a high sampling frequency for a long time, reception is performed. The amount of data can be reduced.

  In the first embodiment, by appropriately setting the operation timing of the direct wave signal reception processing and the operation timing of the scattered wave signal reception processing, the signal power associated with intermittent reception processing is set. Degradation can be minimized.

Embodiment 2. FIG.
In the first embodiment, the amplitude maximum range bin detection means 15a of the range migration compensation unit 15 maximizes the amplitude from the range profile for each pulse after the output of the range compression unit 13 via the clutter suppression unit 14. By detecting the range bin, the amount of range migration of the target signal is estimated.

  Here, in the first embodiment, since the received signal is thinned, if the target is at a long distance and the pulse width is short, the signal-to-noise ratio (SNR) is insufficient. There is a possibility that the target cannot be detected in the range profile for each pulse. In order to avoid this, it is necessary to increase the pulse width. However, when the pulse width is increased, the approximation of equation (18) is not established, and thus the loss of signal power cannot be ignored. Therefore, there is a need for a system that maintains the signal-to-noise ratio as much as possible while reducing the amount of received data. Therefore, in the second embodiment, the pulse division type range compression unit 21 once divides the pulse into a plurality of segments and performs range compression processing for each segment.

  FIG. 8 is a block diagram showing a passive radar device according to Embodiment 2 of the present invention. In FIG. 8, the passive radar device main body 20 has a pulse division type range compression unit 21 instead of the range compression unit 13 of the first embodiment. In addition, the passive radar device body 20 includes a Doppler processing unit 22, a Doppler frequency cell compatible slope compensation unit 23, and a Doppler frequency cell compatible range migration compensation unit 24 instead of the range migration compensation unit 15. Other configurations are the same as those of the passive radar apparatus main body 10 of the first embodiment.

FIG. 9 is a conceptual diagram showing segment division processing by the pulse division type range compressor 21 of FIG. FIG. 9 shows a state where the pulse is divided into H segments. At this time, the length of each segment (hereinafter referred to as “segment width” in the present specification) is T ₀ / H. By shortening the segment width and performing range compression for each segment, the approximation of equation (18) is established for each segment, and loss of signal power due to range compression can be reduced. In the following, the signals of all segments and all pulses output from the pulse division type range compressing unit 21 are expressed as the following Expression (21).

Subsequently, the clutter suppression unit 14 according to the second embodiment performs a process of subtracting the average of all the segments and all the pulses of the range history χ _{n, h} (τ) from each range profile, so that it can be detected from the background stationary object. Suppresses reflected signal (clutter). Here, the processing of the clutter suppression unit 14 is formulated as the following Expression (22).

  Subsequently, the Doppler processing unit 22 performs discrete Fourier transform on the output range history of the clutter suppression unit 14 in the segment direction for each range as in the following equation (23) to obtain a Doppler frequency spectrum.

Here, m is a Doppler frequency cell number, and m = 0, 1,..., M−1. The output signal of the Doppler processing unit 22 is y _n (τ, f _dm ) defined by the equation (23).

Here, as in the first embodiment, the output of the Doppler processing unit 22 will be described assuming that the target is configured with one scattering point. Consider a case where the target Doppler frequency is constant during the pulse width T ₀ and the following equation (24) holds.

When this equation (24) holds, the delay time difference τ _{n, h} in the h-th segment of the n-th pulse can be expressed by a linear equation such as the following equation (25).

  Therefore, the expected value for the result of the discrete Fourier transform in the segment direction in the range bin in which the target signal exists is expressed by the following equation (26).

Here, assuming that the target amplitude does not change between pulse widths, approximation was made as α (T ₀ −τ _{n, h} ) = α (T ₀ −τ _{n, h} ). From this equation (26), it can be seen that a peak occurs in the Doppler frequency cell shown in the following equation (27) in the Doppler spectrum y (τ _n , f _dm ).

However, C is the complex amplitude at the peak and is represented by the following equation (28).

Next, the process of the Doppler frequency cell corresponding inclination compensator 23 will be described. FIG. 10 is a conceptual diagram showing signals before and after processing by the Doppler frequency cell corresponding slope compensator 23 of FIG. Since the Doppler frequency of the signal included in the m-th Doppler frequency cell is f _dm , the delay time τ _{n, m} in the n-th pulse changes in a first order to correspond to this Doppler frequency, It can be represented by the following formula (29).

Therefore, it is possible to substantially compensate for the range of the signal by compensating for the range shift represented by Expression (29) with respect to y _n (τ, f _dm ). Here, the output signal of the Doppler frequency cell corresponding slope compensator 23 is expressed as follows.

  As shown in FIG. 10, the Doppler frequency cell corresponding slope compensator 23 can compensate the first-order slope component of the signal and cannot compensate for the second-order or higher range migration. The Doppler frequency resolution in the Doppler processing unit 22 is a resolution determined by the pulse width, but the pulse width is not set so large. For this reason, the resolution of the Doppler frequency obtained here is not so high. Therefore, a signal included in each Doppler cell may have a primary range migration component corresponding to each Doppler cell and at the same time a secondary or higher range migration component.

  The output of the slope compensation unit 23 corresponding to the Doppler frequency cell is then sent to the range migration compensation unit 24 corresponding to the Doppler frequency cell. FIG. 11 is a block diagram showing the Doppler frequency cell compatible range migration compensation unit 24 of FIG. In FIG. 11, the Doppler frequency cell compatible range migration compensation unit 24 includes an incoherent integration unit 24a, a target detection unit 24b, an amplitude maximum range bin detection unit 24c, a smoothing unit (third smoothing unit) 24d, and a range compensation unit 24e. Have.

  The incoherent integration unit 24a performs incoherent integration in the pulse direction on the output signal of the Doppler frequency cell corresponding slope compensation unit 23 using the arithmetic expression of the following expression (30).

The target detection unit 24b applies target detection processing to the output of the incoherent integration unit 24a. This is performed by comparing a threshold value appropriately set by a method such as CFAR (Constant False Alarm Rate) processing and the signal z (τ, f _dm ). By this target detection processing, it can be considered that the target signal is included in the detected range bin / Doppler frequency cell.

  The maximum amplitude range bin detection unit 24c detects the maximum amplitude range bin for each pulse with respect to the signal included in the Doppler frequency cell in which the target signal is detected by the target detection unit 24b. Here, as in the first embodiment, the position of the range bin detected by each pulse often varies due to the influence of noise, interference, and the like. Therefore, the smoothing unit 24d smoothes the range bin position detected by the maximum amplitude range bin detection unit 24c by a method such as applying a least square method curve, and derives an estimated value of the range migration movement amount. .

  The range compensation unit 24e moves the range profile for each pulse in the range direction based on the estimated value of the range migration movement derived from the smoothing unit 24d, so that the target signals in the range history are aligned in the same range bin. To compensate. As described above, the range migration component of the signal is compensated by the range migration processing by the range migration compensation unit 24 corresponding to the Doppler frequency cell as shown in FIG. The operations of the phase compensation unit 16 and the cross range compression unit 17 are the same as those in the first embodiment.

  As described above, according to the passive radar device of the second embodiment, the direct wave reception processing unit 11 and the scattered wave reception processing unit 12 are configured to intermittently perform signal reception processing to reduce the amount of received data. Repress. At the same time, after the pulse division type range compression unit 21 divides the pulse into a plurality of segments and executes range compression processing, the Doppler processing unit 22 calculates the Doppler spectrum by performing discrete Fourier transform in the segment direction. . With this configuration, the same effects as in the first embodiment can be obtained, and loss of signal components can be suppressed even if the pulse width is set relatively long. As a result, since the pulse width can be set relatively long, the signal-to-noise ratio can be improved as compared with the first embodiment.

Embodiment 3 FIG.
In the passive radar device of the second embodiment, when the change rate of the Doppler frequency of the target signal under observation is large, in the output signal y _n (τ, f _dm ) of the Doppler processing unit 22, as shown in FIG. The target signal may straddle multiple Doppler frequency cells. On the other hand, the passive radar device according to the third embodiment is configured to cope with a case where the target signal straddles a plurality of Doppler frequency cells.

  FIG. 14 is a block diagram showing a part of a passive radar device according to Embodiment 3 of the present invention. In FIG. 14, the Doppler frequency cell-compatible range migration compensation unit 24 of the third embodiment has a divided incoherent integration unit 24f instead of the incoherent integration unit 24a of the second embodiment. The Doppler frequency cell compatible range migration compensation unit 24 further includes Doppler cell coupling means 24g. Other configurations are the same as those of the second embodiment.

  Instead of integrating over all N pulses, the division-type incoherent integration means 24f divides and integrates the signal for each K pulse (for each group) as shown in the following equation (31).

The target detection unit 24b performs target detection processing on the output z _i (τ, f _dm ) of the divided incoherent integration unit 24f. By this target detection process, the range bin and Doppler frequency cell in which the target signal exists can be detected for each combination of K pulses.

  The Doppler cell combining unit 24g solves the problem that the signal straddles the Doppler frequency cell by coherently adding the signals of the plurality of Doppler frequency cells whose targets are detected by the target detecting unit 24b. However, when a plurality of Doppler frequency cells whose targets are detected are greatly separated from each other, it should be considered that a plurality of targets are detected, and it is not desirable to combine the Doppler frequency cells.

  For example, assuming that the target signal is detected in the Doppler frequency cell number m and the range τ in the l-th pulse combination, the target signal is detected in the Doppler frequency cell number m + 1 and the range τ + Δτ in the l + 1-th pulse combination. For example, since continuity of the signal is recognized, it can be determined that the target signal straddles the Doppler frequency cell (relevance evaluation). In the Doppler cell combining means 24g, it is necessary to combine the Doppler frequency cells based on such an appropriate determination. The subsequent processing of the maximum amplitude range bin detection means 24c, smoothing means 24d, and range compensation means 24e can be performed in the same manner as in the second embodiment.

  As described above, according to the passive radar device of the third embodiment, in the output signal of the Doppler processing unit 22, when the target signal straddles the Doppler frequency cell, the Doppler cell combining unit 24g includes the target signal. Join. With this configuration, it is possible to appropriately perform the cross range compression even for a target having a large change rate of the Doppler frequency.

  In the first to third embodiments, the direct wave receiving antenna 2 and the scattered wave receiving antenna 3 are described as different types of antennas. However, the direct wave and the scattered wave are separated by digital beam forming using the signal which received the direct wave and the scattered wave with two or more antennas (direct receiving antenna for direct wave / scattered wave). May be.

  In the first to third embodiments, it is also possible to measure the polarization characteristic of scattering at the target by using two reception antennas having polarization characteristics orthogonal to each other as the scattered wave reception antenna. is there. In this case, two radar images having different polarization characteristics can be generated by applying each process of the first to third embodiments to signals obtained by the two scattered wave receiving antennas. It becomes possible.

Furthermore, in the first embodiment, the direct wave reception processing unit 11 and the scattered wave reception processing unit 12 intermittently perform reception processing as shown in FIG. However, when the pulse width T ₀ and the repetition period Δt are set to coincide with each other, as shown in FIG. 3, a signal equivalent to that obtained when the signal is continuously received is observed. In this case, the signal over the entire observation time is divided into segments for each T ₀ [sec], and each process of the first embodiment is executed. That is, in the first embodiment, the range compression unit 13 sequentially divides the direct wave signal and the scattered wave signal over the entire observation time into segments for each T ₀ [sec], and directly for each segment. The cross-correlation between the wave signal and the scattered wave signal may be obtained. Even in this configuration, correlation calculation processing can be performed in segment units, so that the overall processing time can be shortened, and high-resolution radar images can be generated by a practical method using inverse synthetic aperture radar using passive radar. .
Here, T ₀ as a segment width of the case _{(predetermined} unit time), the amount of change in the Doppler frequency between T ₀ is, it is desirable to set smaller than the Doppler resolution determined by T _0. That is, it is set so as to satisfy the relationship of the following equation.

Here, Δf _d is the rate of change of the target Doppler frequency and is a value depending on the motion of the target. Since the movement of the target to be observed can be estimated to some extent in advance, for example, T ₀ may be set based on the assumed maximum Δf _d .

  DESCRIPTION OF SYMBOLS 1 Transmitting station (radio wave source), 2 Direct wave receiving antenna, 3 Scattering wave receiving antenna, 4 Receiving station, 10, 20 Passive radar device main body, 11 Direct wave receiving processing unit, 12 Scattering wave receiving processing unit, 13 range Compression unit, 14 clutter suppression unit, 15 range migration compensation unit, 15a amplitude maximum range bin detection unit, 15b smoothing unit (first smoothing unit), 15c range compensation unit, 16 phase compensation unit, 16a attention range bin determination unit, 16b Short-time FFT means, 16c maximum amplitude frequency detection means, 16d smoothing means (second smoothing means), 16e phase compensation amount calculation means, 16f phase compensation amount multiplication means, 17 cross range compression section, 18 display section, 21 pulses Division type range compression unit, 22 Doppler processing unit, 23 Doppler frequency cell compatible slope compensation unit, 4 Doppler frequency cell compatible range migration compensation unit, 24a incoherent integration means, 24b target detection means, 24c maximum amplitude range bin detection means, 24d smoothing means (third smoothing means), 24e range compensation means, 24f division type incoherent Integration means, 24g Doppler cell coupling means, 100 targets.

Claims (11)

A plurality of antennas capable of receiving a direct wave, which is a radio wave emitted from a radio wave source and directly reaching from the radio wave source, and a scattered wave obtained by scattering a radio wave from the radio wave source by a target;
A reception processing unit that is connected to the plurality of antennas and performs reception processing for each of the direct wave and the scattered wave received by the plurality of antennas;
The direct wave signal and the scattered wave signal received from the reception processing unit are sequentially divided into a plurality of segments for each predetermined unit time, and the direct wave signal and the scattered wave signal for each segment. A range compression unit that generates a history of a high resolution profile by obtaining a cross-correlation with
With respect to the history of the high resolution profile generated by the range compression unit, the range is a phenomenon in which a target signal representing the target on the history of the high resolution profile moves in the range direction due to the movement of the target. A range migration compensator that compensates for migration;
A phase compensation unit that compensates for a phenomenon in which the phase of the target signal changes due to the movement of the target, with respect to the signal after the range migration compensation obtained by the range migration compensation unit,
A cross range compression unit that improves the resolution in the cross range direction by performing inverse Fourier transform on the signal after phase compensation obtained by the phase compensation unit in the time direction ,
The passive processing device , wherein the reception processing unit shifts the operation timing of the reception processing for the direct wave and the scattered wave according to a distance to be observed . A plurality of antennas capable of receiving a direct wave, which is a radio wave emitted from a radio wave source and directly reaching from the radio wave source, and a scattered wave obtained by scattering a radio wave from the radio wave source by a target;
A reception process that is connected to the plurality of antennas and intermittently performs a reception process in units of pulses having a pulse width that is a preset reception processing time for each of the direct wave and the scattered wave received by the plurality of antennas. And
By obtaining a cross-correlation between the direct wave signal and the scattered wave signal for each pulse of the direct wave signal and the scattered wave signal received from the reception processing unit, the history of the high resolution profile is obtained. A range compression unit to generate,
With respect to the history of the high resolution profile generated by the range compression unit, the range is a phenomenon in which a target signal representing the target on the history of the high resolution profile moves in the range direction due to the movement of the target. A range migration compensator that compensates for migration;
A phase compensation unit that compensates for a phenomenon in which the phase of the target signal changes due to the movement of the target, with respect to the signal after the range migration compensation obtained by the range migration compensation unit,
A cross range compression unit that improves the resolution in the cross range direction by performing inverse Fourier transform on the signal after phase compensation obtained by the phase compensation unit in the time direction ,
The passive processing device , wherein the reception processing unit shifts the operation timing of the reception processing for the direct wave and the scattered wave according to a distance to be observed . From the history of the high resolution profile, by subtracting the average value of the time direction, the passive radar system according to claim 1 or claim 2, further comprising a clutter suppressing module for removing Zerodoppura frequency components. The range migration compensation unit is
A maximum amplitude range bin detection means for detecting a maximum range bin of amplitude for each segment or pulse of the history of the high resolution profile;
First smoothing means for deriving an estimated value of range migration movement by fitting a curve to the position of the amplitude maximum range bin for each segment or pulse detected by the maximum amplitude range bin detection means;
Based on the estimated value of the movement amount of the range migration derived by the first smoothing means, claim 1, characterized in that it comprises a range compensating means for compensating the range migration to claim 3 1 The passive radar device according to item. The phase compensator is
The target range bin determining means for selecting the range bin signal in which the target signal exists, from the signal after the range migration compensation obtained by the range migration compensation unit,
A short-time FFT unit that performs a short-time FFT process on the received signal sequence of the range bin selected by the target range bin determination unit in order to detect a temporal change in the Doppler frequency of the signal;
An amplitude maximum frequency detecting means for detecting a target signal appearing in a signal obtained by the short-time FFT means;
Second smoothing means for deriving an estimated value of the time change of the Doppler frequency of the target signal by fitting a curve to the time change of the amplitude maximum frequency cell detected by the maximum amplitude frequency detection means;
Phase compensation amount calculating means for calculating a phase compensation amount corresponding to an estimated value of a temporal change in the Doppler frequency of the target signal derived by the second smoothing means;
By multiplying the phase compensation amount calculated by the phase compensation amount calculating means, according to claim claim 1, characterized in that it comprises a phase compensation amount multiplying means for compensating the time variation of the Doppler frequency of the target signal 4 The passive radar device according to any one of the above. A plurality of antennas capable of receiving a direct wave, which is a radio wave emitted from a radio wave source and directly reaching from the radio wave source, and a scattered wave obtained by scattering a radio wave from the radio wave source by a target;
A reception processing unit that is connected to the plurality of antennas and intermittently performs reception processing in units of pulses that are a preset reception processing time for each of the direct wave and the scattered wave received by the plurality of antennas;
The scattered wave signal and the direct wave signal after reception processing by the reception processing unit are each divided into segments having a time shorter than the pulse width, and the scattered wave signal and the direct wave signal after the division are divided. A range compression unit that generates a history of high resolution profiles by determining the cross-correlation with the signal for each segment;
A Doppler processing unit that calculates a Doppler spectrum for each pulse by Fourier transforming the history of the high resolution profile generated by the range compression unit in the segment direction of each pulse;
With respect to the history of the high resolution profile generated by the range compression unit, the range is a phenomenon in which a target signal representing the target on the history of the high resolution profile moves in the range direction due to the movement of the target. Among the migrations, a Doppler frequency cell compatible slope compensation unit that compensates for a primary range migration component corresponding to the Doppler frequency cell in the pulse direction;
From the signal after compensation of the first-order range migration component obtained by the Doppler frequency cell corresponding slope compensation unit, the Doppler frequency cell in which the target signal exists is detected, and for the detected Doppler frequency cell signal, A range migration compensation unit corresponding to a Doppler frequency cell that compensates for a secondary or higher range migration component;
A phase compensator that compensates for a phenomenon in which the phase of the target signal changes due to the movement of the target with respect to the signal after compensation of the second or higher order range migration component obtained by the range migration compensating unit corresponding to the Doppler frequency cell When,
A passive radar device comprising: a cross range compression unit that improves the resolution in the cross range direction by performing inverse Fourier transform on the signal after phase compensation obtained by the phase compensation unit in the time direction. The passive radar apparatus according to claim 6 , further comprising: a clutter suppression unit that removes a zero Doppler frequency component by subtracting an average value in a time direction from a history of the high resolution profile of all pulses and all segments. . The Doppler frequency cell compatible range migration compensator is
Incoherent integration means for performing incoherent integration in the pulse direction on the signal obtained by the Doppler frequency cell corresponding slope compensation unit;
Target detection means for performing target detection processing on the signal obtained by the incoherent integration means;
Amplitude maximum range bin detection means for detecting a maximum amplitude range bin for each pulse with respect to the signal of the Doppler frequency cell including the target signal detected by the target detection means;
A third smoothing means for deriving an estimated value of the range migration movement amount by fitting a curve to the position of the maximum amplitude range bin for each pulse detected by the maximum amplitude range bin detection means;
Passive radar device according to claim 6 or claim 7, characterized in that it has a range compensating means for compensating the range migration on the basis of the estimated value of the moving amount of the derived range migration by the third smoothing means . The Doppler frequency cell compatible range migration compensator is
Dividing incoherent integration means for dividing the signals of all observed pulses obtained by the Doppler frequency cell corresponding slope compensation unit into a plurality of groups and performing incoherent integration in the pulse direction for each group;
Target detection means for performing target detection processing on the signal obtained by the split-type incoherent integration means;
When there are a plurality of Doppler frequency cells including the target signal detected by the target detection means, the relevance of the Doppler frequency cells is evaluated, and when the signals of the Doppler frequency cells are determined to be the same target signal, Doppler cell combining means for adding
A maximum amplitude range bin detection unit that detects a maximum amplitude range bin for each pulse with respect to the signal after the Doppler cell combination output by the Doppler cell combination unit;
A third smoothing means for deriving an estimated value of the range migration movement amount by fitting a curve to the position of the maximum amplitude range bin for each pulse detected by the maximum amplitude range bin detection means;
Passive radar device according to claim 6 or claim 7, characterized in that it has a range compensating means for compensating the range migration on the basis of the estimated value of the moving amount of the derived range migration by the third smoothing means . The passive radar device according to any one of claims 1 to 9 , wherein the plurality of antennas include a plurality of scattered wave receiving antennas having different polarization characteristics. The passive radar device according to claim 10, wherein the plurality of scattered wave receiving antennas are two scattered wave receiving antennas having polarization characteristics orthogonal to each other.

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