Echo Removal Device for Pulse Radar and Echo Removal Program for Pulse Radar

Abstract

To prevent an increase in noise floor level due to insufficient removal of undesired order echoes and to prevent the level of desired order echoes from being attenuated due to excessive removal of the undesired order echoes in demodulating the desired order echoes and removing the undesired order echoes in a phase modulation pulse radar.SOLUTION: The present disclosure is a secondary echo cancellation device 7 that removes a secondary echo from a Doppler spectrum from which the secondary echo has been demodulated when the velocity variance of the Doppler spectrum from which the secondary echo has been demodulated is small, rather than large, compared to a given threshold value, and that removes the secondary echo between Doppler velocities of the tail of the secondary echo at which the level of the secondary echo is approximately equal to the level of the noise floor, in the Doppler spectrum from which the secondary echo has been demodulated.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present disclosure relates to an echo removal device for a pulse radar and an echo removal program for a pulse radar that demodulate an echo of a desired order and remove an echo of an undesired order.

Background Art

[0002] An echo removal device for a pulse radar and an echo removal program for a pulse radar that demodulate a primary echo and remove a secondary echo are disclosed in Patent Documents 1 and 2.

[0003] First, a general pulse radar that does not apply Patent Documents 1 and 2 will be described. The target detection process of a conventional general pulse radar is shown in FIG. 1. In the upper left column of FIG. 1, transmission pulse waves T1 and T2 are transmitted at a repetition period t rep . Then, received signal waves R1-1 and R2-1 for the transmission pulse waves T1 and T2 are received at times t and t rep +t after the transmission of the transmission pulse wave T1. Further, although the received signal wave R1-2 for the transmission pulse wave T1 should be received at time t rep +Δt after the transmission of the transmission pulse wave T1, it appears that the received signal wave R1-2 for the transmission pulse wave T2 is received at time Δt after the transmission of the transmission pulse wave T2.

[0004] In the lower left column of FIG. 1, the detection distance from the pulse radar device R is limited by a maximum distance R max (=ct rep / 2). And rainfall C1 corresponding to the received signal waves R1-1 and R2-1 is detected at a distance R (=ct / 2) from the pulse radar device R. Further, rainfall C2 corresponding to the received signal wave R1-2 should be detected at a distance R max +ΔR (=c(t rep +Δt) / 2) from the pulse radar device R, but rainfall C2' corresponding to the received signal wave R1-2 appears to be detected at a distance ΔR (=cΔt / 2) from the pulse radar device R.

[0005] In the right column of FIG. 1, the received signal waves R1-2 and R2-1 that are superimposed are frequency-domain converted to calculate the Doppler spectrum. Then, the peak of the primary echo corresponding to the received signal wave R2-1 is detected, and the peak of the secondary echo corresponding to the received signal wave R1-2 is detected. However, it is impossible to distinguish which of the two echo peaks is the peak of the primary echo and which is the peak of the secondary echo.

[0006] Next, a pulse radar using a phase modulation method to which Patent Documents 1 and 2 are applied will be described. The primary echo demodulation process of a conventional pulse radar using a phase modulation method is shown in FIG. 2. The transmission pulse wave is phase-modulated so that the initial phases of the transmission pulse waves are uncorrelated between the transmission pulse waves. Then, by phase-correcting the received signal wave, the primary echo is demodulated and the secondary echo is removed.

[0007] In the upper left column of FIG. 2, the received signal wave received by the pulse radar device R is frequency-domain converted without phase correction to calculate a Doppler spectrum in which the primary echo and the secondary echo are noise-like (actually, the process in the upper left column of FIG. 2 is not executed).

[0008] In the upper right column of FIG. 2, the received signal wave received by the pulse radar device R is phase-corrected (the phase shift amount of the transmission pulse wave T1 in FIG. 1 is canceled), so that the secondary echo is demodulated and the primary echo is noise-like. Then, the received signal wave in which the secondary echo is demodulated is frequency-domain converted to calculate a Doppler spectrum in which the secondary echo is demodulated.

[0009] In the lower left column of FIG. 2, the secondary echo is removed from the Doppler spectrum in which the secondary echo is demodulated (the white bar portion in the lower left column of FIG. 2). Then, the Doppler spectrum from which the secondary echo is removed is time-domain converted to calculate the received signal wave from which the secondary echo is removed.

[0010] In the lower right column of FIG. 2, the received signal wave with the secondary echo removed is phase-corrected (the phase shift amount of the transmission pulse wave T2 in FIG. 1 is canceled), and the primary echo is demodulated. Then, the received signal wave with the primary echo demodulated is subjected to frequency domain conversion, and a Doppler spectrum with the secondary echo removed and the primary echo demodulated is calculated.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0012] The secondary echo removal process of a conventional phase modulation type pulse radar is shown in FIG. 3. In Patent Documents 1 and 2, a method of setting the range of Doppler velocities from which the secondary echo is removed to an appropriate removal range from the Doppler spectrum with the secondary echo demodulated is not disclosed.

[0013] In the upper left column of FIG. 3, the range of Doppler velocities from which the secondary echo is removed from the Doppler spectrum with the secondary echo demodulated is set to a removal range that is too narrow. In the upper right column of FIG. 3, in the Doppler spectrum with the primary echo demodulated, due to under-removal of the secondary echo, the level of the noise floor rises and the signal-to-noise ratio of the primary echo decreases.

[0014] In the lower left column of FIG. 3, the range of Doppler velocities from which the secondary echo is removed from the Doppler spectrum with the secondary echo demodulated is set to a removal range that is too wide. In the lower right column of FIG. 3, in the Doppler spectrum with the primary echo demodulated, due to over-removal of the secondary echo, the level of the primary echo attenuates (the level of the noise floor also attenuates).

[0015] Therefore, in order to solve the above problems, the present disclosure aims to prevent an increase in the level of the noise floor caused by under-removal of undesired-order echoes and to prevent attenuation of the level of desired-order echoes caused by over-removal of undesired-order echoes when demodulating desired-order echoes and removing undesired-order echoes in a phase modulation type pulse radar.

Means for Solving the Problems

[0016] In order to solve the above problems, when the velocity dispersion of the Doppler spectrum in which the undesired-order echoes are demodulated is small rather than large compared to a predetermined threshold value, the undesired-order echoes are removed from the Doppler spectrum in which the undesired-order echoes are demodulated.

[0017] Specifically, the present disclosure provides an echo removal device for a pulse radar that demodulates an echo of a desired order and removes an echo of an undesired order by phase-correcting a received signal wave in a pulse radar that phase-modulates transmitted pulse waves so that the initial phases of the transmitted pulse waves are uncorrelated between the transmitted pulse waves. The device includes: a non-desired order echo demodulation unit that demodulates the non-desired order echo and noiseifies the desired order echo by phase-correcting the received signal wave received by the pulse radar, and calculates a Doppler spectrum in which the non-desired order echo is demodulated by performing a frequency domain conversion on the received signal wave in which the non-desired order echo is demodulated; a non-desired order echo removal unit that removes the non-desired order echo from the Doppler spectrum in which the non-desired order echo is demodulated when the velocity dispersion of the Doppler spectrum in which the non-desired order echo is demodulated is not greater than a predetermined threshold; and a desired order echo demodulation unit that calculates a received signal wave in which the non-desired order echo is removed by performing a time domain conversion on the Doppler spectrum in which the non-desired order echo is removed, demodulates the desired order echo by phase-correcting the received signal wave in which the non-desired order echo is removed, and calculates a Doppler spectrum in which the desired order echo is demodulated by performing a frequency domain conversion on the received signal wave in which the desired order echo is demodulated. The echo removal device for a pulse radar is characterized by comprising the above units.

[0018] According to this configuration, in a pulse radar using a phase modulation method, when demodulating an echo of a desired order, by appropriately determining whether to remove an echo of an undesired order, it is possible to prevent attenuation of the level of the echo of the desired order caused by excessive removal of the echo of the undesired order.

[0019] Further, the present disclosure provides an echo removal device for a pulse radar, characterized in that the non-desired order echo removal unit sets the predetermined threshold with respect to the velocity dispersion of the Doppler spectrum in which the non-desired order echo is demodulated in the vicinity of half of the Nyquist velocity of the pulse radar.

[0020] According to this configuration, in a pulse radar using a phase modulation method, when demodulating a desired-order echo, it is possible to appropriately determine whether or not to remove an undesired-order echo.

[0021] In order to solve the above problems, it was decided to remove the undesired-order echo between the Doppler speeds at the trailing edge of the undesired-order echo where the level of the undesired-order echo becomes almost equal to the level of the noise floor among the Doppler spectra in which the undesired-order echo has been demodulated.

[0022] Further, in the present disclosure, the undesired-order echo removal unit removes the undesired-order echo between the Doppler speeds at the trailing edge of the undesired-order echo where the level of the undesired-order echo becomes almost equal to the level of the noise floor among the Doppler spectra in which the undesired-order echo has been demodulated. A pulse radar echo removal device characterized by that.

[0023] According to this configuration, in a pulse radar using a phase modulation method, when demodulating a desired-order echo, by appropriately setting the removal range of the undesired-order echo, it is possible to prevent an increase in the level of the noise floor caused by under-removal of the undesired-order echo, and it is possible to prevent attenuation of the level of the desired-order echo caused by over-removal of the undesired-order echo.

[0024] Further, in the present disclosure, the undesired-order echo removal unit multiplies a multiple that increases as the signal-to-noise ratio of the undesired-order echo becomes larger among the Doppler spectra in which the undesired-order echo has been demodulated, and the velocity dispersion of the Doppler spectra in which the undesired-order echo has been demodulated, and removes the undesired-order echo within the calculated Doppler speed range. A pulse radar echo removal device characterized by that.

[0025] According to this configuration, in a pulse radar using a phase modulation method, when demodulating a desired-order echo, the removal range of the undesired-order echo can be appropriately set.

[0026] In addition, in the present disclosure, the undesired-order echo removal unit performs a cyclic shift of the Doppler velocity on the Doppler spectrum in which the undesired-order echo has been demodulated so that a part of the peak of the undesired-order echo is not folded back at the Nyquist velocity of the pulse radar. The desired-order echo demodulation unit performs a cyclic shift of the Doppler velocity in the opposite direction and over the same width as the cyclic shift of the Doppler velocity of the undesired-order echo removal unit on the Doppler spectrum from which the undesired-order echo has been removed. The present disclosure relates to an echo removal device for a pulse radar.

[0027] According to this configuration, even when a part of the peak of the undesired-order echo is folded back at the Nyquist velocity of the pulse radar, the velocity dispersion of the Doppler spectrum in which the undesired-order echo has been demodulated can be appropriately calculated, and the above-described effects can be achieved.

[0028] In addition, the present disclosure relates to a pulse radar echo removal program for causing a computer to sequentially execute each process performed by the undesired-order echo demodulation unit, the undesired-order echo removal unit, and the desired-order echo demodulation unit included in the above-described pulse radar echo removal device.

[0029] According to this configuration, a program having the above-described effects can be provided.

Effects of the Invention

[0030] As described above, in the present disclosure, in a phase modulation type pulse radar, when demodulating a desired-order echo and removing an undesired-order echo, an increase in the level of the noise floor due to under-removal of the undesired-order echo is prevented, and attenuation of the level of the desired-order echo due to over-removal of the undesired-order echo can be prevented.

Brief Description of the Drawings

[0031]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Embodiments for Carrying Out the Invention

[0032] Embodiments of the present disclosure will be described with reference to the accompanying drawings. The embodiments described below are examples of the implementation of the present disclosure, and the present disclosure is not limited to the following embodiments.

[0033] (Configuration of a Pulse Radar Device with a Phase Modulation Method According to the Present Disclosure) The configuration of a pulse radar device with a phase modulation method according to the present disclosure is shown in FIG. 4. The processing of a pulse radar device with a phase modulation method according to the present disclosure is shown in FIG. 5. The pulse radar device R includes an oscillation unit 1, a phase modulation unit 2, a transmission unit 3, a circulator 4, an antenna 5, a reception unit 6, and a secondary echo removal device 7, and can detect rainfall C. The secondary echo removal device 7 includes a secondary echo demodulation unit 71, a secondary echo removal unit 72, and a primary echo demodulation unit 73, and can be realized by installing the secondary echo removal program shown in FIG. 5 in a computer.

[0034] The oscillation unit 1 oscillates a transmission pulse wave. The phase modulation unit 2 phase-modulates the transmission pulse wave so that the initial phases of the transmission pulse waves are uncorrelated between the transmission pulse waves. The transmission unit 3 transmits the transmission pulse wave via the circulator 4. The antenna 5 irradiates the transmission pulse wave and receives the received signal wave. The reception unit 6 receives the received signal wave via the circulator 4. The secondary echo removal device 7 demodulates the primary echo and removes the secondary echo by performing phase correction on the received signal wave. Hereinafter, each process of the secondary echo removal device 7 will be described.

[0035] (Secondary echo demodulation process of the pulse radar of the phase modulation method of the present disclosure) The secondary echo demodulation process of the pulse radar of the phase modulation method of the present disclosure is shown in FIGS. 6 and 7. In the upper left column of FIGS. 6 and 7, the received signal wave received by the pulse radar device R is frequency-domain converted without phase correction, and a Doppler spectrum in which the primary echo and the secondary echo are noise-added is calculated (actually, the process in the upper left column of FIGS. 6 and 7 is not executed).

[0036] In the upper right column of FIGS. 6 and 7, the secondary echo demodulation unit 71 acquires the received signal wave received by the pulse radar device R (step S1). Then, by performing phase correction on the received signal wave received by the pulse radar device R (the phase shift amount of the transmission pulse wave T1 in FIG. 1 is canceled), the secondary echo is demodulated and the primary echo is noise-added (step S1). Further, by performing frequency-domain conversion on the received signal wave in which the secondary echo is demodulated, a Doppler spectrum in which the secondary echo is demodulated is calculated (step S1).

[0037] In the lower left column of FIGS. 6 and 7, the secondary echo removal unit 72 performs a cyclic shift of the Doppler velocity v on the Doppler spectrum in which the secondary echo is demodulated so that a part of the peak of the secondary echo is not folded at the Nyquist velocity ±V of the pulse radar device R nyq (step S2). This is the velocity dispersion σ of the Doppler spectrum in which the secondary echo is demodulated as shown in the lower right column of FIGS. 6 and 7 vThis is for appropriately calculating it (step S3).

[0038] In the upper right column of FIG. 6, a part of the peak of the secondary echo is not folded back at the Nyquist speed ±V of the pulse radar device R, but a cyclic shift of the Doppler speed v is executed so that the maximum value of the peak of the secondary echo is located at the Doppler speed v = 0 (step S2). In the upper right column of FIG. 7, since a part of the peak of the secondary echo is folded back at the Nyquist speed ±V of the pulse radar device R, a cyclic shift of the Doppler speed v is executed so that the maximum value of the peak of the secondary echo is located at the Doppler speed v = 0 (step S2). nyq In the upper right column of FIG. 6, a part of the peak of the secondary echo is not folded back at the Nyquist speed ±V of the pulse radar device R, but a cyclic shift of the Doppler speed v is executed so that the maximum value of the peak of the secondary echo is located at the Doppler speed v = 0 (step S2). In the upper right column of FIG. 7, since a part of the peak of the secondary echo is folded back at the Nyquist speed ±V of the pulse radar device R, a cyclic shift of the Doppler speed v is executed so that the maximum value of the peak of the secondary echo is located at the Doppler speed v = 0 (step S2). nyq In the upper right column of FIG. 7, since a part of the peak of the secondary echo is folded back at the Nyquist speed ±V of the pulse radar device R, a cyclic shift of the Doppler speed v is executed so that the maximum value of the peak of the secondary echo is located at the Doppler speed v = 0 (step S2).

[0039] In the lower right columns of FIGS. 6 and 7, the secondary echo removal unit 72 calculates the velocity dispersion σ of the Doppler spectrum in which the secondary echo is demodulated (step S3). This is for appropriately determining whether or not to remove the secondary echo as shown in FIGS. 8 and 9 (step S5). v In the lower right columns of FIGS. 6 and 7, the secondary echo removal unit 72 calculates the velocity dispersion σ of the Doppler spectrum in which the secondary echo is demodulated (step S3). This is for appropriately determining whether or not to remove the secondary echo as shown in FIGS. 8 and 9 (step S5).

[0040] Here, the velocity dispersion σ of the Doppler spectrum in which the secondary echo is demodulated v is calculated as in Equation 1. In Equation 1, S(v) indicates the spectral intensity, and v ave is the weighted average value of the Doppler speed v within the range of the Doppler speed v = -V nyq to +V nyq . And Equation 1 is appropriately calculated by the cyclic shift of the Doppler speed v.

Equation

[0041] Alternatively, the velocity dispersion σ of the Doppler spectrum in which the secondary echo is demodulated v is calculated as in Equation 2. In Equation 2, R n indicates the autocorrelation of lag n with respect to the received signal wave in the time domain. And Equation 2 is appropriately calculated without the cyclic shift of the Doppler speed v.

Equation

[0042] In the lower right columns of FIGS. 6 and 7, the secondary echo removal unit 72 calculates not only the velocity dispersion σ of the Doppler spectrum of the secondary echo v but also the signal-to-noise ratio SNR of the secondary echo (step S4). This is to appropriately set the removal range of the secondary echo in consideration of the velocity dispersion σ of the Doppler spectrum of the secondary echo as shown in FIGS. 8 and 9 (step S6). v

[0043] Here, the signal-to-noise ratio SNR of the secondary echo is calculated by Equation 3. In Equation 3, S ave (v: near the peak or noise floor) represents the average value of the spectral intensity S(v) within the range of the Doppler velocity v = near the peak or noise floor. [Number]

[0044] Alternatively, the signal-to-noise ratio SNR of the secondary echo is calculated by Equation 4. In Equation 4, R n represents the autocorrelation of lag n with respect to the received signal wave in the time domain. [Number]

[0045] (Secondary Echo Removal Processing of Pulse Radar with Phase Modulation Method of the Present Disclosure) The principle of secondary echo removal of the pulse radar with the phase modulation method of the present disclosure is shown in FIG. 8. In each column of FIG. 8, the secondary echo is a Gaussian function with the same Doppler velocity dispersion but different spectral intensities, and the noise floor is constant and the same regardless of the Doppler velocity v.

[0046] In the left column of FIG. 8, the signal-to-noise ratio SNR of the secondary echo is relatively "large". Then, the velocity dispersion σ of the Doppler spectrum of the secondary echo v ​spreads relatively "narrowly" compared to the Doppler velocity dispersion of the Gaussian function. On the other hand, the range of the Doppler velocity v at the tail of the second echo, where the level of the second echo becomes equal to the noise floor level, is relatively "wide". Therefore, by multiplying the Doppler velocity dispersion σ v of the second echo by a relatively "large" multiple n, the removal range of the second echo can be appropriately set.

[0047] In the middle column of FIG. 8, the signal-to-noise ratio SNR of the second echo is relatively "small". Then, the Doppler velocity dispersion σ v of the second echo spreads relatively "widely" compared to the Doppler velocity dispersion of the Gaussian function. On the other hand, the range of the Doppler velocity v at the tail of the second echo, where the level of the second echo becomes equal to the noise floor level, is relatively "narrow". Therefore, by multiplying the Doppler velocity dispersion σ v of the second echo by a relatively "small" multiple n, the removal range of the second echo can be appropriately set.

[0048] In the right column of FIG. 8, the signal-to-noise ratio SNR of the second echo is "0 dB". Then, the Doppler velocity dispersion σ v is "V nyq / √3". On the other hand, the range of the Doppler velocity v at the tail of the second echo, where the level of the second echo becomes equal to the noise floor level, has a "width of 0". Therefore, if the Doppler velocity dispersion σ v of the second echo is "V nyq / 2 ≈ V nyq / √3 or more", it is possible to appropriately determine that the second echo cannot be removed. Alternatively, by multiplying the Doppler velocity dispersion σ v of the second echo by a multiple n that is "0", the removal range of the second echo can be appropriately set.

[0049] The second echo removal process of the pulse radar using the phase modulation method of the present disclosure is shown in FIG. 9. The second echo removal unit 72 determines that the Doppler velocity dispersion σ v of the Doppler spectrum in which the second echo is demodulated is a predetermined threshold value (≈ Vnyq When it is smaller than (1 / 2) (step S5, YES), the secondary echo is removed from the Doppler spectrum in which the secondary echo has been demodulated (step S6). On the other hand, the velocity dispersion σ of the Doppler spectrum in which the secondary echo has been demodulated v is larger than a predetermined threshold value (≒V nyq / 2) (step S5, NO), the removal of the secondary echo from the Doppler spectrum in which the secondary echo has been demodulated is aborted (step S6 is aborted).

[0050] The secondary echo removal unit 72 removes the secondary echo between the Doppler velocities v at the tail of the secondary echo, where the level of the secondary echo is approximately equal to the level of the noise floor, in the Doppler spectrum in which the secondary echo has been demodulated (step S6). That is, the Doppler velocity v = -nσ calculated by multiplying the multiple n, which increases as the signal-to-noise ratio SNR of the secondary echo increases, and the velocity dispersion σ of the Doppler spectrum in which the secondary echo has been demodulated v ~ +nσ v within the range of (step S6). v The secondary echo is removed within the range of (step S6).

[0051] In the left column of FIG. 9, using a model in which a Gaussian function and a noise floor are superimposed, the multiple n, which increases as the signal-to-noise ratio SNR of the secondary echo increases, is calculated. For example, if the signal-to-noise ratio SNR of the secondary echo is 6 dB or 0 dB, the multiple n is approximately 2 or 0. Here, the function of the multiple n with respect to the signal-to-noise ratio SNR of the secondary echo may be stored as an approximate polynomial. And the function of the multiple n with respect to the signal-to-noise ratio SNR of the secondary echo is applicable regardless of the velocity dispersion σ of the Doppler spectrum in which the secondary echo has been demodulated v is applicable regardless of the velocity dispersion σ of the Doppler spectrum in which the secondary echo has been demodulated.

[0052] In the middle column of FIG. 9, in the range of removing the secondary echo, linear interpolation using the noise floors on both sides is performed, and compared with the right column of FIG. 9, it is possible to prevent the attenuation of the level of the primary echo caused by over-removing the secondary echo. In the right column of FIG. 9, in the range of removing the secondary echo, zero suppression of the spectral intensity S(v) is performed, and compared with the middle column of FIG. 9, it is possible to prevent the increase in the level of the noise floor caused by under-removing the secondary echo.

[0053] The primary echo demodulation process of the pulse radar of the phase modulation method of the present disclosure is shown in FIG. 10. In the upper left column of FIG. 10, a Doppler spectrum with the secondary echo removed is calculated.

[0054] In the upper right column of FIG. 10, the primary echo demodulation unit 73 performs a cyclic shift of the Doppler velocity v in the opposite direction and over the same width compared to the cyclic shift of the Doppler velocity v of the secondary echo removal unit 72 on the Doppler spectrum with the secondary echo removed (step S7).

[0055] In the lower left column of FIG. 10, the primary echo demodulation unit 73 calculates the received signal wave with the secondary echo removed by converting the Doppler spectrum with the secondary echo removed into the time domain (step S8). Then, by performing phase correction on the received signal wave with the secondary echo removed (the phase shift amount of the transmission pulse wave T2 in FIG. 1 is canceled), the primary echo is demodulated (step S8). Further, by converting the received signal wave with the primary echo demodulated into the frequency domain, the Doppler spectrum with the primary echo demodulated is calculated (step S8).

[0056] In the lower right column of FIG. 10, the central Doppler velocity v of the primary echo cen , the signal-to-noise ratio SNR of the primary echo and the velocity dispersion σ of the Doppler spectrum of the primary echo v are calculated.

[0057] Thus, in the pulsed radar device R using the phase modulation method, when demodulating the primary echo and removing the secondary echo, by appropriately determining whether the secondary echo can be removed, it is possible to prevent the attenuation of the level of the primary echo caused by excessive removal of the secondary echo.

[0058] And, in the pulsed radar device R using the phase modulation method, when demodulating the primary echo and removing the secondary echo, by appropriately setting the removal range of the secondary echo, it is possible to prevent the increase in the level of the noise floor caused by insufficient removal of the secondary echo, and it is possible to prevent the attenuation of the level of the primary echo caused by excessive removal of the secondary echo.

[0059] (Processing of the pulsed radar device of the modified example) In the present embodiment, the primary echo is demodulated as the desired order echo, and the secondary echo is removed as the undesired order echo. As a modified example, in order to detect a long distance, the secondary echo may be demodulated as the desired order echo, and the primary echo may be removed as the undesired order echo. As a further development, in order to detect an even longer distance, a higher order echo may be demodulated as the desired order echo, and a lower order echo may be removed as the undesired order echo.

[0060] In the present embodiment, as the pulsed radar device R, a meteorological pulsed radar for detecting rainfall C is applied. As a modified example, as the pulsed radar device R, a general pulsed radar for detecting a target may be applied. Here, in the meteorological pulsed radar for detecting rainfall C, the use of detecting a longer distance is not very required (because the earth is spherical). On the other hand, in a general pulsed radar for detecting a target, the use of detecting a longer distance can be widely required.

Industrial Applicability

[0061] The echo removal device for a pulse radar and the echo removal program for a pulse radar according to the present disclosure can demodulate echoes of a desired order and remove echoes of an undesired order not only in a weather pulse radar that detects rainfall but also in a general pulse radar that detects targets.

Explanation of Signs

[0062] T1, T2: Transmission pulse wave R1-1, R1-2, R2-1: Received signal wave R: Pulse radar device C1, C2, C2’, C: Rainfall 1: Oscillator 2: Phase modulation unit 3: Transmitter 4: Circulator 5: Antenna 6: Receiver 7: Second echo removal device 71: Second echo demodulation unit 72: Second echo removal unit 73: First echo demodulation unit

Claims

1. In a pulsed radar that phase-modulates transmitted pulse waves so that the initial phases of the transmitted pulse waves are uncorrelated between the transmitted pulse waves, an echo removal device for a pulsed radar that demodulates a desired-order echo and removes an undesired-order echo by phase-correcting a received signal wave, By phase-correcting the received signal wave received by the pulsed radar, demodulating the undesired-order echo and noiseifying the desired-order echo, and calculating the Doppler spectrum in which the undesired-order echo is demodulated by converting the received signal wave in which the undesired-order echo is demodulated into the frequency domain, an undesired-order echo demodulation unit; An undesired-order echo removal unit that removes the undesired-order echo from the Doppler spectrum in which the undesired-order echo is demodulated when the velocity dispersion of the Doppler spectrum in which the undesired-order echo is demodulated is not larger but smaller than a predetermined threshold; By converting the Doppler spectrum from which the undesired-order echo is removed into the time domain, calculating the received signal wave from which the undesired-order echo is removed, phase-correcting the received signal wave from which the undesired-order echo is removed to demodulate the desired-order echo, and calculating the Doppler spectrum in which the desired-order echo is demodulated by converting the received signal wave in which the desired-order echo is demodulated into the frequency domain, a desired-order echo demodulation unit; An echo removal device for a pulsed radar, characterized by comprising:

2. The undesired-order echo removal unit is characterized in that it is set in the vicinity of half of the Nyquist velocity of the pulsed radar as the predetermined threshold with respect to the velocity dispersion of the Doppler spectrum in which the undesired-order echo is demodulated. The echo removal device for a pulsed radar according to claim 1.

3. The non-desired order echo removal unit removes the non-desired order echo between Doppler speeds at the tail of the non-desired order echo in the Doppler spectrum in which the non-desired order echo is demodulated, where the level of the non-desired order echo is approximately equal to the level of the noise floor. The echo removal device for a pulse radar according to claim 1 or 2, characterized by this.

4. The non-desired order echo removal unit removes the non-desired order echo within a range of Doppler speeds calculated by multiplying a multiple that increases as the signal-to-noise ratio of the non-desired order echo increases in the Doppler spectrum in which the non-desired order echo is demodulated, and the velocity dispersion of the Doppler spectrum in which the non-desired order echo is demodulated. The echo removal device for a pulse radar according to any one of claims 1 to 3, characterized by this.

5. The non-desired order echo removal unit performs a cyclic shift of the Doppler speed on the Doppler spectrum in which the non-desired order echo is demodulated so that a part of the peak of the non-desired order echo is not folded back at the Nyquist speed of the pulse radar. The desired order echo demodulation unit performs a cyclic shift of the Doppler speed on the Doppler spectrum from which the non-desired order echo has been removed, in a direction opposite to and over the same width as the cyclic shift of the Doppler speed of the non-desired order echo removal unit. The echo removal device for a pulse radar according to any one of claims 1 to 4, characterized by this.

6. A pulse radar echo removal program for causing a computer to sequentially execute each process performed by the non-desired order echo demodulation unit, the non-desired order echo removal unit, and the desired order echo demodulation unit included in the echo removal device for a pulse radar according to any one of claims 1 to 5.

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