JPH06138215A - Radar signal processing method - Google Patents

Abstract

PURPOSE:To improve the secondary echo removing ability in a radar device. CONSTITUTION:The input to a phase code circuit 1 is coded under the control of an optimum code control circuit 3 so that the code polarity may be reversed for each hit in a phase code driving circuit 2. This coded signal is converted into the intermediate frequency by a frequency converter 4 and a local oscillator 5, and in addition, converted into the micro-wave by a frequency converter 6 and a local oscillator 7, and emitted from an antenna 10 through a power amplifier 8 and a transmission/reception switch 9. The received signal is supplied to a matched filter 12 through an amplifier 11 and frequency converters 6a, 4a, and the correlated output for the transmitted signal is obtained. The characteristics of the matched filter 12 are controlled by a driving circuit 13. For the secondary echo with different coding form to be received by the matched filter 12, the pulse compression by the correlation is not realized, and the removing property of the secondary echo is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radar signal processing system, and more particularly to a radar signal processing system having an increased secondary echo removing capability in a pulse radar device.

[0002]

2. Description of the Related Art Generally, in a pulse radar device, transmitted pulses are repeatedly emitted at required repetition intervals.

This pulse repetition period is determined corresponding to the maximum distance of the target to be detected. Therefore, if the pulse repetition period is short, the reflected wave from the distant target will return after the next transmission pulse is emitted, so that it is apparently recognized as a near range target.

That is, this is called a secondary echo, and its occurrence is described in detail in the following published documents.

(1) "Introduction to
Radar Systems "Merrill I.D.
Supervised by Skolnik (McGraw-Hill Boo
kCompany, Inc. , (2) "Radar technology"
Supervised by Takashi Yoshida (The Institute of Electronics, Information and Communication Engineers).

Since this secondary echo has a high possibility of being mistaken for a real signal, it is important to remove it.

As a typical example of removing the secondary echo, SEC. 4.2 "Multiple
and Staged Pulse Repeat
"Tition Frequencies" (P129-
P133).

That is, FIG. 4.18
And FIG. As described in 4.19, the transmission pulse repetition time is set to “T + ε”, “T−ε”, “T + ε”,
Alternately changed to "T- [epsilon]", transmitted, received, and then subjected to correction processing for "[epsilon]" using a delay line or the like, and returned to the equidistant repetition time T, the normal fixed target timing. Is FIG. As shown in 4.19 (a), the position is delayed by "Tr + ε" from the reference trigger and appears at the same position in each hit.

On the other hand, the secondary echo (in the above-mentioned document (1), "Second-time-around ech" is used.
o "or" Second-time-around "
If the same process is performed,
Since its timing is delayed by “Tr1” or “Tr2” (Tr1 ≠ Tr2) from the reference trigger, its position is different for each hit.

This is as shown in the above-mentioned literature.
It is shown that the true target or the false image due to the secondary echo can be separated by taking the correlation of the received signals.

That is, since the echoes appearing at the same timing in each hit are the true targets and the echoes existing at different timings are secondary echoes, the correlations for a plurality of hits are taken and only the correlated signals are output. By,
The secondary echo can be removed.

[0012]

In this conventional secondary echo removing method, the secondary echo separation processing is performed only on the time axis, so that when the spread of the clutter on the time axis is large. , The difference between the transmission pulse repetition times must be made larger than this.

However, in the case of a radar system such as a three-dimensional radar which has a narrow beam width and scans from a high elevation angle to a low elevation angle, it is difficult to secure a time margin. Is difficult to set to a large value, and when there is clutter with a large spread on the time axis, such as large islands or mountains, there is a problem that the secondary echo cannot be sufficiently removed.

The object of the present invention is to solve the above-mentioned problems,
An object of the present invention is to provide a radar signal processing method capable of sufficiently removing secondary echoes even if there are clutters such as large islands or mountains that have a large spread on the time axis.

[0015]

A radar signal processing system according to the present invention comprises a means for encoding a pulse transmission signal of a radar device while inverting the polarity for each hit, and an optimum correlation for the pulse transmission signal on the receiving side. Therefore, it has a configuration including means for pulse-compressing the received signal, and means for performing inverse conversion for each hit in synchronization with the encoding characteristic on the transmitting side and the pulse compression characteristic on the receiving side.

Another radar signal processing system of the present invention is a means for converting a pulse transmission signal of a radar device into a frequency-modulated wave having an inverse time / frequency characteristic for each hit, and an optimum for the pulse transmission signal on the receiving side. It is configured to include means for pulse-compressing the received signal in correlation with each other, and means for performing inverse conversion for each hit in synchronization with the frequency modulation characteristic on the transmitting side and the pulse compression characteristic on the receiving side.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the first exemplary embodiment of the present invention.

The embodiment of FIG. 1 exemplifies a radar device using a pulse compression method. The pulse compression method is described in Chapter 12.2 (P28) of “Radar Technology” in the above-mentioned document (2).
9-P293) and the following document (3) "Radar
Handbook ", Merrill I. Skol
supervised by Nik, McGraw-Hill Inc. , Ch
As is apparent from the apter 20 (P20-1 to P20-37) and the like, it is often used as a means for improving both the detection distance and the detection field capability, and a typical pulse compression method is a code modulation method or a frequency modulation method. There is a method.

The first embodiment shown in FIG. 1 utilizes pulse compression by coded phase modulation, and includes a phase coding circuit 1 for coded phase modulation of an input signal and a modulation signal for the phase coding circuit. A phase-encoded drive circuit 2 for supplying and driving a phase-encoded transmission signal, an optimum code control circuit 3 for inversely converting the polarity content of the phase-encoded transmission signal and the pulse compression characteristic on the receiving side for each hit, and performing an optimum code control; Intermediate frequency of (I
F) Frequency converter 4 and local oscillator 5 for conversion
, A frequency converter 6 and a local oscillator 7 for further converting the IF into a microwave band, a power amplifier 8, a transmission / reception switch 9 and an antenna 10, an amplifier 11 for amplifying a received signal, and local oscillators 5, 7 Drives for controlling the characteristics of the matched filter 12 under the control of the frequency converters 6a, 4a that perform the frequency conversion of the received microwave sharing the same, the matched filter 12 that performs the correlation processing on the received signal, and the optimum code control circuit 3. It has a configuration including a circuit 13.

Next, the operation of this embodiment will be described.

The coded phase modulated signal generated by the phase coding circuit 1 is converted into an IF by the frequency converter 4 and the local oscillator 5, and further the frequency is converted into a predetermined microwave band by the frequency converter 6 and the local oscillator 7. Convert.

After that, the transmission signal amplified by the power amplifier 8 is supplied to the antenna 10 through the transmission / reception switch 9 and is radiated into the air from here.

The signal reflected from the target is transmitted to the antenna 10
Are captured by the converter 1, amplified by the amplifier 11 via the transmission / reception switch 9, and then frequency-converted by the frequency converters 6a and 4a, and supplied to the matched filter 12.

The matched filter 12 is controlled by the drive circuit 13 so as to have a characteristic such that the signal generated by the phase encoding circuit 1 can be optimally correlated, whereby the input signal is a pulse whose amplitude is required. Stacked and increased by the compression ratio.

The input signal to the matched filter 12 cannot secure the optimum correlation with any combination of codes, and the amplitude builds up when the autocorrelation is obtained, but when the autocorrelation cannot be obtained. The amplitude does not build up. That is, even if a signal different from the transmitted signal comes in, pulse compression is not performed, so that it is extremely effective for suppressing interference and interference.

In the present embodiment, as shown in FIG. 2, the phase code of the transmission pulse is changed so that the polarity is inverted every hit.

At the timing of FIG. 2A, the phase code shown in FIG. 2C is used for encoding (hereinafter referred to as phase code A), and the next hit in FIG. 2B is (d). As shown in (c), the code sequence is transmitted as a code string whose polarity is inverted (hereinafter referred to as a phase code B). Examples of these encodings are commonly referred to as Barker codes.

The # 1 reception signal obtained by the # 1 transmission pulse of FIG. 2 (a) is shown in FIG. 2 (e). This is a reflection signal from a normal target, and the signal encoded with the phase code A is subjected to processing such that optimum pulse compression is performed. Therefore, as shown in (g) of FIG. Amplitude builds up with pulse compression. However, when obtaining (g) from (e) of FIG. 2, a certain processing delay occurs.

On the other hand, the # 2 transmission pulse shown in FIG.
Although transmitted as the phase code B, the characteristics of the matched filter 12 shown in FIG. 1 are changed by the drive circuit 13 so that the phase code B has an optimum mutual relationship.

Therefore, the # 2 reception signal obtained by the # 2 transmission pulse in FIG. 2B is as shown in FIG. 2F.

Now, assume that the secondary echo generated by (a) and the normal target obtained by (b) are mixed in FIG. 2 (f).

Since all of these received signals are processed so that the optimum pulse compression is performed for the phase code B, the normal target is pulse-compressed as shown in FIG. It is clear that the secondary echo generated by the code A cannot be autocorrelated by the matched filter 12 and is not output as a signal as indicated by P1.

As described above, the secondary echo can be suppressed by using the pulse compression method by the coded phase modulation and transmitting / receiving the content of the coding by changing the polarity for each transmission hit.

FIG. 3 is a block diagram showing the configuration of the second embodiment of the present invention.

The second embodiment shown in FIG. 3 has the same frequency converters 4, 4a and 6, 6 as the first embodiment shown in FIG.
a, local oscillators 5, 7, power amplifier 9, antenna 10,
In addition to the amplifier 11, a frequency conversion circuit 14 that performs linear frequency modulation (chirp) on the input, a frequency conversion drive circuit 15 that supplies a modulation signal to the frequency conversion circuit 14 to drive it, and time / frequency characteristics of a frequency modulation pattern. Optimum frequency modulation control circuit 16 which has an inverse characteristic every hit
And a matched filter 17 that has a time / frequency characteristic that is inverse to the received chirp modulated wave and that obtains a sharp output by pulse compression, and a drive circuit 18 that controls the characteristic of the matched filter 17 for each hit. Have.

The frequency conversion circuit 14 is driven by the frequency conversion drive circuit 15 under the control of the optimum frequency modulation control circuit 16, and the frequency modulation of the chirp A of the time / frequency characteristic shown in FIG. (A) # 1 transmission pulse and (b) # 2 transmission pulse that is frequency-modulated for chirp B shown in (d) of which time / frequency characteristic is reverse to that of (c) of FIG. And are output alternately for each hit.

FIG. 4E shows the # 1 received signal by the # 1 transmission pulse of FIG. 4A, and FIG.
The # 2 reception signal by the # 2 transmission pulse of (b) is shown.

Now, as shown in FIG. 4 (f), it is assumed that the # 2 received signal includes the secondary echo due to the # 1 transmission pulse in the temporal processing range together with the normal target.

The output of the matched filter 17 of the # 1 received signal by the chirp A is pulse-compressed and sharpened by the customs clearance as shown in FIG. 4 (g).

On the other hand, the normal target of the received signal of # 2 by the chirp B is the matched filter 17, which is pulse-compressed and sharpened by correlation as shown in (h) of FIG. However, since the secondary echo of the # 1 transmission pulse is a signal due to the chirp A, it is not pulse-compressed by the pulse compression processing for the chirp B and does not appear as a signal as indicated by P2 in (h). Removal can be secured.

In this way, the secondary echo can be suppressed by using the pulse compression method by linear frequency modulation and transmitting / receiving the modulation pattern for each hit with the time / frequency characteristic as the inverse characteristic.

[0042]

As described above, according to the present invention, the transmission signal is encoded on the transmission side, and the polarity of the encoding is changed for each hit, or the transmission signal is frequency-modulated, and its time / frequency characteristic is determined. By controlling each hit so as to have an inverse characteristic for each hit, and on the receiving side to obtain optimum correlation in synchronization with the transmission signal and to ensure pulse compression, suppression of secondary echo can be significantly improved. Has the effect.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a first exemplary embodiment of the present invention.

FIG. 2 is a timing diagram illustrating the operation of FIG.

FIG. 3 is a block diagram showing a configuration of a second exemplary embodiment of the present invention.

FIG. 4 is a timing diagram illustrating the operation of FIG.

[Explanation of symbols]

 1 Phase Coding Circuit 2 Phase Coding Driving Circuit 3 Optimum Code Control Circuit 4, 4a Frequency Converter 5 Local Oscillator 6, 6a Frequency Converter 7 Local Oscillator 8 Power Amplifier 9 Transmission / Reception Switch 10 Antenna 11 Amplifier 12 Matched Filter 13 Driving Circuit 14 Frequency modulation circuit 15 Frequency modulation drive circuit 16 Optimal frequency modulation control circuit 17 Matched filter 18 Drive circuit

Claims (2)

[Claims] 1. A means for encoding a pulse transmission signal of a radar device while inverting the polarity for each hit, a means for compressing the reception signal by obtaining optimum correlation with the pulse transmission signal at the reception side, and a transmission side. Radar signal processing method, characterized in that it has means for inversely converting each hit in synchronization with the encoding characteristics of the above and the pulse compression characteristics of the receiving side. 2. A means for converting a pulse transmission signal of a radar device into a frequency-modulated wave whose time / frequency characteristic is an inverse characteristic for each hit, and a receiving side performs an optimum correlation with respect to the pulse transmission signal to pulse-compress the reception signal. A radar signal processing method comprising: a means and a means for performing inverse conversion for each hit in synchronization with a frequency modulation characteristic on the transmitting side and a pulse compression characteristic on the receiving side.