JPS5853317B2 - Pulse compression radar method - Google Patents

Description

[Detailed description of the invention] This invention relates to a pulse compression radar device.

FIG. 1 shows a block diagram of a conventional stepped frequency modulation pulse compression radar device (in the case of 5 frequency divisions).

In the figure, 1 is the frequency f. crystal oscillator, 2 is f.

This is a frequency multiplier that generates a CW wave that is an integral multiple of .

3 is a pulse generator with a pulse width τ, 4 is a delay circuit that gives delays of O9τ, 2τ, 3τ, and 4τ to the pulse wave generated from this pulse generator 3, 5 is a switching circuit, and 6 to 10 are gate circuits f , ~f5 is gated with a pulse of width τ to generate a high-frequency pulse train of width 5τ.

11 is a transmitter that converts the frequency of these pulse trains into microwaves and transmits them; 12 is a transmitter/receiver switch; 13 is a radar antenna; 14 is a receiver that converts the frequency of the received waves and separates them into five waves of frequencies f1f2f3f and f5 using a filter. Machine, 1
5 is a switching circuit that switches in response to switching of the switching circuit 5;
16 to 20 are O2τ and 2τ for each pulse, respectively, so that the received waves are combined at the same time.

Delay circuits providing delays of 3τ and 4τ, 21 a detection circuit for detecting the combined received wave, and 22 an indicating device such as a cathode ray tube.

The pulse compression radar device described here can increase the maximum detection distance without impairing the distance resolution.

The conventional pulse compression radar device described above must have separate delay circuits and gate circuits for transmission and reception.

Each of them also has a crystal oscillator and a frequency multiplier to generate CW waves.

In order to increase the pulse compression ratio and increase the distance resolution, it is necessary to increase the number of frequency divisions, but in that case, the need to have separate circuits for transmitting and receiving is a major obstacle in terms of cost. Become.

Therefore, the present invention aims to reduce the cost of a radar device by using a high frequency impulse to generate a transmission wave and by sharing a filter circuit, a delay circuit, and a gate circuit for transmission and reception.

The pulse compression radar device of the present invention will be explained in detail below.

Conventional pulse compression radar devices use a crystal oscillator, a frequency multiplier corresponding to each stepped modulation frequency, and individual gate circuits to generate a transmission pulse train, as shown in Figure 1. In the device of this invention, an impulse,
In reality, we take advantage of the fact that the spectrum of microwave rectangular modulation waves with extremely narrow pulse widths is flat over a wide area, and extract them using bandpass filters with center frequencies equal to the individual stepped modulation frequencies, delay them, A transmission wave is generated by combining them.

During transmission, the microwave rectangular modulated wave with a very narrow width generated by the impulse generator 23 in FIG. An amplitude modulated wave with the center frequency of the filter as a carrier is obtained.

Figure 3a shows the frequency spectrum components of the microwave rectangular modulated wave extracted by nine filters 25-33; C shows the time response waveforms of each of the filters 25 to 33.

Each filter output has a delay time that differs by a fixed time τ corresponding to each filter 25 to 33 in FIG.
The signals pass through delay circuit No. 2, are gated at a fixed time τ by gate circuits 43 to 51, are amplified by amplifiers 52 to 60, and are then combined by combiner 6.

FIG. 3d shows delay circuits 34 to 42 and gate circuits 43 to 51.
The time relationship of each output after passing through is shown, and FIG. 3e shows the output of the combiner 6.

If a limit is applied to this before transmission, a stepped frequency modulated transmission wave as shown in FIGS. 4a and 4b is obtained.

Since the frequency components of the pulses generated by the impulse generator 23 are not completely flat, they do not become perfectly stepped modulated waves, and slight frequency disturbances occur in each wave, but this has little effect on pulse compression. do not.

As shown in FIG. 1, conventional devices use different filters, switching circuits, and delay circuits for pulse compression during reception, but the device of the present invention compresses pulses as shown in FIG. The same filter 25 to 3 used when transmitting the received pulse
3. Pulse compression is performed using delay circuits 34-42.

The transmitted waves passing through the limiter are shown in Figures 4a-c.

FIG. 4a shows the contact line of the transmitted wave, FIG. 4 shows the frequency modulation characteristics within the transmitted wave, and FIG. 4C shows the frequency spectrum of the transmitted wave.

When fT(t) and its frequency spectrum FT(f) are expressed mathematically, first, the respective waveforms fnr(t) and FnT(f) before being synthesized by the synthesizer 61 are as follows.

represents a pulse waveform with an amplitude An and a pulse width π.

Therefore, the transmitted wave f r(t) and its frequency spectrum Fr(7') are as follows.

Note that An and Bn are constants, and fn and tn are as shown in Figure 4 a, b,
The relationship is as shown in c.

This transmitted wave is reflected by the target and passes through the radar antenna 63 and transmission/reception switch 62 shown in FIG. 2 as a received wave again, and enters the mixer 64.

By selecting the local frequency of the mixer 64 to be twice the center frequency of the frequency spectrum FTCf) of the transmitted wave, the frequency modulation characteristics of the received wave at the output of the mixer 64 are synthesized, as shown in Fig. 5a and b. This is temporally symmetrical with the frequency modulation characteristic of the transmitted wave at the output of the transmitter 61 (FIG. 4b).

Therefore, the frequency spectrum of the received wave at the output of the mixer 64 is expressed by equation (3).

Furthermore, this received wave is filtered through the same filters 25 to 3 as at the time of transmission.
3 subsequent delay lines 34-42 gate circuits 43-51,
The respective outputs passing through the amplifiers 52 to 60 are combined at the same time by the combiner 61, so that pulse compression can be realized.

In the invention described above, by mixing the received wave at a local frequency twice the center of the frequency spectrum of the transmitted wave, pulse compression is achieved using filters 25 to 33 and delay lines 34 to 42 for both transmission and reception. Therefore, cost reduction can be achieved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a conventional pulse compression radar device, FIG. 2 is a block diagram showing an embodiment of the present invention, and FIG.
Figure 3 is a characteristic diagram showing the frequency components of microwave rectangular modulated waves extracted by each filter.
Figure C is a waveform diagram showing the output of the filter, Figures 3 d and e are waveform diagrams showing the output of the delay circuit, gate circuit, and composite image, Figure 4 a is a waveform diagram showing the transmitted wave, and Figure 4 4 is a characteristic diagram showing the frequency modulation characteristics of the transmitted wave, FIG. 4 C is a characteristic diagram showing the frequency spectrum of the transmitted wave, FIG. 5 a is a waveform diagram of the received pulse, and FIG. FIG. 5C is a characteristic diagram showing the frequency modulation characteristics of the mixer 64.
FIG. 3 is a characteristic diagram showing a frequency spectrum of a received wave at the output. In the figure, 23 is an impulse generation circuit, 24 is a transmission/reception switching circuit, 25 to 23 are filters, 34 to 42 are delay circuits, 4
3 to 51 are gate circuits, 52 to 60 are amplifiers, 61 is a combiner, 62 is a transmission/reception switch, 63 is a radar antenna, 64
is a mixer, 65 is a detection circuit, and 66 is an indicator.

Claims (1)

[Claims] 1 Pass a narrow rectangular impulse through bandpass filters with center frequencies that differ by a predetermined frequency, and then pass them through delay lines with different delay times by a fixed amount of time corresponding to the center frequency of each filter.The delay of each delay line is By gated and synthesized at a time equal to the time difference, an expanded pulse frequency-modulated in a desired stepped manner is obtained, and this expanded pulse is used as a transmitted wave, and the received wave reflected by the target and arriving is set to the frequency of the transmitted wave. Pulse compression configured to mix at a local frequency twice the center of the spectrum to make the frequency modulation characteristics temporally symmetrical with that of the transmitted wave, and then compress the pulse by passing it through the above filter and delay line. radar equipment.