JPS6229753B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a coded pulse compression device used for detecting received signals in radar devices, distance finders, and other similar devices.

Recently, pulse compression radars, which can extend detection distance and improve distance resolution even when the peak power of transmission is reduced, have been increasingly used as radar devices. In this pulse compression radar, a transmitted wave is modulated in order to lengthen the pulse width of the transmitted beam and widen the bandwidth of the beam pulse. Typical modulation methods include the chirp method and the coded pulse method. Compared to the chirp method, the coded pulse method does not have the effect of Doppler shift on the moving target and compresses the pulse of the received signal. It is attracting attention because its functions can be easily adjusted, and it also has excellent temperature characteristics and earthquake resistance. This coded pulse method modulates the phase of the transmitted carrier wave at 0 degrees and 180 degrees according to a predetermined code sequence (code) and emits it, and phase-detects the received reflected wave. The encoded pulse is reproduced and the reproduced encoded pulse signal is applied to an encoded pulse compressor to obtain a narrowly compressed pulse output.

However, the conventional encoded pulse compressor used in the encoded pulse type radar described above is configured to include an analog delay element with a tap having a sampling function, and this delay element is driven by a clock. The input encoded pulses are thereby sampled. Since the sample period is equal to one bit longer than the transmitted code, a miss occurs when the timing of the sample pulse coincides with the switching point of the input code due to the asynchrony between the received input encoded pulse and the sample pulse. The distance at which sampling occurs and corresponds to the timing of the sample pulse (hereinafter referred to as the blind distance)
The disadvantage was that the compression characteristics of the received pulses from the range (referred to as a range) were significantly degraded.

This phenomenon will be explained with reference to FIG. FIG. 1a is a system diagram of a conventional pulse compressor. At the time of transmission, the phase modulated signal is phase-detected after reception and the code at the time of transmission is reproduced. however,
The sign of the reproduced code may be completely reversed due to the phase relationship between the received signal before phase detection and the reference signal of the phase detector, but the characteristics of the pulse compressor in this case are as follows: They are exactly the same except for the output polarity.

Now, the reproduced reception code X is sampled as an analog quantity at every clock pulse, and is further transferred stage by stage within the delay element 11 in synchronization with the clock pulse. The contents of each stage of delay element 11 are detected non-destructively through taps and
After multiplying the time reversal codes of the transmission codes W ₁ , W ₂ , . . . Wn (n is the number of bits of the transmission code) by an equal weighting coefficient, they are added in an adder 13 and pulse compressed.

However, generally the received signal
Since CP is asynchronous, for example, sampling at the timing shown in Figure 1b will yield an accurate pulse compression waveform as output U, but as shown in Figure 1c, the clock pulse will coincide with the switching of the received code. If you sample at the same timing, mistakes may occur.
This results in sampling, and the compression characteristics deteriorate significantly. When this compressor is applied to radar, the blind range due to this mis-sampling is
This occurs every CT/2, and once a radar target enters the blind range, it usually stays there for several tens of milliseconds or more, so the existence of the blind range is an extremely serious obstacle in practical use of radar as it deteriorates reliability.

The present invention discriminates the outputs of m pulse compressors (m is an integer of 2 or more) having different sampling timings, and selectively detects the output resulting from optimal sampling in real time.
The object of the present invention is to provide a highly reliable encoded pulse compression device that significantly improves the deterioration of compression characteristics due to sampling errors associated with conventional methods and reduces the dependence of compression characteristics on sample timing.

Embodiments of the present invention will be described below with reference to the drawings. The basic configuration of the present invention includes m pulse compressors having a sampling function and using analog delay elements driven by a clock, a channel selector for selecting the m outputs, and timing compensation for the m compressed outputs. It consists of a channel select signal generator, and m delay lines for correcting time delays between the channel select signal generator and the channel select signal generator.

The configuration and operating principle of the present invention will be explained with reference to FIGS. 2a and 2b. Figure a shows a system diagram of the present invention. The signal X, whose phase has been detected after reception and the transmitted code has been reproduced, is sent to m compressors 21-1, 21-2, 2.
1-m. The configuration of each compressor is the same as the conventional method shown in Figure 1a, but each compressor has τ=T/m (T is 1 bit length of the transmission code) as shown in Figure 2b. Operate at shifted sample timings ST ₁ , ST ₂ , ...STm.
Therefore, the m compressed waveforms U ₁ , U ₂ ......Um have the following:
There is a mixture of problems caused by correct sample timing and problems due to mis-sampling,
The circuit below selects only the compressed waveform that corresponds to optimal sampling. That is, each compressed output is divided into two branches, one of which is connected to the timing compensator 2.
2-1, 22-2, and 22-m, the signal is input to the channel select signal generator 23, and the other signal is input to the channel select signal generator 2.
a delay line 24-1 for correcting the time delay of 3;
Channel selector 2 through 24-2, 24-m
5. The channel select signal generation circuit 23 detects the optimal sampling among U ₁ , U ₂ , . . . Um, and generates a channel select signal C. Channel selector 25
selects the one specified by the channel select signal C from among U ₁ , U ₂ . . . Um, and outputs it as an optimal compressed waveform.

Next, a specific embodiment of the present invention will be described with reference to FIG. This embodiment is an example of a case where two pulse compressors are used in a 7-bit barker code, and a system diagram thereof is shown in FIG. 3a. The configuration of this example includes two pulse compressors 31-
1, 31-2 and 31-2 against 31-1,
In order to sample the received signal at a timing shifted by T/2 (T is 1 bit length of the transmitted code),
A delay line 32 that _{gives a} delay _of T _{/ 2} to a channel select signal generator 34 and two delay lines 35- for correcting the time delay of the channel select signal generator 34;
It consists of 1,35-2. In this embodiment, the timing compensators 22-1, 22-2, . . . in FIG. 2a are used.
...22-m is realized by the pulse stretcher 36.

FIG. 3b shows the compressed waveform of the 7-bit Barker code. 1 is normal sampling, 2 is amplitude value 1/
2 shows the compressed waveform at the time of missampling and 3 shows the compressed waveform at the time of missampling with an amplitude value of 0. Figure 3c shows the compressed output depending on the timing relationship between the compressed inputs X ₁ and X ₂ and their sample timings.
Indicates U ₁ and U ₂ . However, low time sidelobes specific to the code used are omitted. When miss sampling or near miss sampling occurs, the main lobe of the compressed waveform decreases, and the side lobes adjacent to the main lobe increase accordingly, degrading the compression characteristics, but if U ₁ and U ₂ are miss sampled at the same time. It will never become. Therefore, in Figure 3c
By selecting in real time the part indicated by the thick solid line among U ₁ and U ₂ , a compressed waveform with optimal sampling can always be obtained.

The operating principle of the channel select signal generator 34 for realizing this will be explained with reference to the system diagram shown in FIG. 3a. Compression output U ₁ is pulse stretcher 36
Then, as shown by the broken line in FIG. 3c, it is stretched by T/2 (T is the 1-bit length of the transmission code), resulting in U ₁ '. U ₁ ' and U ₂ are each sample pulses having twice the frequency of the compressor clock pulse CP and timing as shown in Figure 3d.
Sampled at SP, AD converter 37-1, 37-
2 to be digitized. These two outputs are compared in magnitude by a magnitude comparator 38, and the output Y is such that U ₁ ' is U ₂
A pulse train synchronized with the clock pulse SP that has a value of 0 if greater than or equal to 0 and 1 if the opposite
a ₁ , b ₁ , a ₂ , b ₂ ......an, bn...... However, as shown in FIG. 3d, an and bn are outputs corresponding to the first SP1 and the second SP2 among the clock pulses SP, with CP as a reference.

This pulse train Y generates a channel select signal C by a logic circuit 39 according to the decision table shown in FIG. 3e. Corresponding to 0 or 1 of this signal C, the channel selector 3 selects and outputs U ₁ or U ₂ . However, here, in order to select between U ₁ and U ₂ , information for 2 clocks in CP is used, so the internal time of the channel selector signal generation circuit 34 is input to each of the two inputs of the channel selector. Assuming that the delay is T', a delay line 35 with a delay time of T'+2T is inserted to achieve synchronization with the channel select signal. Through the above operations, the thick solid line portion in FIG. 3c is selected as the channel selector output V, and a compressed waveform by optimal sampling is obtained.

As explained above, the present invention uses m pulse compressors and operates them at different sampling timings, and selects and outputs the optimally sampled output. This has the effect of eliminating the blind range caused by incidental sampling errors, reducing variations in compression characteristics depending on the sample timing of the received signal, and improving reliability.

[Brief explanation of the drawing]

Figure 1a is a system diagram of a conventional coded pulse compressor, Figures 1b and c are time charts for explaining its operation, and Figures 2a and b are system diagrams of a coded pulse compressor according to the present invention. Fig. 3a is a system diagram of a specific embodiment of the present invention, Fig. 3b is a typical compression waveform thereof, and Figs. 3c and d are illustrations of its operation. FIG. 3e of the time chart used for explanation is a diagram showing a judgment table of the logic circuit included therein. 11... Delay element, 12... Multiplier, 13...
Adder, 21-1 to 21-m, 31-1 to 31-
m... Pulse compressor, 22-1 to 22-m... Timing compensator, 23, 34... Channel select signal generator, 24-1 to 24-m, 32, 35
-1,35-2...Delay line, 25,33...Channel selector, 36...Pulse stretcher, 3
7-1, 37-2...AD converter, 38...Comparator, 39...Logic circuit.

Claims (1)

[Claims] 1. In a coded pulse compressor equipped with a plurality of pulse compressors each having a sample function and including a tapped analog delay element driven by a clock,
Encoding characterized in that it comprises means for operating the pulse compressors at mutually different sample timings, and means for selectively detecting the output with the maximum amplitude among the compressed outputs of the pulse compressor. Pulse compression device.