JPS6222109B2 - - Google Patents

Description

Detailed Description of the Invention The present invention relates to a Doppler frequency compensation method in a coded pulse compression radar, in which the output signal of each Doppler filter is multiplied by a constant phase compensation amount according to the center frequency of that Doppler filter. Doppler frequency compensation for pulse compression radar enables the target Doppler frequency to be compensated for with a frequency accuracy of less than 1/2 of the frequency resolution of the Doppler filter bank, and also makes it possible to deal with multiple targets with different Doppler frequencies. This paper proposes a method.

By the way, in a pulse compression radar, the Doppler frequency shift of the received signal caused by the relative speed between the target and the radar causes adverse effects such as a decrease in compression ratio and an increase in range side lobes.

A typical Doppler frequency compensation method performs Doppler frequency compensation and correlation processing on a received signal, and then detects a target Doppler frequency using a Doppler filter bank after pulse compression processing is completed. Therefore, at the stage of compensating the Doppler frequency, since the Doppler frequency of the target to be compensated is unknown, a method such as performing compensation using the Doppler frequency of a representative target targeted by the radar device is used. Therefore, if the target Doppler frequency differs from the above-mentioned representative value, an adverse effect such as a decrease in pulse compression ratio will occur. In addition, it is difficult to perform Doppler frequency compensation for multiple targets with different Doppler frequencies within the same range bin without increasing hardware such as increasing the number of processing channels. This is particularly a problem for aircraft-mounted radars and anti-aircraft surveillance radars that target targets moving at high speed.

This invention improves these conventional problems by multiplying the output signal of each Doppler filter by a fixed amount of phase compensation according to the center frequency of that Doppler filter at the subsequent stage of the Doppler filter bank. It was calculated. This invention will be explained in detail below using FIGS. 1, 2, and 3.

In FIG. 1, the transmitter 1 has a transmission pulse width τ,
An RF pulse with a transmission repetition period T is generated, and the phase modulator 2 generates an RF pulse as shown in Fig. 2a. Phase modulation is performed within the transmission pulse width using a code sequence.
This signal is sent to the antenna 4 via the circulator 3.
Radiates more towards the target.

The received signal is converted into an IF frequency by a receiver 5, amplified, and then phase-detected by a phase detector 7 using the output signal of a reference oscillator 6 as a reference. This phase detection waveform is amplitude modulated at the target Doppler angular frequency ω _d as shown in FIG. 2b.

Next, this signal is transferred to the sample holder, A/D
The signal is quantized by a converter 8 and input to a Doppler filter bank 9 consisting of an FFT processor and memory. Incidentally, the received signal f _o t is obtained by pulse modulating a continuous wave expressed by the following equation with a pulse width Δγ and a pulse repetition period T.

f _o t = Ae ^j (ωdt + θn) ...... (2) θn = ψ + nωdΔγ + ψn ...... (3) Here, n is the sub-bit number (each pulse with a pulse width Δγ shown in Figure 2 a) number, and ψ is n =0
The initial phase when becomes.

The memory constituting the Doppler filter bank 9 is a sample holder and stores the received signal quantized by the A/D converter 8, and the FFT processor performs Fourier transform discretely at high speed. It is. 0 for N point FFT
It is equivalent to arranging N bandpass filters with a bandwidth of almost 1/NT at a frequency interval of 1/NT within a frequency range of 1/T from converts the above bandpass filter into a Doppler filter, while
A device consisting of an FFT processor and the above memory is called a Doppler filter bank.

Also, as is clear from equation (4), the absolute value of equation (4) is maximum when ω = ωd, so the target Doppler frequency is detected as the center frequency of the Doppler filter with the largest output amplitude. be done. However, as mentioned above, the Doppler filter bank 9 is equivalent to Doppler filters arranged at a frequency interval of 1/NT, so the ability to analyze any frequency is 1/NT, and this is called the frequency resolution of the Doppler filter bank 9.

From the above, when an N-point FFT operation is performed for each range bin corresponding to each sub-bit in the Doppler filter bank 9, the Doppler filter output signal Fn(ω
d) is obtained by setting ω=ωd in equation (4), and Fn(ωd)=Ke ^j {〓 ⁺ⁿ 〓 ^d 〓〓 ⁺ 〓 ⁽ⁿ⁾ }
………(5) K=ANΔγ ………(6) It is expressed as follows. As shown in Figure 3a, the output signal of this Doppler filter is a certain amount (nω) for each range bin due to the influence of the target Doppler frequency.
_d Δγ). The phase compensation circuit 10 converts this phase shift into e ^-j for each range bin.
When compensated by multiplying the phase amount ⁿ 〓 ^d 〓〓, the output signal Fno (ω _d ) of the phase compensation circuit 10 becomes Fno (ω _d )=Ke ^j {〓 ⁺ 〓 ⁽ⁿ⁾ } ………(7) becomes. This signal waveform is shown in FIG. 3b.

Then, when correlation processing is performed by the correlator 11, a compressed pulse waveform as shown in FIG. 3c is obtained.

In the above explanation, it is assumed that the target Doppler frequency and the center frequency of one Doppler filter match, but since Doppler filter banks constructed using FFT have discrete frequency selection characteristics, The maximum phase compensation error in Doppler frequency compensation is 1/2 of the frequency resolution of the Doppler filter bank.

As described above, according to the method of this invention,
1/ of the frequency resolution of the Dotsupura filter bank
The target Doppler frequency can be compensated with a frequency accuracy of 2 or less, and the Doppler filter
Since Doppler frequency compensation is performed at the subsequent stage of the bank, it is also possible to deal with targets with different Doppler frequencies.

Although a configuration example is shown in FIG. 1 as an embodiment, various modifications may be made without departing from the gist of the present invention. Further, in the explanation, a 7-bit Barker code is used as the code sequence for pulse compression, but it goes without saying that the present invention can be applied to other bit numbers, M sequences, etc.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an example of the configuration of this invention, Fig. 2a
2 shows the output signal of the phase modulator, FIG. 2b shows the output signal of the phase detector, FIG. 3a shows the output signal of the Doppler filter bank,
FIG. 3b is a diagram showing the output signal of the phase compensation circuit, and FIG. 3c is a diagram showing the pulse compression waveform. In the figure, 1 is a transmitter, 2 is a phase modulator, 3 is a circulator, 4 is an antenna, 5 is a receiver, 6
is the reference oscillator, 7 is the phase detector, and 8 is the sample oscillator.
A holder, an A/D converter, 9 a Doppler filter bank, 10 a phase compensation circuit, and 11 a correlator.

Claims (1)

[Claims] 1. A transmitter that performs encoded phase modulation on the output signal of a transmitter and transmits it to a target, a radar receiver, a phase detector, a means for quantizing the output of the phase detector, and a means for quantizing the output of the phase detector. A Doppler filter bank that outputs a signal corresponding to a target Doppler frequency among the converted signals, and a phase compensation circuit and a correlator that multiply the output signal of the Doppler filter bank by a certain amount of phase compensation. , the received signal is input to the above Doppler filter bank for each range bin, and the Doppler filter is
After multiplying the output signal of the filter bank by a constant phase compensation amount according to the center frequency of each Doppler filter in the above phase compensation circuit, the Doppler frequency is compensated by performing correlation processing in the above correlator, Furthermore, the Doppler frequency compensation method for pulse compression radar is characterized by making it possible to deal with multiple targets having different Doppler frequencies.