JPH0155433B2 - - Google Patents

Description

Detailed Description of the Invention This invention relates to a Doppler frequency compensation method in a coded pulse compression radar, in which a plurality of bandpass filters with equal bandwidths and different center frequencies are used to detect a target Doppler frequency. (Hereinafter, this band-pass filter and an aggregate of a plurality of band-pass filters are referred to as a "Doppler filter" and a "Doppler filter bank," respectively.) By performing phase compensation, the radar's PRF (Pulse
Doppler frequency compensation of coded pulse compression radar that compensates for the target Doppler frequency even for targets with higher Doppler frequency (Repetition Frequency) with a frequency accuracy of less than 1/2 of the bandwidth of the Doppler filter mentioned above. This paper proposes a method.

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

The normal Doppler frequency compensation method mixes the Doppler frequencies at the front stage of the correlator in front of the Doppler filter bank, but it is possible to freely set the amount of compensation and to handle multiple targets with different Doppler frequencies. This is difficult to deal with, and is particularly problematic for aircraft-mounted radars and anti-aircraft surveillance radars whose targets have a wide speed range.

The present invention aims to solve these problems by multiplying the Doppler filter bank by a fixed amount of phase compensation corresponding to the center frequency of each Doppler filter at the subsequent stage of the Doppler filter bank.

This will be explained in detail below with reference to FIGS. 1, 2, and 3.

In FIG. 1, the transmitter 1 has a transmission pulse width τ,
A high-frequency pulse with a transmission repetition period T is generated, and the phase modulator 2 generates a high-frequency pulse as shown in Fig. 2a. The phase modulation code is used to perform phase modulation within the transmission pulse width for each sub-pulse width Δτ. Here, n is the sub-pulse number. This signal is radiated from the antenna 4 via the circulator 3 toward the target.

The received signal is converted to an intermediate frequency by a receiver 5, then 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 shown in FIG. 2b. Here, A in the figure is the target Doppler angular frequency ω _d . As shown in FIG. 2b, the above phase detection waveform is amplitude modulated at the target Doppler angular frequency ω _d . next,
This signal is quantized by an A/D (Analog-to-Digital) converter 8 and FFT (Fast Fourier
(Transform) processor and memory. where N for each range bin equal to the sub-pulse width
The FFT calculation of the points is performed, and the output signal F _o (ω _dp ) of the above Doppler filter corresponding to the target Doppler frequency is F _o (ω _dp ) = Kej{φ + ωdnΔτ + (n)} = Kej{φ + (mωp + ωdo) nΔτ+(n)}...(2) where K is a constant, φ is the initial phase,
ω _p is the transmission pulse repetition angular frequency of the radar, ω _dp is the apparent Doppler frequency folded back by sampling, and m is an integer. This dotsupura
The output signal of the filter is subjected to a constant phase shift of (mω _p +ω _dp )nΔτ for each range bin due to the influence of the target Doppler frequency, as shown in FIG. 3a. The phase compensation circuit 1
0, the amplitude according to the target Doppler frequency can be calculated by multiplying each range bin corresponding to each sub-pulse of the received signal by the phase compensation amount θ(m)=e ^-j(m 〓 ^p+ 〓 ^do)n 〓〓 The modulation component can be removed, and the output signal F _op (ω _dp ) of the phase compensation circuit 10 becomes F _op (ω _dp )=Kij{φ+(n)} (3). This signal waveform is shown in FIG. 3b.

Next, a method for setting the amount of phase compensation will be described.

As mentioned above, the phase compensation amount θ(m) is expressed as θ(m)=e ^-j(m 〓 ^p+ 〓 ^do)n 〓〓 ...(4). When ω _p is rewritten using the frequency selection characteristic of the N-point FFT, that is, the frequency interval B of adjacent Doppler filters, ω _p =2πNB (5). Also, if M is the Doppler filter number that matches the target Doppler angular frequency ω _dp folded back by sampling, that is, the number assigned to the output signal of the N-point FFT in order from the DC component, ω _dp = 2πMB...( 6) becomes. Therefore, if we rewrite equation (4) using equations (5) and (6), we get becomes. In equation (7), 2πMBΔτ and N/M are constants for each Doppler filter making up the Doppler filter bank 9, so if we set them as C ₁ and C ₂ , respectively, equation (7) becomes θ(m )=e ^-jc ₁ ^(mc ₂ ⁺¹⁾ⁿ ...(8). Here, m is an unknown integer, and the maximum value of m is determined by the speed of the target and the PRF of the radar.
m _p is determined. Therefore, when correlation processing is performed in the correlator 11 while changing m from 0 to m _p , when m corresponds to the target true Doppler frequency ω _d , a pulse compression waveform as shown in Fig. 3c is obtained. can get.

As described above, according to the method of the present invention, even for a target having a Doppler frequency higher than the PRF of the radar, the Doppler filter can be detected with a frequency accuracy of 1/2 or less of the bandwidth of the Doppler filter. Frequency can be compensated.

Furthermore, since the Doppler frequency is compensated at the subsequent stage of the Doppler filter bank, this Doppler frequency compensation method can be similarly applied to a plurality of targets having different Doppler frequencies.

In the example, the phase modulation code for encoded pulse compression was a 7-bit Barker code.
It goes without saying that the present invention can be applied to other numbers of bits or M sequences.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of the configuration of this invention.
Figure 2a shows the output signal of the phase modulator;
Figure b shows the output signal of the phase detector, Figure 3 a
is a diagram showing the output signal of the Doppler filter bank, Figure 3b is a diagram showing the output signal of the phase compensation circuit, and Figure 3c is a diagram showing an ideal pulse compression waveform. 2 is a phase modulator, 3 is a circulator, 4 is an antenna, 5 is a receiver, 6
is a reference oscillator, 7 is a phase detector, 8 is an A/D converter, 9 is a Doppler filter bank, 10 is a phase compensation circuit, 11 is a correlator, and A is a target Doppler angular frequency ω _d .

Claims (1)

[Claims] 1. A transmission system that transmits a high-frequency pulse obtained by performing encoded phase modulation on the output signal of a transmitter to a target, a radar receiver, a phase detector, and A that quantizes the output of the phase detector. /D (Analog-to-Digital) converter,
From DC to radar PRF (Pulse Repetition)
a Doppler filter bank in which a plurality of Doppler filters having the same bandwidth during the frequency) are arranged at equal intervals, a phase compensation circuit, and a correlator;
In a coded pulse compression radar equipped with a receiving system that processes reflected signals from a target, the reflected signals from the target are processed by the Doppler system for each range/bin.
Input into the filter bank, where N is the total number of Doppler filters, M is the number given to each Doppler filter in order from DC, Δτ is the sub-pulse width of the encoded phase modulation, B is the frequency interval of adjacent Doppler filters, When n is the sub-pulse number and m is an integer, the phase compensation amount θ(m) is given by the following formula: θ(m)=e ^-j2 〓(m _N / _M +1)nMB Target for m of Δτ from 0 speed and radar
After multiplying the output signal of the Doppler filter bank by the phase compensation amount θ (m) in the phase compensation circuit while changing it to the maximum value determined by the PRF, the radar's PRF is
A Doppler frequency compensation method for a coded pulse compression radar, characterized in that it is capable of compensating for higher Doppler frequencies as well.