JPH02184785A - Clutter suppression device - Google Patents

Abstract

PURPOSE:To improve the stability of a filter by providing memories stored with the coefficients of lattice filters using the output of a clutter Doppler center frequency computing element as an input address and comparing a clutter with the Doppler frequency of a target. CONSTITUTION:The clutter center frequency arithmetic part 3 inputs a radar received signal of two successive bits. The memories 4a, 4b, and 4c are stored with the shape coefficients of filters which are equal in cutoff frequency band width and differ in cutoff center frequency, e.g. coefficients for realizing the patterned filter shapes. A selector 5 selects cutoff frequency band width by operator's operation. A gain controller 6 makes a final gain adjustment. A computing element 7 converts a target speed into a Doppler frequency. A comparator 8 compares the clutter with the Doppler frequency of the target to judge filter formation 'ON' or 'OFF'. A selector 9 selects and outputs the outputs of the memories 4a-4c under the control of a comparator 8 when the filter formation is 'ON' or a coefficient 'O' when 'OFF'.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] Jin's invention relates to a signal processing device for suppressing clutter contained in radar received signals.

[Conventional technology]

Conventionally, as a signal processing device for suppressing clutter contained in a radar received signal, for example, the IEEE International Conference on Acoustic Signal Processing (IEEE International Conference on Acoustic Signal Processing)
nal Conference on Acousti
css 5peech *and Signal Pr
Proceedings of the 1986 edition Lecture number 5
5.22■, Watanabe et al., “Trade-off Study of Adaptive Filtering Algorithm for Adaptive Moving Target Indicator”
e@on Adaptive Filtering
AlgorithmsUsed For Adapti
ve Moving Target Indicato
The one disclosed in rsχ1 is known.

FIG. 5 is a block diagram of a conventional clutter suppression device using a lattice filter. In fig.

(1a), (1b), (1c) are IPRT(P
pulse RepetitionTime: memory for delaying input data by pulse repetition time);
(14g), (14b), and (14c) are lattice filter coefficient calculation units that adaptively calculate coefficients of a lattice filter having a gain valley at the clutter center frequency according to an input signal; (2a) and (2b).

(2c) is a lattice filter that suppresses clutter. FIG. 6 is a block diagram of the lattice filter.

The conventional clutter suppression device is configured as described above, and attempts to suppress clutter by estimating the power spectrum of clutter contained in a received signal from a radar received signal and automatically configuring an inverse filter thereof. The operations of the conventional device can be expressed numerically as shown in equations (1) to (4).

f', (k) = t knee 1 (k) - AC(k)
g'niji(k) (1) g', z(k)=
gn-7(k) -ph',' (st) t'' (
k) (2) X: Conjugate complex f: (k) = g: (k) = xn(k)
ta>: range bin number kOn hit's radar received signal after A/D conversion The symbols in the above equation correspond to the same symbols in FIG.

Since the conventional clutter suppression device operates according to equations +1) to (4), the center frequency f1 is 0, for example, as shown in FIG.
For clutter with a small spectral spread, use a filter with a narrow cutoff bandwidth at a cutoff center frequency f1, and as shown in Figure 8, for clutter with a large spectral spread at a center frequency of 12, use a filter with a cutoff center frequency f2. Adaptively form a wide bandwidth filter.

[Problem to be solved by the invention]

The conventional clutter suppression device as described above attempts to respond faithfully to the clutter power spectrum in the input signal. However, the spectral shape of clutter, which is a reflected wave from natural phenomena, varies considerably from sample to sample.

If a sufficient number of samples cannot be obtained for estimating the spectrum of clutter, there is a problem that a stable suppression filter cannot be formed. Furthermore, the low stability of the filter characteristics also had an adverse effect on the detection of the target signal.

The present invention has been made to solve this problem, and has the advantage of the conventional device of being able to suppress clutter regardless of the Doppler center frequency of the clutter, while still forming a stable and immune filter. The purpose is

[Means to solve the problem]

The clutter suppression device according to the present invention includes an arithmetic unit that calculates the Doppler center frequency of clutter, a memory that stores the coefficients of a lattice filter whose input address is the output of this arithmetic unit, and a clutter and target Doppler frequency that are compared and suppressed. This device includes a comparator and a lattice filter for determining whether to form a filter or not.

[Effect]

In the present invention, a pre-patterned filter shape is stored in a memory, and a cutoff center frequency is calculated from input data from the filter shape and is determined to correspond to nine clutter Doppler center frequencies.

The cutoff frequency bandwidth is selected manually by the operator to form a stable filter.

Furthermore, by comparing the Doppler frequencies of the clutter and the target, it is prohibited to form a suppression filter near the target Doppler frequency.

〔Example〕

FIG. 1 is a configuration diagram showing an embodiment of the present invention.
(1a), (1b), (2a), (2b), (2
c) It is exactly the same as the rice following device described in 'd-H. +
This is a clutter center frequency calculation unit that receives as input a 31Vi continuous 2-bit radar reception signal. (4a), (
4b) and (4c) are memories storing coefficients having filter shapes having the same cutoff frequency bandwidth and different cutoff center frequencies.

For example, in (4a), coefficients for realizing a patterned filter shape as shown in FIG. 3 are stored. Focusing on a certain clutter center frequency (input address), filter shapes as shown in FIG. 4 are stored at (aa), (4b), and (ac). (5) is a coefficient selector that selects the cutoff frequency bandwidth according to an operator's operation. (6) is a gain controller for final gain adjustment of this device. (7) is an arithmetic unit that converts the target speed into a Doppler frequency. (8)F
A comparator (9) compares the Doppler frequency of the i-clutter and the target and determines whether the filter formation is ``ON'' or OFF. 4a) , (4
b) This is a selector that selects and outputs the coefficient "0#" in the case of "@OFF" from the outputs of (4c).

FIG. 2 is a detailed block diagram of the crafter center frequency calculation section +31. In FIG. 2, n[l is a conjugate complex signal converter, aD is a multiplier, and 03 is a moving adder. I is input! This is a phase difference detection circuit that determines the phase difference between channel and Q channel, that is, the Doppler frequency.

In the clutter suppression device configured as above,
The clutter center station wave number calculation section calculates the clutter center frequency using the following equation (5).

Clutter center frequency Re (・): represents the real part (■ channel) Next, use the above clutter center frequency as the input address and input the above memory (
4m) −(4b) and (4c) output coefficients having a pre-patterned filter shape.

The coefficient selector +51 selects one of these coefficients by an operator's operation, the comparator 181 selects one of these coefficients for filter formation, and the comparator (8) selects one of the coefficients for filter formation. In one case where it is not prohibited, a suppression filter with an arbitrary cutoff frequency bandwidth can be used as the above lattice filter (2a), (2b),
(2c) is formed. The comparator IRI Fi calculates the clutter center frequency from the center frequency calculation section (3).

A target frequency is input from the Doppler frequency converter (7), and if a target exists near the clutter center frequency, filter formation is prohibited.

In addition, the average gain of the filter shape is calculated in advance and the coefficients are stored in the memories (4a), (4h), (4
C), and the gain controller (6) adjusts the gain using this average gain.

〔Effect of the invention〕

Since the present invention is constructed and operated as described in one or more of the above descriptions, it achieves the advantages described below.

Since the cutoff center frequency is determined according to the input signal and the cutoff frequency bandwidth is determined by manual setting, it is possible to improve the stability of the filter while retaining the advantage of the conventional device of being able to suppress clutter regardless of the clutter Doppler frequency. It becomes possible.

Also, since a circuit for calculating the average gain of the filter is not required, (2)/W can be simplified.

Furthermore, by directly determining the clutter center frequency during calculation, it is possible to prevent the target from being suppressed together with the clutter.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention. Figure 2 is a detailed block diagram of the center frequency calculation section in Figure @1, Figures 3 and 4 are diagrams showing the contents of the memory in Figure 1, and Figure 5 shows a conventional clutter suppression device. FIG. 6 is a detailed block diagram of the lattice filter section in FIG. 5, and FIGS. 7 and 8 are diagrams showing the operation of the conventional device. In the figure, (1a), (1b), (Ic) are I
PRT delay memory, (2a), (2b), (2c
) is a lattice filter. (3) is the center frequency calculation section, (4a), (4b)
, (4c) t;j Memo IJ for storing the filter shape,
(51 is a count selector, (6: is a gain controller, (7) is a Doppler frequency converter, (8) is a clutter-target frequency comparator, (9) is a coefficient selector, a3 is a ! channel, Q channel Phase difference detection circuit = (14a) *
(14b) - (14c) are lattice filter coefficient calculation units. It should be noted that the same or equivalent parts in FIG. 0 are denoted by the same reference numerals.

Claims (1)

[Claims] An arithmetic unit that calculates the Klatzta Doppler center frequency in the radar received signal, a memory that stores Latisse filter coefficients with multiple types of cutoff center frequencies and cutoff frequency bandwidths, and their average gain, and a Doppler that calculates the target Doppler frequency from the target speed. a frequency converter, a comparator that compares the Clutter Doppler center frequency and a target Doppler frequency and determines whether to form a suppression filter, a Latisse filter that forms a Clutter suppression filter;
A clutter suppressing device comprising: a gain controller that adjusts the gain of the output of a lattice filter.