JP2619676B2 - Feedthrough nulling circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application field) The present invention relates to a technique for directly transmitting a transmitting wave receiving antenna by coupling of a transmitting antenna and a receiving antenna and reflection from an ambient environment, other than a necessary radar echo in a PRC coded radar. The present invention relates to a radar signal processing device for removing a feed-through signal flowing around.

(Prior Art) As a transmission signal of a recent CW radar, a transmission signal phase-modulated with a pseudo-random signal is used. PR for pseudo irregular signals
C code is used and this radar is called PRC coded radar. The PRC code is a signal whose auto-correlation function has a property close to that of a delta function.
In radar, transmission energy is spread in frequency. Also,
Since the autocorrelation function of this signal is close to the delta function, it is difficult to be received by a third party and has high confidentiality. Furthermore, the ECCM property is high even when interference is applied to this radar. Due to these features, PRC coded radar has recently been receiving attention.
On the other hand, CW radar is intended to receive the echo of a moving target, but since transmission and reception are performed simultaneously because of the handling of CW waves, the feedthrough from the transmitting antenna to the receiving antenna is large, and the target is often lost. If masked by feedthrough or if it is strong, problems with receiver saturation and burnout can occur.

FIG. 3 shows a configuration in which a feedthrough nulling circuit is applied to a PRC coded radar. In the figure, the PRC
It is assumed that a PRC code is generated by, for example, a six-stage PAC coder 8 based on a clock. The output of the transmission oscillator 9 is phase-modulated by the phase modulator 10 using this code, amplified by the transmission amplifier 11, and transmitted. Here, the feedthrough nulling circuit 1, phase with the transmission signal component contained extracted 'the received signal X _M 3' transmit signal X _A 2 to generates a weight W4 such that the amplitude, the weighting A part of the transmission signal is weighted by the weighting mixer 5 by W4, and is subtracted by the subtractor 6 from the reception input signal X _M 3 'to remove a feedthrough component included in the reception signal.

(Problem to be Solved by the Invention) Conventionally, when a feed-through nulling circuit is applied to this type of device, an operation as shown in FIG. It is generally well known that the optimum weight W is represented by the equation (1).

Here, an asterisk * indicates a complex conjugate. (1) In the formula, X _A is a PRC code, also, X _M is a received signal X _M 3 'which is an output that is detected by the video detector 15.
(1) equation by the discrete autocorrelation function of PRC code X _A, in which dividing the discrete cross-correlation of the received signal and the PRC code.

Here, the operation of the feedthrough nulling process shown in FIG. 3 will be described. In the PRC coded radar, the transmission wave modulated by the six-stage PRC code is transmitted from the transmission antenna 18 and hits the target 19 and receives a Doppler frequency shift. , To the receiving antenna 20. This desired wave signal is defined as an _XS component.
On the other hand, a part of the transmission wave directly wraps around as a feedthrough 21 from the transmission antenna 18 to the reception antenna 20, and since this signal is a signal similar to the transmission signal, only the amplitude is reduced by the mutual coupling amount of the transmission and reception antennas. X _A ′ signal,
Receiver input signal is represented by a sum of the X _S and X _A 'as equation (2).

X _M = X _A ′ + X _S (2) For these X _M and X _A signals, the weight W4 of the weight calculator 12 shown in FIG. 3 is calculated by equation (1). Here, the denominator is the discrete autocorrelation function of X _A of, since it is calculated for the signal taken from the PRC code X _A, the fifth is X _A ^* and X _A are in phase
An autocorrelation function of the PRC code as shown in the figure is obtained.
This figure shows that a correlation is obtained when the time difference between two PRC codes becomes completely zero. That is, the maximum value is OdB in the correlated range ± τb, and -3 in other cases.
bdB. On the other hand, considering the cross-correlation between X _M and X _A molecule, 'because the cross-correlation between the signal and the PRC code X _A is taken, X _A contained in X _M signal' X _A contained in X _M signal signal Is calculated so as to cancel. Here, in consideration of the configuration of FIG.
The feed-through 21 wrapping around the air actually causes some time delay because it propagates through space. Further, as a surrounding environment of the radar, an identification clutter signal is also input from a building or the like existing at a short distance, and each of those signals is expressed by the equation (3).

(3) In the equation, X _AO is _calculated from the transmitting antenna 18 to the receiving antenna 20
And has a time delay of the direct propagation path length. X _{A1 to} X _AM are signals having a time delay only for the respective propagation paths. Here, in equation (2),
When the X _A 'signal is obtained by performing the cross-correlation of the numerator of the equation (1) as the equation (3), the autocorrelation function of the PRC code deteriorates in proportion to the time difference between the two signals as shown in FIG. by, because it has a time delay than each component X _a of (3), (1) error occurs in the weight calculation of a sufficient suppression effect had been no drawbacks obtained.

(Means for Solving the Problems) The present invention has been made to solve these drawbacks, and is intended to produce a reference signal having a time delay corresponding to a feedthrough signal from multiple directions in a PRC coded radar. , A plurality of PRC codes are provided in a time-adjustable manner by providing a delay line, and weight calculators are provided by a number corresponding to these, thereby calculating weights W _{O to} W _M corresponding to each feedthrough. Thus, feedthrough signals from multiple directions having a time delay are removed, and the embodiments will be described below in detail with reference to the drawings.

(Embodiment) FIG. 1 is a block diagram of an embodiment of the present invention. Elements having the same functions in FIG. 3 are given the same reference numerals. The PRC code X _A feedthrough circuit of the conventional method in Figure 1,
The PRC code of X _AO 42 to X _AM 44 is made only in accordance with the time delay of the feedthrough 21 by the code delay 41, and the weight calculator 12 corresponding to the number is provided, and the calculated weight W _O 45 to
W _M 47 is summed by a weight synthesis circuit 48, the signal X _A 2 ′ extracted from the transmitting side is weighted by the weight W ₄ , the difference is subtracted by the subtractor 6 from the signal X _M ′ 3, and the feedthrough is removed is there. In the figure, the operation algorithm of the weight calculator 12 is (1)
Implemented by formula. Here, (1) X _A 2 in the formula is a PRC code. Next, the received signal X _M 3 'is expressed by the equation (2). Here, the X _A ′ signal in the expression (2) is expressed by the expression (3) including clutter from other short-distance fixed objects or the like directly wrapping around by a feed-through path. The N feed-throughs have different signal paths but are signals from a fixed target and do not receive a Doppler frequency shift. For this reason, if it has only a time delay, it has a PRC code corresponding to this time delay, executes the weight calculation formula (1) corresponding to each time delay, and synthesizes the weights. Can handle feedthrough. Therefore, delay lines 52 and 53 as shown in FIG. 2 are provided corresponding to each time delay. The input signal X _A of the delay line 52 and 53 are generated by six stages PRC coder 8, which is in the range 51 of FIG. 2. For this code, delay lines 52, 5 corresponding to the time delay of the feedthrough path
Prepare 3 Thus X _A signal, phase shift phi _O. 54 to
X _AO 42, X _A1 43,... _XAM 44 receiving φ _M 58 are PRC codes. Each delay line is made continuously variable within a preset time delay so that it can be adjusted for a signal input with each delay. When weight calculation is performed by each weight calculator 12 from each of the delayed PRC codes X _AO 42 to X _AM 44 and the received detection signal X _M 3, outputs W _O 45 to W _M 47
The composite value W of the weights of (4), the weights W _{O to} W _M corresponding to the respective time delays are calculated, and the weight transmission signal X _A 2 ′
Is weighted by the weighting mixer 5 and is subtracted from the received signal X _M 3 'by the subtractor 6, thereby enabling feedthrough nulling processing in a PRC coded radar corresponding to feedthrough from multiple directions.

(Effects of the Invention) As described above, since weights W _{O to} W _M corresponding to feed-through signals from multiple directions are generated and processing corresponding to each feed-through is performed, a sufficient feed-through nulling effect can be obtained. . Furthermore, even for signals for which correlation can be obtained only when there is a precise match in time, such as a PRC code, the time delay of the PRC code can be varied linearly, providing a sufficient feedthrough nulling effect. There are advantages.

[Brief description of the drawings]

FIG. 1 is a block diagram of an example in which a feedthrough nulling circuit of the present invention is applied to a PRC code radar, FIG. 2 is an explanatory diagram of a PRC code and a code delay line used in FIG.
FIG. 1 is a configuration diagram when a conventional feedthrough nulling circuit is applied to a PRC code, FIG. 4 is a general configuration diagram of a weight calculator, and FIG. 5 is an explanatory diagram of an autocorrelation function of the PRC code. 1 feedthrough nulling circuit, 2 'extracted transmission signal, 3' reception signal, 12 weight calculator, 41 code delay, 48 weight synthesis circuit.

Claims (1)

(57) [Claims] A circuit for determining a weight from a PRC code signal and a reception detection signal and removing a feedthrough signal other than a radar echo required as a reception signal from a difference between a product of the weight and an extracted transmission signal and a reception signal. , A delay line that creates a plurality of PRC code reference signals corresponding to feed-through signals input to the receiving side with a time delay from multiple directions, and a number of weight calculator groups corresponding to the plurality of reference signals And a weight combining circuit output from the weight calculator group, wherein each of the delay constants in the delay line is made continuously variable so that the plurality of reference signals correspond to each of the delay times of the feedthrough signal. A feedthrough nulling circuit.