JPH0445793B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a function for suppressing the influence of unnecessary radio waves such as interference waves incident from the side lobes of a receiving antenna in a receiving device such as a radar, and faithfully reproducing only the desired signal from the main lobe. This relates to the improvement of sidelobe cancellers.

A sidelobe canceller has one or more omnidirectional auxiliary antennas installed in parallel with the main receiving antenna, and has a configuration in which correlation loops are connected to each auxiliary antenna, and the received signal of the main antenna and Based on the correlation value with the received signal of each auxiliary antenna, an estimated signal of unnecessary radio waves incident from the side lobe in the received signal of the main antenna is generated, and this is subtracted from the received signal of the main antenna to obtain the desired signal. It has the function of leaving only the signal. FIG. 1 shows a circuit diagram of a conventional sidelobe canceller. In Figure 1, 1
is the main antenna, and 2 is the auxiliary antenna. For simplicity, this figure shows a case where there is only one auxiliary antenna. Now, the signals received by the two antennas are converted to an intermediate frequency (IF) with a center frequency ωIF by a local oscillator 3 and mixers 4 and 5, which serve as modulation circuits capable of high frequency band modulation of, for example, several tens of GHz. converted into a signal. The input signal from the main antenna is further converted by a local oscillator 6 and a mixer 7 into a signal u having a frequency ωIF+ω ₀ (this is called a main signal). However, ω ₀ is the frequency of the local oscillator 6. On the other hand, the input signal from the auxiliary antenna is represented by a signal x having a center frequency ωIF (this is called a reference signal).

A mixer 8 mixes the reference signal x and the weight signal w to generate a signal y that is an estimated signal of the interference wave signal component included in the main signal. As will be described later, since the center frequency ω of the load signal w is ₀ , the signal y
The center frequency of is ωIF±ω ₀ . 9 is an adder which has a function of subtracting the signal y from the main signal u. Further, 10 is a band filter with a center frequency ωIF+ω ₀ , and the ωIF in the input signal to the band filter 10 is
-ω Cut off the signal component whose center frequency is ₀ . The signal z generated in this way becomes the output signal of the sidelobe canceller, but the signal z
is a signal whose center frequency is ωIF + ω ₀ , and the main signal y
equal to the desired signal component in Furthermore, the output signal z is mixed with the reference signal x by the mixer 11 and converted into a signal with a center frequency ω ₀ . 12 is a narrowband filter with a center frequency ω ₀ , and the mixer 11 and narrowband filter 12 constitute a correlator 13 .
Further, 14 is a band amplifier with a center frequency ω ₀ ,
The load signal w, which is this output signal, is input to the mixer 8, thereby forming a correlation feedback loop.

In the above configuration, it is desirable that the narrowband filter 12 be configured such that the phase component of its input signal is preserved in the output signal. but,
It is difficult to construct a narrowband filter that preserves the phase component in the IF band. The conventional sidelobe canceller shown in FIG. 1 has the above-mentioned structural drawbacks.

In order to compensate for the above-mentioned drawbacks, the present invention has proposed that the processing from mixer 11 to mixer 8 in FIG. quadralure component, hereinafter abbreviated as "Q component")
This has been improved so that phase preservation in narrowband filtering can be performed with high precision using In order to make this improvement, a circuit as shown in FIG. 2 is constructed. In FIG. 2, the local oscillator 6 and mixer 7 in FIG. 1 are removed, and the main signal u
and the center frequencies of the reference signal x are the same. Furthermore, for the reference signal x, a 90° phase shifter 1
5 to newly generate the orthogonal component signal _xQ . 20 is a newly added correlator, and reception 18
and a low-pass filter 19, the orthogonal component signal x _Q
The correlation component between the output signal z and the output signal z is taken. Correlators 17 and 20 generate baseband signals, that is, orthogonal signals r _I and r _Q , which are complex signals. 2
1 and 22 are DC amplifiers. These generate w I and w _Q , which are _I and Q components of the complex weight.
23 and 24 are multipliers, and 25 is an adder, to which the multipliers 23 and 24 are connected in parallel. Therefore, the W _I and W _Q are multiplied by x and x _Q via the multipliers 23 and 24, outputted as first and second correction signals, and inputted to the adder 25. By these, the IF signal y is returned from the signals w _I , w _Q , x, x _Q
You will be asked for.

The above will be explained in more detail as follows. First, let x _{e and} z _e be the complex envelope signals at the IF of the reference signal x and output signal z, and let these amplitude and phase components be a _x , a _z , θ _x , and θ _z, respectively, then x _e = a _x e ^j 〓 ^x ………(1) z _e =a _z e ^j 〓 ^z ………(2) x=R _e (x _e e ^j 〓 ^IFt ) =a _x cos(ω _IF t+θ _x ) …(3) z = R _e (z _e e ^j 〓 ^IFt ) = a _z cos (ω _IF t + θ _z )...(4). Further, the signal x _Q becomes x _Q =I _n (x _e e ^j 〓 ^IFt ) = a _x sin (ω _IF t + θ _x ) (5). Therefore, in the output signals r _I and r _Q of the correlators 17 and 20, the low-pass filters 16 and 19
As a result, the component with the center frequency 2ω _IF is attenuated, and becomes as follows.

r _I =xz=1/2 _{x z} {( _z − _x )} =1/2{R _e ( _{e e} ^* ) ………(6) r _Q =x _Q z=1/2a _x a _z {− sin(θ _z −θ _x ) = 1/2 {−I _n ( _{e e} ^* )} ………(7) However, represents the result of low-pass filtering. Now, assuming that the gains of the amplifiers 16 and 17 are 2g, the I and Q components of the load, w _I and w _Q , are as follows.

w _I = 2g _I = gR _e ( _{e e} ^* ) ………(8) w _Q = 2g _Q = −gI _n ( _{e e} ^* ) ………(9) So w = w _I −jw _Q = g _{e e} ^* ......(10), then the signal y, which is the output signal of the adder 25, is
It will look like this:

y=w _I x+w _Q x _Q = g[R _e ( _{e e} ^* )・R _e (x _e e ^j 〓 ^IFt ) −I _n ( _{e e} ^* )I _n (x _e e ^j 〓 ^IFt )] = gR _e ( _{e e} ^*・x _e e ^j 〓 ^IFt ) = R _e (wx) ......(11). That is, the signal y becomes the real part of the signal obtained by multiplying the signal x by the complex weight w.

Generally, it is not easy to create a low-pass filter that can control the phase of a baseband signal, that is, a complex signal. Taking this into consideration, in this application, the load of a complex signal is calculated separately into the real part and the imaginary part, so that these can be adjusted independently and errors in the phase characteristics of the load can be absorbed. It is something.

Also, mixers may be used instead of the multipliers 23 and 24.

In addition, the baseband band processing is performed by correlators 17 and 20.
This part extends from after the output to the outputs of the multipliers 23 and 24, and can be digitized.

As described above, in the sidelobe canceller according to the present invention, since a part of the correlation loop is composed of baseband I and Q signals, low-pass filtering when determining the complex weight w can also be performed. A stable load can be obtained without loss of phase. Furthermore, since the center frequencies of the main signal u and the reference signal x are the same, the local oscillator 6, mixer 7, and band filter 10 are no longer necessary, simplifying the circuit.

The correlation loop construction method in the sidelobe canceller of the present invention is based on MSN (Maximum S/
N) It can also be applied to an adaptive array control device having a control structure.

[Brief explanation of drawings]

Figure 1 shows the conventional sidelobe in the IF band.
Circuit diagram of canceller FIG. 2 is a circuit diagram of a sidelobe canceller having two correlation loops of I component and Q component according to the present invention. In the figure, 1 is the main antenna, 2 is the auxiliary antenna, 3, 6 are local oscillators, 4, 5, 7, 8, 1
1 and 18 are mixers, 9 and 25 are adders, 10 is a band filter, 12 is a narrow band filter, 14 is a band amplifier, 13, 17, and 20 are correlators, 16, 19
is a low-pass filter, 21 and 22 are DC amplifiers, 2
3 and 24 are multipliers. In the drawings, the same or corresponding parts are designated by the same reference numerals.

Claims (1)

[Claims] 1 Input the received signals received by the main antenna and the auxiliary antenna, suppress the influence of interference waves incident from the side lobe direction of the main antenna, and suppress the signal component due to the influence of radio waves incident from the main lobe direction of the main antenna. In the sidelobe canceller that outputs only
A modulation circuit that performs high frequency band modulation with the center frequency as the center frequency, a signal from the auxiliary antenna at the output of this modulation circuit, and an output signal of the sidelobe canceller are input, and the signal in the intermediate frequency band is modulated in the baseband band, i.e. It has a correlator that converts it into a complex signal, a narrowband DC amplifier that inputs and amplifies the output signal of this correlator, and a multiplication circuit that receives the output signal of this DC amplifier and the signal from the auxiliary antenna as input. As the output of this multiplier circuit, the first
A 90° phase shifter is used to obtain a correction signal from the auxiliary antenna and to take the orthogonal component of the signal from the auxiliary antenna at the output of the modulation circuit, and the output signal from the 90° phase shifter and a sidelobe canceller are used. a correlator that receives the output signal as an input and converts the intermediate frequency band signal into a baseband band, that is, a complex signal;
a narrowband DC amplifier that inputs and amplifies the output signal of this correlator, and an output signal of this DC amplifier;
a multiplier circuit that receives the output signal of the 90° phase shifter as an input, obtains a second correction signal as an output of the multiplier circuit, and further combines this second correction signal and the first correction signal. an adder circuit in which the output multiplier circuits are connected in parallel and receives the first and second correction signals; and a subtracter circuit that subtracts the output signal of the adder circuit from the signal from the main antenna at the output of the modulator circuit. and the output signal of this subtraction circuit is
A sidelobe canceller characterized in that a double correlation feedback loop is formed by using an output signal of the sidelobe canceller.