JPH0369206B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention provides a sidelobe canceller (hereinafter referred to as SLC).
This relates to the improvement of the correlation loop gain of (abbreviated as).

A conventional SLC had a configuration as shown in Figure 1. In the figure, u and x are the carrier waves of the input signals from the main antenna and the auxiliary antenna, respectively.
It represents a signal converted to an intermediate frequency (IF) of w ₁ and w ₂ (w ₁ >w ₂ ) (hereinafter, u and x are called the main signal and reference signal, respectively). 1 is a subtracter, 2 and 5 are mixers, 3 is a narrow band pass filter with a center frequency of w ₁ -w ₂ , and 4 is an amplifier with a gain of g. In this configuration, there is a loop from subtracter 1 through mixer 2 and mixer 5 to subtracter 1 again. This is called a correlation loop.

Next, the operation of this device will be explained. Since the auxiliary antenna is omnidirectional and its gain is about the same as the gain of the side lobe of the main antenna, the power of the signal u is greater than the power of the signal x for radio waves incident from the main lobe of the main antenna. On the other hand, for radio waves incident from the side lobes of the main antenna, the power of the reference signal x is greater than that of the main signal u. This device uses this to estimate components in the main signal u that have a correlation with the reference signal x as a signal y obtained by multiplying the reference signal x by the control weight signal w, and estimates this from the main signal u. It has a structure in which the signal z obtained by subtracting the signal y is used as an output signal, and only the influence of the radio waves incident from the main lobe of the main antenna remains. SLC
The output signal z from the mixer 2 is input to the mixer 2 and fed back. If the output signals of the mixer 2 are v and v, and the signal after passing through the narrow band filter 3 and the amplifier 4 is w, then w becomes a signal with a center frequency w ₁ -w ₂ . Mixer 5 multiplies signal w and auxiliary antenna input signal x and outputs signal y. The above process can be expressed mathematically as follows. (All signal components are expressed as complex numbers.) First, the relationship between the main antenna input signal u and the output signal z is z=u−y (1). Next, if the narrowband filter 3 is a first-order lag filter with a time constant τ ₀ , then the following differential equation holds true with respect to the control load signal w, which is the output signal of the amplifier 4.

τ ₀ dw/dt+w=gzx ^* (2) where x ^* represents the conjugate complex number of x. Also,
Regarding mixer 5, y=wx (3). If (1), (2), and (3) are used here, τ ₀ dw/dt+(1+g|x| ² )w=gux ^* (4). This is a first-order linear differential equation for the control load signal w. In Equation (4), if the value of |x| ² and the envelope signal component of ux ^* change slowly and are almost constant compared to τ ₀ , Equation (4) has the following solution. .

However, in formula (5), w ₀ is the initial value of w when t=0, and τ ₀ and α are T ₀ =τ ₀ /1+g|x| ² (6) α=gux ^* /1+g The value is |x| ² (7). In equation (5), the value of the control load signal w approaches the value α when t becomes sufficiently large.
FIG. 2 shows how the absolute value |w| of the value of the control load signal w converges to the value |α|. The time constant at this time is T ₀ . On the other hand, the output signal z is
From the figure, z=u−wx (8), so the signal suppression ratio (CR) due to sidelobe canceller is CR=<(u/z) ² ＞=<(u/u−wx) ² > (9) If defined as (where <> indicates the time average), then t
When becomes sufficiently large, α in equation (7) is substituted for w in equation (9), resulting in CR=(1+g|x| ² ) ² (10). As is clear from equation (10), the signal suppression ratio CR
depends on the value of reference signal power |x| ² and increases as reference signal power |x| ² increases. This relationship is shown in FIG.

In this way, the convergence time constant T ₀ of the control load voltage w and the signal suppression ratio CR due to SLC are determined by the amplifier gain g
and the reference signal power |x| ² , which is the product g|x| ² . Especially when the reference signal power |x| ² is a small value, the gain g of the amplifier 4 must be set large.
The convergence time constant T ₀ of the control load voltage w becomes large. However, when the gain g is large, the loop gain becomes too large when the reference signal power |x| ² is large, and oscillation occurs due to the nonlinear elements of the circuit. Conventional SLC has the above-mentioned drawbacks.

The present invention attempts to improve the SLC circuit in order to overcome this drawback. The SLC circuit of the present invention is shown in FIG. To explain what has been added to the original SLC circuit in the figure, 6 and 7 are attenuators with different attenuation degrees a ₁ and a ₂ (1>a ₁ >a ₂ );
8 is a selection switch controlled by the signal from the comparator 10, and 9 is a mixer. The output signal of mixer 9 has reference signal power |x| ² . The comparator 10 is |
x| ² to preset values p ₁ , p ₂ (p ₁ < p ₂ )
In comparison, in switch 8, when |x| ² < p ₁ , terminal S ₁ is connected, when p ₁ | x | ² < p ₂ , terminal S ₂ is connected, and when p ₂ ^| ₃ shall be selected respectively. In this way, the equivalent gain from amplifier 4 to the output terminal of switch 8 is: g p 1 when |x| ² < p ₁ ; a ₁ when |x| ² < p ₂ ; g _{p 1 when} |x| ² a ₂ g , and the gain of the correlation loop is controlled according to the power |x| ² of the reference signal. Also, the attenuation degree a ₁ , a ₂
As a setting method, a ₁ = p ₁ / p ₂ (11) a ₂ = p ₁ / pmax (12) (where pmax indicates the maximum allowable value of reference signal power |x| ² ) Then, the gain of the correlation loop becomes as shown in FIG. By determining the degree of attenuation in this manner, the allowable range of reference signal power |x| ² that prevents the SLC correlation loop from oscillating can be widened.

Furthermore, FIG. 6 shows the relationship between the time constant T ₀ at which the control voltage w converges in the correlation loop in this case and the reference signal power |x| ² . According to this, the time constant T ₀ has a value greater than or equal to τ ₀ /(1+gp ₁ ).
Next, FIG. 7 shows the relationship between the SLC signal suppression degree CR and the reference signal power |x| ² . From the figure, signal suppression degree
CR has a value of (1 + gp ₁ ) ² or less. in this way,
For example, when |x| ² < p ₁ , the closer |x| ² is to p ₁ , the more desirable the SLC characteristics are.
Conversely, when the distance is greater than p ₁ , the characteristics as an SLC deteriorate.

As described above, in the SLC according to the present invention, the equivalent gain of the correlation loop can be controlled by the value of the reference signal power |x| ² .
Even when | ² is low, the degree of suppression can be maintained to some extent, and the allowable range of reference signal power |x| ² can be widened so that the correlation loop does not oscillate.

[Brief explanation of drawings]

Figure 1 is a block diagram of a conventional sidelobe canceller (SLC), and Figure 2 is a block diagram of a conventional sidelobe canceller (SLC).
A diagram explaining how the absolute value of the control load voltage in SLC converges to the desired load value over time,
FIG. 3 is an explanatory diagram showing the relationship between the reference signal power and the degree of signal suppression in the SLC of FIG. An explanatory diagram showing the relationship between the reference signal power of the SLC and the gain of the correlation loop, FIG. 6 is an explanatory diagram showing the relationship between the reference signal power of the SLC of the present invention and the time constant of correlation loop convergence, and FIG. FIG. 3 is an explanatory diagram showing the relationship between reference signal power and signal suppression degree in SLC of the invention. 1...Subtractor, 2, 5, 9...Mixer, 3...
Narrow band filter, 4... amplifier, 6, 7... attenuator, 8... switch, 10... comparator. It should be noted that the same or corresponding parts in the figures are indicated by the same reference numerals.

Claims (1)

[Claims] 1. It has a correlation loop for suppressing the received signals of unnecessary radio waves such as interference waves that enter from the side lobe of the main antenna, and also by extracting the correlation component between the reference signal and the unnecessary radio waves received from the auxiliary antenna. , the loop gain in the correlation loop in a sidelobe canceller that suppresses unnecessary radio wave components by estimating the unnecessary radio wave components in the received signals from the main antenna and subtracting them from the received signals from the main antenna. In the loop, there is a changeover switch with multiple terminals after the amplifier to obtain the same, and a circuit in which attenuators having different attenuation characteristics are connected to each terminal of this changeover switch in parallel. Separately, it has a circuit that outputs a voltage proportional to the average power of the reference signal received from the auxiliary antenna, and by controlling the changeover switch in the correlation loop according to this voltage, the loop gain of the correlation loop can be adjusted. A side lobe canceller that is adjustable.