JPH0414801B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention provides a side rope 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 the subtracter 1 through the mixer 2 and mixer 5 to the 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 lobes 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 ropes 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. The output signal z from the SLC is input to 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). Here, using (1), (2), and (3), we get 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 change in the value of |x| ² and the envelope signal component of ux ^* is gradual and 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 T ₀ and α are T ₀ =τ ₀ /1+g|x| ² (6) α=gux ^* /1+g |x| ² (7) is the minimum value. In equation (5), the value of the control load signal w approaches the value α when t becomes sufficiently large. Figure 2 shows the absolute value of the control load signal w | w | is the value |
This shows how it converges to 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) by the siderope 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 circuits have 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
As shown in the figure. In this figure, a more detailed structure of the narrowband filter 3 is shown. 31 in the figure
is a band-pass type integrator having a pass characteristic at the frequency w ₁ -w ₂ point, and 32 is a subtracter. In this configuration, when the signal v is input and the signal w is output, the relationship between them can be expressed as a differential equation as follows.

τ ₀ dw/dt+w=gv (11) Next, 6 is a mixer, which extracts the power component |x| ² from the reference signal x. Also, 7 is a mixer, which combines the power of the reference signal just obtained |x| ² and the output signal τ ₀ of the subtracter 32 in the narrowband filter.
Outputs the product with (dw/dt). Further, 8 is a subtracter which serves to subtract the output signal of the mixer 7 from the correlation loop by feedback. At this time, the signal v
The following formula holds true for .

v=(z=τ ₀ dw/dtx) x ^* (12) By substituting equation (12) into equation (11) and further using (1) and (3), the following equation is obtained.

τ ₀ dw/dt+w=gux ^* /1+g|x| ² = α (13) Solving equation (13) for w becomes. Equation (14), like Equation (5), converges to w and α when time t becomes sufficiently large, and the convergence time constant is a constant value τ ₀ regardless of the magnitude of reference signal power |x| ² . It shows something.

As described above, in the side rope canceller according to the present invention, regardless of the magnitude of the reference signal power |x| ² ,
The control load w can always be converged to a constant value with a constant time constant.

[Brief explanation of drawings]

Figure 1 is a block diagram of a conventional sidelobe canceller (SLC), and Figure 2 is the same as Figure 1.
Diagram 3 explaining how the absolute value of the control load voltage in SLC converges to a desired value over time.
FIG. 4 is an explanatory diagram showing the relationship between reference signal power and signal suppression degree in the SLC of FIG. 1, and FIG. 4 is a block diagram of the structure of the SLC improved according to the present invention.
Each numbered element in FIGS. 1 and 4 represents the following. 1, 8, 32...subtractor, 2, 5, 6, 7...
mixer, 3...narrowband filter, 4...amplifier,
31...Integrator. 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 the purpose of suppressing the received signal of unnecessary radio waves such as interference waves that enter from the side lobe of the main antenna, and it suppresses the correlation component of the reference signal for the unnecessary radio waves received from another auxiliary antenna. By extracting the unnecessary radio wave components contained in the received signal from the main antenna, and by subtracting them from the received signal from the main antenna,
In the sidelobe canceller that suppresses unnecessary radio wave components, the narrowband filter that is a component of the correlation loop is a first-order lag filter equipped with an integrator and a subtracter, and the input signal to the integrator is taken out, This and a signal proportional to the reference signal power are input to a multiplication element, and the output signal is subtracted from the correlation loop by a subtracter.
Canceler.