RU2822466C1 - Phase method of direction finding of broadband signals and phase direction finder - Google Patents

Abstract

FIELD: radar location; radio navigation.

SUBSTANCE: invention relates to radar, radio navigation and can be used to determine angular coordinates of signal radiation sources. Phase direction finder additionally comprises bandpass filters with adjustable pass band, which makes it possible to automatically match the bandwidth of the receiving channels with the spectrum width of the received signals based on the results of spectral measurements, and compensating delay lines.

EFFECT: high accuracy of calculating the cosine of the guiding angle to the radiation source due to matching the pass band of the receiving channels with the width of the spectrum of the received signal.

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Description

The invention relates to the field of radar, radio navigation and can be used to determine the angular coordinates of signal emission sources.

Phase direction finding methods, phase direction finders and structures of receivers of phase direction finders are known (RF patents No. 2631422, RF No. 2669385, RF No. 2681203, Space trajectory measurements. Generally edited by P.A. Agadzhanov et al. M.: Sov. Radio, 1969, pp. 244-245).

The closest in technical essence to the proposed invention is the phase direction finding method and phase direction finder RF patent No. 2681203, which was chosen as a prototype.

The known method is based on receiving a signal at two spaced apart antennas, converting the received signals by two receivers, respectively, measuring the phase difference of these signals, measuring the spectrum of the received signal, calculating the correlation function of the signal, determining the value of the correlation-phase frequency, calculating the delay time of the received signals and calculating the guide cosine angle to the radiation source.

The disadvantage of the prototype is that it does not ensure, during processing, matching the receiver bandwidth with the spectrum width of the received signal, which reduces the accuracy of measuring the delay time of the received signal and, as a consequence, the accuracy of calculating the cosine of the direction angle.

The technical objective of the invention is to increase the accuracy of calculating the cosine of the direction angle to the radiation source by matching the bandwidth of the receiving channels with the spectrum width of the received signal.

The technical result - the patented invention ensures the creation of phase direction finders with increased accuracy in determining the cosines of the direction angles to the radiation source.

The essence of the patented invention is illustrated by the description and drawing shown in Fig. 1.

In fig. Figure 1 shows a block diagram of a patented phase direction finder that implements the proposed phase method for direction finding of broadband signals. The phase direction finder contains two spaced antennas 1 and 2, two high-frequency amplifiers 3 and 4 connected in series with them, two mixers 5 and 6 connected in series with them, two bandpass filters with adjustable bandwidth 7 and 8 connected in series with them, They are two delay lines 9 and 10, respectively, a local oscillator 11, the output of which is connected to the second inputs of mixers 5 and 6, a phase meter 12, the inputs of which are connected to the outputs of delay lines 9 and 10, respectively, a computer 15, the first input of which is connected to the output of the phase meter 12, series-connected spectrum analyzer 13 and correlation function analyzer 14, and the input of the spectrum analyzer 13 is connected to the output of the first mixer 5, the outputs of the spectrum analyzer 13 and the correlation function analyzer 14 are connected to the second and third inputs of the computer 15, respectively, the first output of which is connected to the control inputs of bandpass filters 7 and 8, the second and third outputs of the computer 15 are connected to the control inputs of delay lines 9 and 10, respectively.

It is known that optimal signal processing, ensuring maximum signal-to-noise ratio, involves matching the receiving channel bandwidth Δƒ with the signal spectrum width Δƒ _c [1].

As a result, optimal processing of received signals is ensured and, as a result, the accuracy of measuring the phase difference of these signals is increased. This ratio of the bandwidth of receiving channels and the width of the spectrum of received signals is optimal when the input signal-to-noise ratio is much less than unity. At large signal-to-noise ratios, i.e. when there is no need to select a signal from noise, any filtering leads to a weakening of the energy of the received signal and a decrease in the useful effect. In the limit where the input signal-to-noise ratio is much greater than unity, the optimal filter has an infinitely large bandwidth.

To substantiate this position, let us consider the signal-to-noise ratio at the output of the phase meter, implying that it implements correlation processing of input signals, i.e. multiplies them and averages them.

The output signal-to-noise ratio during correlation signal processing has the form [1]:

where Δƒ is the bandwidth of the bandpass filter;

T - averaging time;

P _input - signal power at the input of the phase meter;

P _sh - noise power at the input of the phase meter;

q _input - input signal/noise ratio.

Let the envelope of the input signal spectrum be described by the expression:

S(ƒ)=S ₀ /1+(2ƒ/Δƒ _s ) ² ,

where S ₀ is the spectral density of the signal,

Δƒ _с is the width of the signal spectrum, and the envelope of the frequency response of the bandpass filter is the expression: K(ƒ)=1/1+(2ƒ/Δƒ) ² , conventionally assuming that the gain of the bandpass filter is equal to unity.

It is known that during correlation processing of broadband signals, the level of the output signal depends on the spatial delay of the processed signals. The greater the spectrum width and delay time of the processed signals, the lower the output signal level due to decorrelation. Therefore, to ensure optimal processing, it is necessary to compensate for the spatial delay of the signals.

We will write the signal power at the input of the phase meter taking into account the influence of the bandpass filter:

We convert the noise power to the form: P _w =S _w πΔƒ/2=S _w πΔƒ _s x/2=P _ws x,

where R _shs is the noise power normalized in the signal band, S _sh is the spectral density of noise.

With this approach, the expression for the input signal-to-noise ratio takes the form:

where q _n is the input signal-to-noise ratio, normalized in the signal band.

Taking into account (2), expression (1) takes the form:

By differentiating expression (3) with respect to x and equating the derivative to zero, we can find the ratio of the passband of the bandpass filter and the width of the signal spectrum, corresponding to the maximum output signal-to-noise ratio

Therefore, to ensure optimal processing of received signals, i.e. To obtain the maximum value of the signal-to-noise ratio at the output of the phase meter, it is necessary to evaluate not only the width of the signal spectrum, but also to calculate the input signal-to-noise ratio normalized in the signal band.

The essence of the proposed phase method for direction finding of broadband signals is as follows. Using spectrum analyzer 13, before starting work, the spectral noise density of the receiving equipment S _w is measured; during operation, the signal spectrum S(ƒ), signal power P _c and signal spectrum width Δƒ _{c are measured.} Calculate the noise power normalized in the signal band, P _shs =S _w πΔƒ _s /2 and the input signal-to-noise ratio, normalized in the signal band, q _n =P _s /P _shs . Calculate the optimal bandwidth of bandpass filters and set this value on bandpass filters. The phase difference of the received signals Δϕ and the central frequency of the spectrum ƒ ₀ are measured. The signal delay time τ ₀ =Δϕ/2πƒ ₀ is calculated and this value is set on the corresponding compensating delay line. Using the correlation function analyzer 14, the correlation function of the signal is calculated Calculate the correlation-phase frequency function and determine the effective value of the correlation-phase frequency which takes into account the shape of the signal spectrum. Calculate the updated value of the delay time of the received signals The cosine of the direction angle, the angle between the direction to the radiation source and the line connecting the spaced antennas, is calculated by the formula where c is the speed of light, l is the distance between the antennas.

Literature:

1. Vinokurov V.I., Vacker R.A. Issues of processing complex signals in correlation systems. M., “Soviet Radio”, 1972, p. 140-148.

Claims (2)

1. Phase method of direction finding of broadband signals, based on signal reception on two spaced antennas, amplification of signals with high-frequency amplifiers, signal conversion using mixers and a local oscillator, filtering signals with bandpass filters, measuring the phase difference of these signals, measuring the spectrum of the received signal, calculating the correlation function signal, determining the value of the correlation-phase frequency, calculating the delay time of the received signals and calculating the cosine of the direction angle to the radiation source, characterized in that they measure the spectral noise density of the receiving equipment, measure the width of the spectrum of the received signal, calculate the noise power within the width of the signal spectrum, calculate the bandwidth of the bandpass filters corresponding to the maximum signal-to-noise ratio at the output of the phase meter, and the bandwidth of the bandpass filters is set in accordance with the calculated optimal value; based on the results of calculating the delay time of the received signals, compensating delays are introduced to eliminate decorrelation during correlation processing of broadband signals. 2. Phase direction finder containing two spaced antennas, two high-frequency amplifiers connected in series with them, two mixers connected in series with them, two bandpass filters connected in series with them, a local oscillator, the output of which is connected to the second inputs of the mixers, a phase meter, a computer, the first input which is connected to the output of the phase meter, a spectrum analyzer and a correlation function analyzer are connected in series, the input of the spectrum analyzer is connected to the output of the first mixer, the outputs of the spectrum analyzer and the correlation function analyzer are connected to the second and third inputs of the computer, respectively, characterized in that the bandpass filters are made with adjustable passband, and the first output of the computer is connected to the control inputs of bandpass filters, two delay lines are introduced, the inputs of which are connected to the outputs of bandpass filters, respectively, and the outputs are connected to the first and second inputs of the phase meter, respectively, while the second and third outputs of the computer are connected to the control inputs delay lines respectively.

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