RU119126U1 - DEVICE FOR INCREASING ANGULAR RESOLUTION OF AMPLITUDE TOTAL-DIFFERENT MONO-PULSE SYSTEM - Google Patents

Abstract

A device for increasing the angular resolution of an amplitude sum-difference monopulse system, containing a signal processing processor and a decision-making device, characterized in that the signal processing processor is made in the form of a multiplication device, to the input of which the analog radio frequency signals of the sum and the difference generated by the receiving device of the radar station are received, which after processing, they enter the dividing device; square-law amplitude detector, at the input of which an analog radio-frequency signal of the difference is received and from the output of which the signal is directed to a divider device, from which it enters a low-pass filter, which generates a signal to a module calculating device, the signal from which is then fed to a sampling device, and then - to an incoherent storage device, which generates a signal entering the buffer memory, the output signal of which, in turn, goes back to the incoherent storage device and then to the decision-making device, at the output of which, in accordance with the used value of the false alarm probability according to the Neumann criterion, Pearson, based on the results of comparing the threshold signal arriving at the decision-making device, a decision is made on the presence or absence of an echo signal in the analyzed resolution element.

Description

The proposed utility model relates to the field of radio engineering and can be used in monopulse radar systems with a phased antenna array, searching and tracking along the angular coordinates of radar objects under the influence of intentional noise interference.

This device allows to increase the angular resolution of the amplitude total-difference monopulse system.

It is known [1] that the solution of the problem of resolving the angular coordinate of two equidistant objects can be considered as a procedure for detecting one of them under the influence of the other. In this case, the resolving power of the direction finder can be determined as the minimum angle between the directions to the object that interferes with and is detected with the required quality indicators.

For the direction finder of the type under consideration, it is customary to characterize the angular resolution approximately equal to 1.5 · θ _0.5p [2]. Here θ _0.5r is the width of the antenna pattern at half power.

The use of the device proposed in this work as part of a typical survey monopulse radar station (radar), when direction finding a pulse signal source against the background of intense noise interference along the main lobe of the antenna radiation pattern can provide a significant increase in angular resolution. In particular, provided that the difference in the angular coordinates of the sources is a fraction of the beam width, and the interference intensity is 10–20 dB higher than the intensity of the useful signal, it can be detected against the background of interference with sufficient reliability and reliability.

This means that it is possible to estimate the range to the target covered by the interference with an accuracy to the resolution element, as well as the bearing estimate with an error depending on the angular base of the director-goal group and the intensity of their radiation. When the signal-to-noise ratio (signal energy to spectral density of the interference power) is close to unity, the proposed device generates a two-peak angular coordinate function. This makes it possible to evaluate bearings of the jammer and the target covered by it with relatively high accuracy (with an error of 0.1 or less on the beam width).

In addition, during the review of space when working on a single radiation source (pulse signal or continuous noise interference), a significant reduction in the envelope duration along the angular coordinate of the received oscillation is provided, which creates conditions for a significant increase in the bearing accuracy in this case as well.

The technical effect in the proposed device is achieved due to additional functional processing of the output signals of the receiver. It is obtained by using the information contained in the ratio of the complex amplitudes of the total and difference signals, in particular, the inverse of the normalized difference signal (normalized angular error signal) generated by the monopulse direction finder.

As the results of simulation, the device that calculates the normalized envelope value not of the total signal, but the quadrature (relative to the signal of the total channel) component of the difference signal has higher quality indicators of solving the problem of increasing the angular resolution. This signal is normalized by performing a division operation, i.e. computing the quotient of dividing the values of the quadrature angular error by the variance of the signal of the difference channel.

The implementation of the proposed utility model does not require significant structural changes in the equipment of a typical version of the survey monopulse radar and is reduced to the introduction of an additional processing device connected to the output of the receiving channels of the sum and difference, which does not violate the normal operation of the equipment in normal mode.

Currently, there are a number of works devoted to the analysis of devices designed to increase the angular resolution for a group of incoherent radiation sources and using functional signal processing. Among them is the work [3 p.165]. The principle of operation of this device is based on the formation of estimates of the correlation and mutual correlation functions of the signals received by the multichannel antenna, and the subsequent solution of systems of equations describing these functions.

The options for solving the problem considered in this paper are of a general theoretical nature and do not take into account many features of their practical implementation. Moreover, the most significant is that the proposed one is associated with the need to use a special (atypical) multi-channel antenna system, which in case of practical implementation will cause difficulties in ensuring the identity and stability of the characteristics of the receiving channels [2].

In relation to a group of coherent radiation sources, a method and a block diagram of a device for increasing the angular resolution of a monopulse radar using the principle of gating along an angular coordinate are known [2, p. 109]. The main element of this measuring device, corresponding to one direction-finding plane, is an antenna with two horn irradiators, forming two partial radiation patterns in space, which are simultaneously excited by corresponding transmitters operating at separated frequencies. Two receivers were used to receive the reflected signals. Each of them is built according to a typical two-channel (respectively, for the total and difference signals) scheme. Due to the frequency spacing, the phase detectors of the receiving channels generate independent angular error signal voltages that contain information about the angular position of the group target. Using a specially introduced sum-difference device, the resulting voltage of angular errors is generated. A zero error signal serves as a criterion for deciding the presence of a single target in a controlled space. If there are two targets in the unresolvable volume of space, the equalization of the signal at the system output becomes zero impossible. This is a sign of the presence of a group target in the direction finding zone [2]. The decision on the nature of the goal is made by the operator based on the analysis of fluctuations of the error signal observed on the oscilloscope screen.

The disadvantages of this device are the design complexity (the need to introduce an additional channel of transceiver equipment into the radar), the lack of a clear quantitative detection criterion, and the operator’s subjectivity in making decisions. In addition, the system is operational only in the tracking mode, provided that the optical axis of the antenna is precisely aligned with the energy center of the target being tracked.

The closest in nature to the problem being solved and the principle of functioning is the device proposed in [4]. The solution option considered in it allows the tracking type direction finder to ensure the detection of a pulse signal against a background of noise interference and to estimate the range to its source with accuracy to the resolution element. As for the angular coordinate, when using this device, it can approximately be taken equal to the estimate of the bearing of the interference director.

The main purpose of the proposed utility model is to increase the angular resolution of the amplitude total-difference overview monopulse system, which provides noise detection under the condition of noise interference, provided that the angular position of its source relative to the interference source is a fraction of the antenna beam width. Moreover, accurate to the resolution element, an estimate of the distance to the signal source, and under certain conditions, estimates of its bearing will be provided. Ultimately, this will allow the radar with the help of the proposed device to provide greater objectivity in assessing the air and interference conditions.

This goal is achieved by the fact that in the receiver of a typical amplitude total-difference monopulse system (see, for example, [2, p.75]), a specialized computing device is added, which includes a signal processing processor and a decision-making device ( figure 1). The inputs of the analog-to-digital converter (ADC) of the receiver of a typical amplitude total-difference monopulse system receive radio frequency signals from the outputs of the amplifiers of the intermediate frequency (UPC) of the sum and difference channels of the antenna. The ADC converts the input signals into the corresponding digital binary codes, which are then used in the proposed computing device according to the developed algorithm.

The block diagram of the analog-digital version of the device, explaining the operation algorithm of the special calculator, is shown in figure 1.

Its composition includes a multiplication device (1), a quadratic amplitude detector (2), a dividing device (3), a low-pass filter (4), a module calculation device (5), a signal sampling device (6), an incoherent storage device (7), a buffer storage device (8), decision making device (9).

The device operates as follows.

Suppose that the radar in question uses a signal corresponding to the model of a single rectangular radio pulse as a probing radar. The radar by moving the beam of the antenna provides a linear overview of the space along the angular coordinate. In the field of view, under the cover of continuous noise interference, there is not an observable but detectable source of a pulsed echo signal. It is believed that according to the results of the review, implemented in normal mode, the bearing of the interference source is determined. Then, to detect the source of the pulse signal, the proposed device is used. For this purpose, the antenna beam in the sector, the bisector of which corresponds to the bearing of the interference source, jumps in discontinuity with discreteness ∆θ _d .

The value of the angular discrete ∆θ _d is selected from the condition ∆θ _d ≤θ ^∗ _0.5p where θ ^∗ _{0.5p is the} angular size of the main lobe of the direction finding relief obtained using the device in question in the case of a single interference source. _{It is} advisable to choose the sector size Δθ _obz equal to (1-1.5) _{-θ 0.5r} , i.e. equal to the angular size of the radar pulse volume.

During the space survey, the analogue radio-frequency signals generated by the radar receiver (at a frequency f _0pch , where f _0pch is the average value of the receiver bandwidth at an intermediate frequency) are and differences arrive at the inputs of the device in question (figure 1). The input channel signal of the sum as a reference goes to the multiplication device (1), the second (main) input of which is fed the signal of the difference channel . The multiplier (1) generates an estimate of the current instantaneous value of the difference channel signal (instantaneous value of the angular error). This assessment as a dividend is fed to the first input of the dividing device (3). As a divisor, an estimate of the square of the current value of the difference signal taken from the output of the quadratic amplitude detector (2) is used. This signal is fed to the second input of the dividing device (3). The low-pass filter (4) provides consistent filtering of the division result, i.e. highlighting the low-frequency fluctuations of the obtained oscillations corresponding to the spectrum of the useful signal, as well as the suppression of high-frequency components of the spectrum. The output low-pass filter signal is a continuous random process. The average value of its envelope is an estimate of the angular error, normalized to the value of the mean square value of the signal of the difference channel. At the same time, the average envelope value of the output filter fluctuations is the inverse of the angular error estimate generated by the direction finder.

The device for calculating the module (5) converts the output signal of the filter into a unipolar voltage, which in the device (6) is converted to a digital signal (subjected to temporal sampling and quantization by level). The period of time sampling Δt _{d is} chosen at least an order of magnitude shorter than the duration of the useful pulse signal τ _and . In the incoherent storage medium (7), an average value of the normalized angular error α is formed from the results of each sounding over a time interval equal to the pulse duration τ _and from a set of discrete samples. These estimates for each cell of the range are recorded in the memory of the buffer storage device (8).

The incoherent drive (7) together with the buffer storage device (8) during the direct path of the radar antenna beam using the set of results from N soundings in each fixed angular direction of the monitored viewing sector Δθ _obz = θ _0.5p implements the formation of all range resolution elements the average statistical values of the estimates of the normalized angular error, i.e. where M [α] is the mathematical expectation of α. As a result of this, a memory zone is formed in the buffer storage device (8), which can be considered as a two-dimensional collection of cells corresponding to a portion of the field of view (Fig. 2). The cells of this zone contain information characterizing in the "angle-range" coordinates the estimates of the average value of the normalized angular error or two-dimensional directional relief of space within the field of view. In this case, the process of recording information is organized so that each fixed angular position of the antenna beam corresponds to its own column in the memory zone. Based on the results of sounding in this direction, estimates are recorded in the cells of this column. for each range resolution element.

Thus, each angular direction in the buffer memory (8) corresponds to its own column of the memory zone. Then, in the cells of one row for a fixed range resolution range, the relief readings appear in all angular directions of the sector being recorded.

To make a decision about the presence or absence in the controlled space of an echo-signal source masked by interference, information from the buffer storage device (8) is sent to the decision-making device (9).

In digital signal processing, the decision-making procedure in the decision-making device (9) can be organized as follows.

The decision making device (9) sequentially implements. two-stage comparison of information received from an incoherent storage device with the corresponding threshold level.

At the first stage, information is read from the buffer storage device (8). The reading is carried out along the lines of the memory zone of the buffer storage device (8), i.e. for each range cell, an array of samples is generated for all the corner elements of the sector. In the process of reading, the array elements of each row are normalized to the maximum value of the count of this row ( ) Then the array of normalized samples is subjected to the operation of binary (single-threshold) quantization by level (amplitude). The threshold level value is selected based on the conditions for ensuring the best detection performance. Let's say this level is -10dB. If this level is exceeded, the threshold device generates a pulse of standard amplitude and duration (unit) or a gap (zero) otherwise.

At the second stage of comparison with the threshold, taking into account the bursty nature of the signal at the output of the binary quantization cascade (in the form of a sequence of ones and zeros), the decision-making procedure is reduced to estimating the duration of the pulse train and comparing it with a threshold value corresponding to a given value of false alarm. As a result of solving this problem, according to the Neumann-Pearson criterion, a decision is made about the presence or absence of an echo signal in the analyzed line (time resolution element).

In the simplest case, with the analog embodiment, the decision-making device can be performed using a typical oscillographic indicator with a raster scan of the beam and a brightness mark. Qualitatively, the screen view of such an indicator is shown in figure 3. Raster scan of the indicator. "Range-angle" ("r-θ") is formed synchronously with the interrogation of cells of the CCD. In particular, the horizontal scanning of the indicator beam is carried out synchronously with the interrogation of the cells of the corresponding row of the memory zone of the CCD (corresponding to a specific range resolution range). The frame scan synchronization is coordinated with the beginning of the survey of the entire memory zone of the ROM. The radar operator, based on the results of a comparative analysis of the average value of the angular size of the interference illumination band and the size of the mark in a specific range resolution range, makes a decision on the presence or absence of an echo signal (target) in it.

In the case of bifurcation of the mark in the angular coordinate, which may occur in the case of comparable intensities of interference and signal (Fig. 4), it is possible to estimate the bearing of radiation sources. If the mark is not divided, then the presence of a displacement of its center of gravity relative to the bearing of the source of interference characterizes the relative angular position of the source of the echo signal.

Thus, the device for increasing the angular resolution of the amplitude total-difference monopulse system can be manufactured using known equipment and known industrial means.

BIBLIOGRAPHY

1. Shirman Y.D. Resolution and compression of signals. - M .: Owls. Radio, 1974.

2. Leonov A.I., Fomichev K.I. Monopulse radar. - 2nd ed., Revised. and add. - M .: Radio and communications, 1984. - 312 p., Ill.

3. Tsarkov N.M. Multichannel radar meters. - M .: Owls. Radio, 1980, 192 p.

4. Pat. No. 102390 of the Russian Federation. A device for detecting a pulsed echo signal under conditions of noise interference along the main lobe of the radiation pattern of a monopulse radar. / S.A. Kuzmin, A.M. Lavrentiev, E.E. Tsubanov. Priority August 23, 2010

5. Kuzmin S.Z. Fundamentals of the theory of digital processing of radar information. M., "Owls. the radio, 1974.

Claims (1)

A device for increasing the angular resolution of the amplitude total-difference monopulse system, comprising a signal processing processor and a decision-making device, characterized in that the signal processing processor is made in the form of a multiplication device, to the input of which analog radio-frequency signals of the sum and difference, which are generated by the receiving device of the radar station, are received, which after processing, they enter the dividing device; a quadratic amplitude detector, to the input of which an analog radio frequency difference signal is received and from the output of which the signal is directed to a dividing device, from which it enters the low-pass filter, which generates a signal to the module calculating device, the signal from which is then sent to the sampling device, and then to an incoherent storage device, which generates a signal entering the buffer storage device, the output signal of which, in turn, is fed back to the incoherent storage device and further, to the decision-making device, at the output of which, in accordance with the used false alarm probability value according to the Neumann-Pearson criterion, a decision is made about the presence or absence of an echo signal in the analyzed resolution element according to the comparison of the threshold signal received by the decision-making device.