RU1841012C - Device for identifying chirp signals - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: invention relates to pulsed information receivers and can be used in electronic surveillance stations and in passive target designation. The result is achieved due to that the device includes an autocorrelator, two threshold elements, a switch, an interval-to-code converter, two registers, a divider unit, four AND elements, an envelope detector, a comparator, four univibrators, a flip-flop, a differentiating element, two pulse counters, an RS a NOT element and an OR element. The listed components are connected to each other in a certain manner.

EFFECT: higher efficiency of identification.

2 dwg

Description

The proposed device for distinguishing the type of FM pulse signals relates to receivers of pulse information and is intended for use in radio intelligence stations and passive target designation systems.

As the first analogue, we consider the device according to ed. testimonial. No. 1840866, application 1575095 dated 02.21.1974. The principle of operation of this device is based on a comparison of the width of the spectrum of the signal at the fundamental and doubled frequencies. To distinguish signals with linear frequency modulation (LFM), the fact is used that the spectrum width of the LFM signal at twice the frequency is 2 times greater than its spectrum width at the fundamental frequency. The device contains meters for the spectrum width of the signal at the fundamental and doubled frequencies, as well as a unit for comparing the measurement results and a threshold detector. A positive quality of the device is a wide range of modulation parameters of the analyzed signals.

High reliability of signal discrimination in this device is achieved with large input signal-to-noise ratios. The requirement of large signal-to-noise ratios causes a low sensitivity of the device.

As a second analogue, we consider the device according to ed. testimonial. No. 1840972, application No. 1597022 dated 12/26/1975. The principle of operation of the device is based on the difference in the forms of responses of the autocorrelator to various types of intrapulse signal modulation. To distinguish the LFM signals, information on the bipolarity of the voltage of the beat signal at the output of the low-pass filter is used. The sensitivity of this device is 4-6 dB higher than the sensitivity of the device considered in the first analogue. But the disadvantages of the device is the narrow operating range of the modulation parameters of the analyzed chirp signals.

As a third analogue, we consider the device according to ed. testimonial. No. 1840896, application 2206387 of 07/05/1976, in which to expand the range of modulation parameters of the LFM signals, separate processing channels of the LFM and phase-shifted / FM / signals are used. Each channel contains autocorrelators, which include delay lines, multipliers and filters, and the signal delay in the autocorrelator of the LFM channel is selected much more than the similar delay in the FM signal channel. This method of implementing the device leads to the fact that when the FM signal is processed, the response of the LFM channel autocorrelator is bipolar and a false sign of receiving the LFM signal is generated at its output. To eliminate false information in the device during the processing of the FM signal, a blanking scheme for the formation of the characteristic of the LFM signal is blanked. Blanking is carried out by the pulse of the FM signal sign.

In this device, the algorithm for distinguishing chirp signals is similar to the algorithm of the device considered in the second analogue. However, the sensitivity of the channel for processing the LFM signal is 5–7 dB higher than the sensitivity of the channel for processing FM signals, which, when the device operates in the dynamic range of input signals, leads to the fact that FM signals whose level is 5–7 dB lower than the sensitivity of the channel for processing the FM signal are perceived from -for the absence of a blanking pulse, like chirp signals. Thus, in the dynamic range equal to the interval between the sensitivity levels of the LFM and FM channels, the device has a low reliability of distinguishing signals by the output of "LFM".

The modern and planned radar systems of the probable enemy are multifunctional. They have a set of different types of sounding signals. The choice of a specific type of signal is determined by the problem being solved by the radar system and the interference environment. Among the signals with frequency modulation / FM /, LFM signals of the "saw" type find practical application. The latter allow to obtain large compression ratios / 300-500 /, high resolution, low level of side lobes, provide high radar noise immunity.

The implementation of compression filters and the formation of chirp signals of the "saw" type are based on the technology of devices based on surface acoustic waves. Surfactant filters are relatively cheap and have high reliability.

When processing an LFM signal of the "saw" type by known signal discriminators, the latter form a sign of receiving a simple / unidirectional / LFM signal, which is their drawback.

The proposed solution is aimed at eliminating the above mentioned disadvantage of the known device.

The known device comprises a series-connected autocorrelator 1, a first threshold element 3, a key 4, an interval-code converter 5, a first register 6, a division unit 7, a second threshold element 8, a second register 9, a coincidence unit 10, and also contains a control channel 2, consisting of an envelope detector, a comparator and a standby multivibrator, connected in series, the output of which is the first output of the control unit and connected to the reset information inputs of the interval-code converter, the first and second registers. The output of the comparator is the second output of the control unit and is connected to the control input of the key, the output of which is also connected to the control inputs of the registers and the division unit. The second input of the division block is connected to the output of the interval-code converter. The inputs of the autocorrelator and the control unit are connected together and are the input of the device, and the output of the matching unit is the output of the device.

Note that the name of the circuit elements and their numbering correspond to FIG. one.

In the future, for the convenience of describing the application, the interval-code converter 5, the first register 6, the division unit 7, the second threshold element 8, the second register 9 and the coincidence unit 10 are sequentially referred to as the LFM sign generation unit, while the control inputs of the registers connected together the division block and the interval-code converter will be the signal input of the LFM sign forming unit, the coincidence block output will be the output of the LFM sign forming unit, and its information reset input will be connected together To reset the interval code converter and registers.

As mentioned above, the disadvantage of the prototype is the inability to distinguish signals of the type of chirp saw.

The aim of the present invention is to expand the functionality of the discriminator of the chirp signals, expressed in the distinction of signals such as chirp saw.

This goal is achieved by the fact that in a known device containing an autocorrelator connected in series, a first threshold element, a key and an LFM sign forming unit, as well as a control unit containing an envelope detector, a comparator and a waiting multivibrator, the inputs of the autocorrelator and control unit are connected together and are the input of the device, and the output of the comparator of the control unit is connected to the control input of the key, a trigger is connected in series, waiting for the multivibrator, the first element is the same I, the second standby multivibrator, the first pulse counter, the first logical threshold element, the second coincidence element, while the trigger input is connected to the output of the threshold element of the known circuit, and the inverse trigger output is connected through the differentiating circuit to the second input of the first coincidence element, the output of the sign forming unit The LFM is connected to the input of the third coincidence element, and also through the second pulse counter and the second logical threshold element with the second input of the second coincidence element, the output of which I it is output by the chirp type indicator of the “saw” type of the device and connected through the inverter to the second input of the third coincidence element, the output of the third coincidence element is the outputs of the “chirp” device attribute, and the output of the standby multivibrator of the control unit and the input of the third standby multivibrator are connected to its third input, the output of which is connected to the information reset inputs of the first and second pulse counter and to the first input of the "OR" element, the second input of which is connected to the output of the second standby multivibrator, and the output of the element “OR” is connected to the reset input of the “LFM” sign forming unit.

Thus, the introduction of new elements and connections into the device made it possible to obtain a new effect — the distinction between chirp signals of the “saw” type. New elements / trigger, first, second and third waiting multivibrators and matching elements; inverter, pulse counters and logic threshold elements; a differentiating circuit, an "OR" element / and communications implement an algorithm for distinguishing chirp signals of the "saw" type.

In FIG. Diagram 1 shows the responses at the output of the autocorrelator when the LFM signal and the LFM signal of the saw type are applied to its input.

As can be seen from FIG. 1, plot III, the time intervals between zero transitions for a simple LFM signal are the same.

The response of the autocorrelator to the chirp signal of the "saw" type is a beating signal whose frequency is not constant. At time instants τ _s ≤t≤T / interval 1 / the frequency of the beat signal is constant and equal to the beat frequency of a simple LFM signal / under the condition of the same speed of signal frequency tuning /. At time T≤t≤T + τ _s / interval 2 / the frequency of the beat signal changes discretely and is approximately equal to the magnitude of the frequency deviation of the chirp signal. The frequency of the beat signal in the interval 1 is 5 ÷ 10 times less than the frequency of the beats in the interval 2.

These features of the responses of the autocorrelator are used in the implementation of the algorithm for distinguishing chirp signals of the "saw" type in the proposed device.

In FIG. 2 shows a block diagram of the proposed device.

The device consists of an autocorrelator 2, a control unit 3, a sign-forming unit "LFM" 12, a key 8, threshold elements 6, 16, 15, trigger 1, waiting for multivibrators 4, 9, 11, matching elements 7, 19, 17, a differentiating circuit 5, inverter 18, pulse counters 14, 13 of the element "OR" 10.

The inputs of the autocorrelator 2 and the control unit 3 are connected together and are the input of the device. The output of the autocorrelator 2 through a sequentially connected threshold element 6, key 9, the block of the sign of the chirp 12 is connected to the coincidence element 19, the output of which is the output of the sign "chirp" device. The output of key 9 is connected to the input of trigger 1, the output of which through the standby multivibrator 4 is connected to the input of coincidence element 7, and through the differentiating circuit 5, the inverse output of trigger 1 is connected to another input of coincidence element 7. The output of coincidence element 7 through the standby multivibrator 9, pulse counter 13 and the logical threshold element 15 is connected to the input of the coincidence element 17, with the other input of which is connected the output of the “LFM” sign forming unit 12 through the pulse counter 14 and the logical threshold element 16. The output of the co-element Adenia 17 is connected through the inverter 18 to the second input of the coincidence element 19 and is the output of the “chirp” feature of the device. The control unit 3 is a series-connected envelope detector, a comparator and a waiting multivibrator. The output of the comparator, which is the first output of the control unit 3, is connected with the control input of the key 8, and the output of the standby multivibrator, which is the second output of the control unit 3, is connected to the third input of the coincidence element 19. In addition, the second output of the control unit through standby The first multivibrator 11 is connected to the reset inputs of the pulse counters 13, 14 and to the input of the OR element 10. The output of the OR element 10 is connected to the reset input of the indicator module LFM 12, and the second input of the OR element 10 is connected to the output of the waiting multivibrator 9.

Consider the operation of the proposed device. For clarity, we use stress plots at various points of the block diagram of the proposed device, shown in FIG. one.

A linear frequency modulation (LFM) signal or a LFM type “saw” signal is input to the device input (Fig. 1). The dependence of the frequency on time of the signals is shown in diagram I of FIG. 1. The response of the autocorrelator to these signals are beat signals at the output of the autocorrelator multiplier and are either harmonic oscillation or oscillation with a discretely varying frequency, as indicated in FIG. 1 plot II.

From the output of the autocorrelator, these oscillations arrive at the input of the threshold element 6, which at times equal to the transition of the beat signal through zero, forms short pulses of zero transitions (plot III, Fig. 1).

In the control unit 3, the input radio pulses are detected by the envelope detector, the comparator generates a standard strobe pulse, the temporary position of which coincides with the envelope of the input radio signal. The strobe pulse opens the key 8 and the sequence of pulses of zero transitions from the output of the threshold element 6 through the key 8 is fed to the input of the LFM sign formation unit 12 and the trigger input 1. When three or more null pulses arrive at the input of the LFM sign formation unit transitions with equal intervals between them, the block generates a pulse of the characteristic "LFM", which is fed to the pulse counter 14 and the element of coincidence 19. However, the sign "LFM" is not issued to the output of the device. The coincidence element is opened by the waiting multivibrator of the control unit only at the end of the action of the input radio pulse, because the standby multivibrator of the control unit is started by the trailing edge of the strobe from the output of the comparator of the control unit.

From the output of the key 8, the pulses of zero transitions also go to the input of trigger 1, which divides the frequency of the pulses of zero transitions into two (diagram IV, Fig. 1). The leading edge of trigger 1 pulse starts the waiting multivibrator 4, which generates pulses whose duration is approximately 2 times less than the minimum duration between zero transitions when exposed to the LFM signal, but 2-3 times longer than the duration between zero transitions when exposed to the LFM signal "saw "in the region of the maximum beat frequency at the output of the autocorrelator (plot V, Fig. 1). These pulses are fed to the input of the coincidence element 7, the other input of which through the differentiating circuit 5 receives pulses from the inverse output of trigger 1 (plot VI, Fig. 1). At the moments of coincidence in time of positive pulses from the outputs of the waiting multivibrator 4 and differential 5, short pulses are formed at the output of coincidence element 7, and under the above condition, pulses are formed only at the moments corresponding in time to the region of the maximum beat frequency at the output of the autocorrelator when the signal is applied to the input of the device LFM saw (plot VII, Fig. 1). The first of the burst of these pulses starts the waiting multivibrator 9, the pulse duration of which is chosen equal to the delay time in the autocorrelator circuit, which eliminates repeated trips (plot VIII, Fig. 1) from the burst pulses.

From the output of the waiting multivibrator 9, the pulse enters the counter 13 and, through the "OR" element, to the reset input of the LFM sign formation unit 12. At the end of the pulse from the output of the waiting multivibrator 9, the LFM sign formation block 12 (when three and more impulses of zero transitions with the same repetition intervals) again forms the impulse of the "LFM" sign, etc.

The pulse counter 14 counts the number of signs "LFM", and the pulse counter 13 - the number of signs "saw". The outputs of the pulse counters are connected to the logical threshold elements 15, 16, and the thresholds of the logical threshold elements are selected based on the required reliability of distinguishing signals such as chirp saw.

The outputs of the logical threshold elements 15, 16 are connected to the inputs of the coincidence element 17, which, in the presence of signals at both outputs, forms a sign of the reception of the LFM saw signal.

This signal is inverted by the inverter 18, the output of which is connected to the input of the coincidence element 19, and gives a ban on the device giving the reception sign "LFM".

After the end of the input signal, by the trailing edge of the strobe, the waiting multivibrator of the control unit 3 is launched from the output of the control unit 3. From its output, the pulses are fed to the input of the coincidence element 19 to enable the output of the receiving signal "LFM" and to the input of the waiting multivibrator 11, which forms a reset pulse on the trailing edge of the input pulse. The reset pulse from the output of the waiting multivibrator 11 is supplied to the reset inputs of the pulse counters 13, 14, and through the "OR" 10 element - to the reset input of the "LFM" sign formation unit 12 and resets them.

Above, the operation of the device when processing a signal of the LFM-saw type is considered.

Upon receipt of a simple LFM signal at the input of the device, the LFM sign forming unit 12 generates a LFM reception signal at the input of coincidence element 19. The waiting multivibrator 9 does not generate a reset pulse; at the output of coincidence element 17 there is no sign of receiving the LFM saw signal. From the output of the inverter 18 to the coincidence element 19, permission is issued for the output of the receiving signal "LFM" and after the arrival of pulses from the second output of the control unit 3, the output of the matching element 19 generates an impulse for the receiving signal "LFM". Its duration is equal to the duration of the pulse of the waiting multivibrator of the control unit 3. At the end of this pulse, the waiting multivibrator 11 resets all elements of the device.

When processing FM and other types of signals, the time distance between the zero-junctions is not the same and the sequence of three or more identical intervals between them (selected depending on the given statistical reliability of discrimination) will be absent. The device does not generate a sign of receiving an LFM signal, and, therefore, a sign of receiving a signal of an LFM saw.

All nodes of the proposed device are made according to well-known standard schemes of modern digital technology.

Using the proposed device in radio intelligence stations and passive target designation systems can improve the quality of solving problems of selection and identification of signals, increase the likelihood of recognition of the type of radar and its carrier.

Claims (1)

A linear frequency-modulated signal recognition device comprising an autocorrelator connected in series, a first threshold element, a key, an interval code converter, a first register, a division unit, a second threshold element, a second register and a first AND element, and an envelope detector, a comparator and a first connected in series one-shot, and the output of the comparator is connected to the control input of the key, the output of which is connected to the control inputs of the first and second registers and the division unit, and the output of the converter and the interval code is connected to the second input of the division unit, while the interconnected inputs of the autocorrelator and the envelope detector are the input of the recognition device, characterized in that, in order to increase recognition efficiency, a trigger, three one-shots, a differentiating element, three elements And, two are introduced a pulse counter, two threshold elements, a NOT element and an OR element, the key output being connected to a trigger input, the first output of which is connected through a second one-shot, the second element is connected in series , the third one-shot and the OR element with zeroing inputs of the interval-code converter, first and second registers, the second trigger output is connected via a differentiating element to the second input of the second AND element, the output of the third one-shot is also connected through the first pulse counter, the third threshold element, and the third the AND element and the NOT element with the first input of the fourth And element, the output of the first And element is connected to the second input of the fourth And element and through the second counter connected in series to them pulses and a fourth threshold element with a second input of the third element And, and the output of the first one-shot connected to the third input of the fourth element And and through the fourth one-shot with the second input of the OR element and zeroing inputs of the first and second pulse counters, while the outputs of the third and fourth elements And are respectively, the outputs of the recognition signal of the sawtooth linear frequency-modulated signal and the recognition signal of the linear-frequency-modulated signal of the recognition device.

Images