RU2357261C1 - Method of obtaining signals for spectral analysis - Google Patents

Abstract

FIELD: radio engineering.

SUBSTANCE: present invention relates to the field of radio engineering and can be used in spectrum analysers and detecting devices for deterministic signals using matched filtration of the latter. The method of obtaining signals for spectral analysis, particularly the determined periodic sequence of radio-frequency pulses with varying carrier frequency, based on spectrum conversion of the received signal by increasing the duration of the latter, mixing the obtained signal with the linear-frequency-modulated oscillations of heterodyning and subsequent spectrum-temporary compression in a dispersive delay line. Increase of the duration of the received signal is carried out with the help of a tapped delay line with equidistantly distributed outlets, outlet responses with which they summarize, and the delay between the adjacent output of the tapped delay line are selected in a multiple relation to the reciprocal value of frequencies carrying oscillation of radio-frequency pulses. Total signal delay in tapped delay lines is assigned less tracking period of the radio-frequency pulse sequence, for example by an order. On the temporary situation of compressed pulses relative to the actuating pulses of the clock-pulse generator the analysed radio-frequency pulses are coded as logical one or zero, delay time of linear-frequency-modulated oscillations of heterodyning is adjusted till the signal-noise ratio at the inlet of the threshold device, which is determined by the maximum compressed pulse amplitude, is obtained.

EFFECT: simplification of the process of increasing the duration of the received radio-frequency pulses while maintaining their coherence.

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Description

The invention relates to the field of radio engineering and can be used in spectrum analyzers and devices for detecting deterministic signals using consistent filtering of the latter.

Consistent filtering is widely used in various radio engineering devices (V.I. Tikhonov, Optimal signal reception, M., Radio and communication, 1983). Broadband signals are widely used in radar systems, the compression of which is carried out in matched filters (C. Cook, M. Bernfeld, Radar signals, trans. From English under the editorship of V.S. Kelzon, M., Sov. Radio, 1971). Spectral-time filters for compressing broadband signals are performed on the basis of dispersion delay lines (DLS), consistent with the spectrum of these signals (S.S. Karinsky, Signal Processing Devices on Ultrasonic Surface Waves, M., Sov. Radio, 1975). Based on the DLZ, parallel-sequential signal spectrum analyzers are performed (V.I. Tverskoy, Dispersion-time methods for measuring the spectra of radio signals, M., Sov. Radio, 1974). Moreover, to increase the signal-to-noise ratio at the output of matched filters of periodically following pulsed radio signals, coherent or incoherent storage devices are used (Yu.S. Lezin, Optimal filters and storage of pulse signals, M., Sov. Radio, 1969).

The closest analogue of the claimed technical solution (prototype) is a device for analyzing the spectrum of signals, known from RF patent No. 2040798 of the same author, published in bull. No. 21 of July 27, 1995, in which a pulsed radio signal is recorded in some storage medium in real time, and reproduced at a substantially slower pace, which accordingly narrows the spectrum of such a signal and extends its duration, after which such a signal is subjected to spectral-time analysis based on the use of DLZ with the duration of the impulse response commensurate with the duration of the converted signal. This allows you to increase the signal-to-noise ratio at the output of the analyzer or detector of deterministic signals.

A disadvantage of the known device is the difficulty of converting the spectrum of the signals with an increase in their duration as applied to periodic sequences of radio pulses with a variable carrier frequency, which are used to transmit binary information in ultra-long-distance communication and telecontrol systems.

The specified disadvantage of the known device (prototype) is eliminated in the claimed method of spectral analysis of the specified class of radio signals. The aim of the invention is to simplify the procedure for increasing the duration of the received radio pulses while maintaining their coherence.

The goal is achieved in a method of spectral analysis of signals, in particular of determinate periodic sequences of radio pulses with a variable carrier frequency, based on transforming the spectrum of the received signal by expanding the length of the latter, mixing the received signal with linear frequency-modulated (LFM) heterodyning oscillation and subsequent spectral-time compression in dispersion delay line (DLZ), characterized in that the extension of the duration of the received signal are set using a multi-tap delay line with equidistant distributed outputs, the output responses from which are summed, and the delay between adjacent outputs of the specified delay line is selected in a multiple to the reciprocal of the used carrier frequencies of the radio pulses, and the total signal delay in the specified delay line is set less than the repetition period of the radio pulse sequences, for example, an order of magnitude.

Achieving this goal in the claimed technical solution is due to the coherence of the cross-linking of responses from the multi-tap delay line in the process of summing them, since the delays between adjacent outputs of the delay line are multiples of the frequency periods of the carrier oscillations of the radio pulse sequence. The addition of noise components is incoherent, since the noise correlation time interval is much less than the reciprocal of the passband of the amplifier of the summed pulse, which is consistent with the increased duration of the radio pulse. This allows you to further increase the signal-to-noise ratio at the output of the specified amplifier. The processing of each of the input radio pulses occurs separately due to the fact that the period of the radio pulse sequence exceeds the total delay time of the signal in the multi-tap delay line.

The operational nature of the proposed method, we consider the example of the device implementing the method shown in the drawing. This device contains a series-connected input low-noise amplifier 1, a multi-tap delay line 2 with N equidistant distributed outputs, respectively connected through compensating amplifiers 3, 4, ... 5 to the adder 6, a strip amplifier 7, a mixer 8, a broadband amplifier 9, a dispersion delay line 10 , a threshold device 11 and a time-to-code converter 12, wherein a linear-frequency-modulated signal generator, a chirp local oscillator 13, which is launched from ervogo clock oscillator output 14 via an adjustable time delay device 15, and a second output clock pulse generator is coupled to the second input transducer "time code".

Suppose that in an ultra-long-distance communication system, the control of an object or the transmission of information is carried out by a serial binary code. The logical unit corresponds to the frequency of the carrier oscillations f ₁ , and the logical zero corresponds to the frequency f ₂ . Information is transmitted periodically by the following radio pulses of duration

τ _and with a constant period T. Thus, the transmission of a data byte 01100010 is carried out by eight consecutive radio pulses with a variable carrier frequency

f ₂ f ₁ f ₁ f ₂ f ₂ f ₂ f ₁ f ₂ during 8T. The passband of the input low-noise amplifier 1 ΔF ₁ is determined by the duration of the radio pulses τ _And equal to ΔF ₁ = 1 / τ _And . The energy of the input useful signal is W _C = P _C τ _And , where P _C is the power of the useful signal at the input of the low-noise amplifier 1. If the spectral noise density G _Ш , determined by the parameters of the input low-noise amplifier 1, then the signal-to-noise ratio at the input of the last η _BX = 2W _C / G _W. With large losses of the useful signal, the signal-to-noise ratio η _ВХ may turn out to be significantly less than unity, which excludes reliable signal reception without special processing. An increase in the signal-to-noise ratio is achieved by increasing the useful signal duration, for which a multi-tap delay line 2 with delays between adjacent outputs Δτ = τ _and the number of outputs N is used. In this case, coherent cross-linking of N line responses in adder 6 is achieved provided that Δτ = K / f ₁ = (K-1) / f ₂ (for f ₁ > f ₂ ), where K >> 1 is an integer of the order of 300, which corresponds to the Siforov condition. Multidrop signal loss in the delay line are compensated using N compensating amplifiers 3, 4, 5, ..., output signals are coherently summed in the adder 6 connected to a bandpass amplifier with a bandwidth of 7 ΔF ₂ = 1 / Nτ _AND. The summed noise components add up incoherently, since the noise correlation interval determined by the passband ΔF ₁ is much shorter than the pulse response of the band amplifier 7, equal to 1 / ΔF ₂ , since ΔF ₁ / ΔF ₂ = N >> 1. Therefore, the power of the useful signal at the output of the strip amplifier increases by N times, and the noise power increases by N ^1/2 , and the signal-to-noise ratio at the output of the strip amplifier increases by N ^1/2 , and it will be equal to η _ПУ = N ^{1 / 2} η _BX .

The signal converted in duration is fed to the mixer 8 to the local oscillator input of which a linear-frequency-modulated oscillation is supplied from the output of the LFM of the local oscillator 13. At the same time, the output of the mixer 8 produces an LFM equivalent signal that passes through the broadband amplifier 9 to the dispersion delay line 10, consistent with LFM equivalent signal. Note that the intrinsic noise of a broadband amplifier practically does not worsen the signal-to-noise ratio at the input of DLZ 10, since the LFM level of the signal equivalent is significantly higher than the noise level of broadband amplifier 9.

The LFM local oscillator 13 is started from the output of the clock pulse generator 14 with a pulse repetition period T _TACT = T, which allows each of the sequence of input radio pulses to be processed separately, provided that

T> NΔτ + Δt _OX , where Δt _OX is the return time in the chirp local oscillator 13.

DLZ 10 is selected with the impulse response τ _LZ , the duration of which is comparable with the duration of the converted signal N Δτ, and the passband

F _{LZ is} selected as high as possible under the conditions of technological manufacturing. At the same time, the base В ДЛЗ 10 is equal to the product of the duration of the impulse response and the passband В = τ _ЛЗ F _ЛЗ . It is known that when chirping the LFM equivalent signal in DLZ 10, the signal-to-noise ratio increases by a factor of ^{1/2 1/2} , so that the resulting signal-to-noise ratio at the input of the threshold device is 11 η _OUT = (BN) ^1/2 η _BX . The duration of the compressed pulse at the output of the DLZ 10 is equal to τ _SJ = 1 / F _LZ . After the compressed signal is limited to a minimum in the threshold device 11, the noise-free signal is fed to the input of the time-code converter 12. The temporary position of the compressed signal relative to the start pulse in the clock generator 14, the second output of which is connected to the second input of the time-code converter ", As you know, is determined by the frequency of the carrier oscillations f of the input radio pulses. The difference in the frequencies of the carrier waves Δf = f ₁ -f ₂ = 1 / Δτ = 1 / τ _AND . Since F _LZ >> Δf, the compressed pulses during the processing of radio pulses with frequencies f ₁ and f ₂ reliably differ in their temporal position, which allows the time-code converter 12 according to the temporary position of the compressed pulses (relative to the triggering pulses of the clock pulse generator 14) encode the analyzed radio pulse as a logical unit or zero.

Since the time of arrival at the input of the device is generally uncertain, that is, does not coincide with the start of the LFM local oscillator 13, the optimal processing of the input radio pulses is achieved by adjusting (once at a given distance from the radiation source) the delay time of the LFM heterodyning signal in an adjustable time delay device 15. The adjustment is made until then, until you get the maximum signal to noise ratio at the input of the threshold device 11, determined by the maximum amplitudes the compressed pulse.

Consider an example implementation of the device.

Let a periodic sequence of radio pulses of duration τ _И = 1 μs with their repetition period T = 1 ms with two carrier frequencies f ₁ = 300 MHz (logical unit) and f ₂ = 299 MHz (logical zero) at K = 300. Let multi-tap delay line 2 have N = 100 outputs with a time difference of delays between adjacent outputs Δτ = 1 μs. Let DLZ 10 has a duration of the impulse response τ _LZ = 100 μs and a passband F _LZ = 10 MHz (base DLZ V = 1000). Then the duration of the compressed pulses τ _SJ = 0.1 μs, which allows you to reliably separate the temporary positions of the compressed pulses, the interval between which is 10 μs. The signal-to-noise ratio at the output of the DLZ 10 for given parameters, in a first approximation, is η _OUT = (BN) ^1/2 η _ВХ = 316 η _ВХ , that is, the ratio of the amplitude of the compressed pulse to the rms noise level increases by 50 dB, which allows it is reliable to receive radio signals that are almost completely indistinguishable at the input of the device due to the noise of the input low-noise amplifier 1. The frequency tuning frequency in the LFM local oscillator is 13 V _f = F _LZ / τ _LZ = 10 ¹¹ Hz / s. When the propagation velocity of the ultrasonic wave in the DLZ is 10ν = 3.2 mm / μs, the total length of the sound duct of this DLZ is slightly more than 320 mm. Interdigital transducers DLZ 10 are sprayed on its substrate, made, for example, of a piezoelectric crystal with a slice that provides the best thermal stability. The same material is also used in the multi-tap delay line 2, which determines the achievement of coherent crosslinking of responses in the adder 6 under conditions of changing ambient temperature. The length of the sound pipe of the multi-tap delay line 2 is in the same order as the DLZ 10.

The passband of the input low-noise amplifier is 1 ΔF ₁ = 1 MHz, and the noise spectral density can be set as G = 10 ^-19 W / Hz, i.e. the rms noise power is R _W = 10 ^-13 W. If, to isolate the signal at the input of the threshold device 11, it is sufficient to have an excess of the level of compressed pulses over the rms noise level equal to 10, then this means that the minimum useful signal power at the device input (from the antenna) is minP _BX = 3.16 · 10 ^-16 W , that is, the sensitivity of the receiving device is 155 dB.

The bandwidth in the strip amplifier 7 is set equal to ΔF ₂ = 10 kHz. Since the carrier frequencies 300 MHz and 299 MHz used for transmitting information differ by 1 MHz, then in a band amplifier 7, two quartz filters with a passband in each 10 kHz and center frequencies respectively 300 MHz and 299 MHz should be used.

Frequency tuning in the LFM local oscillator 13 at a speed of 10 ¹¹ Hz / s is carried out in a range of about 12 MHz wide, that is, for a time of the order of 120 μs, which is much shorter than the period of the radio pulses T = 1 ms. This circumstance explains the need to adjust the start times of the LFM local oscillator 13 using an adjustable delay device 15. To reduce the tuning range of the specified time delay, the frequency of the triggering pulses in the clock generator 14 should be increased to a maximum of eight times with the indicated characteristics of the device, but the frequency of such an increase should be integer. For example, at a clock frequency F _T = 8 kHz, the tuning of the LFM local oscillator 13 occupies the 12 MHz band from 234 MHz to 246 MHz. In this case, the LFM signal equivalent at the output of mixer 8 in frequency varies from 66 MHz to 54 MHz at a carrier frequency f ₁ = 300 MHz or from 65 MHz to 53 MHz at a carrier frequency f ₂ = 299 MHz. In this case, the broadband amplifier 9 has a passband ΔF ₃ = 13 MHz with a center frequency of 60 MHz, corresponding to the center frequency of the passband DLZ 10.

The time-code-converting device 12 has various designs, for example, based on a comparison of time intervals between the occurrence of compressed pulses at the output of a threshold device 11 and pulses from a clock generator 14.

Thus, the proposed set of operations for coherently increasing the duration of radio pulses with binary frequencies that are varied according to a binary law with subsequent LFM conversion and spectral-time compression of the received signal in the dispersion delay line corresponds to the solution of the stated objective of the invention.

Claims (1)

A method of obtaining signals for spectral analysis, in particular, of determinate periodic sequences of radio pulses with a variable carrier frequency, based on converting the spectrum of the received signal by expanding the duration of the latter, mixing the received signal with linearly-frequency-modulated oscillation of heterodyning and subsequent spectral-time compression in the dispersion delay line, characterized in that the extension of the duration of the received signal is produced using multi-tap delay lines with equidistant distributed outputs, the output responses of which are summed up, and the delay between adjacent outputs of the multi-tap delay line is selected in a multiple to the reciprocal of the frequencies of the carrier oscillations of the radio pulses, and the total signal delay in the multi-tap delay line is set less than the period of the radio pulse sequence, for example, an order of magnitude, according to the temporary position of the compressed pulses relative to the triggering pulses of the clock pulse generator, the analyzed the radio pulse as a logical unit or zero, adjusts the delay time of the linear-frequency-modulated heterodyning signal until the maximum signal-to-noise ratio at the input of the threshold device is determined, which is determined by the maximum amplitude of the compressed pulse.