RU2009513C1 - Acoustic-optic spectrum analyzer - Google Patents

Abstract

FIELD: radio measurement technology. SUBSTANCE: analyzer has laser, collimator, four cells, four lenses, four arrays of photodetectors, five indication units, two aerials, frequency converter, intermediate frequency amplifier, four multipliers, three band-pass filters, switch, narrow-band filter, amplitude detector, count pulses generator, AND gate, differentiating circuit, counter, low frequency amplifier, electronic frequency counter, arithmetic unit. EFFECT: improved precision of measurement. 7 dwg

Description

 The invention relates to a radio measuring technique and is intended for the visual spectrum of complex signals and determining the type of modulation.

 The purpose of the invention is the expansion of functionality by accurate and unambiguous direction finding of the radiation source of complex signals with linear frequency modulation.

 In FIG. 1 shows a structural diagram of the proposed analyzer; in FIG. 2 is a possible view of the waveforms on the screens of the display units; in FIG. 3 is a diagram of the mutual arrangement of the symbolic frequencies of signals with multiple frequency manipulation; in FIG. 4 is a phase diagram of a frequency-manipulated signal; in FIG. 5 and 6 are frequency and time diagrams explaining the operation of the analyzer; in FIG. 7 - the principle of direction finding of the LFM radiation source by the phase method in one plane.

 The acousto-optical spectrum analyzer contains a laser 1, a collimator 2, the first, second, third and fourth Bragg cells 3.1-3.4, the first, second, third and fourth lenses 4.1-4.4, the first, second, third and fourth photodetector arrays 5.1-5.4, the first, second, third and fourth display units 6.1-6.4, first antenna 7, frequency converter 8, intermediate frequency amplifier 9, first, second and third multipliers 10.1-10.3, first, second and third band-pass filters 11.1-11.3, switch 12, narrow-band filter 13, amplitude detector 14, generator 15 counting pulses xy, element And 16, differentiating circuit 17, counter 18, second antenna 19, fourth multiplier 20, low-frequency amplifier 21, electron-counting frequency meter 22, arithmetic unit 23 and fifth display unit 24, and installed on the path of the light beam of laser 1 collimator 2 and four Bragg cells 3.1-3.4, and in the path of the diffracted light beam there is a corresponding lens 4.1 (4.2-4.4), in the focal plane of which is placed the corresponding matrix 5.1 (5.2-5.4) of photodetectors, the output of which is connected to the corresponding block 6.1 (6.2 -6.4) indication.

 The spectrum analyzer operates as follows.

 The signal received by the antenna 7, is fed to the input of the frequency Converter 8, consisting of a mixer and a local oscillator. The frequency-converted signal is extracted by an intermediate-frequency amplifier 9 and fed to the piezoelectric transducer of Bragg cell 3.1, where the signal is converted to acoustic vibration.

 The beam of light from laser 1, collimated by collimator 2, passes through Bragg cells 3.1-3.4 and diffracts on the acoustic vibrations excited by the signal. On the propagation path of the diffracted part of the light beam, 4.1-4.4 lenses are installed. In the focal planes of these lenses forming the spatial spectrum of the received signal, matrices 5.1-5.4 of photodetectors are installed. Each resolving element of the analyzed frequency range has its own photodetector.

Cell 3.1 (3.2-3.4) Bragg consists of a sound duct and a hypersound exciting piezoelectric plate made of a niobate-lithium crystal, respectively, X and Y - 35 ^o cut. This circumstance provides automatic Bragg angle adjustment and cell operation in a wide frequency range. Oscillographic indicators can be used as blocks of 6.1-6.4 indications.

If a complex signal with binary phase shift keying (FMN-2) is input to the spectrum analyzer, then it can be analytically written as follows:
u _c (t) = U _c cos [2 π f _c t + φ _к (t) + φ _c ],
0 ≅ t ≅ T _c , where U _c , f _c φ _c and T _c are the amplitude, carrier frequency, initial phase, and signal duration, respectively;
φ _a (t) = 0, π - manipulating component phase mapping law DPSK, wherein φ _a (t) = cons when kT _and <t <(k + 1) τ _u and may vary abruptly at t = k τ _and , i.e., at the boundaries between elementary premises (K = 1, 2,..., N = = 1);
τ _and and N are the duration and number of chips that make up the signal of duration T _c (T _c = N τ _and ).

The specified signal is fed to the input of the frequency Converter 8, the output of which forms a voltage
u _pr (t) = U _pr cos [2 π f _pr t + φ _к (t) + φ _pr ),
0 ≅ t ≅ T _c , where U _pr = 1/2 · KU _c U _g ;
K is the transfer coefficient of the mixer;
f _CR = f _c - f _g - intermediate frequency;
φ _CR = φ _c -φ _g - intermediate initial phase;
U _g , f _g and φ _g are the amplitude, frequency and initial phase of the local oscillator voltage, respectively.

This voltage is allocated by the intermediate frequency amplifier 9 and supplied to the piezoelectric transducer of the Bragg cell 3.1 and to two inputs of the multiplier 10.1, at the output of which a harmonic voltage is generated
u ₁ (t) = U _c cos (4 π f _pr t + 2 φ _pr ),
0 ≅ t ≅ T _c ,
where U ₁ = 1/2 · K ₁ U ² _pr ;
To ₁ - transfer coefficient of the multiplier.

Since 2 φ _к (t) = 0.2 π, phase manipulation is already absent in the indicated voltage. The voltage u ₁ (t) is allocated by the band-pass filter 11.1 and supplied to the piezoelectric transducer of the Bragg cell 3.2 and to two inputs of the multiplier 10.2, at the output of which a harmonic voltage is generated
u ₂ (t) = U ₂ cos (8 π f _pr t + 4 φ _pr ),
0 ≅ t ≅ T _c , where U ₂ = 1/2 · K ₁ U ₁ ² .

This voltage is allocated by the band-pass filter 11.2 and supplied to the piezoelectric transducer of the Bragg cell 3.3 and to two inputs of the multiplier 10.3, at the output of which a harmonic voltage is generated
u ₃ (t) = U ₃ cos (16 π f _pr t + 8 φ _pr ),
0 ≅ t ≅ T _c ,
where U ₃ = 1/2 · K ₁ U ₂ ² . This voltage is released by the band-pass filter 11.3 and applied to the piezoelectric transducer of the Bragg 3.4 cell.

=

= N

) и трансформируется в одиночные спектральные составляющие. Это обстоятельство и является признаком распознавания ФМн-2 сигнала. Спектры принимаемого ФМн-2 сигнала и его гармоник визуально наблюдаются на экранах индикаторов 6.1-6.4 соответственно (фиг. 2а).The width of the spectrum of the FMN-2 signal Δ f _c is determined by the duration of τ _{and the} chips (Δ f _c = 1 / τ _and ), while the width of the spectrum of the second Δ f ₂ , the fourth Δ f ₄ , the eighth Δ f ₈ harmonics is determined by the duration T _{s of the} signal (Δ f ₂ = Δ f ₄ = Δ f ₈ = 1 / T _c ). Therefore, when the phase is multiplied by two, four, and eight, the spectrum of the FMN-2 signal “folds” N times (

=

= N

) and transforms into single spectral components. This circumstance is a sign of recognition of the FMN-2 signal. The spectra of the received FMN-2 signal and its harmonics are visually observed on the screens of the indicators 6.1-6.4, respectively (Fig. 2a).

(t) = 0,

, Π,

] , то на выходе полосового фильтра 11.1 образуется ФМн-2 сигнал [ φ_к (t) = 0, π, 2 π, 3 π] , а на выходе полосовых фильтров 11.2 и 11.3 образуются соответствующие гармонические составляющие u₂(t) и u₃(t). В этом случае на экранах индикаторов 6.1 и 6.2 наблюдаются спектры ФМн-4 и ФМн-2 сигналов, а на экранах индикаторов 6.3 и 6.4 - одиночные спектральные составляющие (фиг. 2б).If the FMN-4 signal [

(t) = 0,

, Π,

], then an FMN-2 signal [φ _к (t) = 0, π, 2 π, 3 π] is formed at the output of the bandpass filter 11.1, and the corresponding harmonic components u ₂ (t) and u are formed at the output of the bandpass filters 11.2 and 11.3 ₃ (t). In this case, on the screens of indicators 6.1 and 6.2, the spectra of FMN-4 and FMN-2 signals are observed, and on the screens of indicators 6.3 and 6.4, single spectral components are observed (Fig. 2b).

(t) = 0,

,

,

, Π,

,

,

] , то на выходах полосовых фильтров 11.1 и 11.2 образуются ФМн-4 и ФМ-2 сигналы, а на выходе полосового фильтра 11.3 - гармоническое напряжение. В этом случае на экранах индикаторов 6.1-6.3 наблюдаются спектры ФМн-8, ФМн-4, ФМн-2 сигналов, а на экране индикатора 6.4 - одиночная спектральная составляющая (фиг. 2в).If an FMN-8 signal [

(t) = 0,

,

,

, Π,

,

,

], then the FMN-4 and FM-2 signals are generated at the outputs of the bandpass filters 11.1 and 11.2, and the harmonic voltage at the output of the bandpass filter 11.3. In this case, on the screens of the indicators 6.1-6.3, the spectra of FMN-8, FMN-4, FMN-2 signals are observed, and on the screen of the indicator 6.4 there is a single spectral component (Fig. 2c).

- средняя частота сигнала (фиг. 3);
φ (t) - изменяющаяся во времени фазовая функция (фиг. 4);
f₁= f_cp+

, f₂= f_cp+

- символьные частоты, то на выходе полосового фильтра 11.1 образуется частотно-манипулированный сигнал с индексом девиации частоты h = 1. При этом спектр трансформируется в спектральные составляющие на частотах 2f₁и 2f₂. На выходе полосового фильтра 11.2 образуются две спектральные составляющие на частотах 4f₁ и 4f₂, а на выходе полосового фильтра 11.3 - две спектральные составляющие на частотах 8f₁ и 8f₂ (фиг. 2г).If the input of the analyzer receives a ChMn-2 signal (Fig. 3a)
u _c (t) = U _c cos [2 π f _cf t + φ (t) + φ _c ],
0 ≅ t ≅ T _c ,
where f _cp =

- the average frequency of the signal (Fig. 3);
φ (t) - time-varying phase function (Fig. 4);
f ₁ = f _cp +

, f ₂ = f _cp +

are symbolic frequencies, then a frequency-manipulated signal with a frequency deviation index h = 1 is formed at the output of the band-pass filter 11.1. In this case, the spectrum is transformed into spectral components at frequencies 2f ₁ and 2f ₂ . At the output of the bandpass filter 11.2, two spectral components are formed at frequencies 4f ₁ and 4f ₂ , and at the output of the bandpass filter 11.3, two spectral components at frequencies 8f ₁ and 8f _{2 are formed} (Fig. 2d).

If the analyzer receives an FMN-3 signal (Fig. 3b), then three spectral components are formed at the output of bandpass filters 11.2 and 11.3 at frequencies 4f ₁ , 4f _cf , 4f ₂ and 8f ₁ , 8f _cf , 8f ₂ , i.e. The continuous spectrum is transformed into three spectral components (Fig. 3d). At the output of the multiplier 10.1, the spectrum of the ChMn-3 signal is transformed into another continuous spectrum, since h <1. Thus, continuous spectra are visually observed on the screen of indicators 6.1 and 6.2.

If the analyzer receives an FMN-5 signal (Fig. 3c), then at the output of the multiplier 10.3 its continuous spectrum is transformed into five spectral lobes with peak values at frequencies 8f ₁ , 8f ₃ , 8f _cf , 8f ₄ and 8f ₂ . At the outputs of the multipliers 10.1 and 10.2, the continuous spectrum of the ChMn-5 signal is transformed into other continuous spectra, since in this case h <1. Thus, continuous spectra are observed on the screens of indicators 6.1-6.3, and five spectral lobes on the indicator screen 6.4 ( Fig. 2e).

- скорость изменения частоты внутри импульса;
Δ f_д - девиация частоты, то преобразователем 8 частоты он переносится на промежуточную частоту
u_пр(t) = U_прcos(2 π f_прt + πγt² + φ_пр),
0 ≅ t ≅ T_c. Напряжение u_пр(t) выделяется усилителем 9 промежуточной частоты и поступает на пьезоэлектрический преобразователь ячейки 3.1 Брэгга и на два входа перемножителя 10.1, на выходе которого образуется ЛЧМ-сигнал
u₁(t) = U₁cos(4 π f_прt + 2 πγt² + 2 φ_пр),
0 ≅ t ≅ T_c. который выделяется полосовым фильтром 11.1 и поступает на пьезоэлектрический преобразователь ячейки 3.2 Брэгга. Так как длительность Т_с ЛЧМ-сигнала на основной и удвоенной промежуточной частоте одинакова, то увеличение γ в 2 раза происходит за счет увеличения в 2 раза девиации частоты Δ f_д. Из этого следует, что ширина спектра ЛЧМ-сигнала на удвоенной промежуточной частоте в 2 раза больше его ширины спектра на основной промежуточной частоте (Δ f₂ = 2 Δ f_c). Аналогично на выходах перемножителей 10.2 и 10.3 ширина спектра ЛЧМ-сигнала увеличивается в 4 и 8 раз (Δ f₄ = 4 Δ f_c, Δ f₈ = 8 Δ f_c).If a linear frequency modulation (LFM) signal is input to the analyzer
u _c (t) = U _c cos (2 π f _c t + πγt ² + φ _c ],
0 ≅ t ≅ T _c ,
where U _c , f _c , φ _c and T _c - amplitude, initial frequency, initial phase and signal duration, respectively;
γ =

- rate of change of frequency inside the pulse;
Δ f _d - frequency deviation, then the frequency converter 8 it is transferred to the intermediate frequency
u _pr (t) = U _pr cos (2 π f _pr t + πγt ² + φ _pr ),
0 ≅ t ≅ T _c . The voltage u _pr (t) is allocated by the intermediate frequency amplifier 9 and supplied to the piezoelectric transducer of the Bragg cell 3.1 and to two inputs of the multiplier 10.1, at the output of which an LFM signal is generated
u ₁ (t) = U ₁ cos (4 π f _pr t + 2 πγt ² + 2 φ _pr ),
0 ≅ t ≅ T _c . which is allocated by the band-pass filter 11.1 and fed to the piezoelectric transducer of the cell Bragg 3.2. Since the duration of T _{with the} LFM signal at the fundamental and doubled intermediate frequencies is the same, a 2-fold increase in γ occurs due to a 2-fold increase in the frequency deviation Δ f _d . From this it follows that the width of the spectrum of the LFM signal at twice the intermediate frequency is 2 times greater than its spectrum width at the main intermediate frequency (Δ f ₂ = 2 Δ f _c ). Similarly, at the outputs of multipliers 10.2 and 10.3, the width of the spectrum of the LFM signal increases by 4 and 8 times (Δ f ₄ = 4 Δ f _c , Δ f ₈ = 8 Δ f _c ).

=

- время запаздывания сигнала, приходящего на антенну 19, по отношению к сигналу, приходящему на антенну 7.Therefore, on the screen of indicator 6.1, the spectrum of the chirp signal is visually observed, and on the screens of indicators 6.2-6.4, the spectra of chirp signals whose width is 2, 4, and 8 times the width of the spectrum of the original chirp signal (Fig. 2g). This fact is a sign of recognition of the chirp signal and the reason for the operator to switch the switch 12 to the closed position. In this case, the received LFM signal u _c (t) from the antenna 7 through the closed switch 12 is fed to the first input of the multiplier 20, the second input of which from the antenna 19 is fed the LFM signal u _c (t)
u _c (t + τ) = U _c cos [2 π f _c (t + τ) + πγ (t + τ) ² + φ _c ],
0 ≅ t ≅ T _c ,
where τ =

=

- the delay time of the signal arriving at the antenna 19, with respect to the signal arriving at the antenna 7.

As a result of multiplication, the resulting voltage u _Σ (t) = u _c (t) u _c (t + τ) = U _b cos (2 π f _b t + φ _b ) + + U _b сos (4 π f _c t + 2 π f _b t + φ _b + 2 πγt ² + 2 φ _s ), where U _b = 1/2 · K ₁ U _c ² ;
To ₁ - transfer coefficient of the multiplier;
f _b = γτ is the beat frequency;
φ _b = 2πf _c τ + πγτ ² is the initial phase of the beats.

.The amplifier 21 low frequency allocated voltage beats (voltage differential frequency)
u ₅ (t) = U _b cos (2 π f _b t + φ _b ), 0 ≅ t ≅ T _c . In this case, the angle of arrival of radio waves β is determined as follows:
β = arccos

.

.Since when the angle β changes, the value of the beat frequency f _b also changes, the latter uniquely determines the bearing to the radiation source of the LFM signals (Fig. 5a). To determine the angle β of the arrival of radio waves, it is necessary to measure the beat frequency f _b and the rate of change of the frequency γ inside the pulse. The beat frequency (Fig. 5b) is measured using an electronically counted frequency meter 22. Short pulses are generated from the continuous alternating voltage u _b (t) of the frequency f _b , the repetition rate of which remains equal to f _b . If we count the number of pulses n ₁ for a known time interval Δ t, then it is easy to determine the desired frequency
f _B =

.

In particular, if Δ t = 1 s, then the measured number of pulses n _{1 is} numerically equal to the unknown frequency. The number of pulses n ₁ from the output of the frequency counter 22 is supplied to the first input of the arithmetic unit 23.

. Этот радиоимпульс поступает на вход амплитудного детектора 14, который выделяет его огибающую. Прямоугольный видеоимпульс с выхода амплитудного детектора 14 (фиг. 6в) поступает на первый вход элемента И 16, на второй вход которого подаются счетные импульсы с выхода генератора 15 (фиг. 6г). На выходе элемента И 16 образуются счетные импульсы, количество которых n₂ подсчитывается счетчиком 18. Видеоимпульс с выхода амплитудного детектора 14 (фиг. 6в) поступает одновременно на вход дифференцирующей цепи 17, на выходе которой образуется два коротких разнополярных импульса (фиг. 6е), причем положительным коротким импульсом счетчик 18 приводится в исходное (нулевое) состояние, т. е. подготавливается к работе, а отрицательным коротким импульсом сосчитанное количество n₂ счетных импульсов переводится в арифметический блок 23, в котором определяется угол β прихода радиоволны в цифровом коде. Последний регистрируется индикатором 24. (56) Авторское свидетельство СССР N 1626182, кл. G 01 R 23/17, 1989.To measure the rate of change of the frequency γ inside the pulse, the voltage u _c (t) from the antenna 7 through a closed switch 12 is fed to the input of a narrow-band filter 13 with a passband Δ f (Fig. 6a). At the output of the narrow-band filter 13, a radio pulse is generated (Fig. 6b) of duration t _u =

. This radio pulse arrives at the input of the amplitude detector 14, which distinguishes its envelope. A rectangular video pulse from the output of the amplitude detector 14 (Fig. 6c) is supplied to the first input of the And 16 element, to the second input of which counting pulses are fed from the output of the generator 15 (Fig. 6d). At the output of element And 16, counting pulses are formed, the number of which n _{2 is} counted by the counter 18. The video pulse from the output of the amplitude detector 14 (Fig. 6c) is fed simultaneously to the input of the differentiating circuit 17, the output of which is formed of two short unipolar pulses (Fig. 6f), moreover, the counter 18 is brought into the initial (zero) state by a positive short pulse, that is, it is prepared for operation, and the counted number of n ₂ counted pulses is converted into an arithmetic block 23, in which the angle β of arrival of the radio wave in digital code is given. The latter is recorded by indicator 24. (56) Copyright certificate of the USSR N 1626182, cl. G 01 R 23/17, 1989.

Claims (1)

 ACOUSTOOPTIC SPECTRA ANALYZER containing a laser, a collimator and four Bragg cells in series, each of which has lenses and a photodetector array in its focal plane, connected to the visual spectrum indication unit, and also a receiving antenna and a frequency converter in series, in the diffracted beam of each , intermediate frequency amplifier, first multiplier, first bandpass filter, second multiplier, second bandpass filter, third per a multiplier and a third bandpass filter, while the inputs of the multiplier and the output of each bandpass filter are connected to the electrical inputs of the corresponding Bragg cells, characterized in that, in order to expand the functionality by accurate and unambiguous direction finding of the radiation source of complex signals with linear frequency modulation, into it a switch, a narrow-band filter, an amplitude detector and an element And, a counting pulse generator connected to the second input of Entente And, a series-connected differentiating circuit, a counter, an arithmetic unit and a fifth display unit, series-connected a second antenna, a fourth multiplier, a low-frequency amplifier and an electronic counting frequency meter connected to the second input of the arithmetic unit, the second input of the fourth multiplier connected to a switch, the output of the element And is connected to the second input of the counter, and the output of the differentiating circuit is connected to the output of the amplitude detector.

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