RU2088945C1 - Method for spectrum analysis of broadband shf noise signals and device for its realization - Google Patents

Abstract

FIELD: SHF measurement technology. SUBSTANCE: method consists of resonance detection of components of spectrum of SHF signal consistent in time, processing of converted signal with gain factor inversely proportional to frequency, additional cross modulation conversion of components frequency of the same signal spectrum, narrow-band filtration of converted signal on one of frequencies multiple of modulation frequency, recording of obtained envelopes of spectrum. Spectrum envelopes of each conversion are compared among themselves and carrier frequencies and amplitudes of determined components are determined by difference of envelopes forms in spectrum of SHF signal. Device for realization of method has two operational modes: basic one, when switch is in open state, i.e. modulator is disconnected and switch connects high-pass filter to broadband amplifier and additional one for detection of determined components in noise. In this case, switch is in closed state, modulator is connected to low-pass filter and switch connects filter to input of selective unit. EFFECT: additional detection of determined components in broadband noise SHF signals, measurement of their parameters (carrier frequency, amplitude) without disturbance of measurement mode of device operation. 2 cl, 3 dwg

Description

 The invention relates to microwave measuring technology and can be used in radar and electronic technology in the study of continuous broadband spectra of microwave noise generators.

A known method of analyzing the microwave spectrum using a local oscillator frequency conversion and based on this method, panoramic microwave spectrum analyzers [1] which, being indicator devices, do not allow measuring the absolute values of the power of an individual radiation and the spectral density of noise power. In addition, the presence of Raman reception channels does not directly determine the presence of weak deterministic components with an unknown frequency and power in the noise spectrum without additional laboriousness or expensive (computer) processing of the obtained spectra [2]
There is also a method of spectrum analysis, which consists in sequentially converting the components of the spectrum of the microwave signal in the lower frequency region by resonant detection in the frequency range of the investigated spectrum, processing the formed spectrum with a gain that is inversely proportional to the frequency, indicating the spectrum envelope of the converted signal and measuring it parameters implemented in the meter [3]
However, the existing method does not allow to detect the presence of deterministic components in broadband microwave noise signals and measure them.

 A known spectral power density meter [3] contains a gyromagnetic converter, the high-frequency output of which is connected to the input of the high-pass filter and the output of the low-pass filter, a modulator, the output of which is connected through a switch to the input of the low-pass filter, an amplifier of the converted signal, the output of which is connected to the input of the unit indications and sweeps, the output of which is connected to the low-frequency input of the gyromagnetic converter. The indication and sweep unit serves to provide synchronous changes in the sawtooth law of the magnetization field of the gyromagnetic converter and the frequency sweep on the indicator unit, as well as to generate a frequency mark and level for direct measurement of the frequency and power spectral density, respectively, and is made in the form of a sawtooth voltage generator, stabilizer current, label and level driver, frequency measuring unit and oscillographic unit.

 The modulator is connected to the device, providing the mode of cross-multiplication of the gyromagnetic transducer, only for their calibration by level to measure the spectral power density, then the modulator is turned off and is not used for measurements. The measurements are carried out without modulating the bias field, i.e. in the resonant detection mode of the gyromagnetic transducer.

 However, this device does not allow to detect the presence of deterministic components in the broadband microwave noise signals.

 The purpose of the invention is to provide additional opportunity to identify deterministic components in broadband noise microwave signals and measure their parameters (carrier frequency, amplitude) without violating the measuring mode of operation of the device.

 This is achieved by the fact that in the known method for analyzing the spectrum of microwave broadband noise signals, which consists in sequentially resonant detection of the components of the microwave signal spectrum, processing the converted signal with a gain inversely proportional to the frequency, recording the resulting spectrum envelope, additionally cross-modulates the frequency components of the spectrum the same microwave signal, narrow-band filtering of the converted signal at one of the frequencies, multiple frequencies modulation registration received spectral envelope, the envelope of the spectrum of each conversion compared to each other and the difference forms the envelopes of the carrier frequencies is determined and the determined amplitude of the noise components in the spectrum of the microwave signal.

 In the device for spectrum analysis of microwave broadband noise signals for implementing the proposed method, comprising a gyromagnetic converter, the high-frequency output of which is connected to the input of the high-pass filter and to the output of the low-pass filter, a modulator, the output of which is connected through a switch to the input of the low-pass filter, an amplifier of the converted signal, the output of which is connected to the input of the display and sweep unit, the output of which is connected to the low-frequency input of the gyromagnetic converter, selective a block with a tuning frequency that is a multiple of the modulator frequency, and a switch to which the output of the high-pass filter is connected to the movable contact, and the input of the converted signal amplifier and the input of the selective block, the output of which is connected to the input of the converted signal amplifier, are connected to the fixed contacts.

 In FIG. 1 shows a block diagram of a device; figure 2 envelopes of the spectrum of the noise signal.

 Curve 1 is formed during resonance detection and broadband processing with a gain of ~ 1 / ω, and curve II during cross-modulation frequency conversion and narrow-band filtering.

Figure 3 shows the components of the spectrum of the converted signal:
where F _W (ω _CR ) continuous spectrum due to beats noise-to-noise;
_Csh F (ω _etc.) due to the continuous spectrum of the beat signal-deterministic noise;
F _c (nΩ) discrete spectrum at frequencies that are multiples of the modulation frequency due to the deterministic signal.

 The proposed method for analyzing the spectrum of broadband noise signals, which allows to identify and measure the determinate components in the noise spectrum, is as follows. A microwave noise signal at a frequency ω undergoes a heterodyne-free frequency conversion with resonant detection, at which the signal spectrum is transferred to the low-frequency region. The spectrum of the converted signal is processed with a gain that is inversely proportional to the frequency, which is important for the proportionality of the input and output envelopes of the noise spectrum. Resonant detection is carried out sequentially at each frequency point in the spectrum of the microwave noise signal, so that the signal converted and processed with k (ω) ~ 1 / ω forms the spectral envelope of the original signal, which is recorded.

 In addition to resonant detection, cross-modulation frequency conversion (cross-multiplication) of the spectrum components of the same microwave noise signal is additionally carried out. In cross-modulation conversion, the resonant frequency of the resonant detecting element is modulated with frequency W (HF range).

 The converted signal is filtered at one of the frequencies that are multiples of the modulation frequency (for example, at a frequency of 2Ω). Cross-modulation conversion is carried out sequentially at each frequency point in the spectrum of the microwave noise signal, so that a second envelope of the spectrum of the same signal is generated and recorded.

 The conversion of a purely noise (continuous) spectrum is the same in both cases (for resonant detection with processing with a gain of k (ω) ~ 1 / ω and for cross-modulation with narrow-band filtering at a frequency nΩ, since the modulation of the frequency of the resonant detector does not affect the noise spectrum .

In the place of the spectrum where additive deterministic (discrete) components are present in the background of noise, the results of spectrum processing during resonance detection and cross-multiplication are different. In resonant detection range converted signal has continuous components due to the noise-noise beats F _w (ω) and the determined signal-to-noise _csh F (ω). During cross-modulation, in the spectrum of the converted signal, in addition to the components coinciding with those indicated during resonance detection, there are discrete harmonics of the modulation frequency Ω, whose amplitudes are proportional to the amplitude of the deterministic component of the microwave spectrum F _c (nΩ). In this case, the filtered and registered signal carries information about the determinate component in the noise spectrum; in this case, the envelope of the spectrum contains an additional peak.

 To determine the deterministic component, a comparison of two spectral envelopes is required. Envelopes due to noise spectrum coincide. The deterministic component is manifested by an additional peak inhomogeneity when comparing two envelopes of the same microwave signal arising from cross-modulation frequency conversion and narrow-band filtering. The amplitude of the peak is proportional to the amplitude of the deterministic component, and the frequency is determined by the position of the peak on the frequency axis during the frequency tuning of the resonant detecting element.

 A device that implements the proposed method contains a gyromagnetic converter 1, the high-frequency output of which is connected to the input of the high-pass filter 2 and the output of the low-pass filter 3, a modulator 4, the output of which is connected through a switch 5 to the input of the low-pass filter 3, the converted signal amplifier 6, the output which is connected to the input of the display and scan unit 7, the output of which is connected to the low-frequency input of the gyromagnetic converter. A selective block 8 and a switch 9 are introduced. The output of the narrow-band block 8 is connected to the input of the broadband amplifier 6. The output of the high-pass filter is connected to the moving contact of the switch 9, and the input of the converted signal amplifier 6 and the input of the selective block 8 are connected respectively to its fixed contacts.

The device operates as follows and has two modes of operation:
1) The main measuring mode, in which the switch 5 is in the open state (i.e., the modulator 4 is turned off), the switch 9 connects to the output of the high-pass filter 2 the input of the broadband amplifier of the converted signal 6 (selective block is turned off).

 In this case, the envelope of the noise spectrum 1 is formed, which is directly proportional to the original envelope.

 The microwave signal is fed to the input of the gyromagnetic transducer 1, performing resonant detection. The converted RF signal passes through the high-pass filter 2, and is fed to the input of a broadband amplifier 6 with a gain inversely proportional to the frequency k (ω) ~ 1 / ω, which compensates for the frequency distortions introduced by the magnetic detector coil during resonance detection. In the display and sweep unit 7, the spectrum envelope of the microwave broadband signal is recorded. The device of block 7 is similar to the same block in the device (3).

 2) An additional mode for detecting deterministic components in noise, in which the switch 5 is closed (the modulator 4 is connected to the input of the low-pass filter 3), the switch 9 connects the input of the selective block 8 to the output of the high-pass filter 2.

 In this case, a second envelope of the noise spectrum is formed with modulation of the bias field (cross-multiplication). If a deterministic component is present in the noise spectrum, then the shape of the envelope of the spectrum changes at the frequency of this spectral component.

 The microwave signal is fed to the input of the gyromagnetic converter 1, which performs cross-modulation frequency conversion (cross-multiplication). The converted RF signal passes through the high-pass filter 2 to the input of the selective block 8, filtering the determinate components in the noise component of the spectrum of the converted signal (the selective block is tuned to a frequency that is a multiple of the modulation frequency W, for example, to its second harmonic). Low-pass filters 3 and high-pass 2 are necessary for frequency separation (decoupling) of the modulation signal and the converted signal, since the converted signal is modulated and removed using the same coil of the magnetic detector, on the basis of which the gyromagnetic converter 1 is made.

 The signal from the output of the selective block 8 is fed to the input of the indication and sweep block 7, with the help of which the second envelope of the spectrum is formed (curve II) and compared with curve I, and the amplitudes and frequencies of the determined components are measured.

A device mockup was made that implements the invention on the basis of the ISPM-1 device, including an additional narrow-band unit (a resonant amplifier with a central tuning frequency equal to twice the frequency of the modulator 2F _Mod 2 MHz). At the first stage, the fundamental inability of ISPM-1 itself to experimentally determine the deterministic components in noise (even with a large signal-to-noise ratio, P _s / (R _w .DF _gp 1-27 (P _s signal power, R _w - noise power, ΔF _rn bandwidth gyromagnetic converter for microwave). The second step was checked experimentally possible to identify the deterministic signals from the additive mixture signal to noise using a layout with an extra narrow-band amplifier in the transition from a resonant detection krossumnozheniyu. Minimum flash signal / noise ratio at which the deterministic signal detected stably, was in this case 0.14, which proves the functionality of the expansion device using therein the narrowband processing unit and administering the test spectrum of the microwave signal in the cross-modulation mode, the frequency conversion.

Literature
1. Martynov V.A. Selikhov Yu.I. Panoramic receivers and spectrum analyzers. M. Soviet Radio, 1964, p. 114, 338.

 2. Test Measurement Catalog, Hewlett Packard, 1992, p. 258.

 3. Panoramic power spectral density meter ISPM-1. Technical description and instruction manual. M. 2.747. 001 TO, s. 11-15.

Claims (2)

 1. The method of spectrum analysis of broadband microwave noise signals, which consists in converting the frequency of each component of the spectrum of the microwave signal by resonant detection, processing the converted signal with a gain inversely proportional to the frequency, forming the envelope of the spectrum of the microwave signal, characterized in that additionally sequentially in time, cross-modulation frequency conversion of each component of the spectrum of the same microwave signal is carried out, I filter narrowly t and form the second envelope, compare both formed envelopes and determine the carrier frequencies and amplitudes of the determined components in the spectrum of the microwave noise signal by the difference in their shapes.  2. A spectrum analysis device for microwave broadband noise signals, comprising a hydromagnetic converter, the high-frequency output of which is connected to the input of the high-pass filter and to the output of the low-pass filter, a modulator, the output of which is connected through a switch to the input of the low-pass filter, and the converted signal amplifier, the output of which is connected with the input of the display and sweep unit, the output of which is connected to the low-frequency input of the gyromagnetic converter, characterized in that a selective unit with a frequency setting a multiple frequency modulator, and a switch, the movable contact of which is connected the output of high pass filters, and fixed contacts connected respectively to the input of the amplifier and the converted signal is input selectively block the output of which is connected to the amplifier input the converted signal.

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