RU136578U1 - Coherent superheterodyne spectrometer of electron paramagnetic resonance - Google Patents

Abstract

Coherent superheterodyne electron paramagnetic resonance spectrometer, including microwave signal and heterodyne generators, two microwave power dividers, reference and signal channel mixers, a circulator with a measuring resonator and an element for tuning the resonant frequency of the measuring resonator, a measuring attenuator, intermediate frequency amplifiers (IF) of the reference and signal channels , two phase-frequency discriminators with filters at the outputs, two synchronous detectors, two IF phase shifters, a reference oscillator, and an operating mode switch, the output of the measuring attenuator connected to the input of the first microwave power divider, one of the outputs of which is connected to the first arm of the circulator, and the second to the signal input of the reference channel mixer, the output of the local oscillator is connected to the input of the second power divider, one of the outputs of which connected to the heterodyne input of the mixer of the reference channel, and the second to the heterodyne input of the mixer of the signal channel, the second arm of the circulator is connected to a measuring resonator equipped with an electric by tuning its resonant frequency, the third arm of the circulator is connected to the input of the signal channel mixer, and its output is connected to the input of the IF signal channel, the output of which is connected to the signal inputs of the first and second synchronous detectors, the output of the first phase shifter is connected to the reference input of one of the synchronous detectors and with the input of the second phase shifter, the output of which is connected to the reference input of the second synchronous detector, the output of the second phase-frequency discriminator is connected to the control electrode heterodyne

Description

The utility model relates to technical physics and can be used in the manufacture of electron paramagnetic resonance (EPR) spectrometers.

Known EPR spectrometer (Guy Rogeret al. Use of a digital PLL in an ESR heterodyne spectrometer // T. Phys R: Sci Instrum, 1981, v.14, p. 335-338.), Containing microwave heterodyne and signal generators, mixers reference and signal channels, a circulator with a measuring resonator, a measuring attenuator. A microwave phase shifter, a frequency discriminator based on a reference high-Q resonator, a modulation system for auto-tuning the frequency of the microwave signal generator, intermediate frequency amplifiers (IFA) of the reference and signal channels, a synchronous intermediate frequency detector, a phase-locked loop (PLL) of a heterodyne generator with a highly stable reference source of intermediate frequency and an operating mode switch, wherein the output of the local oscillator is connected to the local oscillator input of the reference mixer ala and with a phase shifter, the output of which is connected to the heterodyne input of the signal channel mixer, the output of the signal generator is connected to the signal input of the reference signal mixer, the input of the frequency discriminator and the input of the measuring attenuator, the first arm of the circulator is connected to the output of the measuring attenuator, the second to the measuring resonator, and the third with the signal input of the signal channel mixer, the output of the signal channel mixer is connected to the input of the IF signal channel, and its output with the signal input syn intermediate frequency detector, the output of the reference channel mixer is connected to the input of the phase-locked loop system of the heterodyne microwave generator and to the input of the IF amplifier of the reference channel, the output of the IF amplifier of the reference channel is connected to the reference input of the intermediate frequency synchronous detector, the input of the frequency-modulation system via the mode switch is connected to either the output of the frequency discriminator, or with the output of a synchronous detector of an intermediate frequency, and its output is connected to the control electrode of the signal generator of yield heterodyne phase locked microwave generator system is connected to its control electrode.

However, this spectrometer is difficult to configure, which is associated with the need to select the necessary phase relations using an adjustable microwave phase shifter for each installation of the measuring attenuator; it has insufficient stability due to the independence of the tuning of potentially unstable microwave phase shifter and measuring attenuator; insufficient resolution, which is associated with the use of a modulation system of automatic frequency control, which reduces the spectral purity of the microwave signal, but necessary with variable phase ratios, in a device for various settings of the measuring attenuator

Closest to the utility model is an EPR spectrometer (Patent No. 1739751, MPK6 G01N 24/10, publ. 10.10.1995), containing microwave signal and local oscillators, measuring resonator, reference and signal channel mixers, circulator, measuring resonator, reference and signal channels, two phase discriminators, a highly stable reference oscillator, two synchronous detectors, two phase shifters, a third mixer, a third IF amplifier, a harmonic generator, an operating mode switch and an element for tuning the resonant frequency of the measuring a tenator, and the OPC of the reference channel is made as a normalizing amplifier-driver, the phase shifters have a fixed phase shift, the output of the measuring attenuator is connected to the input of the first microwave power divider, one of the outputs of which is connected to the first arm of the circulator, and the second to the signal input of the mixer of the reference channel, the output of the heterodyne generator is connected to the input of the second power divider, one of the outputs of which is connected to the heterodyne input of the mixer of the reference channel, and the second to the heterodyne input of the mixture of the signal channel, the second arm of the circulator is connected to a measuring resonator equipped with an element for tuning its resonant frequency, the third arm of the circulator is connected to the input of the mixer of the signal channel, and its output is connected to the input of the signal amplifier channel, the output of which is connected to the signal inputs of the first and second synchronous detectors , the output of the first phase shifter is connected to the reference input of one of the synchronous detectors and to the input of the second phase shifter, the output of which is connected to the reference input of the second synchronous detector, the output of the second phase-frequency discriminator is connected to the control electrode of the heterodyne generator, and the operating mode switch is made three-position, in the first and second position provides the connection of the frequency control electrode of the signal generator with the output of the first phase-frequency discriminator, and in the third - with the output of the first synchronous detector, in the second position providing an additional connection of the output of the first synchronous detector with the tuning element of the resonant frequency resonator cavity, and the OPC of the reference channel is made in the form of a normalizing amplifier of a voltage driver, while the first and second IF phase shifters are made with a fixed phase shift and the phase shift of the second is ± π / 2.

The disadvantages of the device are that in the stabilization mode of the signal generator frequency according to an external (absolute) standard, the PLL loop operates using the signal obtained by mixing the signal of the stabilized generator with one of the frequency grid signals obtained by multiplying the frequency of the highly stable reference generator, then isolating and amplifying the difference signal special selective amplifier. Such a solution has circuit and structural complexity, has significant dimensions, consumes noticeable power and is a source of additional phase noise of a stabilized generator.

Another disadvantage of the device is the use of both a reference frequency generator and a reference signal in phase discriminators and phase-sensitive (synchronous) signal detectors of a fixed frequency reference highly stable generator, which complicates the construction of PLL loops using integrated microelectronic solutions.

The objective of the utility model is to simplify the device, reduce its dimensions, power consumption and cost, reduce the phase noise of the microwave generator, implement the necessary functionality on standard, commercially available microelectronic components.

The problem is achieved due to the fact that the coherent superheterodyne spectrometer of electron paramagnetic resonance, including signal and heterodyne microwave generators, two microwave power dividers, reference and signal channel mixers, a circulator with a measuring resonator and an element for tuning the resonant frequency of the measuring resonator, measuring attenuator, intermediate amplifiers frequency (UPCH) of the reference and signal channels, two phase-frequency discriminators with filters at the outputs, two synchronous det one, two IF phase shifters, a reference generator and a mode switch, the output of the measuring attenuator connected to the input of the first microwave power divider, one of the outputs of which is connected to the first arm of the circulator, and the second to the signal input of the mixer of the reference channel, the output of the local oscillator is connected to the input of the second power divider, one of the outputs of which is connected to the heterodyne input of the mixer of the reference channel, and the second to the heterodyne input of the mixer of the signal channel, the second arm of the circulator ineno with a measuring resonator equipped with an element for tuning its resonant frequency, the third arm of the circulator is connected to the input of the signal channel mixer, and its output is connected to the input of the signal converter channel, the output of which is connected to the signal inputs of the first and second synchronous detectors, the output of the first phase shifter is connected to the reference the input of one of the synchronous detectors and with the input of the second phase shifter, the output of which is connected to the reference input of the second synchronous detector, the output of the second phase-frequency discriminant pa is connected to the control electrode of the local oscillator, and the operating mode switch is three-position, in the first and second position it provides the connection of the frequency control electrode of the signal generator with the output of the first phase-frequency discriminator, and in the third - with the output of the first synchronous detector, in the second position provides an additional output connection the first synchronous detector with the tuning element of the resonant frequency of the measuring resonator, and the OPC reference channel is made in the form of a normalizing voltage driver amplifier, with the first and second IF phase shifters made with a fixed phase shift and the second phase shift of ± π / 2, additionally contains two frequency dividers, a reference frequency synthesis device, and a signal generator equipped with an additional output, and the output of the reference generator connected to the input of the reference frequency synthesis device, one of the outputs of which is connected to the reference input of the first phase-frequency discriminator, the second to the reference input of the second phase-frequency of the first discriminator, and the third with the input of the first phase shifter, and the auxiliary output of the signal generator through the first frequency divider is connected to the signal input of the first phase-frequency discriminator, the input of the second frequency divider is connected to the output of the IF amplifier of the reference channel, and its output with the reference input of the second phase-frequency discriminator.

The drawing shows a block diagram of a coherent superheterodyne EPR spectrometer.

The spectrometer contains a signal 1 and a local oscillator 2 microwave generators, a measuring attenuator 3, a mixer 4 reference and a mixer 5 signal channels, a circulator 6 with a measuring resonator 7, UPCH 8 reference and UPCH 9 signal channels, phase-frequency discriminators 10 and 11, frequency dividers 12 and 13 , synchronous detectors 14 and 15, phase shifters 16 and 17, tuning element of the resonant frequency of the measuring resonator 18, microwave power dividers 19 and 20, three-position switch 21 operating modes, a device for synthesizing reference frequencies 22, a reference oscillator 23 .

The device operates as follows.

The signal from the main output of the microwave signal generator 1, the electrical oscillations of which are described by the COS function (ω _M t), through the measuring attenuator 3, which raises the phase α, is fed to the input of the power divider 19. A part of the power is branched to the signal input of the mixer 4 of the reference channel, reaching him with an additional phase incursion φ1. To the reference input of this mixer through a power divider 20, a signal of a heterodyne microwave generator 2 is supplied, having the form COS (ω _L t + λ + β1), where λ is the oscillation phase at the output of the heterodyne generator, and β1 is the phase difference on the power divider and connecting line . The difference signal from the output of the mixer 4 is amplified by the amplifier 8 of the reference channel, which is characterized by a wide dynamic range and a small dependence of the delay (phase incursion) on the magnitude of the input signal and is subjected to frequency division by a factor of N2 by the corresponding frequency divider 12. The signal from the output of the frequency divider 12 is fed to the signal input phase discriminator 10,

,as

,

where δ describes the phase incursion from the output of mixer 4 to input 10.

The PLL loop at the intermediate frequency is closed by supplying the output signal of the phase-frequency discriminator 10 through a filter (not shown in the diagram for simplicity) to the input of the local oscillator 2, which controls its frequency. At the reference input of the phase-frequency discriminator 10 is a highly stable signal

,

,

where Ω is the intermediate frequency (IF), and

γ is an arbitrary initial phase, from one of the outputs of the reference frequency synthesis device 22.

When capturing the PLL loop, the equality condition at the frequency inputs

and phases

The main part of the microwave power of the signal generator 1 through the power divider 19 is fed to the first arm of the microwave circulator 6 and then to the measuring resonator 7 connected to the arm 2 of the circulator. The signal reflected from the resonator 7 is returned to the arm 2 of the circulator and then goes to its arm 3, connected to the signal input of the mixer 5 of the signal channel. The signal at this input is described by the function

Г'cos (ω _M t + α + φ2) + Г''sin (ω _M t + α + φ2),

where G 'is the real part of the complex reflection coefficient of the resonator 7, depending on the absorption signal of the EPR,

G "- the imaginary part, depending on the dispersion signal of the EPR and the detuning of the resonator relative to the frequency of the incident wave,

φ2 is the phase advance of the microwave wave from the input of the power divider 19 to the input of the mixer 5.

From the output of the mixer 5, the difference signal is fed to the input of the signal converter channel 9 and then to the signal inputs of the synchronous detectors 14 and 15 in the form

where 77 means the phase advance from the output of the mixer 5 to the inputs of the synchronous detectors 14 and 15.

Under conditions of capturing the PLL loop at an intermediate frequency, relations (1) and (2) apply for frequencies and phases, which leads to the fact that signal (3) takes the form

Thus, the received signal at the intermediate frequency Ω contains two quadrature components, one of which is proportional

G ', i.e., the EPR absorption signal, and the second Г ", i.e., the dispersion and detuning signal of the measuring resonator.

A highly stable reference signal cos (Ωt) from one of the outputs of the reference frequency synthesis device 22 is supplied to the input of the phase shifter 17, giving a phase incursion into. The signal from the output of the phase shifter 17 cos (Ωt + θ) is fed to the reference input of the mixer 14 and to the second phase shifter 16, which rotates the phase by ± π / 2. So, taking, for definiteness, a shift of -π / 2, we obtain at the output of the phase shifter 16 connected to the reference input of the mixer 15, sin (Ωt + θ). As a result of mixing and separation of the difference frequency, we get output 15

and output 14

The phase angle included in the trigonometric functions (5) and (6) does not contain a substantially variable quantity a, depending on the installation of the measuring attenuator 3, but is determined only by constant phase shifts in various circuits of the device. Thus, setting the phase shift in the phase shifter 17 so that the phase angle (γ-δ) N2-β1 + φ1 + β2-β2 + η-θ is equal to π / 2 or 3π / 2, we obtain at the output 15 a pure absorption signal, and at output 14, a signal proportional to the dispersion and detuning of the measuring resonator, regardless of the frequency of the measuring generator 1, its detuning relative to the resonant frequency of the measuring resonator 7 and the power level. The reference signal for the operation of the synthesis device of the reference frequencies 22 is the output signal of a highly stable reference generator 23 at a frequency convenient for operation 22.

. На опорный вход этого дискриминатора подается высокостабильный сигнал с одного из выходов устройства синтеза опорных частот 22 вида

, где ω_M0- номинальная частота измерительного генератора. В положении «1» переключателя рода работ 21 петля ФАПЧ по частоте сигнального генератора замыкается путем подачи сигнала отработки с выхода 11 через соответствующий фильтр (для простоты не показан) на электрод, управляющий частотой 1. Частота сигнального генератора 1 стабилизируется на значении ω_M0, что позволяет провести подстройку резонансной частотыThe device has three modes for stabilizing the frequency of the measuring generator 1 and the resonant frequency of the measuring resonator 7. For absolute stabilization (stabilization by a highly stable standard) of the frequency of the signal generator, the auxiliary frequency output of the signal generator 1 is used. If it is absent, it can be easily created by turning on the directional coupler to the main (single) output of the generator. The microwave signal from the auxiliary output is subjected to division by a frequency divider 13 N1 times to a frequency convenient for comparison on a phase-frequency discriminator 11 and fed to its signal input in the form

. A highly stable signal is supplied to the reference input of this discriminator from one of the outputs of the reference frequency synthesis device 22

where ω _M0 is the rated frequency of the measuring generator. In position “1” of the type of work switch 21, the PLL loop in the frequency of the signal generator is closed by supplying a working signal from output 11 through an appropriate filter (not shown for simplicity) to the electrode controlling frequency 1. The frequency of signal generator 1 is stabilized at ω _M0 , which allows tuning the resonant frequency

measuring resonator 7 to coincide with ω _M0 . In position “2” of the type of work switch 21, the signal from the output of the synchronous detector 14 in the corresponding phase is fed to the tuning element of the resonant frequency 18 of the measuring resonator 7 to automatically adjust its resonant frequency to the stabilized signal generator 1. Finally, in the third position 21, the signal from the synchronous output detector 14 is used to adjust the generation frequency 1 to the instantaneous value of the resonant frequency of the measuring resonator 7, for which it is supplied to the control phase in the corresponding phase pilots at one electrode.

Thus, the operation of the spectrometer, including the isolation of pure absorption and dispersion signals, is ensured by using a standard, commercially available element base (frequency dividers, frequency synthesizers with phase-frequency discriminators), which reduces the dimensions, power consumption and price of the device, increases its manufacturability and reliability, reduces phase noise.

Claims (1)

Coherent superheterodyne electron paramagnetic resonance spectrometer, including microwave signal and heterodyne generators, two microwave power dividers, reference and signal channel mixers, a circulator with a measuring resonator and an element for tuning the resonant frequency of the measuring resonator, a measuring attenuator, intermediate frequency amplifiers (IF) of the reference and signal channels , two phase-frequency discriminators with filters at the outputs, two synchronous detectors, two IF phase shifters, a reference oscillator, and an operating mode switch, the output of the measuring attenuator connected to the input of the first microwave power divider, one of the outputs of which is connected to the first arm of the circulator, and the second to the signal input of the reference channel mixer, the output of the local oscillator is connected to the input of the second power divider, one of the outputs of which connected to the heterodyne input of the mixer of the reference channel, and the second to the heterodyne input of the mixer of the signal channel, the second arm of the circulator is connected to a measuring resonator equipped with an electric by tuning its resonant frequency, the third arm of the circulator is connected to the input of the signal channel mixer, and its output is connected to the input of the IF signal channel, the output of which is connected to the signal inputs of the first and second synchronous detectors, the output of the first phase shifter is connected to the reference input of one of the synchronous detectors and with the input of the second phase shifter, the output of which is connected to the reference input of the second synchronous detector, the output of the second phase-frequency discriminator is connected to the control electrode heterodyne about the generator, and the operating mode switch is made three-position, in the first and second positions providing the connection of the frequency control electrode of the signal generator with the output of the first phase-frequency discriminator, and in the third - with the output of the first synchronous detector, in the second position providing an additional connection of the output of the first synchronous detector with the element tuning of the resonant frequency of the measuring resonator, and the amplifier of the reference channel is made in the form of a normalizing amplifier of the driver in this case, the first and second IF phase shifters are made with a fixed phase shift, and the phase shift of the second is ± p / 2, characterized in that it additionally contains two frequency dividers, a reference frequency synthesis device, and the signal generator is equipped with an additional output, and the output the reference generator is connected to the input of the reference frequency synthesis device, one of the outputs of which is connected to the reference input of the first phase-frequency discriminator, the second to the reference input of the second phase-frequency discriminator, and s - to the input of the first phase shifter and the auxiliary oscillator output signal through a first frequency divider connected to the signal input of the first phase-frequency discriminator, the input of the second frequency divider connected to the output IF reference channel and its output - to the reference input of the second phase-frequency discriminator.

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