RU2189055C2 - Transceiver of homodyne radar - Google Patents

Abstract

FIELD: radio engineering, radiolocation. SUBSTANCE: transceiver of homodyne radar has generator of probing signal with voltage-controlled frequency connected to transmitting antenna, generator of modulating signal which output is connected to input controlling frequency of generator of probing signal, mixer one input of which is connected to receiving antenna and which another input is connected to output of generator of probing signal, amplifier and filter tuned to modulation frequency or its harmonic connected in series to output of mixer, synchronous detector or quadrature synchronous detector connected with first input to generator of modulating signal and with second input to output of filter and connected with outputs to outputs of transceiver. Alternative transceiver determining sign of phase difference of received and probing signals includes second filter connected through amplifier to output of mixer and tuned to another harmonic of modulating signal, second synchronous or quadrature synchronous detector connected with one input to generator of modulating signal and with another input to output of second filter and with outputs to outputs of transceiver. In another variant of transceiver mixer and generator of modulating signal are replaced by autodyne unit performing their functions and connected with SHF signal input/output to transceiving antenna, with input controlling frequency of probing signal to output of generator of modulating signal and with output to input of amplifier. EFFECT: increased sensitivity, potential for determination of sign of Doppler frequency shift. 2 cl, 9 dwg

Description

The invention relates to radio engineering, and in particular to the field of radar. Known radars, called "homodyne", the hallmark of which is the frequency conversion of the received reflected signal by multiplying it on a non-linear element (mixer) with the emitted (probing) signal. The output signal of the mixer transceiver homodyne radar has the form
U _O = U ₀ cos (φ _s -φ _etc.), (1)
where φ _z , φ _CR are the phases of the probing and received signals, U ₀ is the amplitude of the output signal voltage. An analysis of the dependence U _o (t), for a known function φ _z (t), usually performed by a complex of digital processing of radar information, makes it possible to determine the coordinate and (or) its time derivative by known methods. Radars of this type are distinguished by their simplicity of design, low cost and are used, as a rule, in Doppler speed meters, as well as in meters of short distances and heights using frequency modulation (FM radars). A variant of a homodyne is an autodyne radar, in which the functions of the generator and mixer are performed by one indivisible functional element, for example, the Gunn diode. The output signal of the transmitting and receiving devices of these radars lies in the low frequency region (from zero to tens of kilohertz).

 A simplified block diagram of a receiving and transmitting device of a homodyne radar station (radar) is shown in FIG. 1 (see A.S. Vinnitsky, "Autonomous Radio Systems", M., "Soviet Radio", 1986, p. 153, 261). The device comprises a probe signal generator 1 connected to a transmitting antenna 3, and a mixer 2, one of the inputs of which is connected to a generator 1, and the second is connected to a receiving antenna 4. The signal of generator 1 is emitted by a transmitting antenna 3, and the signal reflected from the object is received by a receiving antenna 4 and sent to the mixer, where a signal is generated, defined by expression (1), whose phase is equal to the phase difference of the emitted and received signals. The output signal of the differential phase and, therefore, the frequencies through the filter are fed to the output of the receiving and transmitting device, from where they are sent to the radar information processing complex.

 The disadvantage of this scheme is the lower sensitivity of the receiver at low output frequencies, due to the influence of flicker noise of the mixer. A direct measurement of the noise figure of a homodyne receiver in the 60 GHz range yielded values of about 100 dB at a frequency difference of 10 Hz and 60 dB at a frequency difference of 10 KHz (see V. L. Virchenko et al. "Sensitivity of a millimeter-wave solid-state homodyne radar receiver in the low-frequency range "in the collection" Solid-state generator and converting devices of mm and submm range "Kharkov, IRE AN USSR, 1989., pp. 78-81). Obviously, the value of the noise figure approaches acceptable values only with a frequency difference of the order of units of megahertz.

This drawback is usually eliminated by increasing the frequency of the output signal of the mixer by switching to the superheterodyne principle of signal reception, or by modifying the homodyne circuit by including a frequency shift mixer and a filter between the transmitter and the mixer (see A. S. Vinnitsky, "Autonomous radio systems", M., "Soviet Radio" , 1986, p. 181). An analogue of the present invention is a "Doppler radar with phase modulation of the transmitted and reflected signals" (US patent 4439766 dated March 27, 1984, G 01 S 9/44), in which the frequency increase is achieved by phase-modulation of the probe signal with frequency F, and a useful signal of the form ( 1) receive vector detection of the intermediate frequency signal. Figure 2 shows the structural diagram of this device. To ensure the possibility of working with one antenna, a ferrite circulator 6 is applied, to the two arms of which a generator 1 and a mixer 2 are connected. A phase modulator 7 is connected between the third arm of the circulator and the transmitter-receiver antenna 3, controlled by the signal of the modulating generator 10. To the output of the mixer 2 through the selective an intermediate frequency amplifier (IFA) 8 is connected to a synchronous detector (SD) 9, the second input of which is connected to the output of the modulating generator. As a result of the phase modulator, the reflected signal at the input of the mixer turns out to be phase-modulated by frequency F. Mixer 2 acts as a demodulator, and an intermediate frequency (IF) signal close to the value of F is removed from its output, amplified by IF 8 and detected by synchronous phase detection detector 9. As a result of these operations, a useful signal is determined at the output of the synchronous detector, which is determined by expression (1). The disadvantage of this scheme is the insensitivity of the output signal to the sign of the derivative (φ _s -φ _pr ) / dt, which does not allow, for example, to obtain information about the sign of the Doppler frequency offset, that is, the direction of movement of the object.

 To increase the frequency of the output signal of the mixer, pulse modulation of the probing signal by key devices in the receiving and transmitting channels of the receiving and transmitting device can be used (see the author's patent application for invention 99116167).

The closest analogue of the present invention is a dual frequency modulation radar altimeter (see A. Vinnitsky, Essay on the fundamentals of radar in the continuous emission of radio waves, M., "Soviet Radio", 1961, p. 307). Figure 3 shows the structure of the transmitter-receiver of this altimeter, in which the intermediate frequency signal is obtained due to the frequency modulation of the probe signal. The frequency-modulated output voltage of the generator 10, the signal of the generator 1 is emitted by the receiving antenna 3, and the reflected signal is received by the receiving antenna 4 and sent to the mixers 2a and 2b, where it is multiplied with a probing signal supplied to the mixers with a phase difference π / 2 specified by the phase shifter 7a . The signals of the selected harmonic (multiplicity N) of the modulation frequency are selected by filters (2a and 2b) and added by the adder 13, and the phase of one of the signals changes to π / 2 by the phase shifter 7c. The resulting intermediate frequency signal through the amplifier 8 is fed to the output of the device. The output signal of this device is described by the expression U _o = U ₀ cos [2πNFt + (φ _з -φ _пр )], and its frequency f _pc = NF + d (φ _з -φ _пр ) / dt, that is, the circuit makes it possible to determine the sign of the Doppler frequency shift and eliminates the effect of critical speeds in FM radars.

 A common drawback of these devices is that increasing the frequency of the output signal of the mixer and the ability to determine the sign of the Doppler shift is achieved by introducing one or more additional microwave functional units (mixer, phase shifter, phase modulator, key devices) into the transmitter-receiver device. High complexity and high complexity, typical for microwave nodes, significantly increase the cost of the receiving and transmitting device, which limits their use in a very promising field of medium and short range technological radars, where price is the most important criterion for applicability.

 This proposal is aimed at solving the problems of realizing the high sensitivity of receiving and transmitting devices of homodyne (including autodyne) radars and providing the possibility of determining the sign of the Doppler frequency shift by simple and cheap technical means.

 The problem is solved according to the invention in that the receiving and transmitting device homodyne radar containing a probe signal generator, the frequency of which is controlled by voltage, connected to the transmit antenna, a modulating signal generator, the output of which is connected to the frequency control input of the probe signal generator, mixer, one input which is connected to the receiving antenna, and the second to the output of the probe signal generator, and the amplifier and filter connected in series with the output of the mixer Tuned to an intermediate frequency equal to the modulation frequency or its harmonics is further included a synchronous detector or quadrature synchronous detector is coupled to one input of a modulating signal generator, a second input to the filter output, and outputs - to the device outputs. The two-channel version of the device also has a second filter tuned to a different harmonic of the modulation frequency and connected by an input through an amplifier to the mixer output, and by an output to the input of a second synchronous detector or a quadrature synchronous detector, the second input of which is connected to the output of the modulating generator, and the outputs are with device outputs. Additionally, the device may have a frequency control input of the modulating generator and (or) a phase shifter connected between the output of the modulating generator and the inputs of synchronous detectors. Instead of a mixer and a probe signal generator, an autodyne unit performing their functions can be turned on, connected to the receiving-transmitting antenna by the input / output of the microwave signal, the probe frequency control input to the modulating signal generator output, and the output to the amplifier input.

 Nine drawings are attached to this description.

 In FIG. 1 shows a classic block diagram of a receiving-transmitting device of a homodyne radar.

 Figure 2 shows the structural diagram of an analogue of the invention: a transmitter-receiver with a phase modulator.

 In FIG. 3 shows a block diagram of the closest analogue of the invention: a transmitter-receiver altimeter with dual frequency modulation.

 In FIG. 4 shows a structural diagram of a single-channel version of the proposed transceiver.

 In FIG. 5 shows a block diagram of a two-channel version of the proposed transceiver.

 In FIG. 6 shows a structural diagram of a two-channel version of the proposed transceiver containing a phase shifter.

 Figure 7 shows the dependence of the output voltage of the mixer on the frequency of the probing signal and the timing diagram of the modulating voltage and voltage at the output of the mixer.

 On Fig shows a structural diagram of an autodyne single-channel version of the proposed transceiver.

 In FIG. 9 is a structural diagram of a liquid level meter constructed on the basis of the present invention.

 The receiving and transmitting device of the homodyne radar (Fig. 4) contains a frequency-modulated probe generator 1 with a circular frequency ω = 2πf, the output of which is connected to a transmitting antenna 3 and mixer 2, and the frequency control input to a modulating generator 10 with a circular frequency Ω = 2πF. The second (signal) input of the mixer 2 is connected to the receiving antenna 4, and the output is to the input of the selective intermediate frequency amplifier (UPCH) 8, the output of which is connected to the signal input of the synchronous detector 9. The second (reference) input of the synchronous detector 9 is connected to the output of the modulating generator 10, and the output or outputs with the outputs of the transmitter / receiver. The output of the synchronous detector is connected to the output through an amplifier with a low-pass filter 11. Since this feature is not significant, then it may not be mentioned. The probe signal generator 1 may have an additional frequency modulation input by an external signal.

детектируемого сигнала и разность его фазы и фазы соответствующей гармоники опорного сигнала NФ=arctg(U_(2)сд/ U_(1)сд). Синхронный детектор может быть реализован в вариантах: аналоговом (например, комбинация умножителя частоты, смесителя и фильтра нижних частот), импульсном (на основе схем совпадения), а также цифровом (программа перемножения и цифровой фильтрации функций).We define the synchronous detector, which is also called the vector or phase-sensitive detector in the technical literature, as an amplitude detector, the value of the output voltage of which is determined by the amplitude, and the polarity is determined by the phase of the detected signal. The synchronous detector has a signal input to which the detected signal is supplied, and a reference signal input, the frequency of which is equal to the frequency of the detected signal or differs from it by an integer number of times. In the proposed transmitting and receiving device, the synchronous detector performs the operations of multiplying the frequency of the reference signal by a given integer N, multiplying the received and detected signals and extracting the low-frequency component of the received signals. So, if the reference signal is sinusoidal (U _on = U _0on sinΩt), then for the detected signal U = U ₀ [sinN (Ωt-Ф)] the output signal of the synchronous detector is determined by the expression U _sd = U ₀ [sinN (Ωt-Ф)] sinNΩt = U ₀ сsФ, and for the detected signal U = U ₀ [cosN (Ωt-Ф)], the output signal of the synchronous detector has the form U _cd = U ₀ sinФ. In the usual mode of the synchronous detector, Ф = 0. We call a quadrature synchronous detector a combination of two parallel-connected synchronous detectors, and the detected signal arrives at their signal inputs with a phase difference π / 2. From the above it follows that the signals at the first U _{(1) sd} and second U _{(2) sd} outputs of the quadrature synchronous detector are of the form: U _{(1) sd} = U ₀ cosNФ and U _{(2) sd} = U ₀ sinNФ. Quadrature synchronous detector allows you to determine the module

the detected signal and the difference between its phase and the phase of the corresponding harmonic of the reference signal NФ = arctg (U _{(2) sd} / U _{(1) sd} ). A synchronous detector can be implemented in the following variants: analog (for example, a combination of a frequency multiplier, a mixer, and a low-pass filter), pulse (based on matching schemes), and digital (a program of multiplication and digital filtering of functions).

Transmitter (figure 4) works as follows. The frequency-modulated probe signal of the generator 1 is emitted by the antenna 3, and the reflected signal is received by the antenna 4 and sent to the input of the mixer 2. As a result of the interaction on the nonlinear elements of the mixer, the frequency-modulated probe signal directly coming from the output of the generator 1 and the delayed received reflected signal to the output of the mixer 2 forms a complex oscillation having a linear spectrum, concentrated in the regions of harmonics of the modulation frequency. The amplitude and phase of each component of the spectrum are determined by the function (φ _z -φ _pr ), as well as the function of external frequency modulation. Isolation of one of the harmonics by an intermediate frequency selective amplifier 8 and vector, that is, taking into account the phase, detection by the synchronous detector 9 of one of the harmonics of the output voltage of the mixer allows, as shown below, to obtain a voltage of the form (1) at the output of the synchronous detector, that is, to realize the main function of transmitting device.

а принятый отраженный сигнал на входе смесителя:

где Е₀ - ЭДС зондирующего сигнала на клеммах антенны; ω₀ = 2πf₀ - круговая несущая частота зондирующего сигнала; φ_M(t) - составляющая фазы, обусловленная частотной модуляцией генератора сигналом модулирующего генератора; φ_чм(t) - составляющая фазы, обусловленная внешней частотной модуляцией зондирующего сигнала; τ - время задержки принятого отраженного сигнала относительно зондирующего; γ - коэффициент ослабления сигнала на трассе "передающая антенна-объект-приемная антенна".The probe signal emitted by the transmitter and sent to the mixer, in the General case, has the form:

and the received reflected signal at the input of the mixer:

where E ₀ - EMF of the probing signal at the antenna terminals; ω ₀ = 2πf ₀ is the circular carrier frequency of the probe signal; φ _M (t) is the phase component due to the frequency modulation of the generator by the signal of the modulating generator; φ _hm (t) is the phase component due to the external frequency modulation of the probe signal; τ is the delay time of the received reflected signal relative to the probing one; γ is the attenuation coefficient of the signal on the path "transmitting antenna-object-receiving antenna".

или

где α - коэффициент передачи смесителя, Δφ_M(t,τ) и Δφ_чм(t,τ) - составляющие разности фаз, обусловленные соответственно модуляцией частоты зондирующего сигнала модулирующим генератором и внешней частотной модуляцией. В тригонометрической форме действительная часть выражения (5) приобретает вид:
U_см = U_0смcos[ω₀τ+Δφ_M(t,τ)+Δφ_чм(t,τ)]. (6)
Первое слагаемое в квадратных скобках - произведение постоянной величины (несущей частоты зондирующего сигнала) на постоянное или медленно меняющееся время задержки принятого отраженного сигнала - говорит о наличии на выходе смесителя постоянной составляющей, зависящей от времени задержки (τ), или сигнала доплеровской частоты. Второе слагаемое ответственно за появление на выходе смесителя гармоник модулирующей частоты, а третье слагаемое является следствием внешней частотной модуляции и вносит в сигнал (6) информацию о расстоянии до отражающего объекта. Если выходной сигнал модулирующего генератора есть гармоническая функция времени, а зависимость частоты зондирующего генератора от напряжения управления линейна, то мгновенное значение частоты зондирующего сигнала имеет вид f=f₀+Δf_м=f₀+Δf₀sinΩt, и второе слагаемое выражения (6) определится, как

где Ψ = Ψ₀sinФ, Ψ₀ = 2Δf₀/F - удвоенный индекс частотной модуляции зондирующего генератора, Ф = Ωτ/2, Δf₀ - девиация частоты, Ω = 2πF - круговая частота модуляции.If the probe signal power coming to the mixer is much higher than the power of the received reflected signal, then the amplitude of the low-frequency component of the mixer output signal is proportional to the amplitude of the received reflected signal, and the phase is equal to the phase difference between the probe and received reflected signal:

or

where α is the transfer coefficient of the mixer, Δφ _M (t, τ) and Δφ _hm (t, τ) are the components of the phase difference due to the modulation of the frequency of the probe signal by a modulating generator and external frequency modulation, respectively. In trigonometric form, the real part of expression (5) takes the form:
U _cm = U _{0 cm} cos [ω ₀ τ + Δφ _M (t, τ) + Δφ _hm (t, τ)]. (6)
The first term in square brackets - the product of a constant value (carrier frequency of the probing signal) by a constant or slowly changing delay time of the received reflected signal - indicates the presence of a constant component at the mixer output, depending on the delay time (τ), or the Doppler frequency signal. The second term is responsible for the appearance of harmonics of the modulating frequency at the mixer output, and the third term is a consequence of external frequency modulation and introduces information about the distance to the reflecting object in signal (6). If the output signal of the modulating generator is a harmonic function of time, and the dependence of the frequency of the probe generator on the control voltage is linear, then the instantaneous value of the frequency of the probe signal has the form f = f ₀ + Δf _m = f ₀ + Δf ₀ sinΩt, and the second term of expression (6) determine how

where Ψ = Ψ ₀ sinF, Ψ ₀ = 2Δf ₀ / F is the doubled index of the frequency modulation of the probe generator, Φ = Ωτ / 2, Δf ₀ is the frequency deviation, and Ω = 2πF is the circular modulation frequency.

Согласно теории функций Бесселя (см. А.А.Харкевич, "Спектры и анализ", Москва, ГИФМЛ, 1962, стр.39) справедливо:

С учетом последних соотношений получаем выражение для спектра выходного сигнала смесителя:

где n>0 - целое число, определяющее номер гармоники (N) частоты модуляции (N=2n или N=2n-l).Denoting the desired function Δφ _x = [ω ₀ τ + Δφ _hm (t, τ)], we obtain:
U _cm = U _{0 cm} cos [Δφ _x + Ψsin (Ωt-Ф)].
When Δf ₀ = 0, this expression is reduced to the form (1), which describes the classical homodyne circuit (Fig. 1):
U $\genfrac{}{}{0ex}{}{\text{cl}}{\text{cm}}$ = U _0cm cosΔφ _x , (8)
but in the general case:

According to the theory of Bessel functions (see A.A. Kharkevich, "Spectra and Analysis", Moscow, GIFIF, 1962, p. 39), it is true:

Taking into account the last relations, we obtain the expression for the spectrum of the output signal of the mixer:

where n> 0 is an integer defining the harmonic number (N) of the modulation frequency (N = 2n or N = 2n-l).

Для случая, когда усилитель промежуточной частоты настроен на четную гармонику F, получим аналогично:
U_(2n) = 2kU_0см[cosΔφ_xJ_(2n)(Ψ)cos2n(Ωt-Ф)]
или, если на входе или на выходе усилителя четной гармоники включен фазовращатель на π/2,то

Сигналы вида (10) и (11) синфазны между собой и с опорным сигналом и поэтому удобны для обработки. Поскольку наличие этого фазовращателя не является существенным признаком, в дальнейшем его наличие подразумевается без упоминания.At the output of an intermediate frequency amplifier having a gain k and tuned to a frequency F or its odd harmonic, we obtain an amplified signal:

For the case when the intermediate-frequency amplifier is tuned to even harmonic F, we obtain similarly:
U _(2n) = 2kU _0cm [cosΔφ _x J _(2n) (Ψ) cos2n (Ωt-Ф)]
or, if the phase shifter at π / 2 is switched on at the input or output of the even harmonic amplifier, then

Signals of the form (10) and (11) are in phase with each other and with the reference signal and are therefore convenient for processing. Since the presence of this phase shifter is not an essential feature, in the future its presence is implied without mention.

After detecting the output signal of the amplifier with a synchronous detector, the reference signal of which is the phase-shifted modulating signal, for the output voltage of the synchronous detector in the case of an odd harmonic, we obtain from (10):
U _{sd (2n-1)} = 2kJ _(2n-1) (Ψ) U _0cm sinΔφ _x , (12)
and in the case of even harmonic from (11):
U _{sd (2n)} = 2kJ _(2n) (Ψ) U _0cm cosΔφ _x . (thirteen)
From a comparison of expressions (1), (8), (12) and (13), it is obvious that the form of the function that describes the output signal (13) of the proposed single-channel device (Fig. 4) using the even harmonic of the modulation frequency does not differ from the classical ( 1). Signal (12) is obtained from it by replacing cosΔφ _x by sinΔφ _x (i.e., by a phase shift by π / 2).

The noise figure of this device, reduced to the point "mixer input - antenna output" is calculated by the formula: K _in (units) = K _cm ^pch + K _upch + (K _sd -1) / k, where K _cm ^pch is the noise figure of the mixer at intermediate frequency, K _SD and K _UPCH - noise factors of the synchronous detector and amplifier of the intermediate frequency. Since the sum of the second and third terms does not exceed several units at frequencies of the order of 10 MHz with a sufficiently large gain of the IF amplifier k, the gain in the resulting sensitivity is determined by the ratio of the noise factors of the mixer at low and intermediate frequencies. If the signal frequency at the output of the transmitting and receiving device is of the order of 10 KHz, and the intermediate frequency is 10 MHz, then the gain in sensitivity is 40 dB (see V.L. Virchenko et al. "Sensitivity of the receiver of a solid-state homodyne millimeter-wave radar in the low-frequency range "in the collection" Solid-State Generating and Converting Instruments of mm and submm range "Kharkov, IRE Academy of Sciences of the Ukrainian SSR, 1989, pp. 78-81), which increases the radar range by 10 times (see I. Kogan, Near Radar. M. , "Soviet Radio", 1973, p. 45).

A comparison of signals (12) and (13) makes it possible to determine the sign of the frequency shift in Doppler radars and eliminates the limitations associated with the presence of a “critical speed” in FM locators. For example, if there is a Doppler frequency shift Δω _{x of the} received reflected signal, and Δφ _x = Δω _x t, then the phase difference of the signals (12) and (13) for Δω _x > 0 is positive (+ π / 2), and for Δω _x <0 is negative (minus π / 2).

 The block diagram of a variant of the proposed device, shown in figure 5, has two channels of the received signal connected to the output of the mixer 2, each of which contains a filter (5a or 5b), a synchronous detector (9a or 9b) and a low-frequency amplifier (11a or 11b). One of the channels is tuned to odd, and the other to even harmonics of the frequency of the modulating signal, as a result of which signals of the form (12) and (13) are distinguished at their outputs. Obviously, the proposed device (figure 5) further solves the problem of eliminating the uncertainty of the sign of the frequency offset, more simply than the prototype, since it differs from the block diagram of figure 3 by the absence of a second mixer and phase shifter.

(С - скорость электромагнитных волн) определяет три возможных режима работы приемно-передающего устройства, оптимизация параметров которых достигается некоторым изменением структурной схемы устройства.Since Ψ = Ψ ₀ sin,, signals (12) and (13) vanish at Φ values that are multiples of π, the radar can have blind spots separated by half the wavelength of the modulating signal. The ratio of the specified maximum radar range L _max and the selected wavelength of the modulating signal

(C is the speed of electromagnetic waves) defines three possible modes of operation of the receiving and transmitting device, the optimization of the parameters of which is achieved by some change in the structural diagram of the device.

В этом случае Ф<<1, а sin Ф≈Ωτ/2. Варианты устройств, схемы которых показаны на фиг.4 и 5 предназначены для реализации этого режима.The quasistationary regime is realized when

In this case, Ф << 1, and sin Ф≈Ωτ / 2. Variants of devices, diagrams of which are shown in FIGS. 4 and 5, are intended to implement this mode.

не выполняется, но

В этом режиме слепая зона не попадает в интервал рабочих дальностей радиолокатора, но равная NФ разность фаз сигнала промежуточной частоты и гармоники частоты модуляции на входах каждого из синхронных детекторов может изменяться от нуля до величины Nπ. В этом случае целесообразно (фиг. 6) включение между выходом модулирующего генератора 10 и опорным входом (входами) синхронных детекторов 9 фазовращателя 7, реализующего сдвиг фазы опорного сигнала φ_фв≈-Ф. Значение Ф может определяться, например, по априорным или полученным в процессе работы радиолокатора данным о времени задержки τ_cp отраженного сигнала (Ф = Ωτ_cp/2). Использование квадратурных синхронных детекторов (фиг.6), позволяющих определить главное значение сдвигов фазы NФ в каждом канале, открывает возможность измерения значения Ф и, при необходимости, автоматической установки φ_фв ≈ -Ф.
Динамический режим имеет место при

и отличается наличием "слепых" зон. Поскольку эти зоны расположены на расстояниях, кратных Λ/2, их положение в пространстве будет изменяться при изменении частоты модуляции F и при определенном значении диапазона изменения частоты F обеспечивается последовательный обзор всего заданного пространства. Таким образом, эффект "слепых" зон может быть устранен или его влияние уменьшено применением модулирующего генератора 10 с частотой, управляемой напряжением. При необходимости постоянного сопровождения одного объекта частота модуляции может непрерывно или периодически настраиваться по критерию максимума величины выходного сигнала (U_сд(2n) ²+U_сд(2n-1) ². Применение квадратурных синхронных детекторов (фиг.6) дает информацию о разности фаз сигналов на их входах, что дает возможность осуществить автоматическую подстройку частоты модулирующего генератора 10 по критерию заданной разности фаз сигналов промежуточной частоты и соответствующей гармоники модулирующего сигнала.The quasi-dynamic regime takes place if the condition

not executed but

In this mode, the blind zone does not fall into the range of radar operating ranges, but the phase difference of the intermediate frequency signal and the harmonic of the modulation frequency at the inputs of each of the synchronous detectors equal to NF can vary from zero to Nπ. In this case, it is advisable (Fig. 6) to include between the output of the modulating generator 10 and the reference input (s) of synchronous detectors 9 of the phase shifter 7, which implements a phase shift of the reference signal φ _fv ≈-Ф. The value of Ф can be determined, for example, by a priori or obtained during radar operation data on the delay time τ _{cp of the} reflected signal (Ф = Ωτ _cp / 2). The use of quadrature synchronous detectors (Fig.6), allowing to determine the main value of the phase shifts NФ in each channel, opens up the possibility of measuring the value of Ф and, if necessary, the automatic installation of φ _fv ≈ -F.
Dynamic mode takes place at

and is characterized by the presence of "blind" zones. Since these zones are located at distances that are multiples of Λ / 2, their position in space will change with a change in the modulation frequency F and for a certain value of the frequency range F, a consistent overview of the entire given space is provided. Thus, the effect of “blind” zones can be eliminated or its effect is reduced by the use of a modulating generator 10 with a frequency controlled by voltage. If you need constant tracking of one object, the modulation frequency can be continuously or periodically adjusted according to the criterion of the maximum value of the output signal (U _{sd (2n)} ² + U _{sd (2n-1)} ^2. The use of quadrature synchronous detectors (Fig.6) gives information about the phase difference signals at their inputs, which makes it possible to automatically adjust the frequency of the modulating oscillator 10 according to the criterion of a given phase difference of the intermediate frequency signals and the corresponding harmonic of the modulating signal.

The above mathematical apparatus strictly enough describes the functioning of a receiving and transmitting device with frequency modulation, but does not provide a key to understanding the physical content of non-obvious processes and modes. A fairly simple physical interpretation can be given to the quasistationary regime. Known (see Kaplanov MR, Levin VA, "Automatic frequency adjustment", Moscow, Gosenergoizdat, 1962) multi-frequency discriminator, which is a combination of a phase detector (a synonym for a mixer operating at close frequencies) and a delay line. The dependence of the output voltage of the phase detector on the frequency of the signal that arrives at one of its inputs directly, and at the other through the delay line, is a cosine wave. In our case, the role of the delay line is played by the “transmitting antenna-reflecting object-receiving antenna” path, and the expression for the frequency response for slowly varying frequencies follows from (1). If (φ _s -φ _pr) = ωτ, the U _O = U ₀ cosωτ, a period characteristic equal to 1 / τ. 7, the frequency response is indicated by 7.1
Graph 7.3a shows one period of frequency variation with a modulating signal of a triangular (for clarity) shape. At time 5, the frequency deviation from the central is zero, and the output voltage is minimal. When going to point 6, the output voltage according to characteristic 7.1 changes to the maximum, which is reflected in the time diagram (7.3b) by the appearance of half the period between points 5 and 6. During the transition between points 6 and 7, the operating point moves along characteristic 7.1 from the maximum through minimum to another maximum, and one period appears on the time chart. In the time interval 7-8 (column 7.3a), the operating point returns to the minimum characteristics. Thus, one period of modulation forms two periods of the output signal, that is, if the frequency deviation is equal to half the characteristic period of the multi-frequency discriminator, and the center frequency is set to the extremum point of the output voltage, frequency doubling occurs. Graphs 7.4 a, b similarly explain the process of the appearance of the third harmonic. Note that it takes place at the center frequency set to the zero point of the discriminator characteristics, and the frequency deviation is three quarters of the period. A shift of the center frequency by half the period of the discriminator characteristic changes the phase of each harmonic by π, and graphs 7.2a, b and 7.5a, b show that a shift of the center frequency by a quarter of the period makes these harmonics zero.

 The possibility of reducing the required deviation (while maintaining the output signal level) in the quasi-dynamic mode can be explained with some stretch by the fact that in this mode the frequency response oscillates along the frequency axis with an antiphase probing signal. In the "blind zone" of the dynamic mode, these oscillations are in phase and there is no change in the output voltage.

 Since in all variants of the device (Fig. 4, Fig. 5 and Fig. 6) there are no functional elements between the generator 1 and mixer 2, both of these units in all cases can be replaced, as shown in FIG. 8, by one indivisible autodyne element 12, which performs the functions of generating the emitted signal and multiplying (mixing) the received reflected signal with it. Most often, autodyne functions are performed by Gunn diodes, which have reduced current consumption.

 An example of the application of the invention is a radar liquid level meter using a phase-frequency method for measuring distance (see the author's patent application for invention 99116167). Structural diagram of a meter using a two-channel transceiver circuit and an autodyne unit based on the M55314 module (see Votoropin S.D., Yurchenko V.I., Autodyne on Gunn diodes and devices based on them. Electronic Industry, vol. 1 -2, 1998, p. 110-115), shown in Fig.9. The module has been modified to provide electronic frequency tuning and expand the range of output frequencies to 100 MHz. The role of a modulating generator is played by a 5 MHz crystal oscillator, which is both a synchronizer of microprocessors and a frequency standard. The intermediate frequency channels are tuned to the second and third harmonics of the modulation frequency, the frequency modulation index of the probing signal is four. The intermediate frequency signals from the output of the autodyne node are amplified by an amplifier 8 and separated by two frequency channels (10 MHz and 15 MHz) by filters 5a and 5b. Amplified to the level of several volts by amplifiers 8a and 8b, the signals are fed to synchronous detectors and then to the controller. The controller in accordance with the program sends the signals to the frequency control circuit of the autodyne generator 12, and using the measurement data of the frequency of the probe signal obtained using the frequency divider 14 and the period counter 17, calculates the distance from the meter to the reflective layer of the liquid. The estimated required power level of the probing signal, at which a signal-to-noise ratio of 40 dB is provided, is 64 microwatts.

The use of the invention in a level meter allows you to:
Reduce the number of expensive microwave nodes to a minimum.

 Apply the simplest algorithm for measuring the phase-frequency characteristic.

 Reduce the radiated power to 100 μW and thereby reduce the power consumption to 0.5 W, which is especially important for fire hazardous facilities.

 Reduce the limit price of the meter to $ 150.

 The proposed device can be widely used in technological radars of other applications, Doppler radars of the traffic safety service and altimeters.

Claims (3)

 1. The transmitting and receiving device of a homodyne radar, comprising a probe signal generator, a modulating signal generator, the output of which is connected to the frequency control input of the probe signal generator, a mixer, one input of which is connected to the receiving antenna, and the second to the generator output probe signal, and connected in series with the output of the mixer, an amplifier and a filter tuned to the frequency of one of the harmonics of the modulating signal, characterized in that there is a synchronous detector connected by one input to the modulating signal generator, the second - to the filter output, as well as a second filter connected through the amplifier to the mixer output and tuned to the frequency of the other harmonic of the modulating signal, and a second synchronous detector connected by one input to the modulating signal generator , the second - to the output of the second filter, and the outputs of synchronous detectors are connected to the outputs of the device.  2. The receiving and transmitting device of the homodyne radar according to claim 1, characterized in that the modulating signal generator has a frequency control input.  3. The receiving-transmitting device of the homodyne radar according to claim 1 or 2, characterized in that it further comprises a phase shifter connected between the output of the modulating signal generator and the inputs of synchronous detectors.

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