RU2745796C1 - Fast zero radiometer - Google Patents

Abstract

FIELD: radio heat locating.SUBSTANCE: invention can be used to measure the power of noise signals of fast processes, for example, in space remote sensing systems. Into the radiometer containing the antenna, the first matched load, the first current source and the noise generator connected in series, the first directional coupler, the output of which is connected to the first input of the first high-frequency modulator, the first output of which is connected to the series-connected first radiometric receiver, a preliminary low-frequency amplifier, a synchronous filter, a low-frequency amplifier, a high-pass filter, and the second output is connected to a series-connected second radiometric receiver, a pre-low-frequency amplifier, a lock-in filter, a low-frequency amplifier, a high-pass filter, the outputs of the first and second high-pass filters are respectively connected to the first and second inputs of the first low-frequency modulator, the output of which is connected to the first input of the first comparator, the second input of which is connected to the common bus of the radiometer, while the first matched load, directional coupler, high-frequency modulator, a noise generator, and a current source are installed on a thermostatted board and are in thermal contact with it, the following are introduced (also thermostatted-board installed and maintaining thermal contact): a power divider in half, the first and second high-frequency switches, the second directional coupler, matched load, noise generator, current source, high-frequency modulator, the first output of which is connected to a series-connected third radiometric receiver, a preliminary low-frequency amplifier, a synchronous filter, a low-frequency amplifier, a high-pass filter, and the second output is connected to a series-connected fourth radiometric receiver, a pre-low-frequency amplifier, a lock-in filter, a low-frequency amplifier, a high-pass filter, the outputs of the third and fourth high-pass filters are respectively connected to the first and second inputs of the second low-frequency modulator, the output of the second is connected to the first input of the second comparator, the second input of which is connected to the common bus of the radiometer, an antenna is connected to the input of the power divider, and its first and second outputs are connected to the first inputs of the first and second directional couplers, the second input of the second directional coupler is connected to the series-connected second current source, the noise generator and the high-frequency switch, and its output is connected to the first input of the second high-frequency modulator, the second input of which is connected to the second matched load, the outputs of the first and second comparators are respectively connected to the first and the second inputs of the microcontroller, the first output of which is connected to the combined control inputs of the first and second high-frequency and low-frequency modulators, the second output is connected to the combined control inputs of the first and second high-frequency switches, the third and fourth outputs are respectively connected to the control inputs of the first, third and the second, fourth synchronous filters, and the fifth output of the microcontroller is the output bus of the radiometer, the first matched load is connected to the second input of the first high-frequency modulator and the first high-frequency switch is connected by the input to the first noise generator output, and the output is connected to the second input of the first directional coupler.EFFECT: increased speed of the radiometer without reducing its fluctuation sensitivity and to expand the dynamic range of measurement of the antenna signal.1 cl, 4 dwg

Description

The invention relates to the field of radio thermal location and can be used to measure the power of noise signals of fast-moving processes, for example, in space remote sensing systems during the movement of a satellite scanning the surface of the Earth and the World Ocean in order to build global radio-thermal maps and obtain data for climate forecasting, determining the degree of anthropogenic impact on the environment, as well as in other areas where it is required to build radiothermal portraits of rapidly changing scenes.

Known zero radiometer [Filatov AV, Bordonsky GS. // Zero radiometer. A.S. USSR N 1704107, G01R 29/08, G01S 13/95], the structural diagram of which is shown in Fig. 1, containing a series-connected antenna 1, a directional coupler 2, a high-frequency amplitude modulator 3, a radiometric receiver 9, a low-frequency amplifier 10, a high-frequency filter 11, a synchronous filter 12, a comparator 13 (zero-organ), a control unit 14, at the fourth output of which a digital code of the antenna signal being measured is formed and fed to the bus 15. The automatic input of the reference signal of the noise generator 5 into the directional coupler 2 is carried out through the attenuator 6 according to the control signal from the first output of the control unit 14, through which the direct current source 4 is switched on and generates a current supplying the generator noise. The noise signal generated by the generator 5 is the first reference signal. The second reference noise signal is generated by a matched load 7, which is at the temperature of the thermostatted board 8. To increase the stability of the radiometer, the same board contains a modulator 3, a directional coupler 2, an attenuator 6, a noise generator 5, and a controlled current source 4.

In the radiometer, the reference signal of the noise generator is subjected to pulse-width modulation, and the signal of the antenna and matched load is subjected to amplitude-pulse modulation.

A feature of this radiometer is that the processing of the envelope of the modulated antenna and reference signals at the output of the receiver (at low frequency) includes the operation of eliminating the constant component with a high-frequency filter 11, which does not require the use of synchronous detection. After eliminating the constant component, the polarity of the voltage at the input of the comparator is analyzed in the time interval when the matched load is connected to the input of the receiver. Since in the low-frequency part of the radiometer there are no transformations of the waveforms in order to isolate informative voltage levels, there are no errors associated with these transformations. The principle of zero measurements is carried out in the radiometer, and as a result, the radiometer becomes insensitive to changes in the transmission coefficient of the measuring path.

The described radiometer, chosen as an analogue, is a single-receiver and therefore its sensitivity and speed are worse than those of two-receiver circuits.

Known two-channel zero radiometer [RF Patent No. 2393502, G01R 29/26, G01S 13/95. Two-channel zero radiometer / A.V. Filatov, O.A. Serbinov, A.V. Ubaychin - Application No. 2008148402/09. - Priority from 08.12.2008. - BI No. 18, 2010], which includes (Fig. 2) antenna 1, an input unit, two identical measuring channel receivers, a signal processing unit. The input unit includes a high-frequency modulator 3 installed on a thermostatted board 19, the first 17 and second 22 noise generators, a controlled attenuator 20, the first 2 and second 21 directional couplers, the first 18 and second 23 current sources, a matched load 4. Each measuring channel consists of radiometric receivers 5 and 10, preliminary low-frequency amplifiers 6 and 11, synchronous filters 7 and 12, low-frequency amplifiers 8 and 13, high-frequency filters 9 and 14. The processing unit includes a low-frequency modulator 15, a comparator 16, a control unit 24, a dynamic integrator 25, from the output of which the signal is fed to the output bus 26.

The first 17 and second 22 noise generators are made using semiconductor avalanche-transit diodes, through the active zone of which currents flow, generated by the corresponding first 18 and second 23 current sources. By changing the currents, the output noise power of the generators and, therefore, the reference signals are adjusted.

Signals are modulated in the input block of the radiometer. _{Antenna signals T A} and matched load T _SN are subjected to amplitude pulse modulation. Modulation occurs in the high-frequency modulator 3 according to a symmetric law and includes two equal half-periods with a duration t _AMP . The antenna input signal is fed to the first input of the modulator 3 through a directional coupler 2, in which the signal of the first noise generator 17 is added to the antenna signal, pre-modulated according to the pulse-width law by discrete change in the absorption coefficient of the attenuator 20 according to the control signal t _PWM coming from the fifth output of the unit management. Two levels α and α + Δα of attenuation of the signal of the noise generator T _{gsh1 by the} attenuator are adjusted during calibration. The first level of attenuation of the signal of the noise generator α determines the upper limit of the measurement range, the second - α + Δα - the range span.

The zero balance for each measuring channel is regulated by a corresponding change in the duration of the pulse-width signal t _PWM , and is considered to be set if, in the half-period of the amplitude-pulse modulation with a matched load connected to the receiver input, the channel output voltage is zero, and this case is fixed by the comparator 16 operating in null-organ mode. For this, the outputs of the measuring receivers alternately, with the frequency of amplitude-pulse modulation, through the low-frequency modulator 15 with a 2 × 1 configuration, are fed to the input of the comparator.

When the radiometer is operating and a zero balance is set in each receiving channel between the _PWM duration t and the antenna signal T _A, a linear relationship takes place, and through this duration the antenna signal is indirectly determined. The duration of the pulse-width signal t _{PWM is} not affected by changes in the transmission coefficient of the measuring path and the intrinsic noise of the receiver. The elimination of the influence of these two main destabilizing factors indicates that the radiometer operates on the principle of zero measurements.

The radiometer has the ability to adjust it to an arbitrary measurement range. For this, an additional second noise generator 22, which generates a signal T _gsh2 , and a directional coupler 21 are introduced into the radiometer, and a discrete (two-level) change in the absorption of the signal of the first noise generator 17 is _{implemented. By} changing the signals T op1 and T _op2 (see Fig. 2) you can adjust the upper limit of the measurement range, by changing the signal T _add - the lower limit, i.e. arbitrarily set the measuring range.

The operation of the radiometer is controlled by the control unit 24, which generates the necessary control signals for amplitude-pulse and pulse-width modulations. Analyzing the output signal of the comparator, the control unit changes the width signal accordingly to maintain the measuring paths in a state of zero balance. From the output of the control unit, the digital code is fed to the dynamic integrator 25, in which digital codes of the measured antenna signal are accumulated over a certain time interval and are averaged.

In a radiometer, the fluctuation sensitivity exceeds the sensitivity of one receiving channel by a factor of ^{2 1/2.}

The considered radiometer, chosen as a prototype, has limitations on the measurement speed. In it, the speed can be increased only by a proportional increase in the frequency of amplitude-pulse modulation. But this can be done within small limits, maximum 1.5 times. This is due to the fact that with a large increase in the modulation frequency, the performance of the tracking circuit for maintaining the zero balance is disrupted. To prevent this from happening, it is necessary to reduce the digit capacity of the digital code of the pulse-width signal duration in the control unit, but this will lead to a decrease in the measurement resolution.

The proposed invention solves the problem of increasing the speed of the radiometer without reducing its fluctuation sensitivity and expanding the dynamic range of measurement of the antenna signal.

To achieve this technical result, a radiometer containing an antenna, a first matched load, the first current source and a noise generator connected in series, the first directional coupler, the output of which is connected to the first input of the first high-frequency modulator, the first output of which is connected to the series-connected first radiometric receiver, preliminary a low-frequency amplifier, a lock-in filter, a low-frequency amplifier, a high-pass filter, and the second output is connected to a series-connected second radiometric receiver, a pre-low-frequency amplifier, a lock-in filter, a low-frequency amplifier, a high-pass filter, the outputs of the first and second high-pass filters are respectively connected to the first and the second inputs of the first low-frequency modulator, the output of which is connected to the first input of the first comparator, the second input of which is connected to the common bus of the radiometer, and the first matched load, directional coupler, high-frequency modulator, noise generator, current source are installed on a thermostatted board and are in thermal contact with it, a power divider installed on the thermostatted board and in thermal contact with it, the first and second high-frequency switches, the second directional coupler, matched load, noise generator, current source, high-frequency modulator, the first output of which is connected to a series-connected third radiometric receiver, a preliminary low-frequency amplifier, a lock-in filter, a low-frequency amplifier, a high-pass filter, and the second output is connected to a series-connected fourth radiometric receiver, a preliminary low-frequency amplifier , a synchronous filter, a low-frequency amplifier, a high-pass filter, the outputs of the third and fourth high-pass filters are respectively connected to the first and second inputs of the second low-frequency modulator, the output of the second is connected to the first input of the second comparator, the second input of which is connected to the common bus of the radiometer, an antenna is connected to the input of the power divider, and its first and second outputs are connected to the first inputs of the first and second directional couplers, the second input of the second directional coupler is connected to series connected by a second current source, a noise generator and a high-frequency switch, and its output is connected to the first input of the second high-frequency modulator, to the second input of which a second matched load is connected, the outputs of the first and second comparators are respectively connected to the first and second inputs of the microcontroller, the first output of which is connected to combined together the control inputs of the first and second high-frequency and low-frequency modulators, the second output is connected to the combined control inputs of the first and second high-frequency switches, the third and fourth outputs are respectively connected to the combined control them are the inputs of the first, third and second, fourth synchronous filters, and the fifth output of the microcontroller is the output bus of the radiometer, the first matched load is connected to the second input of the first high-frequency modulator, and the first high-frequency switch is input to the output of the first noise generator, and the output is connected to the second input of the first directional coupler.

FIG. 1 shows a block diagram of an analogue radiometer.

FIG. 2 shows a block diagram of a two-channel zero radiometer - a prototype.

FIG. 3 shows a block diagram of the proposed high-speed zero radiometer.

FIG. 4 shows timing diagrams explaining the principle of operation of the high-speed zero radiometer.

The radiometer includes (Fig. 3) an antenna 1, an input unit mounted on a thermostatted board 19, four measuring channels, a microcontroller 40. The input unit includes a power divider in half 21, the first and second directional couplers 2 and 22, the first and second high-frequency modulators 3 and 23, first and second matched loads 4 and 24, first and second high-frequency switches 20 and 37, first and second noise generators 17 and 38, first and second current sources 18 and 39. Each of the four measuring channels consists of radiometric receivers 5, 10, 25, 30, pre-low-frequency amplifiers 6, 11, 26, 31, synchronous filters 7, 12, 27, 32, low-frequency amplifiers 8, 13, 28, 33, high-frequency filters 9, 14, 29, 34. Output signals filters for the first and second measuring channels are fed to the first low-frequency modulator 15, for the other two channels - to the second low-frequency modulator 35. From the outputs of the modulators, the signals are compared in comparators 16 and 36 with zero potential. Microcontroller 40 controls the operation of the radiometer. To do this, it generates a signal of duration t _AMP with a duty cycle of 2 to control the amplitude-pulse modulation. Analyzes the output signals of the comparators and generates a _{pulse width signal of duration t PWM} to control the pulse width modulation in the input block. Controls synchronous filters in measuring channels. Serves as a digital type dynamic integrator. To do this, it digitally accumulates the signal (performs the addition of codes) and at the end of one measurement interval performs the averaging operation to obtain one result. The number of accumulated codes must be equal to 2 ⁿ , where n is an integer. Then the averaging will consist in the right shift of the sum by n digits. For example, for 16 accumulated codes (2 ⁴ ), the averaging operation will consist in shifting the received sum to the right by 4 digits to obtain the resulting averaged digital signal code. From the output 5 of the microcontroller, the antenna signal in digital form is fed to the output bus 41.

The principle of operation of the radiometer is as follows. Pulse modulation of signals is performed in the input block of the radiometer. _{The antenna signal T A} divided by two in the power divider 21 and the signals T _CH1 and T _{CH2 of the} matched loads 4 and 24 are subjected to pulse-amplitude modulation in high-frequency modulators 3 and 23 according to a control signal of duration t _AMP . In the high-frequency switches 20 and 37, pulse-width modulation of the signals T _rsh1 and T _{rsh2 of} the noise generators 17 and 38 is _{performed using a signal of duration t PWM} . The signals of matched loads and noise generators in the radiometer are reference signals, on which the transfer characteristic of the radiometer depends. These signals are adjusted during the calibration operation (described below).

FIG. 4 shows timing diagrams explaining the principle of operation of the radiometer. In the first half-period of the pulse-amplitude modulation, the antenna signal, halved in the divider, is fed to the input of the first radiometric receiver, and the matched load signal is fed to the input of the second receiver. In the other half-cycle of the pulse-amplitude modulation, the signals are swapped. A noise generator signal is added to the antenna signal through a directional coupler for the duration of the pulse-width modulation control signal. Similar operations take place for the other two measuring channels.

The state of zero balance for each receiving channel is set by changing the duration of the latitude signal, which is carried out by the microcontroller after it analyzes the comparator signal. Since the DC component is excluded in the high-pass filter, a change in the duration at its output leads to a shift of the periodic sequence of signals relative to the zero time axis upward (with decreasing duration) or down (with increasing duration). As a result of the synchronous operation of both low-frequency modulators, only the signals of matched loads alternately pass to the inputs of the comparators. The zero balance state is fixed by the comparator - when the matched load is connected to the input of the receiver, the voltage at the comparator input should be equal to zero. If the voltage is greater than zero, the microcontroller reduces the duration of the pulse-width signal, which leads to a shift of the signals at the output of the high-pass filter downward relative to the zero time axis, if the voltage is less than zero, the duration is increased by the microcontroller.

From the state of zero balance follows the equality of the volt-second areas of the positive and negative pulses at the outputs of the high-pass filters (see Fig. 4) of all four receiving channels. For one channel, the balance ratio is:

where G is the transmission coefficient of the receiving channel of the radiometer, including the gain at high and low frequencies, the transmission coefficient of the square-law detector, k is the Boltzmann constant, Δƒ is the band of frequencies received by the radiometer, Т _А / 2 is the noise effective temperature of the antenna signal divided in half in the divider, Т _but is the noise temperature of the noise generator entering the antenna signal path through the directional coupler, equal to T _but = βT _rs , P is the transmission coefficient of coupled lines in the directional coupler, T _rs = T _rs1 = T _rs2 , T _sn is the noise temperature of the matched load T _SN = T _SN1 = T _SN2 , T _w is the intrinsic noise temperature of the receiving channel.

After reductions and transformations in (1) we get:

Solving (2) with respect to the duration of the pulse-width signal, we finally get:

Thus, with the set zero balance in the measuring channel of the radiometer, the _PWM duration t of the pulse-width modulation control signal is related to the antenna signal T _{A by a} linear relationship. The formula (3) does not include the parameters of the measuring path (coefficient G) and the intrinsic noise with the effective temperature T _w . Therefore, these quantities do not affect the measurement accuracy. In the formula (3) signals T _cn and T _but are reference and are adjusted during calibration (described below).

For the other three measuring channels, after similar calculations, we obtain a similar formula (3).

From (3) we express the antenna signal:

By substituting in (4) two extreme values of the _PWM durations t equal to zero and the _AIM duration t, we obtain the minimum and maximum limits of the measurement range:

Taking into account (5), the span of the measurement range is:

If you adjust the reference signals so that T _cn = T _but , then the lower limit of the range will start from zero degrees Kelvin, T _{A, min} = 0.

Thus, as follows from (6), the span of the measurement range will be determined by the doubled value of the noise generator signal (noise signal) added to the antenna signal through the directional coupler. Compared to the prototype, the measurement range for the proposed structure of the radiometer is doubled. In the prototype, the value of the range swing is equal to the value of the signal T _but .

The fluctuation sensitivity of one receiving channel is estimated by the formula (a generalized formula for zero radiometers with impulse noise was obtained in [Filatov A.V. Zero method in radiometric measurements. Publishing house: Tomsk State University of System Management and Radioelectronics, 2010. - 206 p.]):

, Δƒ - полоса частот принимаемых сигналов радиометром, τ - постоянная времени синхронного фильтра.where dT _A is the range of the antenna signals being measured, determined from formula (6), R is the number of pulse-width signal duration digital codes accumulated in the dynamic integrator of the microcontroller, equal to R = t _meas / 2t _AIM , t _meas is the time interval of one measurements,

, Δƒ is the frequency band of signals received by the radiometer, τ is the time constant of the synchronous filter.

After substituting formula (6) into (7), we get:

The value of the sensitivity of one receiving channel, obtained from (8), is 2 times worse than the sensitivity of the same receiving channel of the prototype. This is due to the fact that the antenna signal is halved in the power divider before entering the measuring channel.

In the considered radiometer, with the simultaneous operation of four channels, during one period of pulse-amplitude modulation, four codes of the duration of the pulse-width signal are accumulated at once, through which the antenna signal is determined. Consequently, the performance of the radiometer for processing rapidly changing antenna signals increases fourfold. If 4R is substituted into formula (8) to calculate the sensitivity instead of the number of accumulations R of signal codes in the dynamic integrator, we obtain that the sensitivity of the high-speed radiometer will be equal to the sensitivity of the prototype.

Calibration of the radiometer includes two stages and is performed using the two-point method. At the first stage, the width of the pulse is set to zero (t _PWM = 0) and during this stage the high-frequency switches in the input unit of the radiometer are open. The first reference noise source is connected to the input with a noise power value that determines the upper limit of the measurement range, that is, equal to T _{et, max} = 2T _SN . By adjusting the temperature of the thermostatted board and, consequently, by changing the noise signals of the matched loads, zero voltages are set at the input of the comparators in both half-periods of the amplitude-pulse modulation. When a logic tester is connected to the comparator output, the latter will record random transitions between the states of logical zero and one.

At the second stage, a standard with a noise temperature, which determines the lower limit of the measurement scale, is connected to the input of the radiometer. In the radiometer, the duration of the pulse-width signal is set equal to the duration of the half-period of the pulse-amplitude modulation, t _PWM = t _AMM , which leads to a permanently closed state of high-frequency switches during this calibration stage. The output power of the noise generators is adjusted by changing the currents supplying the generators of the current sources. The end of the adjustment is fixed in the same way as in the first stage of calibration.

The microcontroller in real time, tracking the signals of the comparators, according to the algorithms described above, adjusts the duration of the pulse-width signal in order to maintain the measuring channels in a state of zero balance. Also, the microcontroller performs the functions of a dynamic integrator of a digital type by accumulating the codes of the duration of the pulse-width signal for a given interval of one measurement and their subsequent averaging to obtain one result. The microcontroller is based on the popular STM8L001 microcircuit with low power consumption.

In the literature, the design of high-frequency units on microstrip waveguide structures is described quite fully: modulators, directional couplers, key elements [Bogdanov A.M., Davidovich M.V., Katz B.M. and others. Ed. A.P. Krenitsky and V.P. Meshchanov. Ultra-wideband microwave devices. M .: Radio and communication, 2001.]. Precision adjustable current sources are made according to common circuits using integrated analog circuitry. Transistor amplifiers are used in the receivers of the measuring channels. Synchronous filters are described in [Frater. Synchronous integrator and demodulator // Instruments for scientific research. 1965. T. 36, No. 5. P. 53]. Low-frequency modulators and analog comparators are used in integral design.

Thus, in the radiometer with the simultaneous operation of four channels, the accumulation of digital codes of the duration of the pulse-width signal occurs four times faster, from which the antenna signal is indirectly determined. Correspondingly, the speed of processing fast changes in the antenna signal increases by the same number of times. In this case, the sensitivity increases in proportion to the square root of the number of accumulations. That is, for four receiving channels, the speed will increase by 4 times, and the sensitivity will increase by 4 ^1/2 - times (that is, twice). The use of a power divider in half in the radiometer at the input allows the measurement range to be doubled.

Claims (1)

A high-speed zero radiometer containing an antenna, a first matched load, the first current source and a noise generator connected in series, the first directional coupler, the output of which is connected to the first input of the first high-frequency modulator, the first output of which is connected to the series-connected first radiometric receiver, a preliminary low-frequency amplifier, a synchronous filter, low-frequency amplifier, high-pass filter, and the second output is connected to a series-connected second radiometric receiver, a preliminary low-frequency amplifier, a synchronous filter, a low-frequency amplifier, a high-pass filter, the outputs of the first and second high-pass filters are respectively connected to the first and second inputs of the first low-pass modulator, the output of the second is connected to the first input of the first comparator, the second input of which is connected to the common bus of the radiometer, and the first matched load directed to a spruce, a high-frequency modulator, a noise generator, a current source are installed on a thermostated board and are in thermal contact with it, characterized in that a power divider in half, the first and second high-frequency switches installed on the thermostated board and in thermal contact with it, are inserted into it, second directional coupler, matched load, noise generator, current source, high-frequency modulator, the first output of which is connected to a series-connected third radiometric receiver, a preliminary low-frequency amplifier, a lock-in filter, a low-frequency amplifier, a high-pass filter, and the second output is connected to a series-connected fourth radiometric a receiver, a preliminary low-frequency amplifier, a lock-in filter, a low-frequency amplifier, a high-pass filter, the outputs of the third and fourth high-pass filters are respectively connected to the first and second inputs of the second low-frequency module yator, the output of the second is connected to the first input of the second comparator, the second input of which is connected to the common bus of the radiometer, an antenna is connected to the input of the power divider, and its first and second outputs are connected to the first inputs of the first and second directional couplers, the second input of the second directional coupler is connected with a series-connected second current source, a noise generator and a high-frequency switch, and its output is connected to the first input of the second high-frequency modulator, to the second input of which a second matched load is connected, the outputs of the first and second comparators are respectively connected to the first and second inputs of the microcontroller, the first output of which connected to the combined control inputs of the first and second high-frequency and low-frequency modulators, the second output is connected to the combined control inputs of the first and second high-frequency switches, the third and fourth outputs, respectively, are connected to the combined together control inputs of the first, third and second, fourth synchronous filters, and the fifth output of the microcontroller is the output bus of the radiometer, the first matched load is connected to the second input of the first high-frequency modulator and the first high-frequency switch is connected by its input to the output of the first noise generator, and the output is connected to the second input of the first directional coupler.

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