SU1626210A1 - Modulation radiometer - Google Patents

Description

one

(21) 4008123/09 (22) 07/03/86 (46) 07.02 91. Bull. (72) In S.Gayevsky, S.V. Marechek Yu In Meshkov. Yu.N. Muskin and V.M. Polkov (53) 621.317 (0888)

(56) Esepkina N.A. and others. Radio telescopes and radiometers M .: Nauka, 1973

USSR Author's Certificate No. 1105832, class G 01 R 29 / 08,1984

(54) MODULATING RADIOMETER

(57) The invention relates to a microwave technique. The purpose of the invention is to improve the measurement accuracy. The modulation radiometer contains antenna 1, modulator 2, directional coupler 3, receiving-amplifying unit 4, synchronous detectors 5, 13 and 14, adder 6, dividers 7 and 16 voltages,

registration blocks 8 and 17 (BR), which assigns Mr. 9 and 11, Mr. 10 noise, switch 12 and subtraction unit 15. In the radiometer, the thermal radiation power of the object under study is received at two different predetermined values of the noise signal power generated by r-10. The goal is achieved by forming a constant voltage at the output of the BD 8, which is proportional to the radiation temperature of the object and does not depend on the transmission coefficient of the radiometer and the reflection coefficient at the antenna-object interface, and at the output of the BR a 17-voltage, which is proportional to the reflection coefficient at the antenna interface, is an object and does not depend t from the transmission factor of the radiometer and the accuracy of temperature 10. g-ra-2-yl.

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The invention relates to microwave technology, in particular to modulation radiometric microwave receivers used to receive and measure electromagnetic radiation of objects adjacent directly to the antenna, for example, to determine the depth of radiation temperature of biological tissue, soil. aqueous solutions and other semiconducting media, as well as for measuring the radiative characteristics of these media at the antenna-object interface.

The purpose of the invention is to improve the measurement accuracy.

Figure 1 shows the structural electrical circuit of the modulation radiometer; 2 shows diagrams for his work.

The modulation radiometer contains antenna 1, modulator 2, directional otvetvitel 3, receiving and amplifying unit 4, first synchronous detector 5, adder 6, first voltage divider 7, first recording unit 8, first master oscillator 9, noise generator 10 the second master oscillator 11, the switch 12, the second 13 and the third 14 synchronous detectors, the subtraction unit 15, the second voltage divider 16, the second registration block 17.

In the simplest case, the receiver / amplifier unit contains a series-connected high-frequency amplifier, a quadratic detector and a low-pass filter.

In the radiometer, the thermal radiation power of the object under study is received at two different predetermined values of the noise signal power, for example, TS2 Tch1, produced by the noise generator 10. This is necessary to measure the reflection coefficient at the antenna-object interface and to accurately determine the radiation temperature under conditions of reflection coefficient fluctuations, as well as to take into account fluctuations in the transmission coefficient of the radiometer path.

The modulation radiometer operates as follows.

The power of thermal microwave radiation of the object under study arrives at the boundary between the antenna and the object. Part of the power. proportional to TR, reflected from the interface and attenuated in the object environment (R-reflectance at the antenna-object interface).

The remaining part of the power is proportional

T (1-P) -TH. (1)

is received by antenna 1 and fed to the input of modulator 2.

The first 9 and second 11 master generators form control voltages.

The dpi and UF2 forms of the meander are the frequencies FI and F2, respectively, the phases of which are synchronized and the frequencies are related by

F2 -2nFi. (2)

where n is an integer 1, 2, 3

0 Figure 2 shows an example of output voltage diagrams of the first 9 and second 11 master oscillators, the output voltage of the receiver / amplifier unit 4, and variations in the generator power.

5 10 noise for the ratio of the modulation frequencies F2 2Fi and T ТШ1 ТШ2.

A control voltage of the type of a square wave with a frequency of FI is fed to the control input of the modulator 2 and provides alternate connection and disconnection of the output of the antenna 1 to the input of the directional response 3. The control voltage of the square wave with the frequency F2 performs modulation of the generator power 10 noise

5 alternately to a temperature TSH1 and TSH2. Since the phases of the oscillations of the control voltages are synchronized, and the frequencies are related by the relation (2), there are four repetitive time intervals,

0 due to different states of the modulator 2 and the noise generator 10 (Fig. 2). The instantaneous values of the voltage Ui, Ua, Oz, 1M arising at the output of the receiving-amplifier unit 4 for each

5 time intervals are defined as follows.

The input of the directional coupler 3 is disconnected from the output of the antenna 1. From the noise generator 10 it goes to the output of the modulator 2

0 through a directional coupler 3 noise power with temperature ТШ1. Further, this noise signal is completely reflected from the closed modulator 2 and passes through the directional coupler 3 to the output of the 5-amp amplifier unit 4

и1 КТШ1 + С, (3)

where K is the dimensional transmission coefficient of the radiometer from the input of the modulator 2 to the output of the receiving and amplifying unit 4;

0 C is a constant component of the voltage, the same for all four time intervals.

The input of the directional coupler 3 is disconnected from the antenna output 1.

5From the noise generator 10 comes to

the output of the modulator 2 through the directional coupler 3 is the noise power with temperature ТШ2, then, similarly to the first time interval,

U2 KTSh2 + S. (4)

The input of the directional coupler 3 is connected to the output of the antenna 1. The power of thermal microwave radiation received by antenna 1, according to (1) is fed through the modulator 2 and the directional coupler 3 to the output of the receiving and amplifying unit 4. From the noise generator 10 enters the output of the module of torus 2 through the directional coupler 3, the noise power with temperature ТШ1, then this noise signal passes through the open modulator 2 to the antenna 1, partially reflects from the interface of the antenna - an object with a reflection coefficient R, passes through the open modulator 2, the coupler 3 to the output of the receiver-amplifier unit 4. The instantaneous voltage value that occurs at the output of the receiver-amplifier unit 4 for the third time interval is proportional to the sum of the signal powers

Кз КТ (1 -R) + KTuii R С. (5)

The input of the directional coupler 3 is connected to the output of the antenna 1. The thermal microwave power of the object under study passes to the output of the receiving-amplifier unit 4, as in the case of the third time interval.

From the generator 10, the noise is fed to the output of the modulator 2 through the directional coupler 3, the noise power with temperature ТШ2, then this noise signal passes to the output of the receiving-amplifier unit 4, similarly to the third time interval.

At the same time, an instantaneous voltage value occurs at its output.

U КТ (1 - R) + КТш2 R + С. (6)

The output voltage of the receiving-amplifier unit 4, which is a periodically repeating sequence of voltages lh, U2, Ua. CM arrives at the inputs of the first synchronous detector 5 and switch 12. The first input of the first synchronous detector 5 is supplied with a voltage of the type square with frequency FI, and its output after integration (smoothing) with a given time constant t 1 / Fi is obtained constant voltage

Uci Кз + lU- Ui - U2

-2kto -) -k (Gsh1 + tSh2H1 -R). (7)

The switch 12, to the control input of which a square-wave type voltage is applied with the frequency FI, alternately connects the inputs of the second 13 and third 14 synchronous detectors to the output of the receiving and amplifying unit 4, respectively.

the outputs of these detectors after integration (smoothing) with a given time constant, respectively, receive a constant voltage 5Uc2 U4 - U3 K (Tm2 - Tu, i) R (8)

and /

UC3 U2 - Ui K - TSH1). (9)

which are fed to subtraction unit 15.

The output voltage of block 15 is subtracted, 10

UC2 UC3 - Uc2 K (Tu, 2 - TyX1 - R) (S) is fed to the input of the first voltage divider 7 and adder 6 to compensate for the constant component voltage UCL 5 due to the presence of the Kch member in (7) (TSH1 + TSSh2X1 R) - Moreover, the transfer coefficients of the inputs of the adder 6 are chosen so that the equality

а () о (ТШ2-ТШО, (11)

Where a, b - transfer coefficients, respectively, of the second and first inputs of the adder.

Thus, the input of the divisible first voltage divider 7 is the voltage

UT 2KaT (1 - R), (12)

and after the division operation in it, the input voltage of the first registration unit 8 receives a constant voltage of 0 ut2 QT (1 -R),.

T Кс2 гЦТшУ-ТиГМТ ТГ) (which is proportional to the radiation temperature of the object, does not depend on the transmission coefficient of the radiometer and the reflection coefficient at the antenna-object interface.

The constant coefficients a and b are determined during instrument calibration. To measure the coefficient of the reflection 0 or at the interface of the antenna - the object at the output of the second divider 16 appears

 Uc2 K (TC, g-TShrR..

LJ K - i | - 7f-rt - v

ISZ K (TSH2 - TSH1) v

5 which is fed to the input of the second registration unit 17. This voltage is proportional to the reflection coefficient at the antenna-object interface and is independent of the transmission coefficient of the radiometer and the accuracy

to maintain generator temperatures

10 noise.

Claims (1)

Claims of the invention: A modulation radiometer comprising an antenna connected in series, a modulator, a directional coupler, a receiver / amplifier unit and a first synchronous detector, a second synchronous detector, a subtraction unit, first and second master oscillators, a generator noise, the first and second registration units, the output of the first master oscillator is connected to the control input of the modulator and the reference input of the first synchronous detector, the output of the second master oscillator is connected to the reference input of the second synchronous detector and to the control input of the noise generator, the output of which is connected to the second input of the directional coupler, the output of the second synchronous detector is connected to the input of the subtracted subtraction unit, characterized in that, in order to improve the measurement accuracy, a switch is inserted, total p, the third synchronous detector and the first and second voltage dividers, the output of the second master oscillator is connected to the synchronization input of the first master oscillator and to the reference input of the third synchronous detector, the output of which is connected to the gateway „ Ufi Tyl and to. and, U: the house of the decremented subtraction unit and the divider input of the second voltage divider, the switch's signal input is connected to the output of the receiver / amplifier unit, the control input to the output of the first master oscillator, the first and second outputs to the signal inputs of the second and third synchronous detectors, respectively, the second output synchronous detector is connected to the input of the divider of the second voltage divider, the output of which is connected to the input of the second registration unit, the first input of the adder is connected to the output of the first synchronous de vector, the second input is with the output of the subtraction unit, and the output is with the input of the divisible first voltage divider, the input of which divider is connected to the output of the subtraction unit, and the output is connected to the input of the first block registration. R / l but,