SU1626205A1 - Radiometer - Google Patents

Abstract

This invention relates to a microwave technique. The purpose of the invention is to improve the accuracy of measuring the radiation temperature of objects. The radiometer includes antenna 1, modulator 2, directional coupler 3, amplifier 4 RF, quadratic detector 5, amplifier 6 LF, multipliers 7 and 14, filters 8 and 15 lower frequencies, weight adder 9, divisor 10 voltages, a registration block 11, r p 12 noise, a phase shifter 13, defining Mr. r 16 and a divider 17 frequency. The goal is achieved by forming a constant voltage at the output of the registration unit 11, 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. 1 il.

Description

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The invention relates to microwave technology, in particular, to modulation microwave radiometers used to receive and measure electromagnetic radiation of objects located in close proximity to the antenna, for example, to study the intrinsic electromagnetic radiation of biological objects, soil, aqueous solutions, etc.

The purpose of the invention is to improve the accuracy of measuring the radiation temperature of objects

The drawing shows a structural electrical circuit of the radiometer.

The radiometer consists of antenna 1, modulator 2, directional coupler 3, high-frequency amplifier 4, quadratic detector 5, low-frequency amplifier 6, first multiplier 7, first low-pass filter 8, weight adder 9, voltage divider 10, unit 11 registration, generator 12 noise, phase shifter 13, the second multiplier 14, the second low-pass filter 15, the master oscillator 16 and the frequency divider 17.

The radiometer works in the following manner.

The measurements of the thermal radiation power of the object under study are carried out at two different predetermined values of the noise signal power, for example, TSH2 TSH1. generated by generator 12 noise. This is necessary to take into account the reflection coefficient at the antenna-object interface and the radiation intensity of the radiometer gain.

The power of thermal microwave radiation of the object under study, which is proportional to the radiation temperature T of the object, arrives at the boundary between the antenna and the object. A part of the power, proportional to TR, is reflected from the interface and dies out in the environment of the object (R is the reflection coefficient at the antenna-object interface).

The remaining part of the power is proportional

T (1-P) TYA, (1)

is received by antenna 1 and arrives at the input of modulator 2.

The master oscillator 16 generates the control voltage of the square wave frequency FI, and the frequency divider 17 generates the control voltage of the square wave frequency Pr. where

Fi 2F2. (2)

The control voltage of the square wave with a frequency Ft is fed to the control input of the modulator 2, which with the frequency Fi provides alternate connection and disconnection of the output of the antenna 1 with the input of the directional coupler 3. The control voltage square wave with the frequency F2 performs modulation of the generator power 12 noise alternately to noise temperatures 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 repeated intervals

time due to different states of modulator 2 and noise generator 12.

The instantaneous values of the voltage Ui, L) 2, Uz and LM, arising at the output of the low-frequency amplifier 6 for each time interval, are determined as follows.

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

12 noise arrives at the output of the modulator 2 through the directional coupler 3, the power of the noise with temperature Tu, i. Further, this noise signal is fully reflected from the closed modulator 2 and passes through

directional coupler 3

Ui КТШ1 + С, (3)

where K is the dimensional gain of the radiometer from the input of the modulator 2 to the output of the amplifier 6 of low frequency;

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

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

12 noise arrives at the output of the modulator 2 through the directional coupler 3 noise power with temperature ТШ2. Further, similarly to the first time interval, have

Ua CT, 2 + C. (4)

The input of the directional coupler 3 is connected to the output of the antenna 1 The power of the thermal microwave radiation, received by the antenna according to expression (1), comes through

modulator 2, directional coupler 3 to the output of the UHF-H, through a quadratic detector 5 to the output of the frequency amplifier.

From the noise generator 12 is fed to the output of the modulator 2 through a directional ottotitel 3 noise power with temperature Tm1, then this noise signal passes through the open modulator 2 to the antenna 1 partially reflected from the antenna interface - the object with the reflectance R does not pass through the open modulator 2. directional coupler 3 to the output of the amplifier 6 low frequency.

In this case, the instantaneous voltage value appearing at the output of the low-frequency amplifier 6 for the third time interval is proportional to the sum of the powers of the following signals

Oz KT (1 -R) + KTsh1K + C (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 low-frequency amplifier 6. From the noise generator 12, it arrives at the output of the modulator 2 via the directional coupler 3, the noise power with temperature ТШ2, then this noise signal passes to the output of the low-frequency amplifier 6 in the same way as the third time interval

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

1M CT (1 - R) + KTutfR + C (6;

The output voltage of the low-frequency amplifier 6 is fed to the first 7 and second 14 multipliers. At the first input of the first multiplier 7, a square wave with frequency F2 is fed. Its output after smoothing in the first low-pass filter 8 with a given constant

time r t-- get a constant voltage

Uci 1 s + U4 - Ui - 1/2 -

-2KT (1 -R) -K (TSH1 + - R) (7)

At the second input of the second multiplier 14, a square wave with frequency G2 is delayed by a phase shifter 13 by one quarter of the period (with a phase shift of 90 degrees). At its output, after smoothing in the second filter 15, the lower frequency of a given time constant is obtained voltage

Uc2 U2-Ui + U4- L 3

 K (TSH2 TSH00-R). (8)

which is supplied as a divider to the voltage divider 10 and to the first input of the weight adder 9 to compensate for the constant component of the voltage Uci. due to the presence in the expression (7) of the term K (Tm1 + Tx2x R) Moreover, the transfer coefficients of the inputs of the adder 9 are chosen in such a way that the equality

a (TSH1 + TSH2) b (TSH2 TSm). (9)

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

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Thus, the second input of the voltage divider 10 is applied as a dividend.

UT 2KaT (1-R), (10)

and after the operation of dividing it, a voltage is applied to the input of the registration block 11

C | 2KaT (1-R) Uc2 K (Tshg-Tsh1) (1 -R)

(11) 2a

TSH2 - TSH1

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.

Claims (1)

Invention Formula A radiometer containing an antenna connected in series, a modulator, directional coupler, high-frequency amplifier, quadratic detector, low-frequency amplifier, first multiplier and first low-pass filter, master oscillator, noise generator, output which is connected to the second input of the directional coupler, and a registration unit, characterized in that, in order to improve the accuracy of measuring the radiation temperature, serially connected frequency divider, phase shifter, second multiplier, second low pass filter and voltage divider, as well as a weight adder, are introduced the output of the master oscillator is connected to the inputs of the noise generator and frequency divider, the output of which is connected to the control input of the modulator and the second input of the first multiplier, the second input of the second th multiplier connected to an output low frequency amplifier, a second low-pass filter output is connected to a first input of weighting summator, a second input coupled to an output of the first lowpass filter, and the output is with the second input of the voltage divider, the output of which is connected to the input of the registration unit.