RU2763694C1 - Radiothermometer - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: invention relates to measuring equipment, namely, to apparatuses for measuring the characteristics of an electromagnetic field, applied in non-destructive testing of dielectrics, medicine. The technical result is achieved due to the fact that the radiometer comprises an antenna and a temperature-controlled circuit board whereon a matched load and a noise generator are placed, and therein differs from the prototype in that the output of the antenna is connected with the first input of the first switch, the output whereof is connected with the first input of the directional coupler and the second and third inputs are connected with the output of the short-circuiting switch and the third output of the control unit, respectively.

EFFECT: increase in the accuracy of measurements and structural simplification.

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Description

The invention relates to measuring technology, namely to devices for measuring the characteristics of an electromagnetic field and can be used, for example, in medicine, veterinary medicine, non-destructive testing of dielectric materials.

Known radiometer for the study of objects directly adjacent to the antenna [RF Patent No. 2431856, IPC G01R29/08 (2006.01), publ. receiver, synchronous low pass filter, high pass filter. The common bus of the radiometer is connected to the second input of the comparator. The first and second outputs of the switch are connected to the second inputs of the first and second directional couplers, respectively. A noise generator and a current source connected in series are connected to the switch input. The control unit is connected to the inputs of the synchronous filter, switch, modulator and output bus through the first, second, third and fourth outputs, respectively.

The presence of two directional couplers at the input of the receiver is redundant and causes the complexity of the design. Directional couplers, especially in the decimeter wavelength range, are relatively large, making it difficult to miniaturize radiothermometers. The absence of a ferrite circulator at the input of the receiver leads to additional measurement errors associated with the occurrence of interference at the input of the receiver when the impedance of the object under study changes. The modulator, which works to disconnect the receiver input from the antenna output, in the open state causes the interference of the receiver's own noise, which leads to an additional measurement error.

Known radiometer for measuring the deep temperatures of an object (radiothermometer) [RF Patent No. 2485462, IPC G01K13/00 (2006.01), G01R29/08 (2006.01), publ. 06/20/2013], selected as a prototype, containing an antenna connected to the first input of a directional coupler, the second and third inputs of which are connected to the first and second outputs of the switch, respectively. The second and third matched loads connected to the second and third inputs of the switch, respectively. A current source connected to the first input of the switch through a noise generator. A circulator, the first input of which is connected to the output of a directional coupler, the second input is connected to the first matched load, and the output is connected to the first input of the comparator through a receiver, a synchronous filter and a high-pass filter connected in series. The second input of the comparator is connected to a common bus, and the output is connected to the input of the control unit, the first, second, third and fourth outputs of which are connected to the control inputs of the synchronous filter, switch, modulator and the output bus of the radiometer, respectively. The modulator, directional coupler, circulator, matched loads, switch, noise generator and current source are placed on a temperature-controlled board.

During the operation of this radiometer, two types of synchronously performed pulse modulations are carried out: amplitude and width modulations. Pulse-amplitude modulation is performed in the modulator. The modulation period consists of two half-cycles of equal duration. Pulse width modulation is carried out in the switch. The radiometer operates on the basis of balancing the energies of the input signal of the antenna and the reference noise sources, which is implemented by changing the duration of the pulse-width modulation signal. The first reference signal is formed from the noise of the first matched load, the second one is connected to the noise generator signal. Compensation for the effect of the antenna reflection coefficient is achieved by changing the direction of the emission of the noise generator signal from the antenna to the receiver in accordance with the amplitude and pulse width modulation signals.

The principle of operation of this radiometer is to change the duration of the pulse-width signal. This change is carried out until the comparator, operating in the mode of comparison with the potential of the common bus, determines the equality of the volt-second areas.

In radiothermometer prototype input passive high-frequency part contains a modulator. In the second half-cycle of the modulation, the modulator opens the antenna output and the input of the directional coupler. Since the decoupling of the circulator arms is not infinite, part of the signal due to the receiver's own noise is fed to the modulator. The receiver noise reflected from the open-loop modulator is fed back to the receiver input and coherently added to the noise propagating from its input to the output, which leads to their interference. The occurrence of self-noise interference leads to measurement errors.

The presence of the second and third matched load is redundant in the design of the prototype radiothermometer. The presence of a relatively large number of elements located on a thermostated board causes additional difficulties for its temperature control, which leads to additional errors in measurements that occur due to the error in maintaining the temperature of a thermostated board at a given level.

The technical result of the invention is to improve the measurement accuracy and simplify the design of the radiothermometer.

The radiothermometer, as in the prototype, contains an antenna, a thermostatic board on which a matched load and a noise generator are placed, a directional coupler, the output of which is connected to the first input of the circulator, the second input of which is connected to the output of the matched load, and the output is connected to the first input of the synchronous filter through the receiver, the output of the synchronous filter is connected to the input of the high-pass filter, the output of which is connected to the first input of the comparator, the second input of the comparator is connected to the output of the common bus, and the output is connected to the input of the control unit, the first output of which is connected to the second input of the synchronous filter, the fourth output connected to the input of the output data bus, the second output is connected to the second input of the second switch, the first and second outputs of the second switch are connected to the second and third inputs of the directional coupler, respectively, and the current source is connected to the first input of the second switch through the noise generator.

According to the invention, the antenna output is connected to the first input of the first switch, the output of which is connected to the first input of the directional coupler, and the second and third inputs are connected to the short circuit output and the third output of the control unit, respectively.

Compared with the prototype proposed radiothermometer allows you to reduce the interference of the receiver's own noise. This leads to an increase in measurement accuracy. Reducing the number of matched loads and elements placed on a temperature-controlled board makes it possible to simplify the design of the proposed radiothermometer.

In FIG. 1 shows a block diagram of the proposed radiothermometer.

In FIG. 2 shows timing diagrams that explain the principle of operation of the proposed radiothermometer.

The radiothermometer (Fig. 1) contains an antenna 1 (A), which is connected to the first input of the first switch 2 (PC1). The output of the first switch 2 (PC1) is connected to the first input of the directional coupler 3 (BUT), the output of which is connected to the first input of the circulator 4 (C). The output of the circulator 4 (C) is connected to the input of the receiver 11 (PR). The output of the receiver 11 (PR) is connected to the first input of the synchronous filter 12 (SF), and its output is connected to the first input of the comparator 14 (K) through the high-pass filter 13 (HPF). The output of the common bus 7 (OR) is connected to the second input of the comparator 14 (K), the output of which is connected to the input of the control unit 15 (BU). The first output of the control unit 15 (CU) is connected to the second input of the synchronous filter 12 (SF), and the second output is connected to the second input of the second switch 6 (PC2), and the third output is connected to the input of the same name of the first switch 2 (PC1), and the fourth output connected to the input of the output data bus 16 (VSH). The output of the matched load 5 (CH) is connected to the second input of the circulator 4 (C). The output of the current source 10 (IT) is connected to the first input of the second switch 6 (PC2) through the noise generator 9 (GSh). The first and second outputs of the second switch 6 (PC2) are connected respectively to the second and third inputs of the directional coupler 3 (BUT). The output of the short circuit 17 (short circuit) is connected to the second input of the first switch 2 (PC1). The matched load 5 (SN) and the noise generator 9 (GSh) are placed on the temperature-controlled board 8 (RTS).

Can be used or horn, or dielectric, or printed antenna 1(A). The first 2 (PK1) and second 6 (PK2) absorbing type switches can be implemented based on the commercially available PE4257 chip. The receiver 11 (PR) can be implemented according to the scheme of direct amplification or with frequency transfer based on commercially available low-noise amplifiers, bandpass filters, diodes [Sokolov M.A. Design of radar receivers. – M.: Higher school. - 1984. - 256 p.].

The high-pass filter 13 (HPF) can be implemented in the form of single-link RC circuits made on the basis of resistors and capacitors produced by the industry. Synchronous filter 12 (SF) consists of three links that can be implemented on switchable RC circuits [Freyter R.N. Synchronous integrator and demodulator // Instruments for scientific research. - 1965. - V.36, No. 5. – S. 53]. Comparator 14 (K) can be implemented, for example, on the basis of commercially available chip LM311. The control unit 15 (CU) can be made on the basis of discrete logic elements, although programmable logic arrays or microcontrollers can also be used for this. Thermostatic board 8 (TSP) is made of a dielectric material and contains a heating element [Gorbach P., Lowe D. Thermostats and coolers in technological processes. Designs, selection, application. - St. Petersburg: TsOP "Professiya", 2012. - 352 p.]. Matched load 5 (SN) can be implemented on the basis of commercially available high-frequency resistors, for example, P1-81. The current source 10 (IT) can be implemented based on the commercially available AD5260 chip. As a directional coupler 3 (NO), a directional coupler NO16-0.5-26-03R-03R, produced by the industry, can be used. The noise generator 9 (GS) can be implemented on either avalanche-transit diodes, or Gunn diodes, or commercially available transistors. As circulator 4 (C), a ferrite circulator FPTSN3-45, commercially produced commercially, can be used. The short circuiter 17 (short circuit) can be implemented on the basis of a short-circuited microstrip transmission line [Volman V.I. Handbook for the calculation and design of microwave strip devices. M.: Radio and communication, 1982, 326s].

The principle of operation of the radiothermometer is illustrated by the timing diagrams in Fig. 2 and is as follows. The control unit 15 (BU) generates signals of pulse-width and amplitude-pulse modulation. At the second output of the control unit 15 (CU) a pulse-width modulation signal is generated. At the third output of the control unit 15 (BU) is formed signal amplitude-pulse modulation, and the first output signals are generated pulse-width and amplitude-pulse modulation.

The signal amplitude-pulse modulation t _AIM is a periodic sequence of rectangular pulses with a duty cycle equal to two. One period of amplitude modulation consists of two half-cycles with equal durations (Fig. 2). The pulse width modulation signal is a periodic sequence of rectangular pulses with variable duration.

Under the action of the signals t _AIM and t _PWM , the first switch 2 (PC1), the second switch 6 (PC2) and the synchronous filter 12 (SF) are controlled. According to the timing diagrams shown in FIG. 2, the control unit generates four combinations of signals t _AIM and t _PWM .

If the control unit 15 (CU) generates control signals t _AIM and t _PWM high level, then the first input of the directional coupler 3 (NO) is connected to the output of the antenna 1 (A) by means of the first switch 2 (PC1), and the output of the noise generator 9 ( GSh) with the second input of the directional coupler 3 (NO) by means of the second switch 6 (PC2). The second switch 6 (PC2) is an absorbing type switch - an inactive output absorbs the signal coming to it.

Therefore, the signal T _{A of the} antenna 1 (A) is fed to the first input of the first switch 2 (PC1). From the output of the first switch 2 (PC1) to the first input of the directional coupler 3 (NO). Further, from the output of the directional coupler 3 (NO) to the first input of the circulator 4 (C). The signal T _CH due to the noise of the matched load 5 (CH) is fed to the second input of the circulator 2 (C). Further, T _{CH is} fed to the output of antenna 1 (A) through a directional coupler 3 (NO) and switch 2 (PC1). Part of T _{CH is} reflected from the antenna 1 (A) with a coefficient R, due to the mismatch of the antenna with the biological environment under study. The reflected signal T _CH R is fed back to the first input of the circulator 4 (C) through the first switch 2 (PC1) and directional coupler 3 (BUT). The current source 10 (IT) provides continuous power to the noise generator 9 (GSh). The signal of the noise generator 9 (GN) is fed to the output of the antenna 1 (A) through the second switch 6 (PC2), directional coupler 3 (NO), the first switch 2 (PC1). Part of the signal T _GSH arriving at the antenna 1 (A) and due to the signal of the noise generator 9 (GSH) is reflected from the antenna 1 (A) with a coefficient R, due to the mismatch of the antenna with the medium under study. The reflected signal T _GSH R is fed to the first input of the circulator 4 (C) through the first switch 2 (PC1) and directional coupler 3 (BUT).

Thus, at the first input of the circulator 4 (C) is formed sum signals T _A, T R and T _{CH GSH} R. From the first input of the circulator 4 (C) signals T _A, T R and T _{CH GSH} R arrive at the first input of the comparator 1 (K) through the receiver 11 (PR), synchronous filter 12 (SF) and high-pass filter 13 (HPF), where the operations of amplification, bandpass filtering, detection, smoothing and exclusion of the constant component are sequentially performed. At the same time, at the first input of the comparator 14 (K), a signal is generated:

where T _A is the noise temperature of antenna 1 (A);

df is the operating frequency band of receiver 11 (PR);

_ТSh – receiver 11 intrinsic noise level (PR);

G – receiver gain 11 (PR);

k is the Boltzmann constant.

Further, in accordance with the timing diagrams shown in Fig. 2, the control unit 15 (CU) generates a combination of control signals of high level t _AIM and low t _PWM . The output of the noise generator 9 (GSh) is connected to the third input of the directional coupler 3 (BUT).

In this case, the signal T _GSh from the directional coupler is fed to the first input of the circulator 4 (C). In this case, similarly to (1), a signal is generated at the first input of the comparator 14 (K):

Further, in accordance with the timing diagrams shown in FIG. 2, the control unit 15 (CU) generates the low-level _{signals t AIM} and t _PWM. In this case, the first input of the directional coupler 3 (NO) is connected to the output of the short circuit 17 (short circuit).

In this case, the signal T _{CH is} reflected from the short circuit 17 (short circuit) and fed to the first input of the circulator 4 (C). In view of the fact that the decoupling of the shoulders of the circulator 4 (C) is not infinite, the signal caused by the noise of the receiver 11 (PR) from its input is fed to the first input of the circulator 4 (C). Further, passing through the directional coupler 3 (NO) and the switch 2 (PC), this signal is reflected in the short circuit 17 (short circuit). After reflection in the short circuit 17 (short circuit) the reflected signal is fed to the input of the receiver 11 (PR). As a result of the interaction of the intrinsic noise of the receiver 11 (PR) and the reflected noise, their interference appears. The magnitude of the signal due to interference is related to the electrical length of the short circuit 17 (SC) and the decoupling factor of the circulator arms 4 (C) and has a wave character.

In this regard, at the first input of the comparator 14 (K) a signal is generated:

where δ is a value that characterizes the interference level of the intrinsic noise signal of receiver 11 (PR).

The level of the interference signal of intrinsic noise is determined by the ratio [Troitsky B.C. On the theory of contact radiometric measurements of the internal temperature of bodies. Radiophysics. - 1981. - No. 9. - S. 1954-1961]:

where γ is the reciprocal of the isolation of the circulator 4 (C), l is the electrical length of the short circuit 17 (short circuit), C is the electrical length of the waveguides from the input of the receiver 11 (PR) to the short circuit 17 (short circuit).

. Выбор электрической длинный короткозамыкателя 17 (КЗ) осуществляется путем настройки физической длинны короткозамыкателя 17 (КЗ) и осуществляется следующим образом. Антенна 1 (1) направляется на радиопоглощающий материал с физической температурой, равной температуре термостатированной платы 8 (ТСП). В этом случает уровень сигналов Т_СН и Т_А одинаков. Далее путем регулирования физической длинны короткозамыкателя 17 (КЗ) добиваются равенства уровней сигналов А и С на входе компаратора 14 (К). В этом случае уровень сигнала интерференционной составляющей

близок к нулю и его дальнейшим влиянием на измерения можно пренебречь.By choosing the electrical length of the short circuit 17 (short circuit) in such a way that the signals due to the intrinsic noise of the receiver 11 (PR) and the reflected noise add up with a phase difference of 180 °, sufficient suppression of the interference component can be achieved

. The choice of electric long short circuit 17 (short circuit) is carried out by setting the physical length of the short circuit 17 (short circuit) and is carried out as follows. Antenna 1 (1) is directed to the radio-absorbing material with a physical temperature equal to the temperature of thermostated board 8 (TSP). In this case, the level of the signals T _CH and T _{A is the} same. Further, by adjusting the physical length of the short circuiter 17 (short circuit), equal levels of signals A and C are achieved at the input of the comparator 14 (K). In this case, the signal level of the interference component

is close to zero and its further influence on measurements can be neglected.

Depending on the state of the signal at the output of the comparator 14 (K) in the control unit 15 (BU), at a low level t _AIM , the duration of the pulse-width modulation signal t _PWM is regulated. If a high level signal is generated at the output of the comparator 14 (K), then the duration of the pulse-width modulation signal t _PWM decreases. If at the output of the comparator 14 (K) a low level signal is generated, then the duration of the pulse-width modulation signal t _PWM increases. The regulation is carried out until the equality of the volt-second areas of the positive and negative pulses at the first input of the comparator 14 (K) is fulfilled. In this case, the average value of the signal in the second half-cycle of the modulation is equal to zero, which is fixed by the comparator 14 (K) in the subsequent first half-cycle of the modulation, when compared with the potential of the common bus 7 (OR). In this case, the equality holds:

Substituting (1), (2) and (3) into (4) we get:

The noise temperature of antenna 1 (A) in view of the resulting reflection from the interface between two media is proportional to:

where T _O is the noise temperature of the object under study.

Solving (5) with respect to t _PWM , taking into account (6), we get:

From the last formula (7), a linear dependence of the _PWM signal t on the input signal of antenna 1 (A) follows. Therefore, the noise temperature of the object is determined through this duration. It also follows from formula (7) that the duration of the pulse-width signal is not affected by changes in the intrinsic noise level _TSH and the transmission coefficient G of the receiver 11 (RP) and the reflection coefficient R. Eliminating the influence of these destabilizing factors indicates that the radiothermometer is working according to the principle of zero measurements.

After accumulating the required amount of pulse width modulation signal value unit 15 (ECU) generates on output line 16 (VS) of the digital code corresponding to signal T _O of the test subject.

Thus, the use of a short circuiter 17 (short circuit) makes it possible to minimize the interference component of the intrinsic noise signal of the receiver 11 (PR) in the second half-cycle of the modulation. Therefore, compared with the prototype, the proposed radiothermometer improved measurement accuracy by reducing the systematic error due to the interference of their own noise.

Compared with the prototype, the proposed radiothermometer reduced the number of matched loads, and thermostatic board 8 (TSP) placed only noise generator 9 (GS) and matched load 5 (SN). The reduction in the number of matched loads and elements located on the temperature-controlled board 8 (TSP) causes a simplification of the design of the proposed radiothermometer. Reducing the number of elements located on a temperature-controlled board reduces its physical dimensions. This makes it possible to reduce the temperature control error. As is known from the theory of reception of noise signals [Esepkina E.A., Korolkov D.V., Parisky Yu.N. "Radio Telescopes and Radiometers". – M.: Science. –1973. –416 pp.], the error of radiometric measurements is related to the error of the reference noise generators, the level of which, in the case of using a matched load, is set by the error of its temperature control. Therefore, the proposed radiothermometer measurement accuracy is increased, compared with the prototype.

Claims (1)

A radiothermometer containing an antenna (1), a temperature-controlled board (8) on which a matched load (5) and a noise generator (9) are placed, a directional coupler (3), the output of which is connected to the first input of the circulator (4), the second input of which is connected with the output of a matched load (5), and the output is connected to the first input of the synchronous filter (12) through the receiver (11), the output of the synchronous filter (12) is connected to the input of the high-pass filter (13), the output of which is connected to the first input of the comparator (14 ), the second input of the comparator (14) is connected to the output of the common bus (7), and the output is connected to the input of the control unit (15), the first output of which is connected to the second input of the synchronous filter (12), the fourth output is connected to the input of the output data bus ( 16), the second output is connected to the second input of the second switch (6), the first and second outputs of the second switch (6) are connected to the second and third inputs of the directional coupler (3), respectively, and to the first input of the second switch (6) a current source (10) is connected through a noise generator (9), characterized in that the output of the antenna (1) is connected to the first input of the first switch (2), the output of which is connected to the first input of the directional coupler (3), and the second and third inputs are connected with short circuit output (17) and third control unit output (15), respectively.

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