SU1758571A1 - Microwave power thermocouple transducer - Google Patents

Abstract

The invention relates to a change in electromagnetic fields, in particular, to devices for measuring their power. The purpose of the invention is to increase the maximum allowable power and the expansion of the dynamic range. The thermocouple microwave power sensor is formed by a dielectric substrate, on one side of which there is a screen, and on the other side, the conductor and the first, second conductors are galvanically connected to the screen, and surface resistors are connected between the conductor and the first, second conductors. The conductor narrows to the outlet and ends with a low-pass filter, and the edges of the first, second conductors are parallel to the edges of the conductor. A dielectric substrate with a battery of thermocouples is installed on the screen, the hot edges of which are located in the immediate vicinity of the surface resistors, and the cold edges are as far as possible from them 2 or more. sl C

Description

The invention relates to the field of measuring electrical and magnetic quantities, in particular to devices for measuring electrical quantities.

Thermocouple microwave power meters are known, based on a calorimetric measurement method, in which power measurement is reduced to measuring the temperature increment of the working fluid of a fluid, as determined using thermocouples.

The disadvantages of the known device are the complexity of the design of the liquid cooling system, the inability to work in harsh mechanical and climatic conditions.

Also known are direct heating sensors, i.e., thermoelements directly heated by microwave and low-frequency power.

The drawbacks of the device are low electrical strength, a narrow temperature range at which it is able to work.

The closest to the proposed is a thermocouple sensor made on a microstrip line with a matched load at the end, in the immediate vicinity of which a thermocouple is installed.

The disadvantages of the prototype should include the low accuracy of the sensor, due to: significant ksti load, leakage of the microwave power; thermocouple induced low sensitivity due to the use of a single thermocouple and a low level of permissible measured powers limited by a small load power.

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The aim of the invention is to improve the accuracy of the sensor while expanding the dynamic range.

The goal is achieved by the fact that in a thermocouple microwave sensor containing a microstrip line, made on a dielectric substrate and loaded on a resistive load, and a thermocouple, the micro-strip conductor is made narrowing to the output to which the low-pass filter is connected, the first and second conductors are inserted located symmetrically with respect to the conductor of the microstrip line in the area of its narrowing, while the distance between the conductor of the microstrip line and the first and second wires In addition, resistive load, made in the form of surface resistors, is permanently installed along the entire narrowing area and is in galvanic contact with the microstrip line conductor and the first and second conductors, respectively, the first and second conductors have galvanic contact with the microstrip line screen and form a shield the conductor on which the battery of thermocouples is located through the dielectric plate; the hot junctions of the battery of thermocouples are located in close proximity to tons of film resistors, and cold - as far as possible from them.

A positive effect is achieved due to the smaller Kc ™ load of the proposed device and the exclusion of the possibility of microwave power entering the thermocouple. In the sensor, the expansion of the dynamic range is ensured by increasing the maximum permissible level of power supplied to the load and the use of a battery of thermocouples installed along the load,

FIG. Figure 1 shows the microstrip and coplanar sensor design; in fig. 2 - electrical load circuit,

In the figures, the following notation is accepted: 1,6-dielectric substrate; 2 - microstrip line; 3- resistive coating; A - grounded conductor; 5 - low pass filter; 7 - screen; 8 - conductor deposited on a substrate, for example copper; 9 - conductor deposited or attached to the conductor 8, for example, constantan, 10-case; W0 is the wave resistance of the microstrip line; W) is the current characteristic impedance of the tapered line; n is the number of steps of the tapering line.

The proposed sensor (Fig. 1, the microstrip variant) contains a dielectric substrate 1 metallized on one side (screen 7) and having strips 2 on the other. Resistors 3 have galvanic contact with a strip 2 and conductors

4, having in turn galvanic contact with the screen 7. At the end of the strip 2 is installed an inductive-capacitive low-pass filter 5. On the screen of the substrate 1 there is a substrate 6, metallized with one

side and having a sequence of conductors 8 and 9, forming a battery of thermocouples, on the other. Conductor 8 has a different coefficient of thermopower than conductor 9, with hot thermocouple junctions

are located on the axis of symmetry of the microstrip line, and the cold junctions are near the body.

The proposed sensor (Fig. 1, coplanar version) contains a dielectric

1, having a central conductor 2, shield conductors 7. Resistors 3 have galvanic contact with conductor 2 and conductors 7. At the end of conductor 2 there is a low-pass filter 5. At

conductors 7 are installed substrate b, metallized on one side and having a sequence of conductors 8 and 9 on the other hand forming a battery of thermocouples,

The device works as follows.

When the power of the microstrip power line P is fed to the input (FIG. 2), the power is separated: part of the power goes to the resistor, part goes to the strip line with the characteristic impedance WL From

conditions for DC harmonization

should be L / 0 -, and the characteristic impedance W0 should be equal to the total resistance of the parallel-connected resistor R and the characteristic impedance Wi,

 4.1 psh - Wo R

w0 wi R and then W1 R-WO

accordingly, the wave resistance of the i-th stage will be equal to

wK-W -1g

1 R-W (-1 UJ

In order to fulfill the condition of uniform heat generation along the load, which is necessary to ensure the same thermal conditions as in DC calibration, it is required that the same voltage U be applied to each resistor R. Power will be released on the first resistor

P U2 U2

R p W0

about

that is, U P W0, so that the voltage across the second resistor is equal to U, it is necessary to provide a value of Wi that satisfies the following equation:

Р 1 Р U2 Р Р

those.

Wi

Next, Wi must be equal to R

Wi

n- 1

An analysis of formulas (1) and (2) shows that they are identical, i.e., the conditions for the ideal matching of this load coincide with the condition for uniform power absorption along the load. Another condition for an identical effect on a thermocouple of a microwave signal and a direct current calibration signal is the requirement to exclude the possibility of microwave power (directing) directly to the thermocouple. This requirement is fulfilled in the device by installing a thermocouple behind a screen where there is no microwave field.

Claims (1)

Claims. A thermocouple microwave power sensor containing a microstrip line made on a dielectric substrate and 0 five 0 five loaded to a resistive load, and a thermocouple, characterized in that, in order to increase the maximum permissible power and expand the dynamic range, the microstrip line conductor is made tapering to the output to which the low-pass filter is connected, the first and second conductors are arranged symmetrically relative to the conductor by microstrip lines in the area of its narrowing, while the distance between the conductor of the microstrip line and the first and second conductors, respectively, is constant along all The narrowing region, a resistive load, made in the form of surface resistors, is installed in the narrowing region and has galvanic contact with the microstrip line conductor and the first and second conductors, respectively, the first and second conductors have galvanic contact with the microstrip line screen, and form a screen conductor, where the battery of thermocouples is located through the dielectric plate, the hot junctions of the battery of thermocouples are located in the immediate vicinity of film resistors, and cold ma most remote from them. : BUT i A I e-S --H 9 ./IZ 1 I. W, fes.2 Wn- wn R