RU2044325C1 - Device for evaluation of microwave field level - Google Patents

Abstract

FIELD: microwave measurement technology; estimation of degree of biological danger of radiation near microwave plants, such as microwave ovens, radars, TV transmitters. SUBSTANCE: device has antenna 1 whose outputs are connected to input terminals of microwave detector 4 and output terminal leads of the latter are connected to integrating circuit 18 incorporating load resistors 19,20 connected to integrating capacitor 21 which is connected in parallel with measuring instrument 22 and light-emitting diode 23. Microwave detector 4 has two pairs of diodes 5,6 and 10,11, each being connected, together with microwave filter capacitors 8,9 and 13,14, respectively, into voltage doubling circuit; microwave diodes of one pair have higher forward d. c. voltage than those of other pair. Each pair of microwave diodes has unlike- polarity electrodes combined and connected through series resistor 7 (and 12, respectively) to first input terminal lead of microwave detector 4 whose second input terminal lead is connected to point of connection of microwave filter capacitors connected in series between other electrodes of given pair of microwave diodes that function, respectively, as first, second, and third, fourth output terminal leads of microwave detector; connected between first and second input leads at microwave detector input is matching resistor 15. First and third output terminal leads of microwave detector are connected to one plate of integrating capacitor 21 through load resistors 19 and 20, respectively; second and fourth terminal leads of microwave detector are connected to other plate of integrating capacitor directly. Limiting diodes 16 and 17 are connected in parallel with outputs of each pair. EFFECT: improved design, enlarged functional capabilities. 2 cl, 2 dwg

Description

 The invention relates to the field of microwave measurements and can be used to assess the degree of biological hazard of radiation near microwave installations, in particular microwave ovens, radars, television transmitters.

 The requirement of high durability and reliability is most often realized in a passive device for assessing the level of the microwave field, i.e. a device that does not have power sources, and small dimensions determine the possibility of using the device as a means of individual use.

 The invention provides a significant reduction in the dependence of the readings of the device on the type of modulation of the microwave signal from continuous to pulse-modulated over a wide range of duty cycle and pulse durations. At the same time, operation in a wide microwave frequency band is simultaneously ensured due to ensuring coordination for the indicated modulation modes.

 In FIG. 1 presents an electrical diagram of the proposed device; in FIG. 2 diagram of the operation of both pairs of microwave diodes at different duty cycle of the microwave signal.

 The proposed device comprises an antenna 1 made in the form of a short-circuited segment of a waveguide 2 with a capacitive coupling 3 used as the first output of the antenna, the second output of which is the waveguide body, and these conclusions are connected to the first and second input terminals of the microwave detector 4, containing two detection circuits with doubling the rectified voltage each, one of which contains the first pair of the same type of highly sensitive semiconductor microwave diodes 5, 6, one of which is the opposite the polarities are interconnected and through an additional resistor 7 with the first input terminal of the microwave detector 4, the other electrodes of the diodes 5, 6 are connected to the first and second output terminals of the detector 4 and with the plates of the series-connected microwave filter capacitors 8, 9, the connection point of which is connected to the second input terminal of detector 4, the second detection circuit is made similarly to the first with the difference that the pair of the same type of microwave semiconductor diodes 10, 11 forming it is selected with a higher constant direct voltage eniya diode than the diodes 5, 6.

 While interconnected electrodes of opposite polarity of the diodes 10, 11 are connected to the first output of the detector 4 through an additional resistor 12, other electrodes 10, 11 are connected to the third and fourth output terminals of the detector 4 and to the plates of the series-connected microwave filter capacitors 13, 14, and the connection point of the latter to the second input terminal of the detector 4, and between the first and second input terminals of the detector 4 at its input is included a matched resistor 15. The first and second, third and fourth output terminals m of the microwave detector 4, the diodes 16 and 17 are connected, respectively, so that the polarity of their electrodes connected to the indicated terminals is opposite to the polarity of the electrodes of the microwave diodes of the detector 4 connected to these terminals.

 The output terminals of the detector 4 are connected to an integrating circuit 18 containing a first load resistor 19, a second load resistor 20, and an integrating capacitor 21. In this case, the first and third output terminals of the detector 4 are connected through one resistor 19 and 20 to one capacitor plate 21, and the second and the fourth terminals of the detector with a different capacitor plate, and a passive direct current measuring device 22 is connected in parallel with the capacitor 21, which can be used as a microammeter or millivolt tr, and in parallel with the measuring device, a light emitting diode 23 is connected, the polarity of the electrodes of which corresponds to the polarity of the electrodes of the measuring device to which it is connected.

 The device operates as follows.

 The input microwave signal, the value of which is determined by the density of the power flux and the effective area of the antenna, is supplied to the antenna 1 and from its output terminals 1 and 2 to the first and second input terminals of the microwave detector 4. The microwave power supplied to the microwave detector creates a microwave voltage resistor 15 matched to the antenna output is proportional to the indicated power. Microwave voltage through an additional microwave resistor 7 is fed to the input of the first pair of microwave semiconductor diodes 5 and 6 having a low forward voltage drop (low potential barrier), and through an additional microwave resistor 12 to the input of a second pair of microwave semiconductor diodes 10 and 11 having, compared with the first pair of microwave diodes, a higher value of the direct voltage drop (potential barrier). Each pair of microwave diodes detects microwave voltage in conjunction with the corresponding microwave capacitors 8, 9 and 13, 14 according to the doubling scheme. Positive half-waves of microwave voltage are detected in the first pair by a microwave diode 5 and a filter microwave capacitor 8, negative by a diode 6 and a filter capacitor 9. The total video signal voltage of the first pair is allocated on the plates of capacitors 8 and 9, connected to the first and second outputs of the microwave detector 4, and the load for this voltage is the load resistor 19 in the integrating circuit 18, connected to the integrating capacitor 21.

 Similarly, voltage detection is performed in the doubling circuit of the second pair of microwave diodes 10, 11 with filter capacitors 13, 14.

где Р_ср средняя входная мощности;
S_эф эффективная площадь антенны.The rectified total voltage of this pair is released on the load resistor 20 and fed to the integrating capacitor 21. The integrating circuit 18, formed by the resistors 19, 20 and the capacitor 21, creates constant components of the pulse sequences of the video currents from the first and second pairs of microwave diodes allocated to the input resistance of the measuring the device 22 connected in parallel with the capacitor 21. Thus, the measuring device 22 registers the sum of the constant components of the pulse sequences of the video currents in two pairs of microwave diodes of the detector 4. The indicated sum of currents is a measure of the average microwave power supplied to the antenna input, and therefore a measure of the power flux density (P)
P

where P _{cf is the} average input power;
S _{eff is the} effective area of the antenna.

 With an increase in duty cycle at a constant average power (see Fig. 2), the first low-barrier pair of microwave diodes 5 and 6 with its additional 7 and load 19 resistors is first detected at first, then with a further increase in duty cycle, the second high-barrier pair of diodes 10 and 11 with its additional 12 and load resistors 20, the proportion of the first pair drops, the second increases so that the sum of the constant components of the video signal currents recorded by the measuring device 22 is approximately constant for a wide range of wells and microwave durations ignals.

The width of the microwave frequency band of the input signal is ensured by matching the detector 4 with the antenna using a matched resistor 15, decoupling both pairs using resistors 7 and 12 with the corresponding detection mode determined by the load resistors 19 and 20. With a fixed average microwave power P _cf , and hence the microwave power flux density, the amplitude of the microwave voltage U _m at the matched input resistor 15 of the microwave detector 4 will increase in proportion to the increase in the duty cycle Q of the input signal.

(1) где Р_имп СВЧ-мощность в импульсе; амплитуда СВЧ напряжения
U

=

(2) где r_с согласованное входное сопротивление СВЧ-детектора (резистор 15);
I Г I модуль коэффициента отражения СВЧ детектора, тогда
U

=

(3)
Для сохранения постоянной зависимости U_mСВЧ (при заданной Р_ср) от Q необходимо примерное постоянство r_c (минимальное влияние входного сопротивления обеих детектирующих пар СВЧ-диодов) и минимизация коэффициента отражения, что также связано с входным сопротивлением диодных пар.Consider three options for duty cycle:
a) Q 1 (continuous microwave signal),
b) Q 10-15 (average duty cycle);
c) Q 100-200 (high duty cycle), which are reflected in FIG. 2. We proceed from the following general relations:
average power
P _cf =

(1) where P _{imp is the} microwave power in the pulse; microwave voltage amplitude
U

=

(2) where r is _the matched input resistance of the microwave detector (resistor 15);
I G I the module of the reflection coefficient of the microwave detector, then
U

=

(3)
To maintain a constant dependence of U _{m microwave} (at a given R _cf ) on Q, an approximate constancy of r _{c is} required (the minimum influence of the input resistance of both detecting pairs of microwave diodes) and minimization of the reflection coefficient, which is also associated with the input resistance of diode pairs.

In FIG. _Figure 2 shows the current-voltage characteristics of the first pair (U _AX1 ) of microwave diodes with a low potential barrier and the second pair (U _AX2 ) with a higher potential barrier. The amplitudes of microwave voltages at the inputs of a microwave detector for various duty cycles are also shown (along the vertical negative axis).

From the formula (3) it is obvious that with a continuous signal (Q 1) the amplitude of the microwave signal U _m (Q 1) is minimal (for a fixed P _cf , see Fig. 2, a). For average values of duty cycle U _m ˙ Q _cp (see Fig. 2, c).

In this case, the amplitude of the video signals on the load resistors of each pair is indicated by U _Ω (with the corresponding index 1, 2), constant voltage on the measuring device U _n , the value of the pulsed microwave current of the diode I _m , the magnitude of the video current in the load resistor of each pair of diodes I _Ω constant component of the video stream in the circuit of the measuring device I ₌ .

(Q= 1), а постоянная составляющая I₌(Q 1). Нагрузка первой пары в этом случае является суммарное сопротивление резистора 19 и входного сопротивления по постоянному току измерительного прибора, превышающего на порядок величину сопротивления 19. Это обеспечивает повышение чувствительности при работе на участке самой низкой крутизны вольтамперной характеристики диодов первой пары (улучшение КПД детектирования).With a continuous signal, the small amplitude of the microwave voltage U _m (Q 1) unlocks the microwave diodes 5, 6 of only the first pair. In this case, the amplitude of the microwave current in the diode I

(Q = 1), and the constant component I ₌ (Q 1). The load of the first pair in this case is the total resistance of the resistor 19 and the DC input resistance of the measuring device, which is an order of magnitude higher than the resistance 19. This provides increased sensitivity when working at the site of the lowest slope of the current-voltage characteristic of the diodes of the first pair (improved detection efficiency).

When operating in a pulsed mode (see Fig. 2, b, c), the amplitude of the microwave voltage increases (see formula 3) with increasing duty cycle, the steepness of the characteristic in the working section U _AX1 (see Fig. 2) increases, but the load is first the pair now becomes only the resistor 19, as the effect of the integrating capacitance 21, shunting the video signal, which evens out the sensitivity of the device for continuous mode and modes of small and medium duty cycles.

(4) Амплитуда видеосигналов на нагрузочном резисторе 19 первой пары определяется как
U_{Ω 1}= I_{Ω 1}˙R₁₉ (5) При этих же скважностях (Q_cp) начинает открываться вторая пара СВЧ-диодов 10,11, имеющая более высокий потенциальный барьер. За счет СВЧ-амплитуды U_m(Q_cp) создается амплитуда СВЧ-тока диодов второй пары I

(Q_cp), при этом амплитуда продектированного тока диодов второй пары в ее нагрузочном резисторе 20 I_{Ω 2}(Q_cp), а постоянная составляющая импульсной последовательности второй пары создается за счет интегрирующей цепи (резистор 20 и конденсатор 21 в цепи измерительного прибора 22).At average Q _{cf the} magnitudes of the duty cycles (see Fig. 2b), the amplitude of the microwave voltage U _m (Q _cp ) creates a large (for the first pair) microwave current in its diodes I _m1 (Q _cp ), while the amplitude of the current detected the video signal in the load (resistor 19) I _{Ω 1} (Q _cp ), the constant component of the current of the sequence of video pulses I _{= 1} (Q _cp ), the duration of the video pulses τ _and (Q _cp ) during their period T _n (Q _cp ). The constant component is defined as
I ₌ =

(4) The amplitude of the video signals on the load resistor 19 of the first pair is defined as
U _{Ω 1} = I _{Ω 1} ˙ R ₁₉ (5) At the same wells (Q _cp ), a second pair of microwave diodes 10.11 begins to open, having a higher potential barrier. Due to the microwave amplitude U _m (Q _cp ), the amplitude of the microwave current of the diodes of the second pair I

(Q _cp ), while the amplitude of the detected current of the diodes of the second pair in its load resistor is 20 I _{Ω 2} (Q _cp ), and the constant component of the pulse sequence of the second pair is created by the integrating circuit (resistor 20 and capacitor 21 in the circuit of the measuring device 22) .

Due to the connection of load resistors 19 and 20 to the total capacitance of the integrating circuit 21 integrates 18 and 22 connecting the measuring device to the container in a meter DC components are summed videotokov both pairs I _{Σ i.p.} = I _{= 1} + I _{= 2} . In this case, the total current I _{Σ i.p.} at medium wells, the proportion of the first pair I _{= 1 is the} main, and the second I _{= 2} is small, and with an increase in duty cycle, the proportion of the second pair increases and the proportion of the first pair decreases due to its limitation by additional resistor 7 and load 19, due to which the sum of the shares of both pairs instrument) remains approximately constant.

≡ U $\genfrac{}{}{0ex}{}{\text{2}}{\text{m}}$ и с учетом формулы (3) I₌≡P_ср/т.к. I_Ω=I₌˙Q=2˙r_c˙P_срx xQ˙(1-I Г I²)/.With a large duty cycle Q _in (see Fig. 2, c), a large amplitude of the microwave voltage U _m (Q _in ) creates a significant amplitude of the microwave current of the diodes of the second pair I _m2 (Q _in ), the amplitude of the video stream in the load resistor 20 of the second pair I _{Ω 2} (Q _in ) also increases and provides the corresponding values of a constant increasing current of the sequence of video pulses from the second pair of diodes I _{= 2} (Q _in ) and the amplitude of the video pulse on the load resistor of the second pair U _{Ω 2} . Open diodes of the first pair in this case provide a microwave current I _m1 (Q _in ), which creates a detected video stream I _{Ω 1} (Q _in ) in the load resistor 19 of the first pair. The magnitude of the load resistor 19 of the first pair, acting in conjunction with the microwave resistor 7, limits the share of the current of the first pair in the total sum of currents, since the first pair, which has high sensitivity, cannot simultaneously provide large pulsed video currents necessary for working with high duty cycle, and work on the plot of maximum non-linearity, which is necessary to ensure an approximately quadratic dependence of the rectified video stream on the applied microwave voltage. Indeed, if I _Ω = U _m ² , then
I ₌ =

≡ U $\genfrac{}{}{0ex}{}{\text{2}}{\text{m}}$ and taking into account formula (3) I ₌ ≡P _{cf /} t.k. I _Ω = I ₌ ˙Q = 2˙r _c ˙P _cp x xQ˙ (1-I Г I ² ) /.

The main part of the constant component at high duty cycle from the second pair, the share of the first pair is small, and their sum (I _{Σ etc.)} due to the proposed scheme and the choice of the corresponding resistor values remains approximately constant when the duty cycle changes.

 The resistance value of the resistor 7 of the low barrier pair of diodes is greater than the resistance value of the resistor 12 for the high barrier pair. At the same time, the resistance value of the load resistor 19 of the first pair of diodes is several times greater than the resistance of the load resistor 20 of the second pair of diodes.

 Such a choice of resistors limits the current of the first pair of diodes and the voltage on its diodes with increasing wells and keeps the sum of the constant components of both pairs approximately constant.

I₌₂=

I₌₁+I₌₂=

Причем, если I_{Ω 1,2}≡KU_m ² (работа на нелинейном участке вольтамперной характеристики СВЧ-диода), то I_{Σ и.п.}= I₌₁ + I₌₂ (k₁ + k₂)˙U_m ² k˙U_m ²;
U_m=

P

≡ I_{Σ и.п}, I_Σ

P где Р плотность потока СВЧ-мощности.Thus. I _{Σ and.p.} = I ₌ (Q = 1) ≈I _{= 1} (Q _cf ) + + I _{= 2} (Q _cf ) ≈I _{= 1} (Q _c ) + I _{= 2} (Q _c )
The total constant component recorded by the measuring device is little dependent on the duty cycle at a constant average power at the microwave detector, and hence at a constant power flux density at the antenna input. Really,
I _{= 1} =

I _{= 2} =

I _{= 1} + I _{= 2} =

Moreover, if I _{Ω 1,2} ≡KU _m ² (work on a non-linear section of the current-voltage characteristic of the microwave diode), then I _{Σ and.p.} = I _{= 1} + I _{= 2} (k ₁ + k ₂ ) ˙U _m ² k˙U _m ² ;
U _m =

P

≡ I _{Σ I.p.} , I _Σ

P where P is the microwave power flux density.

For operation in a wide range of durations of the time constant of the microwave detector (τ _heat), equal to the magnitude of a filter container for microwave load resistance value of any of the pairs of diodes to be an order of magnitude less than the minimum duration (τ _min) of the microwave pulse, ie . τ _load С _{f (8,9,13,14)} ˙r _n (19,20) ≈ 0,1˙τ _min .

In this case, the shape of the video pulse on the load resistor accurately repeats the shape of the microwave pulse, so the above formulas for the constant components of the currents (I ₌ ) and for the video currents (I _Ω ) will be valid.

 It was experimentally confirmed that in the device there is practically no dependence of the readings of the measuring device 22 on changes in the duration of microwave pulses.

To work in a wide range of duty cycles, the time constant of the integrating circuit must be an order of magnitude greater than the maximum period (T _max ) of microwave pulses, i.e.

τ _and.c With _it. ˙r _and.ts. ≥T _max .

 The first and second additional resistors 7, 12 are necessary for the implementation of the following functions: decoupling of each of the pairs of microwave diodes from the matched microwave resistor 15 and from each other to ensure an approximate constancy of the input resistance of the microwave detector, eliminating the bypass of resistor 15 by open pairs of microwave diodes at large wells. The value of the microwave resistor 7, approximately equal to the value of the matched resistor 15, provides a limitation of the microwave voltage and power on the first pair of microwave diodes, and therefore, the fraction of its current in the total when the duty cycle is large (large amplitude of the microwave voltage).

 Decoupling with resistors 7 and 12 also provides a decrease in the reactive component of the input resistance connected to the matched resistor 15 of both pairs of microwave diodes with their inductances and sharply changing capacitances of the transitions when working with low-frequency load resistors 19, 20, i.e. provides minimization of the reflection coefficient G (3).

 Resistors 7, 12 also significantly reduce the quality factor of the serial resonant circuit of the microwave diodes, making it possible to achieve uniformity of the microwave voltage transfer coefficient from the matched microwave resistor 15 to the pn junction of the semiconductor diode.

 Thus, the presence of resistors 15, 7, 12, ensuring the operation of the detector circuit 4 in a wide range of durations and duty cycle, at the same time provides the ability to maintain a small dependence on duty cycle and duration in a wide range of microwave frequencies.

 In addition, the use of a matched resistor 15 allows you to "compress" the dynamic range of amplitudes of the microwave voltage at the microwave detector with a wide dynamic range of microwave power at the input of the device (up to 25-39 dB) and at the same time increase reliability by reducing the maximum amplitudes by Microwave detector 4.

 Limit diodes 16 and 17 in combination with the doubling circuit also significantly increase the reliability of the device, protecting the diodes of both pairs from reverse voltage at high levels of the input microwave signal.

 A light-emitting semiconductor diode 23, connected in parallel with the measuring device, has a voltage drop corresponding to the ignition threshold, greater than the voltage drop across the measuring device when the measured parameter is extreme on the scale of the device. Thus, at microwave power levels dangerous to humans, a light indication is provided while maintaining a small dependence on the duty cycle, duration and frequency of the microwave signal.

 The use of broadband antennas (helical, horn, log-periodic, multivibrator) allows you to significantly expand the range of microwave frequencies of the device. The device allows you to evaluate the level of microwave fields of a wide class of microwave installations.

Tests of the layout of this design using microwave semiconductor diodes of type 2A202 in the first pair and 3A112 in the second pair gave the following results: field levels estimated by the device, 5-50 μW / cm ² ; LED indication level 200-300 μW / cm ² ; microwave pulse duration range 0.1-500 μs; the range of wells 1-200; microwave frequency range (for this design) 2600-3200 MHz; non-uniformity of readings (at a level of 25 μW / cm ² ) does not exceed ± 2 dB in the indicated ranges.

Claims (2)

 1. DEVICE FOR EVALUATING A MICROWAVE FIELD LEVEL, comprising an antenna, two pairs of detector diodes, the first unlike electrodes of the detector diodes of each pair are interconnected, and the second are connected to the first plates of two filter capacitors, the second plates of which are connected to each other and connected to the first output antennas connected in series with the first resistor and capacitor, forming the first integrating circuit, the input of which is connected to the connection point of the electrode of one of the detector diodes and the first lining of one of the phi capacitors of one pair, a second resistor, the first output of which is connected to the connection point of the same electrode of the detector diode and the first lining of one of the filter capacitors of the other pair, and a passive measuring device, characterized in that the third and fourth resistors are introduced, one of the terminals of which is connected to the second terminal of the antenna, and the other terminal of each is connected to the connection point of the first opposite electrodes of the detector diodes of the corresponding pair, the fifth resistor, which is connected between the terminals antennas, and the first and second limiting diodes, connected in the forward direction parallel to the filtering capacitors of the corresponding pair of detector diodes, the second output of the second resistor is connected to the connection point of the first resistor and capacitor and forms a second integrating circuit with which the passive measuring device is connected, at the first limiting diode is connected parallel to the input of the first integrating circuit, and the second limiting diode is connected parallel to the input of the second integrating circuit and a potential barrier diodes of one pair of detector exceeds the potential barrier of the detector diodes of the other pair.  2. The device according to claim 1, characterized in that a light emitting semiconductor diode is connected in parallel with the measuring passive device.

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