RU2234718C1 - Frequency-modulated altimeter - Google Patents

Abstract

FIELD: radar systems.

SUBSTANCE: frequency modulated altimeter includes reference analog signal source, digital control unit for controlling rate of readjustment of frequency of transmitter, modulator, frequency-modulated transmitter, transmitting antenna, receiving antenna, first mixer, difference frequency amplifier, computing counter, clock pulse generator, switch for switching sign of readjustment of transmitter frequency. Novelty is that altimeter also includes comparator, pin-switching unit, second mixer, reference frequency generator, band amplifier, detector, logic gate unit.

EFFECT: lowered instrumental component of error at measuring height occurred due to unstable characteristics of electronic frequency readjustment of transmitter.

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Description

The present invention relates to the field of radar, and in particular to radio altimeters with frequency modulation, and can be used in the design of radio altimeters, which are required high accuracy measurement of height.

Known [1], p.173-174, frequency-modulated radio altimeters in which information about the height H is extracted from the difference between the emitted and received frequencies (beat frequency f _b ), defined as

where ΔF is the frequency deviation of the transmitter (PP);

c is the speed of light;

T _m - period of modulation.

может достигать ±15%, что приведет к такой же относительной погрешности измерения высоты.Under the influence of various kinds of destabilizing factors, the PDP can change by ΔΔF. As noted in [3], p.5, the relative change

can reach ± 15%, which will lead to the same relative height measurement error.

Therefore, decisions are being made aimed at increasing the stability of PPP.

The closest in technical essence is a frequency-modulated altimeter containing a series-connected source of a reference analog signal 12, a digital control unit 11 for controlling the frequency of the transmitter, modulator 1, transmitter 2 with frequency modulation and transmitting antenna 3, connected in series with receiving antenna 4, mixer 5 , a differential frequency amplifier 6 and a counter-calculator 9, the first output of which is connected to the second input of the digital frequency control unit for tuning the frequency of the transmitter and a second output connected to a second input of the amplifier of the difference frequency, series-connected oscillator 10 clock pulse unit 7 allocation measurement interval modulation band, comprising two resonator tuned to frequencies f ₁ and f ₂ corresponding to the lower and upper frequencies, determining NRI switch 8 direction of tuning the frequency of the transmitter, the output of which is connected to the second input of the modulator, while the second output of the transmitter is connected to the second input of the mixer, the third output is connected to the second input of the block dividing the measuring interval of the modulation band, the second output of which is connected to the second input of the counter-calculator, the third input of which is connected to the second output of the clock generator, the third output of the clock generator is connected to the third input of the digital frequency control unit of the transmitter frequency, the fourth input of which is connected to the output of the differential frequency amplifier [2].

The disadvantage of this altimeter is the lack of accuracy in measuring height. As shown in [3], p.16, when using resonators in block 7 to separate the measuring interval, the relative instability of the PDP can reach 2.15%, which leads to the same error in the measurement of height.

The aim of the invention is to improve the accuracy of height measurement.

This goal is achieved by the fact that in the frequency-modulated altimeter containing a clock pulse generator, a direction switch for tuning the frequency of the transmitter, a series-connected source of a reference analog signal, a digital control unit for tuning the frequency of the transmitter, the second input of which is connected to the first output of the clock, a modulator the second input of which is connected to the output of the transmitter frequency tuning direction switch, a frequency modulated transmitter and a transmitting antenna, a receiving antenna connected in series, a mixer, the second input of which is connected to the second output of the transmitter, a difference frequency amplifier and a calculator, the second input of which is connected to the second output of the clock generator, and the first and second outputs are connected respectively to the third input of the digital control unit of the transmitter frequency tuning speed and the second input of the differential frequency amplifier, the output of which is additionally connected to the fourth input of the digital control unit At the speed of tuning the frequency of the transmitter, a comparator is introduced, the first input of which is connected to the second output of the modulator, and the second input is supplied with a fixed voltage, a reference frequency generator, series-connected pin switch, the first and second inputs of which are connected respectively to the first and second outputs of the reference generator frequencies, and the third input with the first output of the comparator, the second mixer, the second input of which is connected to the third output of the transmitter, a strip amplifier, a detector and a block of logic elements s, the second and third inputs of which are connected respectively to the first and second outputs of the comparator, and the fourth input is to the third output of the clock generator, the first output is to the third input of the counter-calculator, the second output is to the input of the transmitter frequency direction switch, and the block logical elements contains the first and second elements AND, connected in series to the third element AND, the first element OR, the second input of which is connected to the output of the first element AND, and the RS-trigger, connected in series to four the first AND element, the second OR element, the second input of which is connected to the output of the second AND element, and the output - with the second input of the RS-trigger, a pulse extender connected in series, the input of which is connected to the output of the first OR element, the fifth AND element, the second input of which is connected with the third output of the clock generator, and a second trigger, the first output of which is connected to the input of the transmitter frequency tuning direction switch with the second inputs of the third and fourth AND elements, and the second output - with the second inputs of the first of the first and second elements And, the first inputs of the first, second, third and fourth elements And are connected to the output of the detector, the third inputs of the first and fourth elements And are connected to the first output of the comparator, the third inputs of the second and third elements And are connected to the second output of the comparator, and the output The RS-trigger is connected to the third input of the counter-calculator.

The essence of the claimed device lies in the fact that the newly introduced blocks more than an order of magnitude increase the stability of the band ΔF adjustment of the transmitter, which accordingly reduces the instrument component of the error of height measurement, resulting from the instability of the parameter ΔF when exposed to various kinds of destabilizing factors.

A comparison of the claimed device with the prototype shows the presence of newly introduced blocks: a reference frequency generator, a second mixer, a pin switch, AND and OR elements, a strip amplifier, a detector, and a logic block.

The introduction of such blocks to improve the accuracy of measuring height from public sources is unknown, which allows us to conclude that the proposed solution meets the criterion of "Novelty."

Newly introduced blocks are known and described in the literature:

- comparators, triggers, AND and OR elements in [4], p.286, 288, 105, respectively;

- pin switch in [5], pp. 50-71;

- reference frequency generator in [6], p.21;

- a strip amplifier in [7], p.187-194, and the newly introduced second mixer is similar to the mixer used in the prototype.

However, their inclusion, in accordance with the described relationships, makes it possible to improve the accuracy of height measurement.

Such a solution does not explicitly follow from the prior art, which meets the criterion of "Inventive step".

Figure 1 presents the functional diagram of the prototype, figure 2 is a functional diagram of the proposed device, figure 3 is a variant of a functional diagram of a transmitter with frequency modulation, figure 4 is a variant of a functional diagram of a block of logic elements, figure 5 is a variant a possible functional diagram of the reference frequency generator, Fig.6 - plot voltage, explaining the principle of operation of the device.

The device (figure 2) contains a source of 1 reference analog signal, a digital control unit 2 for controlling the frequency of the transmitter, a modulator 3, a frequency-modulated transmitter 4, a transmitting antenna 5, a receiving antenna 6, a first mixer 7, a differential frequency amplifier 8, and a counter a calculator 9, a clock generator 10, a transmitter frequency direction switch 11, a comparator 12, a pin switch 13, a second mixer 14, a reference frequency generator 15, a band amplifier 16, a detector 17, a block 18 of logic elements. Communication between these blocks correspond to figure 2.

The transmitter 4 with frequency modulation (figure 3) contains a frequency-modulated generator 19 and a power divider 20.

Block 18 of the logical elements (figure 4) contains the first element And 21, the third element And 22, the first element OR 23, RS-trigger 24, the fourth element And 25, the second element OR 26, the second element And 27, pulse expander 28, fifth element And 29 and the second trigger 30.

The relationship between these blocks correspond to figure 4.

The reference frequency generator 15 (FIG. 5) comprises a crystal oscillator 31, a first frequency multiplier 32, a first resonator 33 tuned to a frequency f ₁ , a second multiplier 34 and a second resonator 35 tuned to a frequency f ₂ .

When turned on, the radio altimeter operates in search mode as follows.

Under the action of the signal from the output of the digital control unit 2 of the transmitter frequency tuning speed, the modulator 3 generates a sawtooth voltage "a", the repetition period of which varies from T _min to T _max. This voltage is supplied to the transmitter 4, generating microwave frequency (microwave) oscillation "b", the carrier frequency of which varies from F _min to f _max . Microwave oscillations of the transmitter are fed to the transmitting antenna 5 and are emitted towards the earth's surface.

Signals of frequency F ₀ reflected from the ground are received by the receiving antenna 6 and fed to the first input of the mixer 7, to the second input of which microwave frequencies of the frequency F are fed _and from the second output of the transmitter 4.

The oscillations of the difference frequency f _p = F _and -F ₀ occurring at the output of the mixer 7 are amplified by the difference frequency amplifier 8 and fed to the input of the counter-calculator 9, the second input of which is supplied with the frequency fluctuations f ₀ from the second output of the clock generator 10. When, as a result of an increase in the modulation period T _{m, the} difference frequency f _p becomes equal to the frequency f ₀ , a signal appears at the first output of the calculator 9 that transfers the digital control unit 2 of the transmitter frequency tuning speed from the search mode to the tracking mode, in which the block of 18 logic elements generates pulses, the duration of which carries information about the height. These pulses are formed as follows. The reference frequency generator 15 generates microwave oscillations of the frequencies f ₁ and f ₂ , respectively, arriving at the first and second inputs of the pin switch 13, the third input of which receives the control voltage U _control from the first output of the comparator 16, the sawtooth voltage being supplied to its inputs U _m from the output of the modulator 3 and the reference voltage

_макс,

_max

where U _{m max} is the maximum output voltage of the modulator. If U _m <U _op , then at the first output of the comparator 12 a logic level 1 occurs at which the lower frequency f ₁ passes to the output of the pin switch 13, and the first and fourth elements And 21 and 25 are open at the third inputs.

If U _m > U _op , then at the first output of the comparator 12 a logic zero level occurs, and the frequency f _{2 of} the reference oscillator 15 passes to the output of the pin switch 13, and f ₂ > f ₁ .

Figure 6 shows the process of managing and generating information. At time t ₀ , when the logic unit is at the 1st output of comparator 12, the frequency f _{1 of} the reference oscillator 15 passes to the output of the pin switch 18.

At the same time, at the second output of the second trigger 30 there is a logic level 1, opening the first element And 21 on the second output. When decreasing at time t ₁ frequency f _prd transmitter 4 to

f _prd = f ₁ + f _f

at the output of the second mixer 14 there is a pulse "in" of the frequency f _f , which is amplified by the amplifier 16, detected by the detector 17 and fed to the first inputs of the elements And 21, 22, 25, 27.

Since all the three inputs at this moment only the first element And 21 is open, the pulse "g" arises at its output, which enters through the second input of the first element OR 23 to the R input of the RS-flip-flop 24 and puts it in the state of logical 0 (pulse " d "), at which the count of pulses of the generator 10 clock pulses in the counter-calculator 9 is stopped. The pulse" g "enters through the first element OR 23 and to the pulse expander 28, forming a pulse" e ", which arrives at the first input of the fifth element And 29, to the second input of which clock pulses "g" are supplied, s 10 clock pulses taken from the third output of the generator. At time t _2, the output of the fifth element And 29 gives an impulse "k", which transfers the control trigger 30 to a state in which at its first output there is a logic level 1 (impulse "l"), according to which the switch 11 of the transmitter frequency tuning direction changes direction modulator 3 changes the voltage by transferring it from falling to rising, thereby causing an increase in the frequency f 4 of the transmitter _TX.

With increasing frequency f _prd to f _prd = f ₂ -f _f (at time t ₃ ), a pulse of frequency f _f arises at the output of the second mixer 14, which is amplified by amplifier 16, detected and fed to the first inputs of elements 21, 22, 25 , 27. However, at this moment, only the fourth element And 25 is open at all inputs. At its output, an impulse "m" arises, coming through the second element OR 26 to the S input of the RS flip-flop 24, translating it into logical state 1, at which possible counting clock pulses counter-calculator 9.

When the voltage of the modulator 3 is increased to a value of U _m > U ₀ , a logic 0 level appears at the first output of the comparator 12, at which the pin switch 13 supplies the frequency f ₂ generated by the reference frequency generator 15 to the input of the second mixer 14.

With increasing frequency f _prd to f _prd = f ₂ -f _f at time t ₄ , a voltage pulse of frequency f _f arises at the output of the second mixer 14, which is amplified by amplifier 16, detected by detector 17 (pulse "n") and fed to the first inputs elements And 21, 22, 25, 27, of which only the third element And 22 is open on the second and third inputs. The pulse "0" arising at its output through the first element OR 23 puts the RS-trigger 24 in state 0, at which the count stops pulses of the generator 10 by the counter-calculator 9. Thus, the counting of pulses tsya for time t ₃ -t _4, wherein the transmitter frequency changes from f ₁ to f _p -f ₂ -f _f. It is important to emphasize that the frequency tuning range of the transmitter does not depend on the tuning frequency of amplifier 16, and departures of the latter will not lead to a height measurement error. The impulse "o" through the first element OR 23 will start the pulse expander 28, forming the impulse "p" supplied to the fifth element And 29, the output impulse of which transfers the first output of the trigger 30 to state 0, at which the sawtooth voltage of the modulator 3 begins to decrease, causing a decrease the frequency of the transmitter 4. At time t ₆ , when f _prd = f ₂ + f _f , at the output of the second mixer 14 there will be pulses of frequency f _f that are detected and fed to the first inputs of the elements And 21, 22, 25, 27. But according to the second and third inputs all of the above elements s And besides of AND 27 will be closed.

The pulse "c" arising at its output through the second OR element 26 will bring the RS flip-flop 24 to state 1, and the counter-calculator 9 will begin to count the pulses of the generator 10 until, at time t ₇ f _prd = f ₁ + f _f and at the output of the second mixer 14, “t” pulses will arise, amplify and detect, which will translate the RS flip-flop 24 into state 0, and the modulation process will be repeated.

The counter-calculator 9, as in the prototype, compares the difference frequency f _p with the frequency f _{0 of} the clock generator 10 and generates at the first output a signal fed to the third input of the digital frequency control unit 2 of the transmitter frequency tuning speed and changing the modulation period so that f _p = f ₀ .

To exclude the capture of a direct signal when measuring small heights, the counter-calculator 9 at the second output generates a signal fed to the second input of the difference frequency amplifier 8 and changes its gain, setting it small when measuring low heights and large when measuring high heights.

We estimate the instability ΔF. For a radio altimeter, you can take f ₁ = 4250 MHz, af ₂ = 4377.5 MHz (ΔF = f ₂ -f ₁ = 4377.5-4250 = 127.5 MHz). Then the frequency of KG 31 can be chosen equal to 42.5 MHz and taken n = 100, ak = 3. According to [4], p.298-300, the relative frequency instability of the quartz resonator does not exceed 10 ^-4 .

не превысит 0,01%. Таким образом, применение предлагаемого технического решения позволяет по сравнению с прототипом в 100 раз уменьшить приборную составляющую погрешности измерения высоты, вызываемую нестабильностью девиации ΔF.In this case, the frequency drifts f ₁ and f ₂ will not exceed Δf ₁ = 425 kHz and Δf ₂ = 437.7 kHz. Therefore, ΔΔF = Δf ₂ -Δf ₁ = 12.7 kHz, and the relative change in deviation

will not exceed 0.01%. Thus, the application of the proposed technical solution allows, in comparison with the prototype, to reduce by 100 times the instrument component of the error of height measurement caused by the instability of the deviation ΔF.

This allows you to use one frequency-modulated altimeter for measuring small and large heights when taking measures to reduce the methodological component of the error in height measurement.

The newly introduced pin switch blocks, the second mixer, and the reference frequency generator can be manufactured using thin-film technology, and the block of logic elements 18 can be performed on one programmable logic integrated circuit, which will not lead to a significant increase in the volume and mass of the proposed PB.

Literature

1. Zhukovsky A.P. and other Theoretical foundations of radio altimetry. - M .: Soviet Radio, 1979, p. 173-174.

2. Digital frequency-modulated radio altimeter. USSR copyright certificate No. 717676 by application No. 2545867 of November 22, 1977, cl. G 01 S 9/24.

3. Frequency-modulated radio altimeter. RF patent No. 2133483 by application No. 98107607 of 04/21/1998, class. G 01 S 13/34, p. 5, 16.

4. W. Titze, K. Schenk. Semiconductor circuitry, Moscow: Mir, 1982, p. 105, 286, 288, 298-300.

5. Weissblat A.V. Microwave Switching Devices with Semiconductor Diodes, M.: Radio and Communications, 1987, p. 50-71.

6. Quartz resonators RG-08. Specifications ShchZH) 338068TU, 1976, p.21.

7. Klich S.M. et al. Design of receiving devices, M .: Soviet Radio, 1976, p.186-194.

Claims (2)

1. A frequency-modulated altimeter comprising a clock generator, a direction switch for adjusting the frequency of the transmitter, a source of an analog reference signal connected in series, a digital control unit for the speed of adjusting the frequency of the transmitter, the second input of which is connected to the first output of the clock, the modulator, the second input of which is connected with the output of the transmitter frequency tuning direction switch, a frequency modulated transmitter and a transmitting antenna, in series connected by a receiving antenna, a first mixer, the second input of which is connected to the second output of the transmitter, a differential frequency amplifier and a counter-calculator, the second input of which is connected to the second output of the clock generator, and the first and second outputs are connected respectively to the third input of the digital speed control unit tuning the frequency of the transmitter and the second input of the differential frequency amplifier, the output of which is additionally connected to the fourth input of the digital control unit of the tuning speed often s of the transmitter, characterized in that a comparator is introduced, the first input of which is connected to the second output of the modulator, and a fixed voltage is applied to the second input, the reference frequency generator, pin-switch connected in series, the first and second inputs of which are connected to the first and second outputs of the generator, respectively reference frequencies, and the third input with the first output of the comparator, the second mixer, the second input of which is connected to the third output of the transmitter, a strip amplifier, a detector and a block of logic elements, the second and third inputs of which are respectively connected to first and second output of the comparator, and a fourth input - to the output of the third clock pulse generator, the first output - to the third input-calculating counter and the second output - to the input of the transmitter frequency direction adjustment switch. 2. The frequency-modulated altimeter according to claim 1, characterized in that the block of logic elements contains the first and second elements AND, connected in series with the third element AND, the first element OR, the second input of which is connected to the output of the first element And, and the RS-trigger, the fourth element AND connected in series, the second OR element, the second input of which is connected to the output of the second AND element, and the output to the second input of the RS trigger, the pulse extender connected in series, the input of which is connected to the second output of the first AND element LI, the fifth element And, the second input of which is connected to the third output of the clock generator, and the second trigger, the first output of which is connected to the input of the switch of the direction of tuning the frequency of the transmitter and to the second inputs of the third and fourth elements of And, and the second output to the second inputs of the first and the second elements And, the first inputs of the first, second, third and fourth elements And are connected to the output of the detector, the third inputs of the first and fourth elements And are connected to the first output of the comparator, the third inputs of the second and three of the three elements AND are connected to the second output of the comparator, and the output of the RS-trigger is connected to the third input of the counter-calculator.

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