RU2412450C2 - Method of reducing lower boundary of low altitude measurement to zero and design of coherent impulse doppler radioaltimetre to this end - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: proposed impulse Doppler radio altimetre uses simple probing signal with period and duration adjusted by range gate delay. In reception of reflected signal on rage gate delay, program provides linear operating mode of receiver. Before coherent accumulation of signal (Doppler filtration), probing signal leakage signals and low-frequency correlated noises are rejected by digitising quadrature signal components. Digitised signal is correlated with range and crab gate. Correlation results are subtracted on range and crab gate from correlation results on range gate delay. Note here that crab gate advance relative to range gate equal the duration of probing signal.

EFFECT: minimum measured altitude reduction to zero altitude in impulse Doppler radio altimetre.

4 cl, 4 dwg

Description

The present invention relates to radar technology and can be used in pulse-Doppler radar for measurements of short ranges, including working on one antenna in the absence of a temporary isolation of the transmitter-receiver.

The problem of measuring short ranges is associated with the possibility of decoupling the receiver from the probing signal penetrating to its input through the antenna switch in radars operating on one antenna, or through the side lobes of the receiving and transmitting antennas in radars working on two antennas (leak signal), and from sufficiently powerful signals reflected from the structural elements of the aircraft of the aircraft, received by the antenna and referred to the amplitude and phase noise. These powerful signals with insufficient spatial, frequency and temporal isolation can lead to saturation of the receiver with loss of sensitivity, to the impossibility of measuring small delays of the reflected signal.

Known approaches to combat leakage signal, amplitude and phase noise. In the method [1], in a radar with a continuous probing signal (the approach is also applicable to radars with a pulsed probing signal, where the inter-pulse continuous signal is not sufficiently suppressed), a part of the transmitter signal power is selected, the delay of the selected signal is equal to the delay time of the leak signal, hereinafter referred to as the local oscillator, from which the amplitude and phase controlled signal of correction is generated, which is subtracted from the leakage signal at the output of the antenna switch in the directional coupler, the remainder transferred to the video frequency by mixing with the local oscillator, additionally delayed for the duration of the leak signal delay, amplified by power, filtered in the working frequency band, detected and used to control the amplitude and phase of the correction signal, equalize the delay of the local oscillator signal and the leak signal to within a fraction of the wavelength sounding signal.

The disadvantage of this method is the complexity of the implementation, which ensures alignment of the delays of the correction signals and the local oscillator with the delay of the leak signal. The degree of leakage suppression cannot be greater than -20lg (2πfδ _τ ) dB, where δ _τ is the temporary mismatch between the compensation and leakage signals, and f is the carrier frequency of the probe signal. So, at a frequency of 4.7 GHz, for decoupling 60 dB, δ _τ <0.3 · 10 ^-4 ns is required, which is technically very difficult to implement (it requires the selection of the cable length used as a delay with an error of less than 0.004 mm).

The device [2] of a pulsed radio altimeter operating in the mm range employs two spaced antennas (receiving and transmitting), the transmitting antenna emits a pulse signal generated from a continuous reference microwave signal by pulsed modulation of a power amplifier. The reflected signals and the leak signal are received by the receiving antenna, amplified by a low-noise high-frequency amplifier, and transferred to the video frequency by a balanced mixer. The reference signal transmitted through the controlled phase shifter is used as the local oscillator. After the balanced mixer, the received signal is amplified in the amplifier, the first output of which through the control circuit is supplied to the control input of the phase shifter, setting it to the position corresponding to the zero leakage signal at the first output of the amplifier (orthogonality of the signals at the inputs of the balanced mixer). The signal at the second output of the amplifier, corresponding to the useful signal, enters the tracking system in range synchronized by the modulator signal. Tracking result - the measured aircraft height is displayed to the consumer on the display.

The disadvantage of the device [2] is the weak isolation of the transmitter-receiver, which is equal to the sum of the isolation, caused mainly by the spatial separation of the receiving and transmitting antennas and the formation of a heterodyne signal orthogonal to the leakage signal (isolation taking into account amplitude and phase noise no more than 15 dB). As a result, the measurement of small heights without a sufficiently large spatial separation of the antennas in the absence of a temporary isolation (temporary overlap) of the probing and reflected signals is impossible.

In the device of the pulse-Doppler altimeter [3], adopted as a prototype, isolation is provided both by temporal isolation of the transmission and reception of the reflected signal, and frequency, in which the coherent accumulation of the reflected signal is in the frequency range of the useful signal exceeding the upper boundary of the low-frequency correlated noise to the maximum possible Doppler lower repetition rate. Low-frequency correlated noises are caused by powerful reflections of the probe signal from the aircraft structures. The total isolation in the working range of heights, for which the delay of the reflected signal is more than tens of durations of the probe pulse, is not less than the communication potential. Temporal isolation is ensured by the fact that the repetition period of the probe signal is tuned in accordance with the delay of the range gate during search and tracking, while the delay of the decay of the range gate relative to the probe is always equal to half the repetition period. In the device, by functional conversion of the repetition period (range gate delay) into the output estimate, the offset of the readings from the height is taken into account.

The disadvantage of the device [3] are: 1) the impossibility of reducing the minimum measured heights to zero due to insufficient isolation of the receiver and transmitter by the antenna switch and, as a consequence, the use of time and frequency isolation between them, 2) there is no consistent filtering of the reflected signal during tunings of the duration of the probe signal from measured height, which reduces the communication potential (maximum measured height).

The aim of the invention is to reduce the minimum measured height in a coherent pulsed altimeter at low altitudes, operating on a single antenna, to zero while increasing the communication potential with increasing measured height.

This goal is achieved by the fact that in the prototype method, which includes coherent radiation of a simple pulse signal with a height-adjustable duration and repetition period, coherent reception of the reflected signal with the acquisition of quadrature components at the video frequency, coherent signal accumulation at the height gate delay in the Doppler frequency band of the signal, reflected from the Earth, exceeding the upper limit of low-frequency correlated noise, the detection of a quadrature signal by calculating the signal power by quad components, threshold detection, by the results of which and subsequent detection, a height strobe delay code is generated proportional to the height strobe delay relative to the probe when searching and tracking, a functional tabular conversion of the height strobe delay code to the corresponding control codes for the period and duration of the probe pulses, control code for the strobe duration height equal to the duration of the probe pulse, and a code for assessing the measured height, the formation of pulses mode According to the invention, an additional functional tabular conversion of the height gate delay code to a gain control signal of the receiver is provided, which provides reception of the gated signal in a linear mode, formation of a lead gate , ahead of the height gate by the duration of the probing and equal to it, analog-to-digital signal conversion pr a receiver with subsequent rejection of the leakage signals, amplitude and phase noise at the delay of the height strobe in the signals subjected to coherent accumulation, while the rejection of leakage signals, amplitude and phase noise is performed by calculating the correlations of the digitized reflected signal with the height and lead gates, then subtracting the correlation result by the delay of the lead of the lead from the correlation result on the delay of the height gate.

где H_max - максимально измеряемая высота полета ЛА, F_dmax - максимальная частота спектра сигнала на задержке, соответствующей переднему фронту отраженного от Земли сигнала, с - скорость света. Формируются два строба (высоты и упреждения) с длительностью, равной длительности импульса передатчика τ_u, при этом задержка строба высоты относительно импульсов передатчика τ_с пропорциональна коду задержки строба высоты, строб упреждения опережает строб высоты на длительность зондирующего импульса, т.е. τ_у=τ_с-τ_u. В соответствии с кодом задержки строба высоты τ_с по расчетной таблице определяется код и соответствующее ему напряжение регулировки усиления приемника R_yc=f₃(τ_c). Производится когерентный прием отраженных сигналов в полосе 1/τ_{г min} с усилением, переносом на видеочастоту и получением квадратурных составляющих у(t)=s(t-τ)+ξ(f)+ν(t)=Rey(t)+jImy(f), где s(t) - модуляция зондирующего сигнала, ν(t) - низкочастотный коррелированный шум, представляющий сумму сигнала утечки сигнала передатчика в приемник с реакций приемника на сигнал утечки и отраженных от конструкций ЛА сигналов (амплитудные и фазовые шумы), ξ(t) - не коррелированный шум приемника в полосе 1/τ_{u min}. Квадратуры сигнала приемника Rey(t)u Imy(t) оцифровываются, после этого производится режекция сигнала утечки, амплитудных и фазовых шумов, вызванных мощными отражениями сигнала от конструкций ЛА, на задержке строба высоты τ_с путем вычисления: а) корреляции стробов высоты и упреждения с отраженным сигналомThe formation of height estimates according to the method of the invention is as follows. A periodic sequence of pulses is generated that modulates the pulses of the transmitter, the period T = f ₁ (τ _c ) and the duration τ _u = f ₂ (τ _c ) of which are selected according to the calculation table depending on the gate delay code of the height τ _c , while the period satisfies the conditions

where H _max is the maximum measured flight altitude of the aircraft, F _dmax is the maximum frequency of the signal spectrum at a delay corresponding to the leading edge of the signal reflected from the Earth, and s is the speed of light. Two gates (heights and lead) are formed with a duration equal to the transmitter pulse duration τ _u , while the delay of the height gate relative to the transmitter pulses τ _{s is} proportional to the delay gate height code, the lead gate is ahead of the height gate by the duration of the probe pulse, i.e. τ _y = τ _s −τ _u . In accordance with the gate delay code of the height τ _s , the code and the corresponding receiver gain control voltage R _yc = f ₃ (τ _c ) are determined _from the calculation table. The reflected signals are coherently received in the band 1 / τ _{g min} with amplification, transfer to the video frequency and obtaining quadrature components y (t) = s (t-τ) + ξ (f) + ν (t) = Rey (t) + jImy (f), where s (t) is the modulation of the probe signal, ν (t) is the low-frequency correlated noise representing the sum of the leakage signal of the transmitter signal to the receiver from the receiver reactions to the leak signal and the signals reflected from the aircraft structures (amplitude and phase noise), ξ (t) is the uncorrelated receiver noise in the band 1 / τ _{u min} . The squares of the receiver signal Rey (t) u Imy (t) are digitized, after which the leakage signal, the amplitude and phase noise caused by powerful reflections of the signal from the aircraft structures, is rejected by the height-gate delay τ _s by calculating: a) the correlation of the height and lead gates with reflected signal

b) the result of rejection z (τ _c ) as the difference of correlations. signal with height gate and lead gate

z (τ _c ) = u (τ _c ) -u (τ _y ) = S (τ _c ) + Δξ (τ _c ) + Δν (τ _c ),

- сигнальная составляющая,Where

- signal component

и дисперсией

Δν - random narrow-band process with mathematical expectation

and dispersion

V _m (τ _c ) is the modulus of the complex amplitude of the low-frequency correlated noise,

Δξ is a random broadband process with a mathematical expectation m _Δξ = 0 and dispersion

ρ _τnch is the correlation radius of the low-frequency process,

k _τnch ( _Δτ ) is the correlation coefficient between samples of the random process ν (t), spaced Δτ from each other.

отрежектированных сигналов z(n,τ_с) подвергается когерентному накоплению в полосовом фильтре с полосой ΔF и частотой настройки F_o,The degree of rejection of the leakage and amplitude noise ν (t) is estimated to be N≥-20lg2πF low _frequency τ _u , dB, and depending on the spectrum width F _{low frequency} can be more than 80 dB. Sequence of

the rejected signals z (n, τ _s ) is subjected to coherent accumulation in a band-pass filter with a band ΔF and a tuning frequency F _o ,

where ΔF = F _dmax -F _min ,

F _min - the upper frequency of the spectrum of low-frequency noise remaining after rejection. As a result of bandpass filtering, we obtain the accumulated signal

- номер частоты настройки полосового фильтра,Where

- frequency setting number of the band-pass filter,

N =] 1 / TΔF [is the number of accumulated pulses,

][ - the integer part of number.

используется для управления поиском и сопровождением сигнала высоты. При Q=0 производится перестройка кода высоты от минимального τ_cmin до максимального значения τ_cmax. При достижении кода верхнего уровня τ_cmax производится сброс кода в нуль, повтор цикла поиска от τ_cmin до τ_c, где обнаруживается сигнал высоты Q=1. С этого момента, пока существует признак захвата Q=1, управление кодом задержки строба высоты τ_c производится через вычисления сигнала ошибки Δ_co=P_o-P_Z(τ_c) и весового суммирования сигнала ошибки с предшествующим значением кодаBy detecting Z (τ _c ), an estimate of the useful signal power P _Z (τ _c ) = [ReZ (τ _c )] ² + [ImZ (τ _c )] ² , which is compared with the detection threshold, is obtained (calculated). Comparison result

used to control the search and tracking of the height signal. At Q = 0, the height code is rebuilt from the minimum τ _cmin to the maximum value τ _cmax . When the code reaches the upper level τ _cmax , the code is reset to zero, the search cycle is repeated from τ _cmin to τ _c , where a signal of height Q = 1 is detected. From this moment, while there is a capture sign Q = 1, the control of the strobe delay code for the height τ _{c is} performed by computing the error signal Δ _co = P _o -P _Z (τ _c ) and weighting the error signal with the previous code value

τ _s (l) = τ _s (l-1) + k _D Δ _co ,

where k _D is the scale factor.

The code for the delay strobe delay of the height τ _{c is} converted into the codes of the repetition period T = f ₁ (τ _c ), the pulse duration τ _u = f ₂ (τ _c ), the delay strobe delay τ _y = τ _c -τ _u , gain control the signal in the receiver R _yc = f ₃ (τ _s ), the result of measuring the height H = f ₄ (τ _c ), which differs from the code τ _c by the amount of the systematic shift of the readings. In accordance with the codes, modulation pulses of the transmitter are generated with the required repetition period and duration, lead-forward and height-strobe pulses, and the analog voltage of the receiver gain control.

As a prototype of a device that implements the method, taken radio altimeter [3].

The invention is illustrated by a further description and drawings of a coherent pulse-Doppler radio altimeter of small heights, implementing the method:

figure 1 is a structural diagram of a radio altimeter,

figure 2 - structure of the notch filter (7) of the Russian Federation,

figure 3 - the structure of the receiver (2) PR,

figure 4 - structure of the transmitter (3) PRD.

Figure 1 presents the structural diagram of a radio altimeter, which adopted the following notation:

1 - antenna system (AC),

2 - single channel receiver (PR),

3 - transmitter (PRD),

4 - generator repetition frequency and shaper delay gates (PPP),

5 - analog-to-digital Converter (ADC),

6 - digital-to-analog Converter (DAC),

7 - notch filter (RF),

8 - band-pass filter (PF),

9 - detector (D),

10 - threshold detector (software),

11 - block search and tracking (BPS),

12 - functional Converter (FP),

13 - control unit (CU).

As the antenna system 1, two options are proposed. The first option with two transmitting and receiving antennas located in close proximity when the transmitter-receiver isolation is greater than or equal to 30 dB. The second option is with one antenna connected to the input of the receiver and the output of the transmitter through an antenna switch (circulator), which provides isolation of the transmitter-receiver 15-20 dB.

The repetition frequency generator and time delay generator 4 can be performed on the basis of programmable logic integrated circuits manufactured by Altera [4].

A notch filter 7, a band-pass filter 8, a detector 9, a threshold detector 10, a search and tracking unit 11, a functional converter 12, and a control unit 13 can be performed both on the basis of a single on-board processor [5] and individual programmable computing modules. In particular, the functional converter 12 can be implemented as a ROM, in which the table for converting the input code for the delay of the height gate to the corresponding control codes for the period and duration of the probe pulses is encoded into a control code for the length of the height strobe corresponding to the duration of the probe pulse to the receiver gain control code, providing reception of the gated signal in a linear mode, and in the code for assessing the measured height. The control unit 13 performs the function of an interface between the nodes of the device and the consumer.

Pulse-Doppler low-altitude radio altimeter (figure 1) contains an antenna system 1, the output of which is connected to the third (signal) input of the receiver 2, series-connected bandpass filter 8, detector 9, threshold detector 10, search and tracking unit 11, functional converter 12 , the output of the detector 9 is connected to the second input of the search and tracking unit 11, the repetition frequency generator and the time delay driver 4 are connected in series, the transmitter 3, the first output of which is connected to the reception input of the same name 2, the second output of the transmitter 3 is connected to the input of the antenna system, characterized in that an analog-to-digital converter (ADC) 5, a digital-to-analog converter (DAC) 6, a notch filter 7, and a control unit 13 are introduced into it, while the output of the receiver 2 is sequential through the ADC 5 and the notch filter 7 is connected to the input of the bandpass filter 8, the third output of the control unit 13 is connected by a data bus to the input of the repetition frequency generator and the shaper of time delays 4 and the input of the DAC 6, the output of which is connected to the second input of the receiver 2, four the first, third and second outputs of the repetition frequency generator and time delay generator 4 are connected to the second, third and fourth inputs of the notch filter 4, respectively, the fourth output of the repetition frequency generator and time delay generator 4 is connected to the second input of the transmitter 3, the output of the functional converter 12 is connected to the first input of the control unit 13, the second input-output of which is the input-output of the radio altimeter, through which communication with the consumer is carried out.

Figure 2 shows the notch filter 7 and the following notation:

14 - the first correlator (KOR 1),

15 - the second correlator (KOR 2),

16 - subtractive device (WU),

17 - memory (PAM).

In FIG. 2, the notch filter 7 comprises a first correlator 14 connected in series, a subtractor 16 and a memory 17 connected to the output of the notch filter 7, the second correlator 15 is connected to the second input of the subtractor 16, while the first input of the notch filter is connected to the first inputs of the first 14 and the second 15 correlators, the second input of the notch filter 7 is connected to the second input of the memory 17, the third and fourth inputs of the notch filter 7 are connected to the second inputs of the first and second correlators, respectively.

Figure 3 shows the structure of the receiver 2, which adopted the following notation.

18 - preselector (Ps),

19 - low-noise high-frequency amplifier (LNA),

20 - valve (B),

21 - balanced mixer (BSM),

22 - video amplifier (VUS).

Figure 3 the third input of the receiver 2 through a series-connected preselector 18, LNA 19, the valve 20, the balanced mixer 21 and the video amplifier 22 is connected to the output of the receiver 2, the first input of the receiver 2 is connected to the second input of the balanced mixer 21, the second input of the receiver 2 is connected to the second input of the video amplifier 22.

Figure 4 shows the structure of the coherent transmitter 3, in which the following notation:

23 - coherent local oscillator (KG),

24 - directional coupler (BUT),

25 - phase manipulator (FM),

26 - key (C),

27 - power amplifier (PA),

28 - pulse modulator (IM).

As a key 26, a switch [7] can be used.

In Fig. 4, a coherent local oscillator 23 is connected through a series-connected directional coupler 24, a phase manipulator 25, a key 26 and a power amplifier 27 to the second output of the transmitter 3, the second output of the directional coupler 24 is connected to the first output of the transmitter 3, the second input of which is connected to the second ( control) the input of the key 26 and through the pulse modulator 28 with the second input of the power amplifier 27, the first input of the transmitter 3 is connected to the second input of the phase manipulator 25.

The operation of the radio altimeter depicted in figure 1, occurs in the following sequence. The repetition period generator and time delay generator 4 generates pulses at the first output that modulate the period Т _о and the duration τ _and microwave pulses at the second output of the transmitter 3. At the fourth output of the repetition frequency generator and time delay generator 4, a meander is generated that manipulates the microwave pulse phase at the third the output of the transmitter 3 to 0 and π / 2, with a period of T = 2T _about . The meander is fed to the second input of the transmitter 3 and to the second input of the notch filter 7. In the notch filter 7, the meander is used to synchronize the reception of quadratures of the signal; arriving through ANN 5 from the output of a single-channel receiver 2. At the third and second outputs of the repetition frequency generator and time delay shaper 4, height and lead gates of duration τ _and equal to the duration of the probe signal are generated, which arrive at the third and fourth inputs of the notch filter, respectively.

Advance of the anticipatory gate τ _in relation to the strobe of height τ _s is equal to the duration of the probe pulse τ _and . From the first output of the transmitter 3 to the same input of a single-channel receiver 2 receives the frequency of the coherent local oscillator. The gain control voltage of the single-channel receiver 2 is supplied from the DAC 6 to the second input of the single-channel receiver 2 and corresponds to the value of the delay of the height gate τ _s relative to the probing signal. Microwave pulses from the second output of the transmitter 3 are fed to the input of the antenna system 1 and emitted by it in the direction to the Earth. The reflected signal is received by the antenna system 1 and fed to the third input of a single-channel coherent receiver 2, where, after amplification and conversion to the video frequency, it passes through the ADC 5 to the first input of the notch filter 7 shown in Fig.2. In correlators 14 and 15, the digitized signal of a single-channel receiver is accumulated in the gates of height and lead, respectively, with the values Re u (n, τ _s ) and Re u (n, τ _y ) being obtained in an even repetition period (“0” meander value at the second input of the notch filter) and the values of Im u (n, τ _c ) and Im u (n, τ _y ) in an odd repetition period (“1” meander value at the input of the notch filter). The subtractor 16 sequentially with time division during the meander period T = 2T _о forms Re z (n, τ _c ) and Im z (n, τ _c ), which are stored in the memory 17. The addresses Re and Im of the parts in the memory 17 are modified meander value at its second entrance. The output signal of the memory 17 of the notch filter 7 enters the band-pass filter 8, where the useful signal is coherently accumulated at a frequency F _o in the band ΔF to obtain a signal Z (τ _c ). The detector 9 by quadratures Z (τ _s ) calculates the power of the useful signal P _Z (τ _c ), which is compared with the detection threshold in the threshold detector 10. The result of detection Q controls the operation mode of the search and tracking unit 11, the synchronization of the search and tracking unit 11 pulses of the generator the repetition rate and the shaper of time delays 4 is not shown. At Q = 0, the height code is rebuilt from τ _cmin to τ _cmax . When the code τ _c reaches the upper level τ _cmax , the code is reset to zero, the search cycle is repeated from τ _cmin to τ _c , where a signal of height Q = 1 is detected. From this moment, while Q = 1 exists, the output code τ _c of the search and tracking unit 11 is controlled by the signal of the detector 9 P _Z (τ _c ). The functional converter 12 according to the table converts the gate delay code of the height τ _c to the codes of the repetition period T = f ₁ (τ _c ), the pulse duration τ _u = f ₂ (τ _c ), the lead gate delays τ _у = τ _c -τ _u , control signal amplification in a single-channel receiver 2 R _yc = f ₃ (τ _c ) and the result of measuring the height H = f ₄ (τ _c ), issued through the control unit 13 to the repetition period generator and time delay generator 4, DAC 6 and the consumer, respectively.

The operation of the single-channel coherent receiver 2, shown in figure 3, occurs as follows. The signal from the output of the antenna system 1 through the third input of the single-channel receiver 2, serially connected preselector 18, LNA 19 and the valve 20 is fed to the first input of the balanced mixer 21. The heterodyne frequency equal to the frequency of the probing signal comes to the second input of the balanced mixer 21. The balance mixer 21 transfers the received signal to the zero intermediate frequency, which is further amplified in the video amplifier 22 and fed to the output of the single-channel receiver 2. The gain of the single-channel receiver 2 is controlled in the video amplifier 22 by an external analog signal arriving at its second input.

The operation of the transmitter 3, shown in figure 4, is as follows. A coherent local oscillator 23 generates a continuous microwave signal whose frequency is stabilized and corresponds to the carrier frequency of the probe signal. Part of the signal power through the directional coupler 24 is output to the first output of the transmitter 3 as a local oscillator. The main power of the coherent local oscillator 23 through a directional coupler 24 is supplied to the first input of the phase manipulator 25, controlled by an external signal (a meander at the output of the repetition frequency generator and time delay shaper 4) supplied through the first input of the transmitter 3. The phase is manipulated at 0 and π / 2 . From the phase-manipulated continuous microwave signal with a key 26 controlled by an external pulse signal, a signal of duration τ is cut out _and , after amplification in the power amplifier 27, is fed to the second output of the transmitter 3. The power amplifier 27 is modulated by a pulse modulator 28, controlled like the key 26 , a common signal of duration τ _and coming to the second input of the transmitter 3

The manufactured model of the radio altimeter and the tests carried out confirmed the claimed result - reducing the minimum of the measured aircraft altitudes to zero.

The technical advantage of the proposed method and device over the prototype is the ability to reduce the minimum measured height to zero with a high level of leakage of the probe signal to the receiver through the antenna system and the absence of temporary isolation of reception and transmission, in the presence of a high level of signals reflected from the stationary structures of the aircraft (amplitude and phase low-frequency noise).

The proposed solution allows you to: a) significantly reduce the separation of the receiving and transmitting antennas of the altimeter up to their touch (option with two antennas), or (the second option with a slightly lower isolation of the transmit and receive channels) use a common antenna for transmission and reception associated with the receiver and the transmitter through the antenna switch (circulator), b) significantly simplify the acquisition of quadrature components of the signal due to the joint use of a single-channel coherent receiver and a transmitter, the microwave signal of which eresperiodno manipulated in phase 0 and π / 2. This ensures the identity of the quadrature reception channels in amplitude and phase, negligible error in the orthogonality of the quadrature components of the signal at the output of the receiver with the simplicity of technical implementation. By reducing the aircraft due to the programmed increase in the spectral width and the duty cycle of the probe signal to the maximum allowable, the average radiation power is reduced over the entire range of working heights (in the prototype it is constant in the range from 5000 to 50 feet), the secrecy of the radio altimeter increases accordingly, c) correlation reception the signal in the strobe, consistent with the duration of the probing, allows you to increase the communication potential of the radio altimeter, respectively, to raise the ceiling of the measured heights in comparison with the prototype.

Based on the above descriptions and drawings, the proposed device altimeter that implements. the proposed method can be manufactured using well-known components of technological equipment known in the electronics industry and used on high-speed aircraft that do not use the hovering mode to ensure low-altitude flight above the Earth's surface.

Claims (4)

1. A method of reducing the lower boundary of measurement of small heights to zero, including coherent radiation of a simple pulse signal with a height-adjustable duration and repetition period, coherent reception of the reflected signal to obtain quadrature components at the video frequency, coherent signal accumulation at the height gate delay in the Doppler frequency band of the signal reflected from the Earth, exceeding the upper limit of low-frequency correlated noise, the detection of a quadrature signal by calculating the power of by quadrature components, threshold detection, by the results of which and subsequent detection, a height strobe delay code is generated proportional to the strobe delay relative to the probing signal during search and tracking, functional conversion of the height strobe delay code to the corresponding control codes for the period and duration of probe pulses, duration control code the height gate corresponding to the duration of the probe pulse and the code for assessing the measured height, modulation pulses of the probe signal and the height gate with a period and duration corresponding to the control codes obtained as a result of the functional transformation, characterized in that an additional functional conversion of the height gate delay code to the receiver gain control signal is introduced, which ensures the reception of the gated signal in linear mode, formation of the strobe lead ahead of the height gate by the duration of the probing signal and equal to it, analog-to-digital signal conversion at receiver with subsequent rejection of leakage signals, amplitude and phase noise at the delay of the height gate in the signals subjected to coherent accumulation. 2. The method according to claim 1, characterized in that the rejection of leakage signals, amplitude and phase noise is performed by calculating the correlations of the digitized reflected signal with the height gates and lead, then subtracting the result of the correlation on the delay of the lead ahead from the correlation on the delay of the height gate. 3. A pulsed Doppler low-frequency radio altimeter that implements the method according to claim 1, comprising an antenna system, the output of which is connected to the third input of the receiver, a series-pass bandpass filter, a detector, a threshold detector, a search and tracking unit that generates a height strobe delay code, functional a converter that converts the height gate delay code into the corresponding codes for the period and duration of the probe pulses, the height strobe duration, the detector output is connected to the second input of the search unit and the leads, series-connected generator of the frequency of repetition and the formation of time delays, a transmitter, the first output of which is connected to the same input of the receiver, microwave (microwave) pulses from the second output of the transmitter are fed to the input of the antenna system, characterized in that an analog-to-digital converter is introduced into it ( ADC), digital-to-analog converter (DAC), notch filter and control unit, while the functional converter additionally converts the height strobe delay code to the control code receiver gain, the receiver output is connected through an ADC and a notch filter to the input of the bandpass filter, the third output of the control unit is connected via a data bus to the input of the repetition frequency generator and the formation of time delays and to the input of the DAC, the output of which is connected to the second input of the receiver, the fourth, third and the second outputs of the frequency generator of repetition and the formation of time delays are connected to the second, third and fourth inputs of the notch filter, respectively, the fourth output of the frequency generator the creation and generation of time delays is connected to the second input of the transmitter, the output of the functional converter is connected to the first input of the control unit, intended for the output of the corresponding conversion results to the frequency generator of repetition and the formation of time delays, in the DAC and the consumer, the second input-output of the control unit is the input the output of the radio altimeter through which communication with the consumer is carried out. 4. The pulsed Doppler low-altitude radio altimeter according to claim 3, characterized in that the notch filter comprises a first correlator, a subtractor and a memory connected to the output of the notch filter in series, the second correlator connected to the second input of the subtractor, the first input of the notch the filter is connected to the first inputs of the first and second correlators, the second input of the notch filter is connected to the second input of the memory, the third and second inputs of the notch filter are connected to the second inputs of the first and second correlators, respectively.

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