RU2508557C1 - Radar range-finder with combined frequency modulation and limiting regressive processing - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: method is carried out through the presence of elements that are new with respect to the prototype: a noise generator, the signal of which is combined with a saw-tooth modulating signal, and a limiting regressive processing device as an analyser, which increases accuracy of range-finding and also cuts off the sensitivity function beyond the operating range and provides invariance of operation of the self-contained information system to the type of the target.

EFFECT: high accuracy of finding range to a distributed or faint point object, high noise-immunity beyond the operating range and invariance of operation of the self-contained information system to the type of target.

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Description

The invention relates to the field of near location and can be used in information-measuring tools and systems operating in the modes of active recognition of low-contrast point or distributed targets against the background of broadband and distributed in space interference.

State of the art

The currently existing autonomous information systems (AIS) of near location (BL) with modulation according to the periodic law have a significant drawback, expressed in the spatial periodicity of the range sensitivity function. The frequency of the sensitivity function leads to the fact that the formulation of active or passive interference from distances exceeding the operating range of the AIS reduces the signal-to-noise ratio at the input of the decision path and can cause false alarms of the AIS. There is also the problem of the non-invariance of the existing AIS BL in relation to the type of surface and the amplitude of the received signal.

An analogue of the proposed device is a range lock [4] with an FM, containing a transceiver, the output of which is connected to the channel for highlighting the nth harmonic of the Doppler frequency signal, the output of which is connected to the first input of the analog comparator; and a channel for extracting the n + kth harmonic of the Doppler frequency signal, the output of which through the integrator is connected to the second input of the analog comparator; the comparator output through the amplifier-limiter and the pulse counter is connected to the input of the actuator,

The disadvantage of this device is its low noise immunity, since it is known that a recirculator is a matched filter for a pulse sequence. Thus, the processing method used in this device is not optimal according to the criterion of the maximum signal-to-noise ratio. The device also has a periodic sensitivity function, which can lead to false alarms at ranges greater than the working one.

The closest in technical essence to the developed device is AIS BL with frequency modulation (FM) and spectral processing [1], selected for the prototype.

Figure 1 shows the transmitting part of the AIS BL, consisting of a frequency modulator 1, a generator 2, a transmitting antenna 3, and the receiving part of the AIS BL, consisting of a receiving antenna 4, a microwave processing path 5, a mixer 6, N spectral processing channels and a spectrum analyzer 11, implementing joint signal processing. Each spectral processing channel consists of a frequency multiplier 7, a harmonic filter amplifier 8, a mixer 9, a Doppler frequency detector-amplifier 10; a frequency modulator modulates with a periodic signal. The analyzer determines the distance to the object by calculating the ratio of the amplitudes of the signals at the outputs of the Doppler channels.

The disadvantage of this device is the periodicity of the range sensitivity function and, as a consequence, low noise immunity. The most dangerous are the active interference from powerful relay stations that re-emit the received signal in the direction of the AIS, simulating the signal from the target. When working on point, low-contrast targets, passive interference outside the operating range is also dangerous. Therefore, to ensure the required noise immunity when working on point and distributed targets, it is necessary to form a sensitivity function equal to zero outside the working range of the AIS.

In the proposed device, the noise immunity is proposed to be increased by using the extreme regression processing of the Doppler frequency signal, and the frequency of the sensitivity function should be eliminated using a combined FM sawtooth signal and noise.

Disclosure of invention

The objective of the invention is to increase the accuracy of fixing the range to a distributed or low-contrast point object, as well as providing high noise immunity beyond the working range and the invariance of the AIS with respect to the type of target.

The problem is solved by the presence in the proposed device — a radar range fixer — of elements new relative to the prototype: a noise generator, the signal of which is added with a sawtooth modulating signal, and a device of maximum regression processing as a spectrum analyzer, which increases the accuracy of range fixation and also provides a cutoff of the sensitivity function beyond the working range and the invariance of the AIS with respect to the type of target.

Comparison with the prototype shows that the accuracy of range fixation and the protection of AIS from false alarms by artificial and natural broadband and spatially distributed interference outside the operating range are increased. This allows us to conclude that the proposed solution meets the criterion of "inventive step".

List of figures

Figure 1 is a typical block diagram of a near-radar system (SBRL) with periodic frequency modulation of the emitted signal (prototype);

Figure 2 is a structural diagram of a range lock with continuous frequency modulation according to a sawtooth and random laws;

Figure 3 is a structural diagram of a spectrum analyzer that implements the ultimate regression processing;

Figure 4 - types of normalized range sensitivity functions with periodic (24), noise (23) and combined (22) FM.

The implementation of the invention

Figure 2 shows the transmitting part of the radar range lock, consisting of a sawtooth FM signal generator 1, a noise generator 12 connected through an adder 13 to a controlled carrier frequency generator 2; transmitting antenna 3, and the receiving part of the radar range lock, consisting of a receiving antenna 4, a microwave processing path 5, mixer 6, N spectral processing channels at the Doppler frequency and spectrum analyzer 11, and the second output of the controlled carrier oscillator connected to the heterodyne input of the balanced mixer 6 frequency.

Each Doppler frequency channel consists of a harmonic filter amplifier 8 connected to a mixer 9, the second input of which supplies a signal corresponding to the number of the harmonic channel from frequency multiplier 7, and also from a Doppler frequency filter amplifier 10.

Figure 3 presents the structural diagram of the spectrum analyzer 11. The spectrum analyzer consists of N channels similar to each other, processing Doppler signals received from the receiving unit. Each channel of the spectrum analyzer 11 consists of an inertial detector 14, a divider 15, a subtraction device 16, a threshold device 17, a matching circuit 18; in addition, in each channel, with the exception of the first, after the inertial detector 14, the signal branches and through the divider 15 is fed to the second input of the subtractor 16 of the previous channel. The outputs of all channels are combined by an OR 19 circuit, which, in turn, is connected to the output device 20.

Figure 4 shows a graph of the normalized range sensitivity function for periodic, noise and combined FM. The result of applying the above FM is the suppression of the sensitivity function at ranges determined by the deviation of noise modulation.

The proposed device operates as follows.

The number of channels in the device is determined by the range of fixed ranges and the resolution of the device in range. It is known that the range resolution of sawtooth FM devices depends on the frequency deviation:

$$R=\frac{\mathrm{<figure-callout\; id="2"\; label="c"\; filenames="00000007.png,00000008.png"\; state="\{\{state\}\}">c</figure-callout>}}{2\Delta f,}\left(\mathrm{one}\right)$$

where R is the resolution in range; c is the speed of light; ∆f is the frequency deviation.

For example, in order to evaluate ranges of 3, 6, and 9 meters with an accuracy of 1 m, a three-channel system with a 150 MHz sawtooth FM frequency deviation is required, with channels tuned to the 3rd, 6th, and 9th harmonics, respectively the differential frequency signal received from the mixer 6.

The spectrum of the difference frequency signal at the output of the mixer 6 is a set of harmonics with frequencies that are multiples of the sawtooth FM repetition frequency and shifted due to the Doppler additive. The latter is explained by the frequency of the difference frequency signal received at the output of the mixer 6 with a period equal to the FM period. In each Doppler frequency channel, a harmonic corresponding to the channel number is extracted from this signal using filter 8, then the received signal undergoes a second frequency conversion on mixer 9, and the Doppler frequency signal is extracted from it by Doppler frequency filters 10.

Each channel of the analyzer 11 operates as follows. The inertial detector 14 selects and stores the envelope of the Doppler signal; subtractor 16 calculates the difference between the accumulated signals in the current and next channels, and the signal of the next channel undergoes attenuation with a coefficient equal to k _n β _{n, n + 1} , where n is the number of the channel in question, k _n is the coefficient taking into account the features of the propagation of electromagnetic waves in the atmosphere of the operating range, and attenuation corresponding to the channel m-th harmonic of the signal after the mixer 9 due to additive noise in the _FM, β _{n, n + 1} - attenuation coefficient output from the inertia ion detector n + 1-th channel at its subtraction in subtractor 16 from the signal of n-th channel; threshold device 17 compares the difference with a predetermined threshold; match circuit 18, which is a key that opens when the channel number matches the setting, passes the output signal of the threshold device 77 to the OR circuit 19; the signal of the OR circuit 19 controls the output device 20.

Thus, as soon as at the input of any pair of n and n + 1 adjacent channels of the analyzer Doppler signals appear such that inequality (2) is satisfied, the threshold device 17 of the nth channel will give a single logic level at its output. The resulting logic level can affect the state of the OR circuit 19 only if n and the channel number match according to the range setting.

$$x_n-k_n{\beta }_{n,n+\mathrm{one}}{x}_{n+\mathrm{one}}>U_n.\left(2\right)$$

where x _n , x _{n + 1} - signals at the outputs of inertial detectors 14 channels n and n + 1, respectively; U _n - the threshold value in the device 17.

Inequality (2) according to [2] solves the problem of joint signal detection and recognition. By selecting the magnitude of the coefficients β _{n + 1, n} and k _n it is possible to increase the accuracy of the range fixation; the coefficient k _n takes into account the physical characteristics of the propagation of electromagnetic waves of the operating range in the atmosphere, as well as the attenuation corresponding to the channel number of the mth harmonic of the signal after mixer 6 due to the noise addition in the FM.

As a periodic modulating signal, a sawtooth signal with zero return stroke was selected, the normalized range sensitivity function during spectral processing for which has the form:

$$B_m=\frac{\sin \pi \left[\Delta f\left({\tau }_c-{\tau }_g\right)-m\right]}{\pi \left[\Delta f\left({\tau }_c-{\tau }_g\right)-m\right]},\left(3\right)$$

where B _m is the amplitude of the m-th harmonic of the difference frequency signal; τ _c - signal delay; τ _g - delay signal generator; ∆f- frequency deviation.

This sensitivity function is periodic (figure 4) and can have high values outside the working range of the AIS, which can lead to false alarms. The proposed solution to this problem is to supplement the FM according to the sawtooth law of the noise FM. The sensitivity function in this case according to [3] has the form:

$$F_m\left(\Delta \tau \right)=\frac{\sin \pi \left[\Delta f\cdot \Delta \tau -m\right]}{\pi \left[\Delta f\cdot \Delta \tau -m\right]}\exp \left(-\frac{\mathrm{<figure-callout\; id="2"\; label="\Delta \; \omega \; \xi "\; filenames="00000007.png,00000008.png"\; state="\{\{state\}\}">\Delta \; </figure-callout>}{\omega }_{\xi }^{}{}_2^{}\cdot \mathrm{<figure-callout\; id="2"\; label="\Delta \; \tau "\; filenames="00000007.png,00000008.png"\; state="\{\{state\}\}">\Delta \; </figure-callout>}{\tau }^{}{}^2}{2}\right);\left(\mathrm{four}\right)$$

where ∆ω _ξ is the deviation of the noise modulation frequency; ∆τ is the arrival delay of the probe signal.

By choosing the deviation of the noise modulation frequency, it is possible to control the slope of the attenuation of the sensitivity function in range:

$$\Delta {\omega }_{\xi }{\tau }_0=\alpha \left(5\right)$$

where α through the exponent in (4) determines the attenuation of the sensitivity function at a distance corresponding to the delay of the probe signal equal to τ ₀ .

When developing an AIS BL, it is often required to ensure the smallest dimensions of the device, as well as reduce its power consumption. It should be noted, in this case, that the fixation of n different ranges is possible in the two-channel version of the presented device. In this case, according to the established fixed range, the selection of the sawtooth FM deviation is made while ensuring the frequency of the working harmonic is constant. As an example, table 1 presents the frequency deviation values when operating at ranges of 3, 6, and 9 meters at a constant repetition frequency of a sawtooth FM at 2 MHz.

Table 1 Working harmonics at a constant repetition rate Actuation height, m Repetition Frequency, MHz Working harmonic frequency, MHz Frequency of the adjacent harmonic, MHz Frequency Deviation, MHz 3 2 6 8 150 6 2 6 8 75 9 2 6 8 fifty

Information sources

1. Kogan I.M. Near radar (theoretical basis). - M.: Soviet Radio, 1973. - 272 p.

2. Khokhlov V.K. Detection, recognition and direction finding of objects in the near location. Publishing house of MSTU named after N.E.Bauman, 2003.

3. Pechenkin A.O., Lyapin B.D. Frequency-modulated radio transmitters with spectral processing of the resulting signal. M .: TSNIINTI, 1982 - 121 p.

4. Patent RU 2379701 C1.

Claims (1)

A range radar with continuous emission of a signal with combined frequency modulation according to sawtooth and random laws and limiting regression processing, which includes a transmitting unit consisting of a modulating signal generator, one output of which supplies a harmonic signal with a modulation frequency to the inputs of frequency multipliers tuned to the corresponding harmonics of the Doppler frequency signal in the channels of the spectral processing of the receiving unit, a controlled carrier frequency generator, one output to of which is connected to the transmitting antenna, and the second is connected to the heterodyne input of the balanced mixer of the receiving unit, the receiving unit containing the receiving antenna connected to the input of the microwave processing path, the output of which is connected to the first input of the balanced mixer, to the heterodyne input of which is connected the second output of the controlled carrier generator frequencies, the output of the balanced mixer is connected to the inputs of the spectral processing channels, each of which contains a bandpass filter, connected by an output to the first input of the mixer and to based on the value of the Doppler frequency at the corresponding channel number of the difference frequency signal received from the output of the balanced mixer, the mixer heterodyne input is connected to the corresponding frequency multiplier of the transmitting unit, the mixer output is connected to the input of the Doppler frequency filter amplifier, the output of which is connected to the input of the inertial detector of the corresponding the channel of the spectrum analyzer, and a spectrum analyzer, characterized in that in the transmitting unit the modulating signal generator is a second output connected to the input of the adder, to the second input of which the output of the noise generator is connected, and the output of the adder is connected to the control input of a controlled carrier frequency generator, the spectrum analyzer contains a limit regression processing circuit consisting of N similar channels, while the output of the inertial detector of each (nth ) the analyzer channel is connected to the first input of the subtractor of the same channel, to the second input of which, through the divider, the output of the inertial detector of the next (n + 1st) processing channel is connected; the output of each subtractor is connected to the input of the threshold device, the output of which through the key is connected to the OR circuit, while the key of each channel has the ability to open it with the corresponding installation signal in range.

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