RU1841344C - A method for creating flickering interference for radars and seekers with continuous or quasi-continuous radiation using target selection by Doppler frequency shift - Google Patents

Abstract

FIELD: radio countermeasures.

SUBSTANCE: invention relates to the field of radio countermeasures, in particular, to methods for creating flickering interference to radar stations (RLS) and homing heads (GOS), using continuous or quasi-continuous radiation and target selection by Doppler frequency shift. In the claimed method of creating flickering interference radar and seeker with continuous or Quasi-continuous radiation is simultaneously created on the object accompanied by the radar, leading to interference up to speed, and on the other object - signals with false Doppler frequencies by modulating the retransmitted signal in frequency with a sinusoidal voltage, while the interference power at the end of each half-cycle is reduced from maximum to zero.

EFFECT: technical result is to provide the possibility of alternate transfer of the seeker and radar to track each of the flickering targets.

1 cl, 1 dwg

Description

This proposal relates to the field of radio countermeasures.

Until now, flickering interference of radars and seekers using continuous or quasi-continuous radiation and circuit selection by speed (by Doppler frequency shift) was created as follows [1]:

- relay-type jamming stations installed on two or more objects moving in the same formation intermittently (non-synchronously or synchronized in antiphase) re-radiate amplified signals from radars irradiating the object, modulating them in frequency with noise, the spectrum of which is somewhat wider than the possible difference in Doppler frequency increments for signals reflected from different building objects. At the same time, in those periods of time when the absence of re-emission from the object being tracked by the radar coincides with the presence of re-emission on the neighboring object of the formation (and provided that the interference power at the input of the radar receiver exceeds the power reflected from the tracked object), the radar switches from tracking at the corners of the first target to accompany the second.

The disadvantage of this method is sharply increased, in relation to other types of interference, the requirements for the energy of the interference station. Indeed, if for the majority of interferences created from one point to systems with continuous radiation, the energy sufficiency condition is determined by the relation

where K _p is the loss factor due to the mismatch between the polarization of the interference and the radiation of the radar;

S _CR - the area of the receiving antenna of the repeater;

K _y - repeater gain;

- коэффициент направленности передающей антенны ретранслятора;

- directivity factor of the transmitting antenna of the repeater;

δ - reflective surface of the object - target;

K - the excess of the interference signal over the reflected one for the generally accepted method of creating a flickering interference. The energy requirements are determined by the ratio

where A _θ - the ratio of the maximum gain of the radar antenna (in terms of power) to its gain in the direction of the object, trying to cause the transition of the angular support to itself;

B _f is the ratio of the width of the interference spectrum to the bandwidth bandwidth of the selective gate of the radar.

Relation (2) is valid for all ranges from the radar, at which the relay path has a linear amplitude characteristic.

With B _f =3÷5 and both targets being within the main lobe of the radar antenna diagram (A _θ =3÷10) to create flickering interference, it was required, ceteris paribus, to increase the repeater gain by 15÷25 dB, and for large bases between objects (locating one of the objects outside the main lobe A _θ =20÷100), the required increase in K _y reaches 30÷45 dB, which is practically unrealizable.

A method is proposed for creating flickering interference for radars and seekers with continuous and quasi-continuous radiation, using target selection by speed, requiring less energy potential (gain) from interference repeaters or allowing, with equal energy potentials, to significantly increase the flicker base (distance between protected objects - interference carriers). Its fundamental difference from the method described above lies in the fact that with it the radar (or GOS) is forced to stop tracking one of the targets and switch to tracking another with interference radiation from the target that was previously accompanied; in this case, interference signals are received by the maximum of the radiation pattern, and their spectrum is such that it completely passes through the selective strobe of the radar (GOS), i.e. for them, the energy ratios are valid, which are common for most types of relay interference and described by expression (I). The desired effect is achieved as follows: the object followed by the radar creates a stealing noise in terms of speed (Doppler frequency), and after the output of the reflected signal from the radar strobe, the power of the stealing signal gradually decreases to zero. Due to this, the radar is forced to switch to the speed (frequency) search mode at the maximum sensitivity of the receiving devices. At the same time, on the second object, the retransmitted signal is modulated in frequency by a sinusoidal voltage, due to which several frequency-shifted interference signals appear on both sides of the signal reflected from the second object.

The value of the frequency shift is chosen so that the frequencies of the interference signals from the second object cover on both sides the frequency of the signal reflected from the first object. The frequency selection system, being in the search mode with maximum sensitivity, "stumbles" on the interference signals of the second object, captures them, and thereby transfers the radar or seeker to tracking at the corners of the second object.

(R - расстояние от объекта до РЛС).Although the interference signals from the second object at the output of the radar or seeker are less than from the first (due to power scattering over the spectrum and its reception along the slopes or side lobes of the radar antenna diagram), their effectiveness is determined not by expression (2), but by the excess of the interference signal over threshold sensitivity of the locator in frequency search mode. At the maximum range of the radar Rm, these conditions are equivalent, however, as the object approaches the radar, the magnitude of the interference signal at the input of the radar, ceteris paribus, grows proportionally

(R is the distance from the object to the radar).

Thus, with the proposed flickering method, as objects approach the radar, the distance between objects at which flickering interference is possible increases, while with the previously used method, it quickly falls.

In the currently known domestic and foreign GOS, the search by frequency during an attack from the front hemisphere is carried out from the upper frequencies to the lower ones and starts either from the edge, or from the point of loss of the target, or from an arbitrary random point of the Doppler frequency range. Ensuring successive capture for tracking of each of the targets in all the indicated modes of searching for signals in the GOS is possible only with a combination of speed-stealing interference with false Doppler frequencies.

The amount of drift in speed (Doppler frequency - ΔFuv), necessary only to disrupt the tracking of the reflected signal by the radar or seeker speed selector, should lie within

where ΔFstr is the bandwidth of the selective gate.

On fig. 1 shows the sequence of emission of interference signals from interference carriers during synchronous flicker with a flicker period equal to Tm. The open boxes show the behavior of the velocity selector, which starts at the end of the Doppler range after losing the target. The shaded lines show the movement of the selector, the search in which starts from the point of loss of the target. When searching from a random point, the hit of the speed strobe on one or another component of the spectrum of each of the interfering stations is equally probable and therefore is not given.

The wavy lines show the position of the Doppler frequencies of the signals reflected from the targets. Dashed and dash-dotted lines show the position of a series of interfering signals at false Doppler frequencies.

The interference power is reduced (until the path is completely blocked) after condition (I) is met according to the law (see Fig. 1b, 1c).

On fig. 2 shows a block diagram of the implementation of this method of creating flickering noise.

The sawtooth oscillation generator (3) is connected through a phase inverter (5) and a switch (6) to the TWT helix (1), where it performs phase modulation of the retransmitted signal, creating an interference spectrum according to Fig. 1.

The generator (3) in the mode of creating a speed noise is modulated by the control voltage passing through the switch 8 from the generator of control oscillations (7), which changes the frequency of the generator (3) according to the law of drift. In this mode, from the output of the switch (6) to the TWT, sawtooth oscillations arrive, producing phase modulation of the retransmitted signal with a modulation index of 2π - a smooth frequency shift (steer) [1].

Generator (3) also creates false Doppler constant frequency components. In this mode, instead of the control voltage from the generator (7), a constant voltage (9) is connected to the sawtooth oscillation generator (3) using a switch (8). At the same time, the trigger (4) is launched in the counting mode by the reverse pulses of the generator (3). The latter switches the switch (6), as a result of which triangular sawtooth oscillations (3) are formed at the output of the latter.

It is known that with phase modulation by a triangular voltage with a modulation index of 2π, a symmetrical spectrum is formed, consisting of 4 components and a suppressed carrier. These components are false Doppler frequencies.

If the switch (8) is controlled by a voltage of the "meander" type with a period of 50+300 Hz, then the drift and false Doppler frequencies on the speed selector of the radar and seeker act as if they exist simultaneously. As a switching voltage, you can use the "meander" voltage of the sliding frequency, while simultaneously creating interference with the goniometric coordinator of the radar and seeker with conical space scanning.

The power reduction (until complete blocking) in the relay path is performed synchronously with the withdrawal in the power reduction circuit (12), from which a voltage is applied that changes the power at the TWT-2 output according to the required law (Fig. 1b, c).

The proposed method can also be applied in the non-synchronous flicker mode.

Claims (1)

A method for creating flickering interference to radar stations (RLS) and missile homing heads (GOS) with continuous or quasi-continuous radiation, using target selection by Doppler frequency shift, characterized in that, in order to alternately transfer the GOS and radar to track each of the flickering targets, simultaneously they create on the object followed by the radar a stealth interference in speed, and on the other object - signals with false Doppler frequencies by modulating the retransmitted signal in frequency with a sinusoidal voltage, while the interference power at the end of each half-cycle is reduced from maximum to zero.

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