RU2731875C1 - Adaptive antenna array for bistatic radar system - Google Patents

Abstract

FIELD: radar ranging.

SUBSTANCE: present invention relates to radar ranging and can be used to create a bistatic radar system using a probing radio signal of a ground-based transmitter as a signal for illuminating aerial targets. Disclosed is an adaptive antenna array for a bistatic radar system, consisting of an antenna array having N elements, a beam-forming circuit having N units of weight coefficients, an adder, an adaptive processor, which consists of a gradient generation unit, a graduation unit, a gain calculation unit, a weighting coefficient generating unit, a unit for normalizing weight coefficients, a delay unit having links to each other, outputs of N elements of the antenna array are connected to inputs of N units of weight coefficients of the diagram-forming circuit and to inputs of the unit for generating a gradient, outputs of the gradient forming unit are connected to inputs of the gradation rating unit, outputs of the gradation unit of the gradient are connected to inputs of the unit for generating weight coefficients and with a unit for calculating the gain, output of amplification unit is connected to input of weight coefficients generating unit, one outputs of the unit for generating weight coefficients are connected to the unit for normalizing weight coefficients, other outputs are connected to delay unit, outputs of which are connected to other inputs of gradient formation unit, outputs of unit for normalizing weight coefficients are connected to inputs of N units of weight coefficients, outputs of which are connected to adder, output of adder is connected to one of inputs of unit of gradient formation.

EFFECT: high rate of adaptation and low dispersion of residual noise at low signal amplitude reflected from the air target, to amplitudes of the probing signal from the radio transmitter and signals reflected from the large-size objects.

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Description

The proposed invention relates to radar and can be used to create a bistatic radar system (radar), using the sounding radio signal of a ground transmitter as a signal to illuminate air targets.

When radar of small-sized mobile air targets of a bistatic radar, the radar receiver receives the reflected signal from the air target, the probing signal of the radar transmitter and signals reflected from large-sized objects located in the coverage (operation) of the bistatic radar. At the same time, the level of the probing signal from the radio transmitter and signals reflected from large objects significantly exceed the level of the signal reflected from the air target. In fact, these signals are interference that mask a weak signal reflected from the target, which does not allow detecting the presence of an air target and determining the parameters of its movement. Thus, in a bistatic radar, an urgent problem arises to compensate for the sounding signal from the radio transmitter and signals reflected from large-sized objects.

Known bistatic radar [1], consisting of a transmitter and a receiver. The work of the radar is to emit a sounding radio signal by the transmitter, measure the distance to the air target and the direction to the air target. But in this bistatic radar, there is no possibility of compensating for the sounding radio signal from the radio transmitter, which can come from the transmitter directly to the receiver, and signals reflected by large objects.

Known adaptive antenna array [2], containing N antenna elements connected through complex weight multipliers with the inputs of the common adder, N adaptive circuits, the first inputs of which are connected to the outputs of the corresponding antenna elements, and the second inputs - to the output of the common adder. The first outputs of the adaptive loops are connected to the corresponding inputs of the complex weighting multipliers. The first and second inputs of the output power maximization unit are connected, respectively, with the first and second outputs of the adaptive circuits, and its outputs - with the corresponding inputs of the adaptive circuits. The Adaptive Antenna Array (AAP) has a greater immunity to interference signals regardless of their frequency band.

The disadvantage of this AAA is that it does not provide compensation for the sounding signal from the radio transmitter and signals reflected from large objects in the bistatic radar.

The closest analogue (prototype) is an adaptive antenna array [3, p. 13, fig. 1.1], which includes N antenna elements, a diagrammatic circuit consisting of N blocks of complex signal weighting and an adder, and an adaptive processor. Complex weighing is performed using devices with quadrature channels. One of the outputs of each antenna element is connected to the input of the corresponding complex signal weighting unit, the outputs of the complex signal weighting units are connected to the inputs of the adder, the output of which is the output of the adaptive antenna array. The second outputs of the radiators are connected to the inputs of the adaptive processor, the control input of which is connected to the output of the adaptive antenna array. The signal outputs of the adaptive processor are connected to the control inputs of the complex signal weighting units. In the adaptive processor, a vector of weight coefficients is formed

W (t) = W (t-1) + ks (t) [X * (t) -W (t) s * (t)],

where ⁿ is the operator of transposition and complex conjugation,

t = 1, 2, ... - discrete time readings,

* - operator of complex conjugation

k - scalar gain,

s (t) - signal at the output of the antenna array,

- вектор весовых коэффициентов w₁(t), w₂(t), …, w_N(t),

- vector of weight coefficients w ₁ (t), w ₂ (t), ..., w _N (t),

- вектор входных сигналов x₁(t), x₂(t), …, x_N(t).

- vector of input signals x ₁ (t), x ₂ (t),…, x _N (t).

The constant k characterizes the gain of the adaptation loop, which affects the stability and speed of optimization. Obviously, for a fixed value of k, it is impossible to simultaneously provide a high adaptation rate and a small dispersion of residual noise. In order to satisfy these two contradictory conditions, it is necessary to have a large coefficient k in the transient mode and relatively small in the steady-state adaptation process.

The technical objective of the invention is to provide a high adaptation rate and low dispersion of residual interference with small ratios of the amplitude of the signal reflected from the air target to the amplitudes of the sounding signal from the radio transmitter and signals reflected from large objects.

The essence of the invention of an adaptive antenna array for a bistatic radar system is illustrated by the following figures. FIG. 1 shows a block diagram of the AAP, FIG. 2 shows the results before compensation: a) the responses of the matched filter connected to the output of the adder to the probing signal u ₁ from the radio transmitter, to the signals u ₂ and u ₃ reflected from large objects, and to the signal u _u reflected from the air target, in lack of compensation for powerful signals; b) AAR radiation pattern; in fig. 3 shows the results after compensation: a) responses of the matched filter connected to the output of the adder to the probing signal u ₁ from the radio transmitter, to the signals u ₂ and u ₃ reflected from large-sized objects, and to the signal u _u reflected from the air target after compensation powerful signals; b) AAR radiation pattern.

An adaptive antenna array for a bistatic radar system consists of an antenna array 1 consisting of N antenna elements ln (n = 1, 2, ..., N), a diagramming circuit 2, consisting of N blocks of weight coefficients 2.n, an adder 3, an adaptive processor 4, consisting of a gradient generating unit 4.1, a gradient normalization unit 4.2, a gain calculation unit 4.3, a weight coefficient generation unit 4.4, a weight coefficient normalization unit 4.5, a delay unit 4.6.

The outputs of the elements 1.n of the antenna array 1 are connected to the inputs of the blocks of weighting coefficients 2.n of the diagramming circuit 2 and to the inputs of the block for generating the gradient 4.1.

The outputs of the block for generating the gradient 4.1 are connected to the inputs of the block for normalizing the gradient 4.2.

Outputs of the block for normalizing the gradient 4.2 are connected to the inputs of the block for generating weight coefficients 4.4. and with a gain calculation unit 4.3.

The output of the block for calculating the gain of 4.3 is connected to the input of the block for the formation of weight coefficients 4.4.

Some outputs of the unit for generating the weight coefficients 4.4 are connected to the unit for normalizing the weight coefficients 4.5, other outputs are connected to the delay unit 4.6, the outputs of which are connected to other inputs of the unit for forming the gradient 4.1.

The outputs of the block for normalizing the weight coefficients 4.5 are connected to the inputs of the blocks of the weight coefficients 2.n, the outputs of which are connected to the adder 3.

The output of the adder 3 is the AAP output and is connected to one of the inputs of the gradient shaping unit 4.1.

An adaptive antenna array for a bistatic radar system works as follows. Each element ln of the antenna array 1 receives input signals x _n (t), n = l, 2, ..., N, where N is the number of elements of the antenna array 1, in the form of an additive mixture of M signals u _m from radio emission sources and signals, reflected from various objects, which are then fed to the blocks of weight coefficients 2.n of the diagram-forming circuit 2 and to the block of gradient formation 4.1 of the adaptive processor 4.

Having entered the blocks of weight coefficients 2.n of the diagram-forming circuit 2, the input signals x _n (t) are multiplied by the weight coefficients w _n (t), n = 1, 2, ..., N and are transferred to the adder 3 where the output signal s (t ) = W ^H (t) X (t).

The gradient shaping unit 4.1 receives a vector of input signals X (t), an output signal s (t), and a vector of weight coefficients W (t-1) from the output of unit 4.4, delayed by one time sample in a delay unit 4.6, on the basis of which the gradient G (t) = s (t) [X * (t) + W (t-1) s * (t)] of the mean square E {s ² (t)} of the output signal s (t) is formed.

, где

- норма градиента, после чего нормированный градиент G_H(t) передается в блок расчета коэффициента усиления 4.3 и в блок формирования весовых коэффициентов 4.4.The generated gradient G (t) from the gradient formation block 4.1 enters the gradient normalization block 4.2. The gradient normalization block 4.2 is used to normalize the gradient

where

- the norm of the gradient, after which the normalized gradient G _H (t) is transmitted to the block for calculating the gain factor 4.3 and in the block for generating the weight factors 4.4.

Based on the normalized gradient G _H (t) received in block 4.3 in the current time sample t, and the values of the normalized gradient G _H (t-1) stored in block 4.3 and the value of the gain k (t-1) in the previous time count t- 1, the current value of the gain is calculated

where 0 <α <1 is a constant that provides the rate of change of the gain k (t), Re is the real part of the complex number, which is transmitted to the unit for generating weight coefficients 4.4.

The unit for generating weight coefficients 4.4, having received the normalized gradient G _H (t) and the gain k (t), based on the stored in it the previous value of the vector of weight coefficients W (t-1), produces the current estimate of the vector of weight coefficients W (t) = W (t-1) + k (t) G _H (t), which is transferred to the weight coefficient normalization unit 4.5. and into the delay block 4.6.

The delay unit 4.6 provides a delay of the vector of the weight coefficients W (t) by one time sample and the output of the delayed vector of the weight coefficients W (t-1) to the gradient formation unit 4.1.

где

- норма вектора весовых коэффициентов, после чего весовые коэффициенты w_n(t) (n=1, 2, …, N) передаются в блоки 2.n весовых коэффициентов диаграммообразующей схемы 2, где происходит умножение входных сигналов x_n(t) на соответствующие весовые коэффициенты w_n(t), после чего они передаются в сумматор 3 для формирования выходного сигнала

In the weight coefficient normalization block 4.5, the weight coefficient vector is normalized

Where

- the norm of the vector of weight coefficients, after which the weight coefficients w _n (t) (n = 1, 2, ..., N) are transferred to the blocks 2.n of the weight coefficients of the diagram-forming circuit 2, where the input signals x _n (t) are multiplied by the corresponding weight coefficients w _n (t), after which they are transferred to adder 3 to form the output signal

Thus, for the operation of the adaptive processor 4, only the vector of input signals x ₁ (t), x ₂ (t), ..., x _n (t) from the channels of the antenna array 1 and the output signal s (t) are required.

When simulating the operation of an adaptive antenna array for a bistatic radar system, a sounding signal u ₁ from a radio transmitter, signals u ₂ , u ₃ reflected from large objects, and a signal u _c reflected from an air target were set.

Antenna array 1 - annular, with a radius of 0.6 m, contains 7 antenna elements with a circular directivity pattern, located evenly on the circumference.

As the probing signal u ₁ , a phase-shift keyed signal with spreading of the spectrum with an M-sequence of 1023 samples with 10 digital samples per sample is used. The carrier frequency of the signal is 300 MHz. The amplitude of the probing signal u _{1 of} direct propagation at the input of the antenna array 1 is equal to 1000. The amplitudes of the two signals u ₂ and u ₃ reflected from large objects are equal to 500 and 150. The amplitude of the signal u _c , reflected from the air target, is equal to 20, which is 50 times less than the amplitude of the probing signal u _{1 of} direct propagation and 25 and 7.5 times, respectively, less than the amplitudes of the signals u ₂ and u ₃ reflected from the surrounding objects. The root-mean-square value of the additive noise in the antenna array channels is 20, i.e. the noise level is comparable to the level of the signal reflected from the air target.

Directions of arrival of radio signals are: 30 ° - direction of arrival of a direct sounding radio signal, 60 ° and 90 ° - directions of arrival of radio signals reflected from surrounding objects, 120 ° - direction of arrival of a signal reflected from an air target.

The radar signal reflected from the air target is delayed relative to the direct propagation radar signal by 5870 counts, the radio signals reflected from the objects are delayed relative to the direct sounding signal by 1170 and 3130 counts.

FIG. 2a shows the responses of the matched filter connected to the output of the adder 3 of the adaptive antenna array, to the probe signal u ₁ , to the signals u ₂ , u ₃ reflected from large objects, and to the signal u _c reflected from an air target, in the absence of their compensation. FIG. 2b shows the radiation pattern of the antenna array 1 in the initial state (the weights are equal to 1), expressed in decibels. This diagram is circular at about 9 dB.

FIG. 3a shows the results of compensation of the probing signal and reflected signals from large-sized objects at the output of the matched filter, as well as the result of separating the signal reflected from the air target u _c . FIG. 3b shows the post-compensated AAR pattern, expressed in decibels. In this case, the constant α providing the rate of change of the coefficient k (t) was equal to α = 0.15.

From FIG. 3b, it can be seen that in the directional pattern in the directions to the sounding signal, as well as to signals reflected from large objects, deep, about 50 dB, dips are formed. In the direction to the signal reflected from the air target u _c (120 °), the level of the radiation pattern decreased slightly relative to the level for the case without compensation. In this case, the adaptation process ends during the time of receiving the first M-sequence of the signal.

Thus, the proposed adaptive antenna array for a bistatic radar system allows:

- to compensate for the direct sounding signal and signals reflected from stationary objects, significantly exceeding the level of the signal reflected from the target;

- to select a useful signal reflected from the target.

A source of information.

1. Kovalev F.N. V.V. Kondratyev Features of the goniometric-rangefinder method for determining the location of the target in translucent bistatic radars. Journal of Radioelectronics: electronic journal. No. 4, 2014.

2. Patent 2099838 RF, IPC H01Q 21/00. Adaptive antenna array / A.V. Kolinko and others (RF); Military Academy of Communications (RF) - No. 9595114216; Stated 08/08/1995; Publ. 12/20/1997 - 14 p .: 12 ill.

3. Monzingo R.A., Miller T.U. Adaptive antenna arrays. Introduction to theory / Per. from English. M .: Radio and communication, 1986 .-- 448 p.

Claims (1)

An adaptive antenna array for a bistatic radar system, consisting of an antenna array with N elements, a diagramming circuit with N weight coefficient blocks, an adder, an adaptive processor, characterized in that the adaptive processor consists of a gradient formation block, a gradient normalization block, a gain calculation block , a block for generating weight coefficients, a block for normalizing weight coefficients, a delay block that have connections with each other, the outputs of N elements of the antenna array are connected to the inputs of N blocks of weight coefficients of the diagram-forming circuit and to the inputs of the block for forming a gradient, the outputs of the block for forming a gradient are connected to the inputs of the block for normalizing a gradient , the outputs of the gradient normalization unit are connected to the inputs of the unit for generating weight coefficients and with the unit for calculating the gain coefficient, the output of the unit for generating the weights coefficients is connected to the input weight coefficients are connected to the weight coefficient normalization block, other outputs are connected to the delay block, the outputs of which are connected to other inputs of the gradient formation block, the outputs of the weight coefficient normalization block are connected to the inputs of the N weight coefficient blocks, the outputs of which are connected to the adder, the adder output is connected to one of the inputs of the gradient shaping block.

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