RU2593595C1 - Method of measuring angular coordinates in nonlinear radar - Google Patents

Abstract

FIELD: radar.

SUBSTANCE: present invention relates to radar, particularly to short-range radar, to which belong nonlinear radar stations searching objects with radioelectronic elements. Technical result is unambiguous measurement of azimuth in wideband nonlinear radar, as well as high azimuth resolution. Said results are achieved due to that in method of measuring angular coordinates in nonlinear radar, including measurement of azimuth coordinates using an interferometric method by comparison of signals reflected from object received simultaneously in two matching phase beam patterns, to determine azimuthal coordinates of search object, two independent transmitting antennae S1 and S2 are used, said antennae being dipoles radiating orthogonal signals at a distance a=2λ from each other, and two independent receiving antennae 1 and 2 located at distance b=λ. Between each pair of receiving and transmitting dipoles a virtual receiving channel (K1, K2, K3, K4) is formed, signal delay in each of which corresponds to delay in a single transceiving dipole arranged in middle of base between real dipoles. When observing said distances between receiving and transmitting dipoles distance between virtual dipoles is λ/2. Second harmonic signal is transmitted to dipoles, where spectrum of said signal is twice wider than spectrum of first harmonic signal, and central frequency

. To ensure unambiguous measurement of azimuth direction of target distance between receiving dipoles must be twice less than distance between transmitting dipoles. Between each pair of adjacent channels phase difference is measured Δφ, as a result average value of phase difference Δφ_avg is calculated and angular direction towards target is determined by formula:

where k = 2π/λ is wave number, d is distance between phase centres of virtual antennae.

EFFECT: such an arrangement of elementary dipoles provides formation of a virtual aperture in non-linear radar.

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Description

The present invention relates to the field of radar, in particular to the field of near radar, to which belong non-linear radars (NRL) that search for objects containing electronic components. The effectiveness of NRL is based on the use of radio-frequency resonance properties of search objects. For more efficient excitation of resonances in the search objects, it is advisable to use a broadband noise signal as a probe, the spectrum width of which is comparable to an octave, which is determined by the maximum spectrum width at which separate reception of higher harmonics signals is possible. Octave signals are, by definition, ultra-wideband [1, p. 16].

An NRL with an ultra-wideband probe signal has specific features that are associated with the need to use appropriate radio equipment. In particular, the range of ultra-wideband transceiver antennas should overlap the frequencies of the first and second harmonics of the signal. The greatest difficulty in creating an ultra-wideband receive path is to ensure its linearity, since the excitation of spurious higher harmonics in the transceiver paths creates additional interference. The linear passage of the echo signal from the target (the second harmonic of the probe signal) allows correlation processing to maximize the energy storage of the received oscillations. The correlation processing of an ultra-wideband signal allows one to improve the resolution of the NRL in range, that is, it makes it possible to measure the range coordinate of the target. Another problem of nonlinear radar is the measurement of angular coordinates. Requirements for the mass and size characteristics of near-location systems do not allow the use of antenna systems characteristic of classical radar with a large aperture opening.

The well-known method of synthesizing the antenna aperture described in [2] allows one to achieve high accuracy in measuring the angular coordinate of the target in a nonlinear radar using a small antenna system. This method is not applicable in stationary radars and requires taking into account the speed of the radar carrier. When creating the most universal method applicable for measuring the angular coordinate in both stationary and mobile nonlinear radars, it is most expedient to use small-sized antenna arrays consisting of two elementary radiators.

An interferometric method based on the principle of monopulse radar is selected as a prototype of the proposed method for measuring azimuth, the essence of which is to compare the reflected signals from the object, taken simultaneously from two mismatched phase radiation patterns [3, p. 15].

, обусловливает их сильное взаимодействие на максимальных частотах в спектре

, где

- ширина спектра сигнала, и появление дифракционных лепестков на минимальных

. Фактически близкое расположение усиливает взаимное влияние между приемными антеннами сверхширокополосного радиолокатора, и измерение координат становится невозможным.The disadvantage of the prototype is the ambiguity of measuring the angle with increasing distance between the receiving antennas of the interferometer by more than λ / 2, where λ is the wavelength of the signal. The spatial arrangement of the antennas at λ / 2 in practice is possible only for narrow-band signals with close maximum and minimum frequencies in the spectrum. For ultra-wideband signals, these differences are significant, therefore, maintaining the distance between the antennas equal to λ / 2 relative to the center frequency

, determines their strong interaction at maximum frequencies in the spectrum

where

- the width of the signal spectrum, and the appearance of diffraction lobes at minimum

. In fact, the proximity increases the mutual influence between the receiving antennas of the ultra-wideband radar, and coordinate measurement becomes impossible.

A known method of forming a virtual aperture of elementary vibrators [4], the distance between which is reduced relative to real antenna elements without increasing mutual influence. The disadvantage of this approach is its non-adaptation to the features of non-linear radar.

The technical result of this invention is the unambiguous measurement of azimuth in ultra-wideband NRL with high accuracy.

An additional technical result is an increase in resolution in azimuth.

. То есть для обеспечения однозначного измерения азимутального направления на цель расстояние между приемными вибраторами должно быть в два раза меньше расстояния между передающими. Только такая расстановка элементарных вибраторов обеспечивает формирование виртуальной апертуры в нелинейном радиолокаторе.These technical results are achieved by the fact that in the known method for measuring angular coordinates in a nonlinear radar, including measuring the azimuthal coordinate using the interferometric method by comparing the reflected signals from the object received simultaneously from two mismatched phase radiation patterns, two independent transmitters are used to determine the azimuthal coordinate of the search object antennas S1 and S2, which are vibrators emitting orthogonal signals located on p = 2λ and Normal distance from each other, and two separate receiving antennas 1 and 2, located at a distance b = λ (see. FIG. 1). A virtual receiving channel (K1, K2, K3, K4) is created between each pair of receiving and transmitting vibrators, the delay of the signal in each of which corresponds to the delay in a single transceiver vibrator placed in the middle of the base between the real vibrators. Moreover, subject to the indicated distances between the receiving and transmitting vibrators, the distance between the virtual vibrators will be λ / 2. The second harmonic signal arrives at the receiving vibrators, the spectrum of which is twice as wide as the spectrum of the first harmonic signal, and the center frequency

. That is, to ensure an unambiguous measurement of the azimuthal direction to the target, the distance between the receiving vibrators should be half the distance between the transmitters. Only such an arrangement of elementary vibrators provides the formation of a virtual aperture in a nonlinear radar.

To measure the azimuthal direction using a virtual aperture, the phase difference Δφ between the virtual elements is measured. The phase difference between the virtual elements is determined by the ratio depending on the distance between the phase centers of the virtual vibrators:

,

,

where d is the distance between the phase centers of virtual vibrators with serial numbers n and m, θ is the angular direction to the target. To measure the phase difference, it is convenient to use the broadband correlator scheme with a split aperture and the Hilbert transform [5, p. 373], then Δφ will be calculated by the formula:

,

,

соответствует преобразованию Гильберта сигнала s₂.where s ₁ , s ₂ - signals of virtual emitters, expression

It corresponds to the Hilbert transform of the signal s _2.

In the studied system (Fig. 1) four virtual channels are formed, which makes it possible to measure the phase difference between each two virtual emitters, the distance between which allows you to unambiguously measure the azimuth. For example, measuring the phase difference between the channels K1K2, K2K3, K3K4, respectively Δφ ₁ , Δφ ₂ , Δφ ₃ , we obtain an analogue of the sliding window through the channels of the virtual aperture (Fig. 2).

раз, что эквивалентно увеличению энергетического потенциала НРЛ за счет увеличения размеров виртуальной апертуры. Угловое направление на цель определяется по формуле:As a result, averaging a series of three Δφ _avg measurements, the absolute error of azimuth measurement decreases in

times, which is equivalent to an increase in the energy potential of the NRL due to an increase in the size of the virtual aperture. The angular direction to the target is determined by the formula:

,

,

where k = 2π / λ is the wave number.

The technical solution is new, since there is no known method that makes it possible to unambiguously measure the azimuth in an ultra-wideband NRL with high accuracy and to obtain a high azimuth resolution.

A feature of monopulse radar methods for measuring angular directions is that in each of the elements of range resolution there is only one brilliant point. In near radar, as a rule, small-sized apertures with a wide radiation pattern (LH) are used, if within the LN there are targets that are not resolvable in range, it is also impossible to resolve them in azimuth.

The formation of four virtual receiving channels allows us to improve the azimuth resolution, since the linear phase shift is preserved in the virtual channels depending on the azimuthal direction. The summation of the four signals gives the narrowing of the beam pattern of the virtual antenna array (AR) in azimuth, similar to a real linear AR. That is, the summation of the signals in the virtual channels gives an improvement in azimuth resolution. The narrowing of the azimuthal pattern reduces the space sector. To expand the viewing sector, it is necessary to take into account the fact that all four virtual channels, in contrast to the elements of a real AR, operate independently and the bottom of each channel corresponds to the bottom of the elementary emitter. Summing the signals of virtual vibrators with the corresponding linear delays τ (Fig. 3) allows you to organize scanning in azimuth [6, p. 8].

The formation of four to five orthogonal rays (Fig. 4) covers the entire field of view of space, which allows to reduce the search time for objects containing electronic components.

Thus, the formation of a virtual aperture makes it possible to unambiguously measure the azimuthal coordinate of a target using the interferometric method with high accuracy using a sliding window through the channels of a virtual aperture in an ultra-wideband NRL and to further increase the azimuth resolution.

Literature

1. Chapursky V.V. Selected problems of the theory of ultra-wideband radar systems. M .: MSTU im. N.E. Bauman, 2012, 279 p.

2. RF patent for the invention No. 2397509 "Non-linear radar with a synthesized aperture of the antenna", G01S 13/90. Published: 08/20/2010.

3. Rhodes D.R. Introduction to monopulse radar. M .: Soviet radio, 1960, 160 p.

4. Chernyak B.C. About a new direction in radar: MIMO radar // Applied Radioelectronics, 2009, Volume 8, No. 4, p. 477-489.

5. Burdick B.C. Analysis of sonar systems. L .: Shipbuilding, 1988, 392 p.

6. Vendik O.G. Aerials with non-mechanical beam movement. M .: Soviet Radio, 1965, 360 p.

Claims (1)

A method for measuring angular coordinates in a nonlinear radar, in which the azimuthal coordinate is measured by the interferometric method by comparing reflected signals from an object received simultaneously from two mismatched phase radiation patterns, characterized in that two independent transmitting antennas are located at a distance of a = 2λ, and two receiving antennas located at a distance b = λ, forming four virtual aperture channels in the middle between each other, then between each pair of neighboring windows rutal channels measure the phase difference Δφ, as a result, calculate the average value of the phase difference Δφ _sr and determine the angular direction to the target according to the formula:
$${\theta }_{\mathrm{from}R}=\arcsin \left(\frac{\Delta {\varphi }_{\mathrm{from}R}}{kd}\right)$$

where k = 2π / λ is the wave number, d is the distance between the phase centers of the virtual antennas.

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