RU2593595C1  Method of measuring angular coordinates in nonlinear radar  Google Patents
Method of measuring angular coordinates in nonlinear radar Download PDFInfo
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 RU2593595C1 RU2593595C1 RU2015132508/07A RU2015132508A RU2593595C1 RU 2593595 C1 RU2593595 C1 RU 2593595C1 RU 2015132508/07 A RU2015132508/07 A RU 2015132508/07A RU 2015132508 A RU2015132508 A RU 2015132508A RU 2593595 C1 RU2593595 C1 RU 2593595C1
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Abstract
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The present invention relates to the field of radar, in particular to the field of near radar, to which belong nonlinear radars (NRL) that search for objects containing electronic components. The effectiveness of NRL is based on the use of radiofrequency 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, ultrawideband [1, p. 16].
An NRL with an ultrawideband probe signal has specific features that are associated with the need to use appropriate radio equipment. In particular, the range of ultrawideband transceiver antennas should overlap the frequencies of the first and second harmonics of the signal. The greatest difficulty in creating an ultrawideband 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 ultrawideband 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 nearlocation systems do not allow the use of antenna systems characteristic of classical radar with a large aperture opening.
The wellknown 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 smallsized 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].
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 narrowband signals with close maximum and minimum frequencies in the spectrum. For ultrawideband 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 ultrawideband 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 nonadaptation to the features of nonlinear radar.
The technical result of this invention is the unambiguous measurement of azimuth in ultrawideband NRL with high accuracy.
An additional technical result is an increase in resolution in azimuth.
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:
,
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).
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 ultrawideband 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, smallsized 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 ultrawideband NRL and to further increase the azimuth resolution.
Literature
1. Chapursky V.V. Selected problems of the theory of ultrawideband radar systems. M .: MSTU im. N.E. Bauman, 2012, 279 p.
2. RF patent for the invention No. 2397509 "Nonlinear 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. 477489.
5. Burdick B.C. Analysis of sonar systems. L .: Shipbuilding, 1988, 392 p.
6. Vendik O.G. Aerials with nonmechanical 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:
$${\theta}_{\mathrm{from}R}=\mathrm{arcsin}\left(\frac{\Delta {\varphi}_{\mathrm{from}R}}{kd}\right)$$ where k = 2π / λ is the wave number, d is the distance between the phase centers of the virtual antennas.
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RU2642883C1 (en) *  20170131  20180129  Акционерное общество "Всероссийский научноисследовательский институт радиотехники"  Method of angular superresolution by digital antenna arrays 
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