K.Yu. Gavrilov – Dr.Sc.(Eng.), Deputy Director of RPC «Radiolocation Systems Development» 

of the Institute of Radioelectronics, Infocommunication and Informational Security,  Moscow Aviation Institute (National Research University)

E-mail: gvrk61@mail.ru

K.V. Kamenskiy – Post-graduate Student, 

Moscow Aviation Institute (National Research University) E-mail: kvkmai@mail.ru

When probing a regular extended target with linear-frequency modulated continuous wave, distortions, leading to the distortions in radar range profile of a target and to the loss of information about the structure of an extended target, appear in the spectrum of the deramped signal. These distortions are based on the phenomenon of mutual interference of signals reflected from the individual points of a regular extended target. Such distortions are an actual problem in mapping and radio monitoring, worsening the quality of radar images and appearing on the latter in the form of speckle noise and alternating bands of different intensity (moire pattern), and in some cases leading to almost complete disappearance of an object, while only its front and rear edges remain visible.

An extended target model describing a deramped signal in a radar with a linear-frequency modulated continuous wave was analyzed. In this model a regular extended target is represented by a set of evenly spaced point reflectors. The parameters of the model that affect the distortion of the converted signal spectrum were determined: the initial frequency of the emitted signal, the frequency rate of the linear frequency modulated signal, the relative height of the target, the distance between points of the target, and the phase shift of the signal reflected from the extended target.

For each of these parameters a series of experiments was performed based on the modeling of the expression describing the deramped signal in the time domain. To analyze the obtained results, the spectrum distortion index based on the use of the desired spectrum of the converted signal is proposed. The desired spectrum of the deramped signal is a spectrum which amplitudes are equally correlated with the reflectivity of the extended target elements.

When the initial frequency of the signal is varied, the distortion of the spectrum of the deramped signal is significant, information about the structure of the target is lost – this is evident by the distortion index values close to one. The increase in the frequency rate of the linear-frequency modulated signal allows to reduce the distortion of the spectrum of the converted signal. The variation of the relative height of the target weakly affects the distortion of the spectrum of the deramped signal. The addition of a random component to the coordinates of the point reflectors breaks the regularity of the extended target, but reduces the distortion index, while the nature of the distortion of the spectrum of the converted signal changes and becomes close to speckle noise. The addition of a random variable to the phase of the signals reflected from the target allows to reduce the spectrum distortions, which take the form of speckle noise.

The developed restoration methods of the radar profile of an extended target can be divided into two groups: applicable in the processing of a real signal and applicable in simulation.

The first group of methods includes multi-frame processing, in which the probing signal consists of a periodically repeated sequence of pulses with different initial frequency values. Then the averaging of individual frames based on each of these pulses is performed. The second group of methods includes varying the values of the relative height of a target to trace the outlines of the undistorted radar profile in the animation of the process. In addition, a combination of the relative height of a target and the position of the front and rear edges of a target can be found on the infinite axis of beat frequencies, so that for the entire radar profile distortion index will be close to zero.

The second group of methods also includes the addition of a random variable with uniform distribution to the coordinates of point reflectors or phase shifts of the reflected signals. A side effect of such approach is the inability to completely eliminate distortions which will get the form of speckle noise.

1. Komarov I.V., Smolskii S.M. Osnovy teorii radiolokatsionnykh sistem s nepreryvnym izlucheniem chastotno-modulirovannykh kolebanii. M.: Goryachaya liniya–Telekom. 2010. 366 s. (In Russian).
2. Batet Torrell O. Investigation of continuous-wave range-resolved lidar systems for gas detection and concentration measurement. Tesi doctoral, UPC, Departament de Teoria del Senyal i Comunicacions. 2011. URL = http://hdl.handle.net/2117/116296.
3. Batet O., Dios F., Comeron A., Agishev R. Intensity-modulated linear-frequency-modulated continuous-wave lidar for distributed media: fundamentals of technique. Applied Optics. 2010. V. 49. № 17. P. 3369−3379.
4. Gavrilov K.Yu., Kamenskii K.V., Kanashchenkov A.I., Panyavina N.S. Analiz otrazhennykh signalov pri zondirovanii protyazhennykh tselei nepreryvnym modulirovannym kolebaniem. Sb. trudov. XII Vseros. konf. «Radiolokatsiya i radiosvyaz». M.: IRE im. V.A. Kotelnikova RAN. 26−28 noyabrya 2018. S. 152−156. (In Russian).
5. Gavrilov K.Yu., Kamenski K.V., Kanaschenkov A.I., Panyavina N.S. Signal spectrum distortion for an extended target in a radar with a continuous frequency-modulated signal. Amazonia Investiga. 2019. № 8(20). P. 210−218.
6. Gavrilov K.Yu., Kanashchenkov A.I., Nuzhdin V.M., Panyavina N.S. Obrabotka signalov pri sintezirovanii apertury v radare s nepreryvnym izlucheniem. Informatsionno-izmeritelnye i upravlyayushchie sistemy. 2018. T. 16. № 6. S. 31−46. (In Russian).
7. Kulpa K., Samczy´nski P., Malanowski M., Gromek A., Gromek D., Gwarek W., Salski B. and Ta´nski G. An advanced SAR simulator of three-dimensional structures combining geometrical optics and full-wave electromagnetic methods. IEEE Trans. Geosci. Remote Sens. 2014. V. 52. № 1. P. 776−784.
8. McGillem C.D., Riemer T.E. Moire' Patterns and Two-Dimensional Aliasing in Line Scanner Data Acquisition Systems. IEEE Transactions on Geoscience Electronics. 1974. V. 12. № 1. P. 1−8.
9. Goodman J.W. Some fundamental properties of speckle. J. Opt. Soc. Am. 1976. № 66. P. 1145−1150.
10. Petrov Yu.V., Byzov A.N., Petrov N.Yu., Yukhno S.A. Analiz vliyaniya destabiliziruyushchikh faktorov na iskazheniya traektornykh signalov v bortovom radiolokatore vysokogo razresheniya. Vestnik VGU. Ser. «Sistemnyi analiz i informatsionnye tekhnologii». 2015. № 1. S. 67−75. (In Russian).