International Journal of Antennas and Propagation

Volume 2017 (2017), Article ID 2345491, 8 pages

https://doi.org/10.1155/2017/2345491

## Adaptive Countering Technique for Angle Deception Based on Dual Polarization Radar Seeker

College of Air Traffic Management, Civil Aviation Flight University of China, Guanghan 618307, China

Correspondence should be addressed to Qiang Zhang

Received 27 December 2016; Revised 1 April 2017; Accepted 2 May 2017; Published 22 May 2017

Academic Editor: Pierfrancesco Lombardo

Copyright © 2017 Qiang Zhang and Weijun Pan. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### Abstract

Angle deception jamming makes the monopulse radar seeker track to itself but not the real target, which is catastrophic for the guidance radar. In this paper, an adaptive technique based on dual polarization radar is presented to counter it. How angle deception jamming acts on the monopulse tracking radar is first investigated. An angle estimation technique of the real target is then derived from the conventional monopulse method, although it is being interfered with by angle deception jamming. Meanwhile, the polarization ratio characteristic of the angle deception jamming could be adaptively estimated in current practical scene. Furthermore, the similar characteristic of Jones vectors is defined as the rule to judge whether the target is being interfered with by jamming. It can make the radar seeker select different techniques for angle estimation adaptively. Finally, two major factors of angle estimation accuracy are analyzed by simulation and the effectiveness of the proposed technique is proved through experiments.

#### 1. Introduction

Angle deception jamming is a significant electromagnetic interference for monopulse radar seekers, which is in the same range unit and beam unit with the target, and making the seekers track to themselves but not the real target. In [1–4], the direction of arrival (DOA) estimation of two unresolved targets was developed, but the estimation techniques were for the same type targets and needed radar cross sections (RCSs) as prior information. However, including chaff clouds, active jamming, corner reflectors, arbitrary combinations of them, and so forth, angle deception jamming is quite different from the real targets. What is more, the RCSs of jamming and targets could not be obtained priorly. A main-lobe jamming suppression technique based on the spatial polarization characteristics (SPCs) of the antenna of a single polarization radar seeker was proposed [5–7]. It can suppress the echo signal from main-lobe jamming and obtain the DOA of the target by orthogonal polarization decomposition, polarization estimation, and spatial virtual polarization filtering. Whereas the technique needs to know the direction of jamming and the SPCs are just present in offset reflector antennas. In [8], a detection technique for centroid chaff jamming was developed, while it needed information from not only the monopulse radar but also GPS (Global Position System) or INS (Inertial Navigation System). As mentioned above, information acquired by single polarization radar seekers is not sufficient, so multipolarization radar seekers with the ability of achieving more polarization information would be widely chosen to counter interference, improve recognition rate of targets, and so forth [9]. According to public reporting, there are a radar seeker at 94 GHz carried by a brimstone missile [10] and a multirole modular seeker (MRMS) [11] on active service. They are all in possession of dual polarization system and developed by MBDA missile systems. Dual polarization radar seekers usually possess two orthogonal polarization channels all with sum, azimuth difference, and elevation difference, which differ greatly from the conventional monopulse radar seekers with single polarization. A scheme of adaptive polarization filtering based on dual polarization radar seeker was put forward in [12]. The polarization characteristics could be dynamically acquired by tracking jamming and the target with Kalman estimator, and then the polarization filter was utilized to suppress angle deception jamming. Yet the angle estimation technique for the real target is not provided. In [13–16], oblique projection technology was introduced into the polarization domain. It employed disjoint polarization subspaces to construct polarization oblique projection operator, which could remain undistorted target signal and absolutely suppress jamming signal, whereas the polarization oblique projection operator based on dual polarization radar is very sensitive for estimation error of the polarization characteristic.

This paper puts forward an adaptive countering technique for angle deception jamming based on dual polarization radar seeker. It can be utilized to acquire the actual angle information of the real target under angle deception jamming without any prior knowledge. The paper provides a study of the countering technique just in azimuth, since it is also valid in elevation. The remainder of this paper is organized as follows. In Section 2, the theory of angle deception jamming for monopulse tracking radars is revealed. Section 3 addresses the angle estimation technique for the real target being interfered with by angle deception jamming based on dual polarization radar. Then an adaptive countering technique by establishing a judgmental rule is formulated in Section 4. Angle estimation error analyses and experimental results are demonstrated in Sections 5 and 6. Finally, Section 7 concludes the paper.

#### 2. Theory of Angle Deception

For monopulse radars with sum and difference patterns of amplitude, their measurements of the target angle depend on the ratio of difference signal to sum signal. Being smaller than the width of the sum beam, the angular deviation of the target from the radar boresight obeys approximately linear relationship to the ratio of difference signal to sum signal. Thus the principle of monopulse angle measurement is defined as where represents the difference signal, represents the sum signal, is the angular deviation of the target from the radar boresight, is the difference slope constant closely related to the radar system [17, 18].

When the target is being interfered with by angle deception jamming, such as corner reflectors, chaff clouds, active jamming, and arbitrary combinations of them, the difference signal and the sum signal received by the radar are all composed of echoes from both the target and jamming. As a result, the sum signal can be defined as Something to note in the whole paper is that subscript denotes the target, denotes jamming, and denotes the target and jamming existing simultaneously.

Combining (1) with (2) gives us the difference signal expression as where and are respective angular deviations of the target and jamming from the radar boresight.

The complex ratio of jamming signal to target signal is expressible aswhere is the amplitude ratio of them and is the phase difference between them. Notably, the value of is great because jamming usually has a much larger RCS than the target.

Substitutions of (2), (3), and (4) into (1) yield (5). When RCS of angle deception jamming is much larger than that of the target, (5) can be simplified as (6). The result of angle measurement is much closer to the jamming but not the target. Then, the monopulse radar will track to the angle deception jamming.

The schematic diagram of angle deception jamming is shown in Figure 1. The angle value of the target acquired by the monopulse radar is the DOA of the signal contributed by the target and jamming together. The real target and the angle deception jamming are, respectively, with the angle of and from the boresight. is the angle estimation value of the target under jamming, which is much closer to the angle deception jamming. In other words, if the value of can be calculated by some means, which means the angle deception jamming has no influence on the monopulse tracking radar.