Fresnel Based Frequency Domain Adaptive
Beamforming for Large Aperture Distributed Array
Radar
Honggang Zhang, Jian Luo, Xinliang Chen
*
, Quanhua Liu, Tao Zeng
Beijing Key Laboratory of Embedded Real-time Information Processing Technology, Radar Research Laboratory
School of Information and Electronics, Beijing Institute of Technology
Beijing 100081, China
chenxinliang@bit.edu.cn
Abstract—Distributed array radar is a significant radar system,
which can not only improve radar detection capability and
measurement accuracy, but also suppress mainlobe interference
effectively. However, due to its equivalent large aperture, the
plane wave assumption fails. What’s worse, target signals
arriving at each array may have the envelope migration problem,
thus the traditional adaptive beamforming method becomes
invalid. This paper proposes a Fresnel based frequency domain
adaptive beamforming method for large aperture distributed
array radar. Instead of plane wave model, it uses the Fresnel
model based steering vector to improve accuracy. Meanwhile, it
transforms the time domain signal to frequency domain, and
using the traditional adaptive beamforming method for each
frequency point respectively. Finally, it accomplishes the
frequency domain adaptive beamforming by an inverse Fourier
transform (IFFT). In result, this method could eliminate the
envelope migration problem effectively. Simulations illustrate the
effectiveness of the proposed method.
Index Terms—Distributed array radar, large aperture, Fresnel
model, envelope migration, frequency domain adaptive
beamforming.
I. I
NTRODUCTION
Distributed array radar has been widely concerned in recent
years due to its superiority in many aspects [1]. MIMO radar is
a kind of distributed array radar. Wherein, co-located MIMO
radar mainly uses waveform diversity, enables the MIMO radar
superiority in parameter identifiability, direct applicability of
adaptive arrays for target detection and parameter estimation
[2]. While widely separated MIMO radar capture the spatial
diversity of the target’s radar cross section (RCS), and it is able
to obtain a diversity gain for target detection and for estimation
of various parameters [3]. Moreover, Lincoln laboratory has
put forward the distributed coherent aperture radar, which
enables coherent synthesis in signal level, leading to a N
3
times
signal-to-noise ratio (SNR) promotion [4].
Inspired by the traditional sidelobe interference cancellation
technique of phased array radar [5], a novel method for
mainlobe interference cancellation based on a large aperture
auxiliary array for ground-based radar is proposed [6]. Uniting
the main radar and auxiliary array, the whole array’s equivalent
antenna aperture is greatly increased, making the target signal
and mainlobe interference signal distinguishable in spatial
dimension. Utilizing the traditional adaptive beamforming,
very narrow null can be formed in the direction of mainlobe
interference. Therefore, this technique is suitable for mainlobe
interference suppression of large aperture distributed array.
Moreover, it is capable of eliminating the distortion and
mainlobe peak offset problem caused by the traditional
sidelobe interference suppression method.
However, due to the large aperture of the distributed array,
the angles arriving at each receiving array of the target signal
may be different. Hence, this signal cannot be approximated to
a plane wave model anymore. And there is an urgent need to
establish a more accurate signal model in order to achieve a
better interference suppression performance. In addition, the
target signal may arrive at each receiving array with different
time delays because of the large aperture, resulting in severe
envelope migration. This makes traditional spatial adaptive
beamforming method unable to use. Thus it is necessary to
propose a novel method to resolve this problem for the large
aperture distributed array radar.
The paper is organized as follows. Section 1 introduces the
superiorities of distributed array radar, and expounds the
problems when using the traditional adaptive beamforming to
the large aperture distributed array. Section 2 describes the
signal model of large aperture distributed array radar. Section 3
proposes the Fresnel based frequency domain adaptive
beamforming method, it uses Fresnel model to replace the
plane wave model to improve model accuracy. Meanwhile, it
transforms the time domain signal to frequency domain, and
employs traditional adaptive beamforming method to each
frequency point respectively, then accomplishes the frequency
domain adaptive beamforming by an IFFT. Section 4 verifies
the effectiveness of the proposed algorithm through simulation.
Finally, section 5 draws the conclusion.
II. S
IGNAL MODEL
Large aperture distributed array radar arrange in a one-
dimensional uniform linear array (ULA), which consists of
M
independent arrays, as shown in Fig. 1.
This work was supported by the Chang Jiang Scholars Programme under
Grants T2012122, 111 Project of China under Grants B14010 and the
N
ational Natural Science Foundation of China under Grants 61301189.
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