Journal of Signal and Information Processing, 2013, 4, 14-18

doi:10.4236/jsip.2013.43B003 Published Online August 2013 (http://www.scirp.org/journal/jsip)

SAR Imaging of Moving Target Based on Quadratic Phase

Function

Chao Wang, Shaobin Li

School of Electronics information Engineering Harbin Institute of Technology Harbin, China.

Email: wangchao517@hit.edu.cn, lishaobin411@163.com

Received March, 2013.

ABSTRACT

In this paper, a novel signal processing technique has been developed to refocus moving targets image from their

smeared responses in the Synthetic Aperture Radar (SAR) image according to the characteristics of the received signals

for moving targets. Quadratic Phase Function is introduced to the parameters estimation for moving target echo and

SAR imaging. Our method is available even under a low SNR environment and acquiring an exact SAR image of mov-

ing targets. The simulated results demonstrated the validity of the algorithm proposed.

Keywords: Synthetic Aperture Radar; Moving Targets; Quadratic Phase Function

1. Introduction

Airborne synthetic aperture radar (SAR) detection and

imaging of moving targets on the ground has been a sub-

ject of long-standing interest in both civil and military

applications such as battlefield reconnaissance, fire as-

sessment, traffic management and monitoring ocean cur-

rents. If there are moving targets in the observed scene,

SAR cannot simultaneously produce clear images of both

stationary and moving targets because they have different

Doppler frequency respectively, the target motion in-

duced phase errors, which interact with the matched filter

processing or cross-range compression, cause these im-

ages to be mislocated in the cross-range dimension and

smeared in both the cross-range and the range domains,

we can only focus on either the stationary target or the

moving target. How to detect moving targets in the

background of stationary objects called clutter is premise

for SAR imaging of moving targets, this problem is usu-

ally solved by applying the displaced phase center an-

tenna (DPCA) [1] or its modern extension, the space-

time adaptive processing (STAP) [2]. Radar returns from

terrain and stationary objects can be suppressed after

using DPCA or STAP, only the returns from moving

targets are used to reconstruct radar images.

Moving targets echo signal is generally characterized

by the linear frequency modulated (LFM) signal, before

obtain the focused images of moving targets, the pa-

rameters of LMF should be estimated firstly, and then

construct correct match filter of range and azimuth direc-

tions for imaging. In which, initial frequency and chirp

rate as the basic parameters of LMF, their estimation

problem has been an important research content of the

signal processing. In previous investigations, several

parameter estimation methods based on Maximum Like-

lihood (ML) [3] estimation cannot be implemented in

engineering because of a huge amount of computation.

Some signal processing methods such as Radon-Wigner

Transform (RWT) [4], Radon-Ambiguity Transform

(RAT) [5], Fractional Fourier Transform (FrFT) [6] have

been usually used in estimation of LMF parameters. It is

worth mentioning that WVD combine with Radon

Transform as a commonly used method of detection and

estimation for LMF can achieve an idea result. However,

there is cross-term interference associated with the WVD.

When the signal contains more than one component, the

WVD will generate cross-term interference between

components that occurs at spurious locations of the

time-frequency plane.

In this paper the Quadratic Phase Function (QPF) [7]

[8] is introduced to the SAR moving target imaging, and

a new SAR imaging algorithm based on the Quadratic

Phase Function is presented. This method can achieve an

idea result for moving targets imaging. The simulated

results demonstrate the validity of this algorithm.

2. Radar Returns of Moving Targets

In this section, we setablish the signal model for the

received signal in SAR imaging of moving targets, here,

take the ground coordinate system for the reference co-

ordinate system and without considering the rotation of

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