An Analysis of Phase Array Radar System on a Moving Platform J. Wang, R. Dizaji, A. M. Ponsford Raytheon Canada Limited, 400 Phillip Street, Waterloo, O.N., Canada Key Words: moving platform, pulsed Doppler radar ABSTRACT In this paper, we derive a time-varying model for the steering vector of a phased array pulse Doppler radar system installed on a moving platform. Six oscillating motions are included in the derived model as well as the forward motion of the platform. We also present the sensitivity analysis of the derived model and analyze the effect of the perturbation between the true and measured array manifold on the accuracy of the motion compensation algorithm. From the simulation, it can be shown that the platform motions have no prominent effects on the targets power spectrum in moderate sea states (up to 3). However the barges forward motion is a problem if the targets fall in the spreading spectral region of the sea clutter. 1. INTRODUCTION In our analysis, we consider the ship borne high frequency surface wave radar (HFSWR) system. This radar is a pulse Doppler radar with phased receive array designed to detect and track ships and low altitude targets beyond the horizon. The land-based radar has successfully demonstrated a long-range detection providing a real-time, continuous, and all weather surveillance of surface targets within the 200 nm Exclusive Economic Zone (EEZ) 1. The characteristics of the clutter of moving HFSWR are different from those of the land-based radar. For instance the first-order sea clutter is broadened because of the radar platforms forward motion which can affect the targets detection in this region. The oscillating motions such as pitch and roll bring additional modulation to both targets and clutter. It is important to study the effects of platform motion prior to install the radar system. Several papers have been recently published that discuss the effects of ships movement on HF radar (2 - 4). The use of space-time processing techniques to identify the distribution of the sea clutter is presented by Xie et al. in 2. A more detailed scheme is proposed in 5. Gurgel et al. 3, 4 conduct a performance analysis of the ocean currents mapping by using shipborne HF radar. In addition to the effects of the ships forward average velocity, the authors also mention the dependency of estimation results to the pitch and roll motion of the radar platform, resulting in the enlarged estimation variances. Ponsford et al. 6 point out a way to enhance the target detection performance in the Doppler spreading region by applying steering nulls in those areas that contribute the main spreading energy. Following this idea, a more recent paper 7 applies symmetric nulls around the interested target direction to improve the radar detection performance, however this technique has the disadvantage of losing the azimuth of targets. An orthogonal weighting function is proposed in 8, which overcomes the above disadvantage. All of the above methods assume a constant velocity of the radar platform and neglect the effects of other oscillating motions such as pitch and roll. Several performance studies have been reported for time- varying arrays (12-13), however they do not consider the effects of coherent integration. In this paper, we propose a new time-varying array steering vector in pulse domain, which models the effects of forward and oscillations motions. This model provides a tool to better understand the motion effects on the performance of any phased array radar, which can then be used to develop motion compensation methods to improve target detection. The paper is organized as follows. In section 2, a time- varying array model is described as a function of the platform motions. A sensitivity analysis is conducted in section 3 to quantify the effect of motion measurement errors on array manifold. Numerical examples are presented in section 4, and the conclusions are presented in section 5. 2. MOVING ARRAY STEERING VECTOR MODEL In this paper, we assume a moving barge is adopted as the radar platform. When deployed in the ocean, the barge is subject to six oscillating motions besides the forward motion. These motions are the results of barge interaction with ocean waves and are characterized by barges dynamic features, and its heading with respect to ocean wave direction. The positive directions for these motions are shown in Figs. 1 and 2, respectively, and the six oscillating motions are described as follows. Pitch ( ) t degrees): the angular motion with respect to the barges transverse axis. Roll ( ) t degrees): the angular motion with respect to the barges longitudinal axis. Yaw ( ) t degrees): the angular motion with respect to the barges vertical axis. Surge ( )x t meters): body motion forward and backward along the longitudinal axis. 0-7803-8882-8/05/$20.00