Contents I. Introduction
A high resolution inverse synthetic aperture radar (ISAR) imaging technique for a controllable rotating target has been used in various application areas, including modeling and analysis of radar targets [1]. Also, it has been adopted as a diagnostic method to support the medical and physical sciences and used to develop the target detection, recognition, and classification techniques [2], [3]. In stepped frequency ISAR, generally the reflected radar signal is sampled on the polar coordinates of frequency and observation angle [4]. This method will be referred to as the conventional sampling method in this paper. For a small observation angle, a high resolution image can be achieved with short processing time using the unfocused reconstruction algorithm because the received data can be modeled by samples of the Fourier transform on rectangular coordinates [5], but if the angle range is not very small, the unfocused image is degraded by the blur effect. Also, the matrix pencil method was proposed to achieve much higher resolution than the conventional FFT method in case of small data aperture [6], but it is not evaluated on the performance for a wide angle. The blur effect can be removed by the reformatting of received data on rectangular lattice using the interpolation in the focused image. However, the additional interpolation process causes a longer processing time than the unfocused algorithm and the image degradation due to artifacts. In this paper, a new sampling method is proposed to obtain a focused image for a wide observation angle without an interpolation process. The simulation and experiment results show that this method has a lower complexity and shorter processing time than the conventional method, and the image degradation due to artifacts has been reduced remarkably.
Measurement coordinate for new sampling method.
