Photonics-based super-resolution phased array radar detection applying two-dimensional multiple signal classification (2D-MUSIC)

The emerging photonics-based radar breaks the bandwidth limitations of traditional radar, making it possible to achieve a high range resolution. While, the angular resolution of a photonics-based radar is still limited by the size of its equivalent aperture. To achieve both high range and angular resolution, we propose a super-resolution radar detection method that is achieved by a photonics-based phased array radar applying two-dimensional multiple signal classification (2D-MUSIC) algorithm. The broad bandwidth enabled by the photonics-based system can ensure a high range resolution, and the 2D-MUSIC method helps to achieve a high angular resolution. Feasibility of the proposed method is experimentally verified through a photonics-based 1×4 phased array radar with a bandwidth of 4 GHz (22-26 GHz). With the capability for highly precise target detection in both range and angular direction, the proposed scheme has great potential in future radar applications.

I. Introduction

High-resolution radar detection has wide applications in both military and civilian areas, such as reconnaissance, automatic driving, medical diagnosis and so on [1], [2]. The range resolution is determined by the radar bandwidth, i.e., a large bandwidth helps to achieve a high range resolution. While, current electric radars are difficult to work in a wide bandwidth due to the bandwidth limitations of electrical devices or subsystems. To deal with this problem, microwave photonic technology has been applied for radar applications, featuring a very broad operation bandwidth. Previously, we have demonstrated photonic-based radars that have a bandwidth up to 12 GHz [3] –[5], and a range resolution as high as 1.3 cm has been achieved. In the same period, broadband photonics-based radars with a high range resolution have also been successfully demonstrated by other research groups [6] –[9]. As the range resolution is greatly improved by a photonics-based radar, the angular or cross-range resolution is still limited by the radar aperture. To achieve a high angular resolution, phased array radar technique can be applied to enlarge the equivalent aperture size. Recently, we have proposed a photonics-based phased array radar [10]. In this system, the transmitting linearly frequency modulated (LFM) signal is generated by photonic frequency multiplication. In each receiving element, photonics-based broadband de-chirping is implemented, which makes it possible for low-speed digital sampling and real-time signal processing. This photonics-based phased array radar can achieve a high range resolution enabled by a large operation bandwidth, and it can realize squint-free beam steering by digital true time delay (TTD) compensation. A photonics-based 1×4 phased array radar having a bandwidth of 4 GHz (22-26 GHz) was demonstrated, in which the angular resolution was 2.68°. To further increase the angular resolution, a large phased array is required, which leads to very high system complexity and cost, considering that individual photonic signal processing and digital sampling are needed in each receiving element of the array. The difficulty in increasing the size of the photonics-based phased array makes it not feasible in practical applications.