Stepped Frequency Radar with Broadband Signal Generation by Period One Laser Dynamics

We propose a stepped frequency (SF) radar that utilizes period one (P1) dynamics of an optically injected semiconductor laser to generate broadband SF signals. An SF signal with a bandwidth of 4 GHz (12–16 GHz) and a frequency step of 100 MHz is generated by dynamically controlling the optical injection strength. The broadband radar echoes are subjected to stretch processing in the receiver through electrical IQ mixing. The range resolution of the established radar is tested to be 3.84 cm, and the detection of multiple targets is demonstrated through which the high range resolution detection capability of the proposed radar is verified.

I. Introduction

Radars are widely used in military and civilian applications. In order to achieve accurate target detection and identification, it is necessary to improve the radar resolution [1]–[2]. Stepped frequency (SF) signal is an important high-resolution radar signal that has been extensively studied [3]–[6]. SF signal offers numerous advantages such as narrow instantaneous bandwidth for easy reception, increased detection range through high average power transmission, robust interference resistance, and effective suppression of clutter with good signal-to-noise ratio. For an SF radar, the high-resolution range profile can be obtained by performing inverse discrete Fourier transform (IDFT) to the received radar echoes. However, the implementation of SF radar systems in electronic hardware is complex, expensive, and limited by signal bandwidth. In recent years, microwave photonic technology has emerged as a solution for generating and processing broadband radar signals for radar systems [7]–[13]. Among these microwave photonic radars, the scheme based on an optically injected semiconductor laser operating in period one (P 1) dynamics has gained lots of attention due to its simplicity, compact size, low cost, and good tunability. Previously, a high-resolution radar imaging system was demonstrated that generates a linear frequency-modulated (LFM) with a bandwidth of 12 GHz based on an optically injected semiconductor laser and adopts a modified incoherent back projection (BP) algorithm to reconstruct the radar image [9]. Besides, there are high-resolution microwave photonic radars that generate broadband nonlinear frequency-modulated (NLFM) signals [10] and frequency hopped linear frequency-modulated (Ph-FHLFM) signals [11] based on an optically injected semiconductor laser. These microwave photonic radars allow flexible control of the bandwidth, pulse width, and frequency step of the generated broadband microwave signals by adjusting the master-slave detuning frequency and optical injection strength.