Abstract

Vortex electromagnetic (EM) radar is able to image the target with high azimuth resolution in forward-looking scenarios. In this paper, to enhance the range resolution, a photonics-based broadband vortex EM generation and imaging system is proposed using a multi-channel microwave photonic phase shifter to precisely control the phase of signals fed into a uniform circular array. Compared with electrical phase shifters, the microwave photonic phase shifter implements more accurate control of both the phase and amplitude over a large spectral range. In the experiment, broadband vortex EM waves with 8-GHz bandwidth (18–26 GHz) and seven orbital angular momentum (OAM) modes (l = 0, ±1, ±2, and ±3) are generated, of which the field patterns and frequency-dependent beam divergence properties are analyzed. A radar imaging experiment is also conducted to verify the feasibility of forward-looking imaging with remarkably enhanced range resolution. We believe the proposed method can provide effective solutions to constructing broadband vortex EM systems, which are expected to bring significant improvements compared with narrow-band systems.