Design of a Rotman Lens-Based Circularly Polarized Planar Multi-Beam Antenna

In this paper, a planar circularly polarized multibeam antenna is presented with passive beam scanning capability. The antenna consists of a leaky-wave antenna (LWA) array based on substrate integrated waveguide (SIW) and a Rotman lens beamforming network. The LWA serves as the radiating element, achieving circularly polarized radiation by loading non-resonant radiation slots with 90° sequential rotations on the SIW transmission line. To achieve the capability of low-cost beam scanning, a Rotman lens is implemented as the antenna's feeding network. The antenna design, with its dual-layer structure and the LWA array positioned above the Rotman lens, achieves system miniaturization. Simulation results confirm that the antenna achieves good impedance matching and circular polarization beam scanning of ± 44° across the 9.5 to 10.5 GHz frequency band, and each beam maintains an axial ratio below 3 dB within its 3 dB beamwidth.