Compact Planar Zero-Ground-Clearance End-Fire CP Antenna With Integrated Slow-Wave Structure for Mobile Terminal Applications

This paper introduces a novel compact planar end-fire antenna system featuring circularly polarised (CP) radiation and zero ground clearance. The system is constructed using a half-wavelength TE_0.5,0 mode open waveguide, which inherently generates vertically polarised electric components. By incorporating a slow-wave (SW) structure in the form of metallised blind via holes within the waveguide, a significant SW effect is achieved, resulting in a 40% reduction in the waveguide longitudinal size compared to the conventional counterpart design. Furthermore, by etching an open-ended slot in the top metallic surface of the waveguide, the edges of its aperture are enabled to generate an electric dipole mode. In this way, the horizontally polarised electric components can be achieved without increasing the antenna's footprint. With the proper combination, the design can effectively achieve the required 90°-phase difference in the end-fire direction for these two components. Finally, a 2.5 GHz antenna was designed and optimised. Aiming to mimic the practical environment of mobile terminal devices, a large metallic ground was adopted under the antenna in the simulation and experiment. The measured results indicated that an overlapped impedance |S₁₁| < −10 and axial ratio (AR < 3) bandwidth of 2.7% from 2.495 to 2.562 GHz is achieved. The proposed antenna shows great potential in wireless communication applications for mobile terminal devices.