Design of Low-Profile Multi-Band Half-Mode Substrate-Integrated Waveguide Antennas

An effective method of designing low-profile cavity-backed multi-band antennas is introduced based on half-mode substrate-integrated waveguide (HMSIW) technique. By loading U-shaped strips outside the radiating aperture of an HMSIW cavity, additional resonances can be produced, thus leading to the realization of multi-band capability. An inset 50 Ω microstrip feedline is employed to energize the HMSIW cavity, whereas the loaded strips are excited through proximity coupling from the radiating aperture of the HMSIW. The proposed antenna is constructed on a single-layered substrate with a low profile of 0.024 free-space wavelength. To validate the multi-band responses, prototypes of the single-band HMSIW antenna as well as dual-band and triple-band antennas are fabricated and measured, respectively. The experimental results show that the proposed antennas possess advantages of stable radiation patterns with a gain of 5-5.9 dBi as well as acceptable front-to-back (FTB) ratio of larger than 10 dB over different frequency bands.