Two low profile hybrid antennas are presented. One of the structures provides linearly polarized (LP) wave and the other one produces circularly polarized (CP) radiated field. Half-mode Substrate Integrated Waveguide (HMSIW) technique is used to make a semi-circular cavity for reducing the antenna size. Using proximity effect, TM010 mode of a rectangular patch is excited by the HMSIW cavity. An inset microstrip line is used to excite the structure which leads to capability of planar circuit integration. The effects of the HMSIW cavity-backed antenna with and without patches are investigated. The simulated results show that adding the patch increases bandwidth and improves antenna gain. Both proposed hybrid antennas are made on a single-layer substrate using printed circuit board (PCB) process. Two prototypes of the proposed antennas are designed, simulated and fabricated. It is shown that broadband impedance bandwidth of 10% and maximum gain of 7.5 dBi is obtained for the LP antenna. In case of CP antenna, Axial Ratio (AR) bandwidth is at least 1% with maximum gain of 6.8 dBi. The proposed hybrid antennas are low profile and offer attractive features such as high gain, low cross polarization level and high front to back ratio (FTBR).

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