Low-profile ring slot SIW antenna based on higher-order cylindrical cavity modes

A novel ring slot substrate-integrated waveguides (SIW) antenna is presented based on higher-order cylindrical cavity mode. First, TM02 is used to realise a conical beam antenna. Electric field distribution on slot aperture generates four pairs of magnetic monopoles, each rotated 90° with respect to the centre of the cavity, resulting in a conical beam. By applying an offset to the feed point, the loading effect of slots generates a hybrid mode, which is a combination of TM31 and TM12. The hybrid mode aligns the magnetic monopoles; thus, a high-gain antenna with broadside radiation can be realised. The measured results show a 10.5% impedance bandwidth, 11.5 dBi gain, and 90% radiation efficiency. The proposed antenna is low-profile and compact with a planar structure that could be integrated with other planar circuits; therefore, it could have many practical applications in communication systems.