Aperture coupled planar feed circuits for a rotating-mode radial line slot antenna

Planar feed circuits using a ring slot for a radial line slot antenna are presented. It is attractive for integration with active RF planar circuits. In order to avoid radiation loss from the lower plate of the radial waveguide, the ring slot is placed on the upper plate. It is coupled with a microstrip line through an aperture on the lower plate. A two-point feed is designed and fabricated in the 4 GHz band and the excitation of a rotating mode is confirmed. A one-point feed is also designed for the 12 GHz band. It enhances the bandwidth in terms of the purity of the rotating mode by adopting a large waveguide height