A Wideband High Gain Cavity-Backed Slot Ring Antenna using Higher Order Modes

An improved design of a cavity-backed slot ring antenna is presented. The antenna maintains its radiation characteristics and good impedance matching over at least 10 % frequency band. Over the band, the antenna does not show any beam tilt. Two higher order resonant modes are used to obtain high gain. The improved antenna characteristics is obtained by elevating a part of the top cavity plate containing the ring slot. A prototype antenna is designed and fabricated for 2.25-2.5 GHz short-range indoor radar applications. The antenna provides a measured gain of
$7\pm 0.5\text{dBi}$
over the entire band. The overall dimension of the antenna is
$0.64\lambda_{0}\times 0.64\lambda_{0} \times 0.08 \lambda_0, \lambda_0$
being the free space wavelength at the mid-band frequency. Design guidelines are provided for the frequency scaling.