Cavity-backed circular aperture antenna constructed using a triplate transmission line

An aperture antenna is constructed using a triplate transmission line. The top and bottom conducting plates of the triplate transmission line have circular apertures. The aperture in the bottom plate is backed by a circular cavity of depth D-cav. The radiation characteristics of this antenna are analysed using the finite-difference time-domain method. It is found that the cavity reduces the undesirable parallel-plate mode power remaining in the triplate transmission line. As a result, the radiation efficiency eta(rad) is improved from approximately 54% for D-cav = 0 (the case without the cavity) to more than 90% for D-cav greater than or equal to lambda(12.45)/4, where lambda(12.45) is the wavelength at a test frequency of 12.45 GHz. It is also found that as the cavity depth D-cav increases, the crosspolarisation component decreases and the gain increases.