Improved Bandwidth Formulas for Fabry-Pérot Cavity Antennas Formed by Using a Thin Partially-Reflective Surface

The power bandwidth of Fabry-Pérot-cavity antennas comprised of a thin partially-reflective-surface (PRS) above a perfectly conducting ground plane, based on its transverse-equivalent-network model and the simple susceptance model of a thin PRS, is studied. Considering the frequency variation of the PRS susceptance model, a new formula is proposed to estimate the power density bandwidth and thus (approximately) the gain bandwidth of such cavities. The application and accuracy of the proposed formula are investigated using both numerical (i.e., based on full-wave simulations) and analytical (i.e., based on a transmission-line model of the antenna) methods. Finally, the accuracy of the proposed formula is investigated for cavities formed using a finite versus infinite PRS.