A small size dual-mode patch filter

Abstract

A small size dual-mode square patch resonator with slots etched in symmetrical shape is proposed. The filter response is obtained by exciting the degenerate modes and the first higher order mode of the proposed resonator through asymmetrical feeding. Area saving more than 80% with respect to the conventional degenerate dual-mode square patch filter and more than 20% with respect to the non-degenerate dual-mode patch filter can be achieved. Beside its compact size, the fractional bandwidth of the proposed structure can be reduced to half of the non-degenerate dual-mode filter; hence, more design flexibility. A bandpass filter is designed at 1.74 GHz with 6.9% fractional bandwidth on FR4 material with 4.2 dielectric constant and 0.78 mm thickness. Simulations are performed using full wave IE3D simulator. Simulations agree well with the experimental results.