Grounded open-loop resonator as a dual-mode structure and its applications in filter design

In this paper we propose a grounded open-loop resonator which exhibits dual-mode behaviour. The proposed resonator is analysed in detail and then used to design two microstrip bandpass filters: a single-band filter operating at 3.5 GHz and a dual-band filter operating at 2.4/5.2 GHz. Both filters are characterized by good performance and a small size.