A dual-band bandpass filter using a dual-mode ring resonator with two short-circuited stubs

In this paper, a high selective dual-band bandpass filter using a dual-mode ring resonator with angle perturbation and two short-circuited stubs is proposed. For dual-mode resonance, the ring resonator is directly connected with nonorthogonal feed-line via coupling capacitors. And two different short-circuited stubs are simultaneously placed at two corners along the symmetric plane of the ring resonator. These two stubs make it possible to provide a transmission zero near the lower second passband edge. The proposed dual-band filter was fabricated. As a result of measurement, it exhibits center frequency (fractional bandwidth) of 2.3 (15.8%) and 4.9 GHz (25.7%) with insertion loss of 0.74 dB and 0.56 dB, respectively. So, the proposed filter has attractive features of low insertion loss and wide bandwidth compared to other dual-band filters. Thus, it should be well suited not only for wideband WLAN applications but also for any other communication systems.