Single-mode ring resonator for microwave bandpass filter applications

Topologies of two microwave bandpass filters are presented. The first topology comprises of a single mode ring resonator which is fed along one of its quarter-wavelength sides. The second topology is constructed based on the first topology whereby two series cascaded ring resonators with a quarter wavelength coupled line in the middle of the structure to obtain a 4^th order bandpass filter with a good out-of-band rejection level. Observation on the controlling parameters of the 4^th order bandpass resonator is conducted to investigate the effect of each parameter in terms of bandwidth, matching level and the transmission zeros. The proposed concept is demonstrated using microstrip technology with operating frequency at 2 GHz. The substrate used in this simulations is Tachonic with characteristics of: ε_r = 4.5, h = 1.63 mm, tan δ = 0.0035. The filter layout is presented in this paper along with the simulation results to show its feasibility.