Wideband Bandpass Filter Composed of Dual-Path Resonators Using Coupled-Line and Transmission Line With Inductive Elements

A dual-path resonator for a wideband bandpass filter (bandpass filter) is proposed by using a coupled-line and a transmission line with inductive elements. It realizes a dual-mode resonance by an open-circuited interdigital coupled-line and a transmission zero near the lower cutoff frequency due to the effect of the dual-path. The wideband BPF composed of two resonators and two open-circuited stubs is also presented. The presented filter shows that steepness at both the lower and upper cutoff frequencies and high attenuation level at the stopband are obtained. Measurement result with electromagnetic simulation is observed and they are good agreement. Its bandwidth is about 1.7 GHz and the fractional bandwidth is about 44% on compact size of 22×17 mm².