A dual-wideband bandpass filter with closely spaced passbands using coupled lines and shunt transmission lines loaded with end-connected coupled lines

Abstract

A fourth-order bandpass filter with dual-wide passbands is proposed in this article. The novelty of the proposed work is the realization of a dual-band bandpass filter with closely spaced passbands, wide passband bandwidth, high rejection between the passbands, using a novel combination of open stub tapped series coupled lines (CLs) and shunt transmission line loaded with end connected CLs. The characteristics of the proposed dual-wideband bandpass filter are investigated by adopting even–odd mode analysis. The transmission zeros generated by the transmission line loaded with an end-connected CL and open stub are utilized to achieve a high skirt rate. A rejection better than 55 dB is achieved with a single transmission zero between the two passbands indicating high isolation and close passbands. The dual-wideband filter is designed and manufactured to operate at 1.33 and 2.32 GHz. The experimented 3-dB fractional bandwidths of the two pass frequency bands are 40.6% and 24.13%. The proposed filter’s tested frequency responses agree well with simulated results. The proposed device can be used in various applications such as telecommunications, satellite communications, radar systems, imaging, and spectroscopy.