Dual-Band Bandpass Filter Design Using a Novel Feed Scheme

A planar dual-band bandpass filter based on a novel feed scheme is presented in this letter. The proposed filter employs two sets of resonators operating at diverse frequencies to generate two passbands. A novel scheme is introduced to feed the resonators. One set of resonators is utilized to not only generate the lower passband but also feed other resonators. Source-load coupling for upper passband is inherently realized. This scheme provides sufficient degrees of freedom to control the center frequencies and bandwidth of the two passbands. Four transmission zeros can be created close to passband edges, resulting in high skirt selectivity. To validate the proposed idea, a demonstration filter is implemented. The design methodology, filter sensitivity and experimental results are presented.