Dual-band Bandpass Filter Based on Frequency Transformations With Enhanced Inter-band Isolation

The coupling matrix approach is used to synthesize a dual-band filter. The two Chebyshev passbands are in close proximity and symmetric about a designated frequency, where two neighboring zeros are allocated for enhancing inter-band isolation. In the synthesis, two successive frequency transformations originated from lowpass domain are employed to establish the dual-band response. With the aid of source-load coupling, two extra zeros close to outer passband edges are further created to greatly improve the frequency selectivity. A microstrip filter is fabricated and tested for validation. Measured results show good agreement with simulation responses.