Design of a dual-band bandpass filter with a wide stopband

A novel wide-stopband dual-band bandpass filter with a modified coupled line and lowpass filters is proposed. The modified coupled line is realised with two open stubs added to the conventional coupled line's open ends. With this proposed circuit, additional transmission zeros will appear around two passbands. Moreover, these predictable transmission zeros can be utilised to tune the two passbands’ bandwidths. Furthermore, with the lowpass filter embedded, located at the input/output port, a wide stopband can be obtained. Finally, agreement between measurement and the theoretical prediction validates the proposed structure.