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.