Analysis and design of three transmission zeros bandpass filter utilizing triple-mode dielectric loaded cubical cavity

An equivalent circuit for the third-order triple-mode cross-coupled asymmetric response filter is proposed which includes the direct-coupling between the input and output ports. Based on this circuit, the existence of three transmission zeros for the filter is established through mathematical expressions derived for the computation of the zeros. To verify the accuracy of the theoretical transmission zeros, a triple-mode cross-coupled asymmetric response filter with a centre frequency at 1.705 GHz, is designed and implemented, using a dielectric loaded cubical cavity resonator. Very close agreement between the computed and measured results of the filter is achieved.