Triple mode dielectric resonator hybrid reflection filters

A new class of dielectric resonator filter is described. These devices use the triply degenerate TE_11δ mode in a cubic dielectric resonator. A simple theory is used to show the similarity between this mode and the TE_10δ mode in a cylindrical resonator. The cubic resonator is used in a hybrid reflection mode filter where the even and odd subnetworks of a bandpass filter are connected to two ports of a 3 dB quadrature hybrid. The transmission response through the other two ports is then the reflection coefficient of the bandpass filter. The design approach only requires the realisation of simple one port ladder networks and is ideal for realising complex filters using triple mode resonators. A design example is presented for a degree 6 elliptic function bandstop filter operating in the 850 MHz cellular radio band. A threefold size reduction is achieved when compared to single mode filters with similar electrical performance