Multi-Mode Dielectric Resonator Bandpass Filter Utilizing Higher-Order Modes to Achieve a Broad Bandwidth with Sharp Transition

In this paper, two broadband sixth-order bandpass filters based on two coupled dielectric triple-mode resonators are presented. By introducing side cavities and asymmetries, the resonant frequency of two orthogonal HEM11d modes can be shifted specifically. In combination with a TM01d mode, this enables a strong mode coupling and the realization of a sixth-order bandpass filter. Furthermore, the external coupling allows two higher-order modes (HOM) to be positioned close to the passband, which can be integrated into the filter response through minor adjustments, thereby realizing an eighth-order bandpass filter. With this optimization, a center frequency of 4.287 GHz and a bandwidth of 1233 MHz were achieved, corresponding to a fractional bandwidth of 28.76 %. Finally, the filter was manufactured, measured and compared with the simulations.