Compact broadband waveguide filter with wide spurious-free range based on mixed TM and combline resonators

The design of a C-band filter centered at 6.175 GHz with 500 MHz bandwidth (FBW=8.3%) is presented. The proposed filter shows good performance in terms of loss and stop-band spurious-free range. The filter consists of a total of 9 resonators: 5 TM resonators and 4 comb-line resonators yielding a very compact structure. The TM resonators allow for good performance in terms of in-band loss and filter length, while the 4 comb-line resonators allow removing the spurious frequencies generated by the TM resonators avoiding the need of bulky low-pass filter. With respect to the conventional solution a length reduction of about 60% is obtained. The feasibility of the proposed approach is demonstrated through the measurements of the manufactured prototype.