Dielectric TM Mode Extracted Pole Filters with Large Spurious Free Range

In this paper, filters based on the extracted pole technique revealing a large spurious free region are presented. The filters consist of classical TM010 mode dielectric resonators. However, special attention is given to the realization of the non-resonating node (NRN), which is required for implementing extracted pole filters. A coaxial as well as a TM mode resonator is used as an NRN, enabling a comparison of the spurious mode performance of both realizations. To validate the results, various measurements with a different numbers of extracted pole sections are realized and compared. This is accomplished by using a modular design, which allows the combination of different sections without requiring to manufacture various prototypes.