A Dispersive Quadruplet Structure for Monoblock Dielectric Resonator Filters

In this article, a dispersive quadruplet structure that can flexibly control the rejection response of a high-
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monoblock dielectric resonator (MDR) filter using a shared cavity is introduced. Being simple in structure, traditional partitioning walls for positive couplings are replaced by metalized through holes. The dispersion effect of the blind hole for negative coupling can be effectively compensated by parasitic cross couplings by appropriately managing the through holes, leading to a shared rectangular cavity for the resonators. With the aggregated effort of the blind hole and through holes, the rejection response can be well controlled to a certain extent. The closed-form mathematic transformation from the dispersion-less to dispersive coupling matrices of the quadruplet is also given for explaining the working principle of the dispersive quadruplet and providing a design guideline. Two design examples are presented: a quadruplet MDR filter with two symmetric transmission zeros (TZs); and an eight-pole MDR filter consisting of a proposed quadruplet and a box unit, showing superior performance of the MDR quadruplet structure in realizing a wide range of rejection responses and validating the theory for practical applications. The experimental result demonstrates that the MDR quadruplet is particularly useful when rejection specifications near the passband are stringent.