A Novel Technique for the External Coupling of Coaxial Dielectric Microwave Filters

International audienceCoaxial dielectric resonators made from materialswith high relative permittivity, including ceramics, have goodtemperature stability and quality factors of the order of 1000in the UHF band. At these frequencies, large wavelengths aredisadvantageous from the point of view of size, but high dielectricconstants, up to 90, can be used to minimize them. However,coupling the input/output of filters, i.e., their excitation, remainsa critical issue, especially when wide passbands are required.The objective of this paper is to present a novel technique tomake this coupling, to solve problems that arise when usingclassic techniques. The approach consists of nesting a conductingrod in each central core of the input/output resonators, whichcreates another coaxial TEM mode that will couple with thefundamental TEM mode of the input/output resonator. Thelength and/or position of the rod provide the opportunity to easilyand accurately tune input/output couplings over a wide dynamicrange. In this paper, we show the effectiveness of the solution,presenting the experimental results of sixth-order filters centeredat 435 MHz, one made on the basis of a standard input/outputcoupling and the other on the basis of the new solution proposedhere