A WAVE-GUIDE BANDPASS FILTER MADE OF HIGH-PERMITTIVITY CERAMICS

A rectangular waveguide was formed with ceramics having a high relativ e permittivity of 93. This waveguide is divided into two in the E-plan e. This structure was used for the design and fabrication of a bandpas s filter of small size and light weight which can be surface mounted. Inductive strips are formed on the E-plane so that the center frequenc y of the one-half wavelength resonator and the coupling coefficient be tween the resonators are adjusted. Further, by choosing a structure in which the filter is connected directly from a microstrip line, the st ructure is miniaturized. In the design, first the dimension dependence of the characteristic values of the composite resonators, e.g., the c enter frequency and the coupling coefficient, was found experimentally . Then a general filter theory was applied. Further, the characteristi c values of the resonator were studied theoretically so that the dimen sion dependence can be explained qualitatively.