A Temperature Compensated Light Weight Coaxial Band Pass Filter for Aero-Space Applications

One of the challenges in designing coaxial band pass filters for aero-space applications is to simultaneously minimize the temperature drift and weight. In this paper, the authors have addressed this issue in a simple yet effective manner. In a high Q coaxial cavity resonator (where tuning screw loading is not significant), the solution proposed is to employ invar for resonator post and aluminum for rest of the housing. To validate the proposed concept, a 4th order filter at C band is designed, fabricated and measured. The active temperature measurements of the filter from -55° C to 125° C reveal that the equivalent temperature coefficient of frequency variation of the filter, evaluated based on the center frequency shift, is less than 4.8 ppm/°C. The weight of the filter is less than 90 grams.