A Temperature-Compensation Technique for Substrate Integrated Waveguide Cavities and Filters

A new temperature compensation method is proposed and demonstrated in this paper for cavities and filters realized in substrate integrated waveguide (SIW). The SIW structures largely preserve the well-known advantages of conventional rectangular waveguide, namely, high Q and high power capacity, and have the advantages of microstrip lines, such as low profile, small volume, and light weight. In this paper, we demonstrate that by an adequate selection of substrate properties, SIW cavities can provide self-temperature drift compensation. The compensation is achieved by using an appropriate ratio between the coefficient of thermal expansion and the thermal coefficient of the permittivity. The theoretical prediction is confirmed by an experimental investigation using inductive post filters. Three commercially available substrates are used to design cavities at 10 GHz with the Roger TMM10 substrate providing a close fit to the required characteristics for temperature compensation. The results for the cavity show a stability of 2 ppm/degrees C in calculation and 8 ppm/degrees C in measurement. A SIW fourth-order Chebyshev filter, centered at 10 GHz with 1-GHz bandwidth, has also been designed. The measured frequency drift is 9.1 ppm/degrees C and the bandwidth variation is +/-0.13% over the temperature range of -40 degrees C to +80 degrees C.