CST – Computer Simulation Technology

Modelling Cavity Filter Temperature drift in CST MWS

Metallic and dielectric cavity resonator filters continue to play an important role in the wireless infrastructure market. Particularly due to an increasing need co-site and co-locate several old and new standards performance requirements are getting more stringent. This is especially true for filter guard band gaps. One of the contributors to the filter bandwidth margin is the temperature drift allowance. This allowance is to allow for the filter response change due to (i) material thermal expansion/contraction, and (ii) change in the dielectric constant. A very useful technique has previously been developed to estimate the coaxial resonator temperature drift. This technique has extensively been verified in practice. However, its main limitation is that it relies on closed-form mathematical expressions, thus being applicable only to the canonical structures. In this paper we first reproduce in CST MICROWAVE STUDIO® the expected temperature drift results for commonly-used filter resonators. We then go on to show that this new methodology can be applied to structures of arbitrary shape, with an arbitrary number of elements, and with arbitrary material composition. Finally, we consider temperature drift for structures where dielectrics as well as metals change their properties at different operating temperatures.

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