MEMS-based fine tuning of high Q-factor E-plane filters

This paper presents a new concept for the fine tuning of high-Q bandpass filters to compensate for small response deviations due to manufacturing tolerances and temperature variations. Discrete frequency tuning steps are obtained using a rectangular waveguide resonator loaded with a reconfigurable E-plane circuit. Ohmic micro electromechanical systems (MEMS) switches can be placed along thin E-plane metal strips so as to modify the E-field distribution of the TE101 resonant mode, thus the central frequency of the filter. As an example, 0.1% frequency steps can easily be obtained in a 10 GHz resonant cavity. The use of low-loss substrates ensures high-quality factors of the order of 1000. The feasibility of the proposed approach is demonstrated both by full-wave simulations and by fabricating and measuring an X-band hardwired prototype.