Discrete-tunable high-Q E-plane filters

This paper presents a new concept for the design of high-Q tunable bandpass filters with discrete steps in frequency using a rectangular waveguide resonator loaded with a reconfigurable E-plane circuit. Ohmic MEMS switches are placed along thin E-plane metal strips so as to modify the TE₁₀₁ mode resonant frequency, thus the central frequency of the filters. Tuning ranges up to 5% are achieved with unloaded Q-factors higher than 1000 if low loss substrates are used. Preliminary measurements of a 3^rd order bandpass hardwired filter at 9.75 GHz show two frequency shifts with a maximum of 420 MHz (4.3%) and Qs above 1000. The filter response in terms of fractional bandwidth and return loss is robust over tuning. The final version using actual RF MEMS is being fabricated.