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This paper presents a novel type of tunable bandpass filters with constant bandwidth and wide tuning range. A constant absolute pass-band has been obtained by integrating a low-pass filter at the input and the output of the filter. The filter fabricated on duroid substrate can be tuned from 690MHz up to 1130MHz, by using RF-MEMS switches mounted in series with fixed capacitors. Matching is better than -12dB and the 3dB passband is 65MHz+/-5MHz. Measured insertion loss is less than 1.7dB at the upper end of the band and 3.3dB at the lower end. The filter shows no compression up to 1Watt of input power, and no measurable degradation of ACPR at the same power level.Index Terms-tunable filter, constant bandwidth, impedance matching, RF MEMS.

We developed a distributed-parameter model (partial differential equations and associated boundary conditions) that describe the coupled torsion and bending motions of the Digital Micromirror Device (DMD) using the extended Hamilton principle. The work done by the electrostatic field is expressed in the form of a potential energy. It is found that coupling between the torsion and bending motions appears in the boundary conditions. The nonlinearity is mainly due to the application of the electrostatic forces and moments. Nonlinear terms appear only in the boundary conditions. The developed model provides a basis for a thorough study of the static and dynamic behaviors of the electromechanical device. The static response of the DMD for different DC loads shows the occurrence of pull-in (snap-down) instability at critical voltage values corresponding to the collapse of the yoke to mechanical stops. Estimates of the voltage, angle, and deflection at pull-in are given. The dynamic behavior of the DMD is analyzed by plotting the natural frequencies versus the applied DC voltage. We conducted a study of the sensitivity of the static and dynamic behaviors of the micromirror to variations in the geometric parameters of the DMD. It is found that the thickness and width of the hinges are the key parameters influencing the occurrence of static pull-in and the values of the voltage, angle, and deflection at pull-in.

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