High Performance, Continuously Tunable Microwave Filters using MEMS Devices with Very Large, Controlled, Out-of-Plane Actuation

TL;DR

This paper presents a novel microwave filter design using MEMS actuators with large out-of-plane motion, enabling wide, continuous tuning from 4 to 15 GHz for advanced software defined radios.

Contribution

The paper introduces a new filter architecture utilizing extreme throw MEMS actuators for continuous, wide-range tuning in microwave frequencies, surpassing previous narrowband or switchable filters.

Findings

Achieved continuous tuning from 4 to 15 GHz.

Demonstrated large, controllable out-of-plane actuation of MEMS.

Enabled high-Q, low-loss, wideband microwave filters.

Abstract

Software defined radios (SDR) in the microwave X and K bands offer the promise of low cost, programmable operation with real-time frequency agility. However, the real world in which such radios operate requires them to be able to detect nanowatt signals in the vicinity of 100 kW transmitters. This imposes the need for selective RF filters on the front end of the receiver to block the large, out of band RF signals so that the finite dynamic range of the SDR is not overwhelmed and the desired nanowatt signals can be detected and digitally processed. This is currently typically done with a number of narrow band filters that are switched in and out under program control. What is needed is a small, fast, wide tuning range, high Q, low loss filter that can continuously tune over large regions of the microwave spectrum. In this paper we show how extreme throw MEMS actuators can be used to build such filters operating up to 15 GHz and beyond. The key enabling attribute of our MEMS actuators is that they have large, controllable, out-of-plane actuation ranges of a millimeter or more. In a capacitance-post loaded cavity filter geometry, this gives sufficient precisely controllable motion to produce widely tunable devices in the 4-15 GHz regime.