Soft radio frequency microstrip bandpass filter: Precise design and demonstration

Abstract

A soft and tunable microwave bandpass Chebyshev microstrip end-coupled filter is demonstrated on a polydimethylsiloxane substrate based on high electrically conductive composites made of silver nanoparticle-covered flakes, even with large strain. To achieve a precise design, key microwave parameters such as the impedance, S-parameters, and transmission matrix are defined as a function of strain. This strain vector polar coordinate is used to represent the relationship between the type and the performance of a filter. Then, the most important Chebyshev or quasi-Chebyshev type of filter can be accurately realized by looking up its polar coordinates to find the corresponding strain magnitude and direction of stretching. An end-coupled Chebyshev microstrip bandpass filter with a center frequency of 12.8 GHz and bandwidth of 22% was designed and fabricated for demonstration. Experimentally, at a lateral elongation of 8% and 10.7%, the center frequency decreases by 0.61 and 0.88 dB, respectively, matching the simulation results very well. One potential application for this tunable filter is a front-end module mounted on the biomimetic robot driven by its mechanic movements.