L-band tunable microstrip bandpass filter on multilayer organic substrate with integrated microfluidic channel

This paper presents, for the first time, a tunable microstrip microfluidic bandpass filter, with a center frequency of 1 GHz, on liquid crystal polymer (LCP). A 60 mil cavity, initially filled with distilled (DI) water (ε_r = 80), is placed below a 2 mil LCP layer. Based on this multilayer structure, the dimensions of microstrip lines are determined. In order to tune the filter center frequency, DI water is replaced by acetone, with a dielectric constant that is 4 times lower than that of DI water (ε_r = 20.7). A micropump is used to inject the different fluids and provide the necessary pressure to trap the liquid inside the microfluidic channel. Measured results show 50% tuning which translates into a maximum center frequency shift of 500 MHz. The insertion loss is 1.4 dB and the return loss is 25 dB at 1 GHz for the DI water filter while the insertion loss is 1.3 dB and the return loss is 15.8 dB at 1.5 GHz for the acetone filter.