A 1.33-1.88 GHz microfluidically tunable filter with controllable coupling

In this article, a continuously microfluidically tunable filter using two microstrip resonators is proposed. By injecting different amount of water into the tubes, the resonant frequency as well as coupling intensity between two resonators can be controlled. As a result, the fractional bandwidth (FBW) of the proposed band can keep constant when tuning the frequency. As far as the authors know, most of the state-of-the-art microfluidics tunable filters are discontinuous, and the tuning range is limited. In this article, the wide tuning capacity of the frequency is realized by placing some tubes between the microstrip resonators and the ground. By increasing or decreasing the amount of water in the pipes, the local dielectric constant and the equivalent electrical length of the transmission line are changed simultaneously. Therefore, it plays a key role in resonant frequency tuning. In the other hand, the coupling coefficient can be controlled by injecting the amount of water into the tube between the two resonators. Finally, through the analysis of computer simulation technology simulation and measurement, it can be seen that the tuning range of resonant frequency is up to 41.3%, with the central frequency varying from 1.33 to 1.88 GHz. The insertion loss is less than 3.09 dB and the return loss is higher than 15 dB, while the FBW is 3.4% +/- 0.2%. The measurement matches well with the simulation results, verifying the proposed design methodology.