A 10–14 GHz RF MEMS tunable bandpass filter

This paper reports a bulk micromachined microwave tunable bandpass filter whose tunability is accomplished by MEMS bridges. This kind of tunable bandpass filter is based on elliptic function lowpass prototype filters. The proposed filter is constructed by the combination of a tunable lowpass filter and a highpass one which can either be tunable or not. In this way, the tunable bandpass filter can change its higher band cutoff frequency by shifting the cut off frequency of the lowpass filter. The tunable lowpass filter is realized by adjusting the first transmission zero (FTZ), while the tunable bandpass filter, if it is realizable, is achieved by adjusting the last transmission zero (LTZ). The method of shifting the transmission zero of the elliptic filter is to load capacitive MEMS switches at the end of the branch where the particular transmission zero lies in. Experiments show that the simulated 3 dB cutoff frequency changes about 600 MHz after one more MEMS switch is activated.