RF-MEMS tunable Evanescent Mode Cavity filter in LTCC technology at ku-band

Frequency-agile Evanescent Mode Cavity (EMC) filters were designed as Substrate Integrated Waveguide (SIW) components in LTCC technology. The tuning of the center frequency was performed by open ended microstrip stubs, whose length can be adjusted by RF-MEMS switches. Two different coupling methods of the tuning structures to the filter were designed and the frequency responses of the filters in each tuning state were measured and analyzed. A shift of the center frequency of 4 % and 6 % was realized with the different coupling methods. The minimal insertion loss is between 2.51 dB and 5.57 dB and the 3 dB bandwidth is between 537 MHz and 728 MHz, depending on the coupling method and the tuning status of the filters. The unloaded Q-factor is 167 and 148 for the filter with inductively coupled tuning structures for the two tuning states of the center frequency. A comparison to a similar, frequency-agile standard cavity filter is presented, to show the benefit of the evanescent mode approach.