Development of High-Speed Mechanical Tuning System for HTS Filters

We developed a high-speed ( ~1 second) mechanical tuning system for HTS microstrip line (MSL) filters using a dielectric tuning plate, dielectric trimming rods, and conducting trimming rods. The tuning plate has windows through which the dielectric and conducting trimming rods pass. It was designed for a 3-pole filter with 5 GHz center frequency (f_c) and 100 MHz bandwidth (BW) using a 3-dimensional electromagnetic simulator. The simulation of 500 MHz frequency shift induced by dielectric tuning plate was done and, in addition, by using both kinds of trimming rods an improvement of insertion loss (IL), pass-band ripples reduction and increase of bandwidth was achieved. In the experiment, the positions of the plate and the rods above the filter were adjusted by using high-resolution operating at room temperature step motors. The minimum step of moving the plate and the rods was 0.001 mm. We found that the fc was shifted by 500 MHz while retaining the IL, pass-band ripple, and BW by experimental evaluation. The time taken by the 500 MHz tuning was less than 1 second. These results indicate that our method and system will be useful for the next generation of wireless communication systems.