Design Method for MMW LC Tunable Microstrip Periodic Filters

With the ever-increasing global pressure to develop higher data rate/wider bandwidth networks, most telecommunication service providers are considering MMW as the mainstream technology to provide mission-critical capabilities such as superior speeds and low latencies. The license free internationally assigned MMW spectrum are not utilized normally and indeed sections of the spectra are engaged in different countries around the world. Therefore, tunable filters performing frequency selection are essential elements of the MMW equipment. Microstrip periodic structures on Liquid Crystal (LC) substrate are the most cost-effective solution for the required MMW tunable filters. A novel method is proposed for LC MMW microstrip periodic filter using a new design approach. The designed filters perform at 60 GHz with 3.5-5 GHz bandwidth. The structure composed of periodic Microstrip stubs on BL037 LC substrate. Changing the bias voltage of LC provides a tunability from 58.5 to 62 GHz, while maintains the fractional bandwidth around 5%. The return loss of passband is better than 10 dB with insertion loss variation from 3.8 to 5 dB.