Research On Microwave Fractal Reconfigurable MEMS CPW Band-Pass Filter

In recent years due to the urgent needs of multi-band in microwave, millimeter wave band, broadband wireless communication systems, the MEMS reconfigurable filters used in microwave and millimeter-wave frequency ranges have been made greater development. Moreover, in the multi-standard receivers, reconfigurable filters can significantly reduce the size of analog front-end subsystem which is in application of multi-band, and can inhibit the dynamic interference signals. So MEMS reconfigurable filter will be an important component part in a new generation of wireless communications systems, such as high-tunable, low-cost and low-power wireless and satellite communication networks, as well as radar, navigation tunable location identification systems, self-guided smart weapons Intelligent RF front-end device.In this paper, the present research status of tunable filters is briefly introduced and then designs a kind of coplanar waveguide band-pass filter in microwave wave-band that is on the basis of self-similar fractal theory, CPW transmission-line periodic structure and Multi-contact MEMS switch. First of all, the filtering features and self-similar fractal principle of band-pass filter are introduced first, beginning with CPW transmission-line band-pass unit structure combined the microwave transmission line theory, and then through loading MEMS switches to change transmission-line structure it can achieve the purpose of adjustable frequency. Details of the band-pass filter design, electromagnetic simulation, layout, and process flow are presented, and a complete general MEMS process is gained. By the end experimental samples are tested, and analyze the testing results.In this paper, the results of research are as follows:[1] Based on the slow wave structure and periodic self-similar fractal theory, a coplanar waveguide transmission line band-pass filter unit structure was introduced, and the simulation results and the test results proved that the unit structure has a good filter characteristics.[2] MEMS switch contacted Multi-contact which was big size and difficulty to realize in process was researched. The MEMS switches that were already fabricate had good isolation and transmission characteristics, the size was 610×160 (μm×μm), the down- voltage was 25 V, and the contact resistance was of a 2 ohm, and the lifetime of golden bridge was about 10~5. And summarized a complete general silicon surface MEMS process. [3] Using CPW transmission line band-pass filter unit structure and reconfigurable MEMS switches constitute a band-pass filter. Through actuating switches to change the structure and size of transmission lines, and then this can finish the conversion between the different frequency bands in accordance with the demand. The center frequency of band-pass filter that was presented in this paper was from 40 GHz changed to 16 GHz after reconfigured, and the switching frequency can be approximated as the ratio of 3:1.[4] The band-pass filter unit structure was researched and extracted lumped parameters equivalent circuit of the band-pass filter element. Analyzed theoretically the main factors that could affect band-pass filtering performance and lay the foundation for the future to further design and study.