Precise frequency and bandwidth control of switchable microstrip bandpass filters using diode and microelectro-mechanical system technologies
In this study, two reconfigurable bandpass filters are presented. The first filter is able to switch between WiFi and universal mobile telecommunications (UMTS) transmit band standards. Centre frequency, bandwidth and power specifications are precisely met by a switchable filter topology that includes two folded resonator extensions switched by only two PIN diodes. Design specifications require two filter states, one at 2.440 GHz with a 80 MHz bandwidth and a second state at 1.955 GHz with a 140 MHz bandwidth for the WiFi and UMTS transmit bands, respectively. The filter should handle a maximum power of 16 and 21 dBm for the WiFi and UMTS states, respectively. Measured results show very good agreement with the simulations. The filter topology meets power requirements of both standards. The second filter was designed using ohmic-contact cantilever-type MEMS able to switch between two different states with a centre frequency tunable range of 24% in C band. This design includes two additional switches to provide precise input and output couplings for each state. The filter was designed to have centre frequencies of 5 and 6.2 GHz, with a fractional bandwidth of 7 and 3%, respectively. Filter specifications were successfully met with the proposed topologies.