Coupled stepped-impedance resonator based dual-band reconfigurable bandpass filters

This paper reports design of concurrent dual-band reconfigurable band-pass filters (BPFs) using microstrip coupled stepped-impedance resonators (CSIRs) for WLAN/GSM/DSC applications. Semiconductor varactor diodes have been used as tuning element. Tuning can be introduced in one or both bands by properly incorporating the tuning elements in the CSIR structure. Three cases of frequency tunability have been considered. Varactor diode incorporated in series configuration with the CSIR structure provides tuning in lower band while upper band is fixed. In the second case, varactors incorporated in the shunt configuration with the CSIR structure are used to obtain tuning in upper band while lower band has been kept fixed. In the last case, varactor diodes have been used in a series-shunt combination with the CSIR structure for introducing tuning in both frequency bands independently. Design approach and analysis have been provided along with simulation and measurement results.