A reconfigurable bandpass filter (BPF) with constant centre frequency and wide tuning range of bandwidth is presented. The proposed filter is based on the novel configuration of two modified asymmetrical… Click to show full abstract
A reconfigurable bandpass filter (BPF) with constant centre frequency and wide tuning range of bandwidth is presented. The proposed filter is based on the novel configuration of two modified asymmetrical $\pi $ -sections with folded shorted stubs loaded on a ring resonator. The novel topology allows the implementation of three reconfigurable passband states. A detailed theoretical analysis for calculating the transmission zeros using ABCD parameters is shown, and the design approach of implementing the random offset–x-, asymmetrical $\pi $ -sections with the folded stubs to get the bandwidth reconfigurability is thoroughly explained. PIN diodes are utilized as switching elements to achieve narrowband/mediumband/wideband response. The measured results indicate an absolute bandwidth tuning range of 1.3 GHz, whereas the −3 dB fractional bandwidth (FBW) can be varied from 37% to 92% while the centre frequency remains constant at 2.4 GHz. The fabricated prototype reconfigurable BPF demonstrates one of the widest 3-dB FBW tuning ranges and one of the highest absolute tuning ranges with a sharp-skirt characteristic. It has also more than 20 dB attenuation in the upper stopband which is extended to 2.7 times the centre frequency.
