A Compact C-Band Programmable Bandpass Filter

Abstract

This article presents a compact, programmable bandpass filter (BPF), leveraging an independently reconfigurable architecture to achieve encoded control across multiple bandwidth states. The filter consists of bandpass striplines positioned midway between two ground planes, where rectangular defected ground structures (DGSs) are integrated with fence units. The DGSs significantly enhance the initial bandwidth, whereas the fences are employed to adjust the coupling with the striplines through active control. By indirectly adjusting the even-mode capacitances and coupling coefficients, the structure achieves a precise bandwidth tuning range. Such reconfigurability is governed by an FPGA-driven programmable scheme, wherein specific metallic fence switching states are precisely mapped to predefined bandwidth responses. A total of 17 discrete operating bandwidths are achieved by FPGA encoding. The measured FBW exhibits a continuous-like reconfigurability from 28% to 78% with negligible center frequency deviation at 5.9 GHz. Across the entire tuning range, the in-band return losses (RLs) remain superior to 9.78 dB, while the insertion losses (ILs) are maintained below 6.46 dB. Featuring a compact footprint of $0.25\lambda _{0}^{2}$ and autonomous digital control, the proposed filter is well-suited for adaptive satellite communications or radar systems.