A compact wideband voltage-controlled tunable filtering attenuator based on FHRR

A compact wideband voltage-controlled tunable filtering attenuator is implemented based on folded hairpin ring resonator (FHRR) in this paper. The proposed FHRR is realized by outward folding two open-ended stubs of a hairpin ring resonator. Meanwhile, two open-ended stubs are loaded to introduce two additional transmission zeros (TZs), which enhance the selectivity. Moreover, four PIN diodes are loaded at the open-endedinterdigital coupled-linestructure, therefore integrating the filtering response and attenuation functionality simultaneously. By leveraging the property of PIN diodes, whose impedance is continuously adjustable with bias voltage, dynamic control of the transmitted signal amplitude is achieved. To demonstrate the validity of the design, a filtering attenuator was fabricated and measured. The measured results show a good agreement with the electromagnetic simulations. The measurement results demonstrate that the filtering attenuator operates across a passband from 1.75 GHz to 3.95 GHz, achieving a fractional bandwidth (FBW) of 77.2% and can realize the attenuation range of 2.6 dB to 25.6 dB.