A Novel Voltage-Controlled Tunable Filtering Attenuator Based on Lossy-Tuned Ladder-Type Microstrip Filter

A novel voltage-controlled tunable filtering attenuator is proposed based on tunable lossy resonators and lossy coupling, featuring wide attenuation tunable range, improved in-band flatness, and bandwidth stability. The proposed component is implemented through an eighth-order ladder-type microstrip filter tuned by p-i-n diodes. The symmetrical feature of the component enables comprehensive analysis through odd- and even-mode methods, facilitating precise parameter optimization. A proof-of-concept prototype has been fabricated and measured. The measurement results demonstrate an attenuation tuning range from 4.4 to 50 dB while maintaining a flat passband of 907 MHz (±7.4%) or 46.9% (±3.2%) at 1.93 GHz and show the switch-off ability of in-band suppression of 53–74 dB. The multifunctional integration of filter, voltage-controlled attenuation, and switch is achieved.