Compact Tunable Broadband Filtering Attenuator Based on Variable Resistors

In this letter, a compact microstrip broadband filtering attenuator based on variable resistors is proposed with high-frequency selectivity. It can achieve tunable attenuation characteristics over a broad frequency band by changing the resistance of the variable resistors. Due to the symmetry of the circuit structure, it is analyzed using odd- and even-mode methods. For demonstration, a filtering attenuator prototype is fabricated and measured, which operates from 1.3 to 2.8 GHz and realizes tunable attenuation from 3.26 to 15.61 dB. The results of theoretical calculations, simulations, and measurements agree well with each other, which validates the feasibility of the proposed design.