Filtering Attenuator with Electronically Tunable Attenuation

This paper presents a design of a filtering attenuator. Conventional microstrip line resonators of a bandpass filter are loaded with PIN diodes and the resultant component provides band selectivity as well as electronically tunable attenuation. The diode is used as a variable resistor. Detail design steps are provided. A prototype filtering attenuator is fabricated to validate the theoretical approach. It provides an equal ripple bandwidth of 17% at 2.4GHz. The bandwidth can be changed according to application requirement. Hairpin resonators are used for the implementation. Measurement results show that the passband insertion loss of the filtering attenuator can be tuned over 3.8-30.4 dB maintaining a minimum return loss of 10dB.