A novel, varactor-based microwave attenuator with wide tuning ratio and flat insertion loss response

This paper presents, for the first time, the design of a varactor-based variable attenuator with wide tuning range and flat insertion loss response. It is accomplished by the combination of a variable power divider (with anti-phase outputs) and a Wilkinson power combiner. This circuit offers several advantages including zero DC power consumption, single control voltage, and wide tuning range of attenuation from 4 to 35 dB with typical tuning diodes (small capacitance ratio). For verification, both simulated and measured results of a 1 GHz attenuator implemented on microstrip are shown.