A Varactor-Based Variable Attenuator Design With Enhanced Linearity Performance

This paper presents, for the first time, the linearity study of a varactor-based microwave attenuator. In particular, a novel technique is proposed to linearize the attenuator in terms of both main-tone and intermodulation distortion (IMD) performance. The enhancement circuit is simple to implement and can offer a reduction of the IMD level of over 20 dB. Linearization is achieved by shifting the biasing point of the tuning diodes (under large attenuation operation) away from the highly nonlinear region. For verification, both simulated and measured results of a 1-GHz variable attenuator with and without linearization are given.