Mathematical analysis of novel low phase deviation variable attenuator

A conventional variable attenuator has phase deviation characteristics on an attenuation process. In this paper, a novel phase deviation compensating method in a variable attenuator design is proposed and analyzed mathematically. The proposed method uses a transmission line terminated with the PIN diode. By control characteristic impedance and electrical length of the transmission line, a trace of input reflection coefficient at the transmission line can be crossed the zero point of Smith chart on an attenuation process. The fabricated variable attenuator shows a 2.9° of phase deviation for 33 dB signal attenuation at 2.14 GHz. And the reflection characteristics also have measured less than -27 dB on the overall attenuation range.