Design and analysis of variable attenuator with simultaneous minimized flat amplitude error and insertion phase variations

This paper presents a design of an analog variable attenuator with simultaneous minimized flat amplitude error and insertion phase variation over a wide bandwidth and high attenuation range. The parasitic of PIN is compensated with series transmission lines loaded and shunt capacitors to achieve minimum flat amplitude error and insertion phase variation. Mechanism for simultaneous reduction in flat amplitude error and phase variations is obtained by developing an analytical design equation using the PIN diode equivalent circuit model. For the experimental validation, two kinds of proposed attenuators are designed and measured over 1 GHz bandwidth at a center frequency (f₀) of 3.5 GHz. The measurement results are consistent with the simulation results. From the experiments, design-I provides an attenuation variation of 0.9 dB to 20 dB with a maximum flat amplitude error of 0.65 dB and insertion phase variation of 5.70° over 1 GHz bandwidth. Similarly, the design-II provides an attenuation variation of 1.06 dB to 20 dB with a maximum amplitude error of 0.49 dB and insertion phase variation of 3.19° over the same 1 GHz bandwidth.