X-band voltage variable attenuators using PIN diodes

We present the design of PIN diode based medium-power Voltage Variable Attenuators realized on microstrip in the frequency range of 9.1-9.6 GHz. These reflective variable attenuators have a topology based on 90° hybrid couplers. Single hybrid coupled attenuators can be used for broadband operation. A double hybrid coupler design eliminates the ripple response in the high attenuation state, thereby increasing the dynamic range. Both the approaches have been presented in this paper. They not only exhibit good linearity, but also have a good VSWR match over the full frequency range and over all the attenuation levels.