An extremely wide band balanced amplitude controller in coplanar waveguide technology

A versatile amplitude controller is presented, which is intended for phased array applications or QAM-modulators operating directly at the desired radio frequency. Due to the small geometry and the 0.2 ¿m GaAs/GaAIAs HEMT technology, a bandwidth from 15 to 60 GHz could be achieved. Coplanar waveguides and lumped elements were used as passive circuit elements. The main topology consists of a differential amplifier and a coplanar balun. The control voltages of the differential amplifier are applied in a push-pull scheme. The balun operates as 180°-power combiner and subtracts both RF-signals. In this way, the common mode is rejected and the phase of the output signal changes by 180°, when the amplitude crosses zero.