RF vector sum phase shifter using a novel variable directional coupler

In this paper, a vector sum phase shifter system has been implemented using a novel RF variable directional coupler. The variable coupler uses micro-fluidics to vary the coupling between the through and coupled ports of a single-section broadside coupled quarter-wave stripline coupler. An in-phase combiner is then used to recombine the through and coupled signals to achieve a variable linear phase shift with frequency over the 8-12 GHz band. The use of this RF variable directional coupler makes the system very simple compared to photonic implementation techniques. The losses associated with the optical conversions are also avoided.