A tunable quasi-lumped microstrip coupler and RF applications

In this paper, we present the design of a tunable quasi-lumped quadrature coupler (QLQC). This circuit consumes no power and its size is reduced compared to a classical branchline hybrid coupler. The first presented application is a polarization reconfigurable antenna for diversity purposes. This structure can provide a full set of linear or circular polarization states by simply changing the DC bias of a switch and two varactor diodes. In a second part, two QLQC's are combined to form a phase shifter using vector sum method for phased array applications. This phase shifter circuit delivers two evenly split signals phase shifted over a 240deg controllable range.