Design high-directivity parallel-coupled lines using quadrupled inductive-compensated technique

A high-directivity parallel-coupled lines based on an inductive compensation technique, which is achieved by connecting the optimum inductors at all coupler's ports, is presented in this paper. Based on a quasi-static model, the optimum inductor and the coupler's electrical length are given. Analysis, simulated, and measured results of a 0.9 GHz 10-dB uncompensated and quadrupled inductive-compensated couplers are compared. The measured results obtained from the proposed coupler exhibit more than 25 dB improvement of the directivity over the uncompensated design at the operating frequency.