Class of miniaturised/arbitrary power division ratio couplers with improved design flexibility

This study describes a new class of couplers using single-layer microstrip lines that reduce the occupied area, suppress the harmonic components and provide arbitrary power division ratios. It consists of lumped reactances between transmission lines to reach realisable impedances and shorten line lengths. To provide a design guideline, closed-form formulas are derived and five different designs are produced and built to investigate the couplers performance and design accuracy. The simulation results prove to be in good agreement with measurements. More than 70% size reduction with respect to the conventional structures, 12 dB harmonic suppression and high power division ratios (9:1) achieved in various presented branch line, rat race and multi-section Wilkinson dividers. This proposed class of coupler structures can effectively be used in miniaturised and/or arbitrary power division ratio couplers with harmonic suppression.