Wideband 3 dB quadrature microstrip line coupler with unequally reduced wave impedances and asymmetrical configuration in parallel lines

Computational and experimental studies of a wideband two-section 3 dB hybrid coupler using microstrip lines are conducted. By unequally reducing the wave impedances of longitudinal and transverse branches in the two-section hybrid splitter, broadband responses with almost twice bandwidth compared to the ideal two-section hybrid were obtained while maintaining identical overall size. Furthermore, the two-section microstrip line coupler has wide bandwidth of 44%, amplitude imbalance of ± 0.5 dB, and isolation of 17 dB in the range of frequencies from 1.71 GHz to 2.72 GHz by taking asymmetrical configuration between top and bottom parallel transmission lines with reduced wave impedances.