A wideband 90�° hybrid coupler has been presented and implemented in planar microstrip circuit. With similar structure of\nconversional 2-section branch-line coupler, the proposed coupler consists of a lumped high-pass network but not the quarter\nwavelength transmission at the center. The values of all lumped elements were optimized to replace a quarter-wavelength\ntransmission line with a phase inverter. To demonstrate the proposed concept, a 1-GHz prototype was fabricated and tested. It\nachieves 90% impedance bandwidth with magnitude of S11 less than -10 dB. Within this bandwidth, more than 13 dB port-toport\nisolation, less than 5.0 degree phase imbalance, and less than 4.5 dB magnitude imbalance are achieved, simultaneously. The\nproposed coupler not only achievesmuch wider bandwidth but also occupies less circuit area than that of the conversional 2-section\nbranch-line coupler.
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