Miniaturized Wideband 90° Coupler Based on Shorted 4-line Coupled-Line Sections

In this paper, a miniaturized wideband 90° coupler is proposed. Without defected ground planes and a multilayer process, a wider bandwidth and compact size are obtained by using shorted 4-line coupled-line sections. For demonstration, a miniaturized wideband 90° coupler operating at 3.5 GHz is designed, simulated, and measured. The measured fractional bandwidths for 20-dB $\vert S_{11}\vert$, 22-dB isolation, phase difference (±5°) and amplitude imbalance (±1.6 dB) are 62.45%, 62.01%, 72.18%, and 55.23%, respectively, which sufficiently validate the proposed methodology.