Miniaturized broadband branch‐line coupler

This article introduces a new miniaturized branch-line coupler for wideband applications. The coupler can be realized in microstripline with one layer of metal, without additional lumped elements. Significant size reduction is achieved using the proposed configurations. Explicit design formulas of the proposed coupler are analytically derived. Then it has been simulated with HFSS and fabricated. Return loss and isolation loss are both better than 20 dB in about 31% fractional bandwidth. Over this frequency band, the phase unbalance between two quadrature outputs is less than 2°. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:740–743, 2014