Compact wideband stripline hybrid coupler with an imbedded ground strip

In this paper, a compact and wideband stripline 180° hybrid coupler with a simple design structure is proposed. For wideband capability and a size reduction, the long branch of the conventional ring hybrid coupler is substituted with a coupled line with two quarter‐wavelength short‐circuited stubs having a narrow gap and a rectangular ground strip. The ground strip is embedded in a dielectric substrate between the coupled line and a ground plane, and the operating bandwidth can be widened in the ground strip design to control the parasitic capacitance and inductance. The proposed coupler has a 71% wide operating bandwidth at the center frequency with a ±0.5 dB power split error and a high isolation of below 20 dB. The phase difference between two output signals is within ±5°, and the reflection coefficient for all ports is less than −10 dB in the operating bandwidth. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2433–2437, 2016