A Dual-Band 180-Degree Hybrid Coupler Based on Coupled-Line Sections

This letter presents a novel 180 degree hybrid coupler structure based on coupled-line sections which offers a compact circuit and a dual-band operation. The structure is based on 90 degree and 180 degree coupled lines suitable to offer a 180 degree hybrid coupler behavior at two frequency bands when the even and odd impedances of the coupled-line sections are properly determined. The circuit presents a symmetry plane that enables an even/odd analysis. The dual-band operation of the structure has been verified by means of a prototype implemented in microstrip technology operating at 2.4 and 5 GHz.