An ultra wideband, high directivity 3 dB coupler

High directivity is achieved in a 3 dB directional coupler operating over the 6-18 GHz range. A symmetric, tri-sectional microstrip structure is employed with tight and weak coupling at the center and adjacent sections, respectively. To enhance directivity and return loss in the weak coupling sections, a new design methodology is used, based on manipulating the gap and metal lines such that even and odd modes phase velocities are equalized. The tight section is designed in a tandem structure. A small physical size (3×8 mm²) is also attained. The method is established with simulations and measurements.