Wideband Three-Section Symmetrical Coupled-Line Directional Coupler Operating in Differential Mode

In this letter, a concept of wideband multisection symmetrical coupled-line directional couplers operating in a differential mode has been presented for the first time. The required different coupling coefficients for each of the coupled-line sections have been achieved by introducing a multilayer dielectric structure and by placing sections on different metallization layers. The theoretical investigation has been supported by measurements of an exemplary three-section symmetrical 3-dB coupled-line directional coupler operating in a differential mode at the center frequency of f
₀
= 3 GHz.