A multisection ultra wideband directional coupler in multilayer broadside coupled stripline technology

In this paper, we present a multisection directional coupler providing a tight coupling of 10 dB with an equal ripple of 0.8 dB across the frequency range of 360 MHz to 5.8 GHz, which corresponds to a relative bandwidth of 177 %. To maximize coupling and reduce dispersion effects, the coupler uses broadside coupled striplines in a multilayer setup. The four ports of the coupler are connected via standard SMA-connectors through a stripline to microstrip transition that does not make use of vias. The design process is verified by EM simulations and measurements performed on a prototype.