Design and fabrication of stripline type of a broadband quadrature hybrid couplers with transitions of coaxial-microstrip-stripline

A broadband quadrature hybrid coupler is designed and fabricated. In the technical points of suppressing unwanted resonances and improving hand-soldering workability, a transition composed of a coaxial line, a microstrip line (MSL), and a stripline (SL) is proposed and configured. It has better frequency characteristics than a transition composed of a coaxial line and an SL. The quadrature hybrid structure with proposed transitions is fabricated. It is found that negative effects of air-layer in SL structure strongly influence the broad frequency characteristics. Although it is necessary to improve them in the future, it is in almost agreement with the simulated frequency characteristics by an electromagnetic simulator.