Microstrip coupler for microwave signals

A microstrip coupler for microwave signals having a certain terminal impedance comprising:

• a plurality of coplanar thin microstrip conductors having terminal portions, coupled portions extending over a certain distance with their edges in closely spaced parallel relation, and connecting portions between said terminal and coupled portions, said coupled and connecting portions being substantially wider than said terminal portions;
• conductive means providing an electrical ground plane having different ground plane surfaces in different planes including a first planar surface having a certain dielectric spacing to said terminal microstrip portions in accordance with the characteristic terminal impedance of said coupler, a second planar surface having a certain dielectric spacing to said coupled microstrip portions larger than said terminal spacing, and a connecting surface between said planar surfaces;
• a first thin electrically conductive coupling member between one face of said coupled microstrip portions and said second ground plane surface and of a length less than the length of said second ground plane surface;
• and a second thin electrically conductive coupling member extending over and dielectrically spaced from the opposite face of said coupled microstrip portions;
• said connecting microstrip portions of said microstrip conductors extending in length between said first coupling member and at least said connecting ground plane surface to compensate for capacitive coupling between said connecting microstrip portions and said connecting ground plane surface.