Interlevel stripline coupler

An apparatus for coupling signals between levels of multilevel stripline circuits comprising:

• first and second ground planes having a region therebetween divided into three sections, a middle section, and two outer sections with first and second boundaries between said middle section and said two outer sections;
• a first metallic inner conductor of horseshoe shape positioned at said first boundary, having an arcuate section, an open end, and first and second ports on either side of said open end respectively coupled to first and second metallic strip conductors at said first boundary;
• a second metallic inner conductor of horseshoe shape positioned at said second boundary in an energy coupling relationship with said first horseshoe shaped inner conductor, having an arcuate section, an open end, and third and fourth ports on either side of said open end respectively coupled to third and fourth metallic strip conductors at said second boundary, said arcuate section and said open end of said second horseshoe shaped inner conductor respectively facing said open end and said arcuate section of said first horseshoe shaped inner conductor to position said first and third ports and said second and fourth ports with electrical distances therebetween;
• and
• first metallic means positioned substantially equidistant between said first and second ground planes and located in regions external to areas covered by said first and second horsehoe shaped inner conductors for providing common ground planes for strip conductors at said first and second boundaries to establish a first half height asymmetric stripline and a second half height asymmetric stripline.