Multi-element planar array antenna

A multi-element planar array antenna comprising:

• a substrate having a first and a second principal surface;
• a conductor formed on said first principal surface;
• a first and a second slot line formed in said conductor, and intersecting each other;
• a first and a second microstrip line formed on said second principal surface, and traversing said first slot line respectively at positions corresponding to both end sides of said first slot line;
• a third and a fourth microstrip line formed on said second principal surface, and traversing said second slot line respectively at positions corresponding to both end sides of said second slot line;
• a first antenna element electromagnetically coupled to one end of said first microstrip line and to one end of said third microstrip line through said substrate;
• a second antenna element electromagnetically coupled to one end of said second microstrip line and to the other end of said third microstrip line through said substrate;
• a third antenna element electromagnetically coupled to the other end of said second microstrip line and to one end of said fourth microstrip line through said substrate;
• and
• a fourth antenna element electromagnetically coupled to the other end of said first microstrip line and to the other end of said fourth microstrip line through said substrate,
• wherein each of said antenna elements is a slot line antenna element formed on said first principal surface and capable of being excited in two directions.