The present invention relates to a half mode substrate integrated antenna structure 1, 10, 11 for electromagnetic signals, comprising a substrate 2 with a top 2a and a bottom side 26, said substrate being essentially of a flat shape with a main plane M, a conductive layer 3a arranged on said top and a conductive layer 3b arranged on said bottom side, a series of conductive vias 4 extending between the conductive layers 3a, 3b of the top and the bottom side of the substrate so that a waveguide having a feeding end 5 and an antenna end 6 is formed, wherein said antenna end 6 is formed by end regions 7 of said conductive layers 3a, 3b and said substrate 2 so that a radiation pattern of said antenna structure 1 essentially extends in the main plane M.