reply to ivan

a electromagneic wave consists of two cordinates H AND E.

H is magnetic field vector and E is electric field vector.both are perpendicular to each other.

now iF direction of wave travelling is parallel to E vector it is horizontal polarisation. if direction of wave is parallel to H vector it is vertical polarisation.

if in hopp design there are number of buildings in between two antennas we use vertical polarisaion only and one thing important at both side of hopp polarisation should be kept same V-V or H-H