Abstract: The invention relates to a device for changing the polarization of an incident electromagnetic wave. Existing devices to change the polarization of an incident electromagnetic wave preserve signal decoupling, i.e., the relation between useful polarization and cross-polarization of the incoming signal. Furthermore, known prior art devices are far too big for many applications. The aim of the inventive device is to improve signal decoupling. During transmission of an electromagnetic wave through the transmission polarizer, the cross-coupled fraction of an incoming signal is greatly reflected thus leading to improved decoupling of the transmitted signal. Furthermore, the transmission polarizer can be manufactured in the form of a single planar printed board. The transmission polarizer is particularly useful to change the polarization of an incident electromagnetic wave, i.e.