Antennae with a basic dipole construction or uniformly arranged groups of dipoles, are linear polarised antennae. For an optimum reception, linear polarised antennae should always be aligned to the same plane of polarisation. A measurement for the isolation between the planes of polarisation, is the polarisation decoupling. This measure of attenuation specifies the reduction in the reception of a wave when the plane of the antenna is rotated by 90 about its own axis.