However, if black body radiation is received with two orthogonal antennas with identical radiation pattern, a cross yagi for example, the voltages that can be measured at the antenna terminals are completely uncorrelated. Therefore the black body radiation can be regarded as a pair of polarised signals. It may seem uninteresting to discuss black body radiation, but for a radio amateur trying to hear an EME signal at 144MHz, the problem is that the black body radiation from our galaxy is much stronger than the signal. Orthogonal Antennas Assume we have two similar antennas with orthogonal polarisation. Orthogonal polarisation does not necessarily mean 90 degrees angle between something.
Orthogonality is a mathematical concept.
I am not going to be very mathematical, I try to describe these things by physical concepts. H and V are not orthogonal, it is possible to orthogonalise them by the use of an appropriate balancing network connected between the two feed points. Not being orthogonal means that feeding power into one produces an attenuated signal in the other. Balancing simply means feed an equal amount of signal of the opposite phase between the two ports for example by a tuning capacitor at an appropriate point along the two feed lines. If H and V are not orthogonal, electronic polarisation control becomes impractical because the feed point impedance then becomes different for different polarisations.