Very Short Horn Antennas for Arbitrary Polarisation

The paper deals with new types of horn antennas with minimised lengths. Four different antennas for various applications are presented. The shape of these antennas was found by a combination of experimental and CAD-techniques. Providing a smooth transition in two steps from the 50¿ coaxial feeding cable to the aperture, these horns are capable of covering a frequency range of at least an octave. Two of the antennas are designed for linear polarisation, two others can receive or transmit any wanted polarisation by properly combining the signals of two orthogonal feeders. The horns are self-balanced with the exception of one unsymmetrical antenna for flange-mounting on metal surfaces. A special design with an optimum shaped central conductor is used to ensure sufficient decoupling and a minimum of phase and amplitude difference between the orthogonal channels of the horns for arbitrary polarisation.