A pair of dipole antennas for controlling polarizations

A technique for reducing the fading pattern appearing when an antenna on a marine vessel receives direct signals from an satellite and interfering signals from reflections off the sea surface is presented. Fading is suppressed by controlling the polarization in the reserved direction, i.e., the polarization is opposite to that from the reflected signal. Numerical models are defined for two half-wave dipole antennas on an infinite reflector. Waves reflected from the sea are either elliptically or left-handed polarized. Increasing the antenna axis ratio in the reserved direction permits control of the polarization in that direction. Inclusion of an attitude monitor on the vessel allows automatic correction of antenna swing and incorporation of pre-calculated current distributions allows maintenance of the correct polarization in the reserved direction. Tests show that only 6 dB gain is possible with the configuration, compared to a required 8 dB. Sufficient gain may be available if two units are used or by installing an array of Yagi elements.