Active polarization-agile microstrip patch antennas

There is increasing interest in active microstrip antennas, and in particular, active transmitting antennas comprising patches with integrated sources for use in phased arrays. We describe an active transmitting antenna consisting of a pair of double-layer patches, mounted with their axes at right angles. Each patch is equipped with a transistor source, and varactor diodes fitted to both patches are used to control the relative phase of the orthogonal components of the radiation. Hence, by appropriate selection of the diode bias voltages, linear or circularly polarized radiation is produced. Possible applications for this type of antenna are as elements in larger phase arrays, or individually in short range communication systems where polarization control is required to combat multipath and other propagation effects