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A polarisation-agile active antenna has been constructed and tested. The radiation can be selected to be circularly polarised in either sense, or linearly polarised in the vertical, horizontal or either diagonal plane. The antenna consists of two varactor diode loaded active patches using npn bipolar transistors in the common base configuration as sources, and with the patch axes at right angles to each other. The two oscillators are locked to an external source, and the phase from each patch element is controlled by varying the diode bias voltage. By appropriate combination of the phase relationships, the various polarisations are produced.