Active patch antennas incorporating Schottky diodes used as tuning devices have been constructed and tested. npn bipolar transistors operating in the common-base configuration are employed as sources, and the antenna itself is a multilayer structure which enables isolation of the diode biasing circuitry from the transistor circuitry, while being inherently wideband, and capable of realising desirable radiation patterns. Tuning ranges of up to around 100 MHz at 2.2 GHz (4.4%) have been obtained, with good radiation patterns over the entire frequency range.