An electronically scanned antenna that is manufactured using semiconductor material and device fabrication technology. The antenna has a semiconductor substrate having a plurality of stubs projecting from one surface. The semiconductor substrate may be silicon, gallium arsenide, or indium phosphide, for example. A first conductive layer formed on the surfaces of the semiconductor substrate and along sides of the stubs so that the stubs are open at their terminus. The conductive layers form a parallel plate waveguide region. A diode array having a plurality of diode elements is formed in the semiconductor substrate that are disposed transversely across the semiconductor substrate and longitudinally down the semiconductor substrate between selected ones of the plurality of stubs. The diode array may comprise an array of Schottky or varactor diodes, for example. The diode array provides a voltage variable capacitive reactance and hence a phase shift to the electromagnetic energy propagating in selective regions of the waveguide region. This results in a scanning of the antenna beam radiated from the studs. A beam steering computer is coupled to the plurality of diode elements of the diode array which controls the voltage applied thereto to control steering of a beam radiated by the antenna.