Studies on optical control of active integrated antennas

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Optical control of the oscillation frequency and optical beam scanning of the radiation of active antennas were experimentally realized based on the change of the oscillation condition by the optical illumination to the active elements. The prototype antennas have FET oscillators and microstrip patch radiators ; one type has two circular patches, the other has rectangular patches. First the oscillation and the radiation characteristics of a single active antenna have been investigated, and two element arrays have been characterized for both anti- and in-phase cases. Then array antennas of three elements have been studied. In each case, the change of the characteristics were measured for the dark and the illuminated states, and the measured radiation patterns were compared with the calculated ones. The phase differences of the elements were evaluated from the comparison. It is verified from these results that (1) the intrinsic frequency of the active antenna changes by the illumination to the FET of the oscillation circuit, (2) the phase relationship between the oscillators changes by the illumination in case of active antenna arrays which are weakly coupled via free space radiation, (3) the synthesized radiation pattern of such arrays can be scanned by optical means. These results can be developed to an array antenna of many elements which has a narrow beam width and whose beam can be scanned by optical means. Such new type of antennas have no phase shifters, no rf feeders, nor any lines for the coupling, and only have dc bias lines, so their structure is very simple. Optical control has inherently high speed comparing with the electronic control, and good isolation characteristics, due to which the designs for rf circuits and their controlling circuits could be independently performed. This fact is useful for the design simplification and the miniaturization of the circuits.