Circularly polarized active integrated antenna

The paper presents a new design of a circularly polarized microstrip patch antenna integrated with a push-pull transistor oscillator. The microstrip patch is excited in two points with signals having 90/spl deg/ phase shift. At the outputs of the push-pull oscillator the signals have 180/spl deg/ phase shift. The additional 90/spl deg/ phase shift is obtained by a quarter-wavelength long microstrip line. The oscillator and the line are placed inside an opening in the patch. In this way the active antenna maintains small dimensions. The antenna prototype is fabricated and its characteristics are experimentally verified. Frequency tuning is obtained by changing the dc bias voltage. The antenna radiates a left-handed circularly polarized wave. The spectrum is clean and no spurious components are observed. The radiation pattern is not disturbed by the modifications in the patch and by the active circuitry.