Novel Structure and the Characteristics of A Microwave Circular Polarization Antenna

This paper gives a novel structure of circular polarization antenna at the X-band. This antenna is made as plane antenna composed of a feedand a reactance-elements on a wide ground plate. The feed element is made by a circular disc cut linearly at the both sides along x-axis. The resonant frequencies are fH and fL along xand yaxes respectively. Degeneration is achieved by shifting the resonant frequencies to be fH > fL which correspond to resonant lengths along xand yaxes. By defining the position of the feeding point, π/2 phase difference is provided for circular polarization with the current iL and iH. The reactance element is made of a circular disk smaller than the feed element. This element expands the bandwidth fH fL of resonances, which brings expansion of effective band width of circular polarization. A circular polarization plane antenna with 0.7 GHz bandwidth was realized at 10GHz without spurious radiation between 5 ~ 15GHz. Key-Words: Circular polarization, Plane antenna, Degeneration of resonances, spurious frequencies, Axial ratio, X-band antenna.