Halo antenna with cylindrical conductor for space of feed circuits

Slim and lightweight base station antennas are required in the next wireless communication systems to achieve low construction cost. Authors have investigated Halo antenna with parasitic element as a slim omni-directional horizontal-polarization antenna in past research. Halo antenna has symmetrical and cylindrical configuration and feed circuits should be inserted in the symmetrical plane to avoid impedance shift and pattern distortion. Thus Halo antenna has difficulties achieving high gain and beam tilt functionality because the feed circuits for high gain antennas and beam tilting antennas must be large and complex. In this paper, a cylindrical conductor for electrostatic shielding effects is inserted in Halo antenna, and the feed circuits are inserted in the cylindrical conductor without any effects on the antenna performance. The pattern distortion due to scattering current on the cylindrical conductor is canceled out by the symmetrical flow of scattering currents, thus, the cylindrical conductor is also inserted in Halo antenna without pattern distortion. The impedance and bandwidth of the Halo antenna depends on the size of cylindrical conductor. The numerical results, obtained by changing the size of cylindrical conductor, verified more than 1/3 space in Halo antenna can be assigned for feed circuits.