Radiation Pattern Roundness Improvement of Off-center Monopole Antenna Using Electromagnetic Band-gap (EBG) Structure

A suspended circular electromagnetic bandgap (CirEBG) ring is proposed for improving the radiation pattern roundness of a quarter-wavelength monopole placed off the center of a square ground plane. The study shows that the proposed CirEBG structure localizes the surface currents on the ground plane within a controlled symmetric boundary so that the un-roundness of the off-center monopole antenna is reduced by 65%. The antenna is prototyped and measured to validate the method of the design.