Analysis and design of an omni-directional antenna with enhanced E-plane directivity using cylindrical EBG surfaces

In this paper, a new method is presented for increasing the E-plane directivity of single dipole antennas by incorporating cylindrical metallo-dielectric electromagnetic bandgap (CMEBG) surfaces. Initially, the proposed structure is analysed for infinite CMEBG array length which is centre-fed by a simple radiating source using 3D full-wave simulation techniques. The analysis yields insight for the design and realisation of an omni-directional H-plane CMEGB antenna with enhanced E-plane directivity. The use of aperture arrays is employed to achieve significantly smaller unit cell. A comparative study between aperture and conducting CMEBG arrays illustrates what are the advantages and disadvantages of each structure. The cylindrical MEBG arrays behave as partially reflecting surfaces (PRSs) forming a cylindrical resonant cavity. A balanced dipole antenna is used as the feeder at the centre of the cavity. The directivity enhancement is demonstrated with simulated and measured results for an antenna prototype operating at about 2.4 GHz. A maximum directivity improvement of about four times is achieved.