Design of multibeam antenna for wireless local area network applications

Abstract

The current trend in most access point in conventional wireless local area network (WLAN) is to use omnidirectional antennas, which radiates and receives power equally in all directions. This attribute however gives result of lower power efficiency and decrease network performance due to co-channel interference that arrived from undesired directions. One of the proposed solutions to overcome these constraints is to use multibeam antenna on WLAN access points. Multibeam antennas are antenna arrays that make use of beamforming networks to produce multiple independent beams that directed to different directions. In this project, multibeam antenna comprises of linear antenna array and beamforming network is presented. It was designed at 2.4 GHz to suit the application of WLAN at 802.11b/g. Butler Matrix 4 x 4 is chosen as a beamforming network which was designed to provide four different progressive phase shifts, -45°, +135°, -135°, +45° that coupled to antenna array. It is made up from four 90° hybrid coupler, two 0 dB crossover and two -45° phase shifter. Each component is designed and simulated using Agilent ADS software and fabricated on FR4 board. This network is then combined with a linear antenna arrays with the aim to produce four independent beams at four different directions. Three types of antenna array that having different kind of radiation patterns have been implemented which are square patch antenna, 4 x 2 planar antenna array and dipole antenna. The obtained result shows that 4 beams are generated by each design where square patch antenna array produce Half Power Beamwidth, HPBW for each beams about 30° and manage to cover 120° of coverage area, 4 x 2 antenna array has HPBW about 7° and cover 30° while dipole antenna produce two kind of beams, broader and narrower beams. Finally, it can be concluded that the objectives of this project are achieved.