Analysis And Design Of Low Profile Broadband Circularly Polarized Antenna With AMC Reflector

In the past decade,with the development of wireless technology and the increasing demands of wireless devices,antenna with good performance is facing more challenges.Wireless communication system can achieve stable communication in the complex environment by increasing the stability of the antenna.Circularly polarized antenna has the advantages of multipath interferences,avoiding polarization loss and Faraday rotation effect.Therefore,circularly polarized antenna is very common in the fields of RFID technology and WLAN.The realization of wide axial ratio bandwidth,high gain and low profile for circularly polarized antenna always is an important research topic.During the design of low profile broadband circularly polarized antenna,Artificial Magnetic Conductor(AMC)is favored by scholars because of its special phase characteristics.In order to avoid the interference between the incident wave and the reflected wave,the metal reflector is placed at quarter wavelength away from the radiation antenna.At this time,the profile of the antenna is at least one fourth of the wavelength.However,the AMC reflector has a reflection phase of 0 degree,so it can be placed close to the antenna to make the incident wave and the reflected wave superpose in phase.This can enhance the gain of the antenna and reduces the profile of the antenna.With the development of miniaturized wireless devices and broadband network,the broadband circularly polarized antenna based on AMC has more extensive valuable in both research and application.In this thesis,we will focus on improving the gain and broadening the axial ratio bandwidth of low profile circularly polarized antenna with AMC reflector.Firstly,a wideband circularly polarized antenna with AMC reflector to improve the gain is designed.The antenna works in the C-band of3.7-4.2 GHz.Two small square patches are embedded in the diagonal of the square slot,then two orthogonal surface currents are generated and right-handed circularly polarized radiation is realized.A stub is introduced between the L-shaped patch and the feed line to improve the impedance matching of the antenna,then the wide working bandwidth and axial ratio bandwidth are obtained.In addition,a 4×4 AMC reflector is loaded under the proposed antenna to improve the gain of the antenna,and the unidirectional radiation of the antenna is realized.The height of the profile is 0.07_L?.Secondly,a circularly polarized antenna with corner-truncated AMC reflector is designed.The antenna works in N79(4.4-5.0 GHz)band of5G mobile communication.A pair of rectangular cross dipole is connected by a dual vacant-quarter ring to generate circularly polarized radiation,and four parasitic strips are introduced to widen the bandwidth.A 5×5 AMC reflector is loaded under the dipole antenna to broaden the AR bandwidth and improve the gain,and the profile height is 0.13_L?.Finally,a novel broadband circularly polarized antenna with AMC reflector is designed.A pair of novel cross dipoles with three unequal arms is introduced to generate circularly polarized radiation.In order to broaden the AR bandwidth and improve the gain of the antenna,AMC reflector is composed of 5×5 truncated metal elements.The operating frequency band includes TD-LTE band(2.3 GHz/2.5 GHz/2.6 GHz),and the profile height is 0.19_L?.