Design Of Low-Profile Circularly Polarized Antennas With EBG And Dual-Band Antennas

The low-profile circularly polarized antennas with the EBG structure can realize the agility from the linear polarization to the circular polarization, and their low-profile characteristic has attracted extensive attention recently. As a kind of dual-band antennas, the printed monopole is a hot topic in the antenna research area, owning to its simple structure, easy fabrication and lower cost. This thesis is mainly engaged in the application of the EBG structure to the low-profile circularly polarized dipole antennas and design of the dual-band WLAN antennas.First, a reflect-array element of the EBG structure is presented. CST Microwave Studio, a kind of electromagnetic simulation software, is used to analyze the reflection phase for the designed element. With the proposed element, a circularly polarized dipole antenna is designed. Its center frequency is 3.66 GHz. The influence of the element number, the ground size and the metallic vias on the circularly polarized antenna is analyzed. Then, a circularly polarized dipole antenna, whose center frequency is 2.5 GHz, is designed and measured. Experiment results show that the frequency bandwidth is 200 MHz for a -3dB axial ratio and S11<-10dB criteria. This kind of circularly polarized dipole antennas working in several frequency bands are easy fabricated, which is suitable for engineering applications.Then, a dual-band printed monopole for the WLAN applications is designed and measured. The proposed antenna consists of a T-shaped monopole in the back and a U-shaped monopole in the top. The U-shaped monopole antenna is fed by a 50? microstrip line and the T-shaped monopole antenna is coupling-fed by the U-shaped antenna. Measured results show that the antenna resonates at 2.46 GHz and 5.55 GHz with bands from 2.30-2.68 GHz and from 5.13-6.04 GHz with good radiation patterns.