Study On The Techniques Of Dual Band Microstrip Antennas With High Frequency Ratios

Microstrip antennas are most desirable candidates for the antennas in wireless mobile communications because of their features such as low profile, light weight,compact size, easy fabricated and integrated with other microwave circuits. Therefore,they are widely utilized in the areas of wireless communication. However, as the number of mobile communication users is rapidly growing, existing ratio spectrum resources are increasingly constrained. To widen the channel capacity, microstrip antennas working at dual bands or more are in desperate need. Specially, when applied to WLAN or satellite communication, the frequency band ratio of a dual band antenna is usually so high that the radiation pattern of the antennas will be split. Thus, the studies on dual band microstrip antennas with high frequency band ratio are of great significance.This thesis is mainly focused on meeting the pattern bandwidth needs of8021.11b/g/n/a. Two different dual band antennas with high frequency ratios are proposed and designed with experimental verifications. The main contents of this thesis are as follows:Firstly, the aim and significance of the study in this thesis are introduced, and some classic theories of microstrip antennas for accomplishing dual-band, broadband or size reduced characteristics are reviewed.Secondly, a coaxial probe fed and easily fabricated dual band microstrip antenna with high frequency ratio is designed. The antenna was then fabricated and measured.Experimental results show that the propsed antenna has a very high frequency band ratio of up to 2.4:1,with a stable radiation and good antenna characteristics.Thirdly, based on the aperture-shared technique of microstrip antennas,a novel dual port, dual band microstrip antenna with high frequency band ratio is designed.Throughout slot perturbation, mutual coupling between the two bands is reduced to a large extent. Numerical results show that the radiation efficiency of the designed antenna exceeds 70% at both bands, and the antenna characteristics behave good.