Investigation Of Broadband Planar Antenna

The rapid development of wireless communications technology is bringing about more and more wireless devices to meet the demands of various kinds of applications. Communication requirements for different applications have rigorous restricts for the wireless communication protocol and the performances of hardware. Antenna is one of the key equipments in wireless communication systems; its performance will have a direct impact on the performance of communication. Over the past decades, due to the advances in integrated circuit technology, the integration level of communication equipments becomes higher and higher, so that the broadband planar antennas, which have the features of low-profile, small in size, flexible structure and easily integrated, attract more and more attention.The dissertation mainly focuses on the broadband techniques of planar antennas. Several methods for increasing the bandwidth of planar antennas are investigated. Firstly, the analytical theory and numerical methods for designing microstrip antennas are introduced, as well as realization of circular polarization and the working principle. Based on the common rectangle microstrip antenna, considering the design factors including pattern characteristics, impedance bandwidth, mutual coupling, size constraints, and processing errors, the antenna impedance bandwidth is extended by using corner-chopped method, and the axial ratio bandwidth is improved by using sequential rotation array method. With these broadband techniques, the narrow impedance bandwidth of single patch impedance is effectively extended, as well as the narrow axial ratio bandwidth. A high performance 2×2 elements right-hand circular polarization microstrip antenna array has been proposed and fabricated, and some useful design specifications and guidelines. And the experiment results validate the validities of the proposed antenna by comparing with the full-wave analysis data and measured results; it also shows that the proposed antenna satisfies the design requirements.Secondly, based on cylindrical monopole, the function for estimating resonate frequency of planar monopole is deduced, as well as the aspect ratio to obtain the best impedance bandwidth. The resonate frequencies estimated from the function and the full-wave analysis results are in good agreement, which shows that the function can be used to estimate approximate dimension or resonate frequency of planar monopole. The initial broadband planar antenna based on asymmetric feed structure is modified from conventional rectangular planar monopole. After investigating the current distribution of planar monopole, a ground notched structure is implemented in order to reduce the ground size。Then by adding an additional stub on the ground continue to enhance the bandwidth, we gain a -10 dB return loss bandwidth up to5.6:1(140%),with the frequency from 2.96 GHz to 15.58 GHz.Finally, a summary is made for the proposed design methods and the experimental results, and the achievements and shortcomings are outlined, as well as the prospects for further researches.