The Research On The Improving Methods Of Microstrip Dual Circularly Polarized Antenna Performance

Blood flow velocity measurement technology can give doctor timely, accurate and effective information in the surgery, thus having a significant and practical worth in the medical applications. Measurement equipments based on microwave/RF Dopper effect are required to transmit and receive orthogonal polarized signals, which makes the circularly polarized antennas a perfect choice. In this case, both transmitting and receiving functions can be achieved by using only one single antenna, which can not only simplify the antenna module, but also reduce the cost of the whole system.With the development of science, there have been increasingly wide applications in the wireless communication. As an inevitable module of wireless devices, antennas are required to have better performance in various aspects. Microstrip dual circularly polarized antennas enjoy both the advantages of microstrip antennas and circularly polarized antennas, thus having a great researching value.The main researches of this thesis are focused on several aspects listed as follows.(1) Based on the project of blood velocimeter, a microstrip dual circularly polarized antenna with transceiver function is designed and fabricated. The transmitting port transmits left-handed circularly polarized wave and the receiving port receives right-handed circularly polarized wave. Furthermore, different methods are proposed to improve the performance such as the size, bandwidth, gain, efficiency and FBR of this antenna.(2) With respect to the antenna miniaturization, several methods are put forward, such as increasing the ratio of patch area, loading diagonal-shaped and L-shaped tail respectively, loading substrate integrated metal walls in the axis and diagonal directions respectively and loading tail and substrate integrated metal walls simultaneously. Under the best situation, the size of the antenna can be reduced to52%of that of the original one. With respect to the bandwidth and FBR enhancement,3cases of loading RIS structures (normal substrate with RIS structures, high permittivity substrate loaded with RIS structures and Magneto-dielectric substrate loaded with RIS structures) are analyzed and compared in the bandwidth, directivity, radiation efficiency and FBR. It can be concluded that antennas using Magneto-dielectric substrate loaded with RIS structures have the best performance. With respect to the gain improvement, one structure of metameterial, namely coupled square-shape split ring resonators (CSSSRR) are introduced and its impact on the gain improvement is analyzed. However, the performance improvement in a specific aspect may lead to the deterioration of other performance parameters. For instance, antennas may have lower radiation efficiency, narrower bandwidth, less gain and worse radiation pattern while achieving the miniaturization. Thus tradeoff among several performance indexes should be taken into consideration during optimization.(3) Apart from the above researches, another two microstrip circularly polarized antennas are analyzed here. One is a stack-up circularly polarized antenna with elliptical ring slot, which is compared with the corresponding antennas with circular ring slot. Furthermore, a elliptical patch is adopted so as to achieve wider bandwidth. The other one is loaded with DGS structure in order to suppress surface wave of the antenna.