A Study Of LTE Base Station Antennas And Low Profile Circularly Polarized Antennas

Along with the rapid develop of communication technology, the requirements of the communication system have become increasingly harsh. As a vital part of a communication system, antenna has a direct impact on the communication system performance. Dipole antennas have been widely used in base station antennas. However, they always have a high profile which is usually more than 0.25λ. Microstrip antennas have attract more and more attention for its unique advantages, such as low profile, low cost, etc. Circularly polarized(CP) antennas have two advantages. Firstly, they are very effective in combating multi-path interferences or fading. Secondly, there is no strict orientation required between transmitting and receiving antennas. CP antennas have been widely used for mobile communications, global position system(GPS), wireless local area network(WLAN) and satellite communications. This thesis mainly focus on a new Balun, low profile base station antennas and low profile circularly polarized antennas. The main contributions of this thesis could be summarized as follows:1. A broadband power divider and its applications are studied. Firstly, single and double section broadband power dividers are designed. Secondly, a new broadband 180°power divider is proposed. Two different methods which mainly improve the return loss, insertion loss and transmission phase of the input port are proposed base on the new broadband 180°power divider. The simulation results shows that these two methods achieve good results. Lastly, dipole antenna with balun structure is proposed. Prototype of the antenna is fabricated and measured, the measured results show that the dipole antenna has good electrical properties and radiation characteristics.2. A base station array antenna with the characteristics of dual-band, low profile and high isolation is studied. Firstly, single and double layer microstrip antenna elements using “dual-feed” technique are proposed. Isolation of the two input ports can be highly improved by using this technique. And the dual-layer microstrip antenna is used as the elements of an antenna array for base stations. Secondly, 2×1 and 4×1 antenna arrays are designed for base stations. The effect of the distance between the two elements on the performance of the antenna array are also discussed. Thirdly, a prototype of a 4×1 antenna array is fabricated and measured, and the measured results show that the antenna array has a good performance.3. A low profile, circularly polarized antennas is studied. Firstly, a linear polarized magnetic dipole antenna is proposed. The influence of various parameters on the performance of antenna is also discussed. Secondly, circularly polarized GPS antenna with the shallow and embedded structure based on the linearly polarized magnetic dipole is proposed. Prototype of the antenna is fabricated and measured, and the measured and simulated results are in good agreement. Thirdly, in order to verify the antenna can be embedded in the aircraft, a model of the proposed antenna and the metallic aircraft it is installed on is simulated using the commercial software Ansoft HFSS. The simulated results indicate that the aircraft has little effect on the proposed CP antenna.