Research On Tri-polarization Capacitive Loading Slot Antenna

MIMO is a technique that has ability to increase the capacity of communication systems without need to increase the transmission power and the spectrum. Polarization diversity can effectively improve the efficiency of spectrum; tri-polarized communication system can obtain three times chanel capacity as the unipolarized communication system in the same volume. To achieve freedom multi-polarity brings, the design of multi-polarized antenna is crucial. In this paper, three orthogonal polarized slot antennas with capacitive loading is presented.(1) This paper presents a slotline with capacitive loading. The gap of the slotline is loaded with capacitors to reduce the characteristic impedence and the phase velocity of the slotline, which lay the foundation for miniaturization of antenna.(2) It proposes a slot antenna with capacitive laoding. The antenna is a commination of ordinary slot antenna and slotlines with capacitive loading, which forms the step impedance slot antenna. The slot of the antenna is also added with periodical stub on conductor surface. All of this help achieve the miniaturization of the antenna. Simulations of the impact of the capacitive loading position and other parameters on antenna performance are conducted, and then an optimized size is choosed. Also manuly adjust the capacitive loading position to compensate the difference between the simulation and reality. The capactive loading comb-shaped slot antenna, whose length and width is 35 mm and 30 mm, respectively, center slot length and width is 30 mm and 2mm, respectively. Experimental results show that this antenna works at 2.4GHz with 150 MHz bandwidth. Beside, in E-plane the difference between the co-polarization and cross-polarization is greater than 10 dB at 2.4GHz. This antenna can be applied to volume-demanding condition.(3)It proposes a capacitive loading comb-shaped tri-polarized MIMO slot antennas with microstripline feed, which has a symmetrical structure. The proposed antennas work at 2.3GHz-2.43 GHz with 130 MHz bandwidth. The three-port isolation between antenna elements is greater than 25.1dB. In E-plane the difference between the co-polarization and cross-polarization is greater than 10 dB at 2.4GHz. This antenna is suitable for condition of high polarization purity and isolation, especially for polarization diversity applications on abundant scattering environments.The miniaturized tri-polarized antennas can improve the isolation of the sub-channel in MIMO systmes, which can achieve the high capacity.