Design Of WLAN MIMO Antenna Based On Polarization Diversity

With the rapid development of wireless communication technology, people’s requirement for the wireless network become more and more urgent, the existing communication systems are difficult to meet the demand, the capacity, speed, reliability of communication system needs to be improved. At present, spectrum resources are limited, it is very difficult to improve capacity and rate for the communication system by improve the bandwidth of the communication system, therefore, the current research hot topic is making full use of the limited spectrum resources by improving the spectrum utilization. At present, an effective way to improve spectrum efficiency is the multiple input multiple output (MIMO) technology. In order to improve the throughput, transmission distance and reliability of wireless local area network,the MIMO technology is introduced into the new generation of WLAN802.11n standard. There are two basic requirements for MIMO antenna. First, the antenna can meet the application requirement of MIMO system, and it can use the smallest space to obtain good diversity gain and multiplexing gain, and solve the problem of isolation between antennas; Second, the antenna manufacturing cost is low, structure is simple, economical and practical. Therefore, in this paper, the design and implementation method of WLAN MIMO antenna was studied.In this paper, WLAN and MIMO technology were introduced, firstly, and then the mutual coupling between multiple antenna unit was analyzed by theoretical method, the requirements for MIMO antenna design were given out. According to the requirements of the research topic, microstrip patch antenna structure was used to design the antenna unit, which has the feature of simple structure and low cost. In order to improve the gain and the impedance bandwidth of antenna unit, the microstrip patch was loaded with the coupled square-shape split ring resonators (CSSSRR) structure. On this basis, this paper designed three WLAN MIMO antenna arrays. The first antenna array is a4-elements vertical/horizontal double polarization linear array, the antenna adopts the method of orthogonal double feeding point feed to achieve double polarization, parallel feed network structure was used to feed antenna array; the second antenna is a±45°dual-polarization microstrip antenna, vertical/horizontal double polarization of aperture coupled feeding microstrip antenna was transformed by using vector synthesis method, thus constitutes the±45°dual-polarization microstrip antenna; the third antenna is a double circular polarized antenna array, the antenna is a2X2array structure to improve high gain and direction, feeding network using rotation of amplitude with phase shift technology to realize the double circular polarized antenna array properties.This paper used the method of theory design combining with electromagnetic simulation software simulation to carry on the design, and according to the design results, the antennas were fabricated and tested. The tested results show that the designed three antennas have the well directivity, high gain, and high isolation degree, and have the simple structure and low cost, satisfy the requirements of WLAN MIMO system for antenna.