Design Of High-Performance Antennas For MIMO System

Multiple-Input Multiple-Out (MIMO) is a multi-antenna technology, in which multiple antennas are placed separately both at the transmitting and the receiving ends. Being one of the key technologies in the next generation (behind 3G or 4G) mobile communication, MIMO can enhance capacity and frequency spectrum utilization efficiency of communication system while maintaining bandwidth, improve link reliability, and reduce bit error rate. Along with the development of MIMO technology, the development of high-performance antennas for MIMO system is very urgent, and will be also of theoretical significance and practical value.First, two miniaturization antennas, one Z shape (horizontal polarization) and one T shape (vertical polarization), with omni-directional patterns at 2.4GHz band (2.4~2.4835GHz) are developed. By printing the"Z"patch on the top plane of substrate, and the reverse"Z"patch on the bottom plane, a current loop is formed, and a horizontally polarized wave is radiated. The T-shaped antenna is a monopole fed with coplanar waveguide (CPW), and has a broad bandwidth. With the simulation software HFSS, the effect of different dimensions of the T-shaped strip, CPW and substrate board on the input reflection coefficient is discussed in detail, and the parameters of the antenna are determined. In order to reduce the size of T-shaped antenna further, we print a parasitic path on the bottom plane of substrate, which parallels the vertical arm of the T-shaped strip. Thus the bandwidth of the antenna is enhanced, and its radiation performance is effectively improved. Taking a common 14 inch notebook computer as an example, we design two arrays with the Z-shape and T-shape antennas as the array elements respectively. The former array consists of twelve (3×4) elements, and the latter has eight (2×4) elements. Considering the dual-band applications, we also design nine microstrip monopole antennas, which can operate both at 2.4GHz band and 5.2GHz band (5.15～5.35GHz). The measurement results show that the developed antennas have good bandwidth and pattern performances, which are suitable for MIMO system.