Study Of Electrically Small Smart Antenna With Muli-feed Ports For Mobile Station

This dissertation is mainly focused on the key technologies of smart antenna for mobile station: (1) the electrically small antennas with two ports, (2) the performance evaluation of smart antenna for mobile station, and (3) the retrodirective antenna with multi-feed ports.In chapter 1, the research background and recent developments about the smart antennas for mobile station are reviewed. Meanwhile, main works and contribution in this dissertation are pointed out.In chapter 2, a diversity wire antenna with two isolated ports has been optimized by using genetic algorithm and moment method (GA+MOM). The experimental results show the bandwidth of the antenna with 10dB return loss for both ports can achieve 6%, and the isolation between two ports is greater than 20dB across about 2.5% bandwidth. The antenna can provide high isolation and low return loss in a compact space with simple fabrication, no needing complex feed network. The envelope correlation of two ports is smaller than 0.1, and easily meet the correlation requirement for achieving diversity.In chapter 3, a novel planar polarization diversity antenna that has two feed ports with more than 20 dB isolation has been proposed. The antenna design is based on using capacitive loads and slits on two crossed narrow patches with via fed-through feed system, which can reduce the size of the antenna, improve the isolation between two ports and keep considerable bandwidth respectively. The top plate area of the introduced antenna is 2.7 2.7cm2, which is smaller than at 900MHz. The simulation results by FDTD show that the bandwidth determined from 10dB return loss for both feed ports is about 7%, and the isolation between the two ports is greater than 20dB across the entire band. The envelope correlation of two ports is smaller than 0.1, making the antenna suitable for handset diversity application.In chapter 4, a simulation approach is presented, which combines the outdoor radio propagation model, the eigen-driven patterns of handset diversityantenna with two feed ports and combining schemes of receiving signals, to investigate the performance of a dual antenna handset under co-channel interference(CCI) and multi-path fading environment. The performance of a planar polarization diversity antenna on the handset with optimum combining and equal ratio combining is then studied.In chapter 5, a simulation model to predict the diversity performance for the two-port antenna system with a given correlation coefficient has been developed. This model has the ability of analyzing the effects of some key system parameters, such as the signal correlation coefficient, speed of the mobile, and the update rate of combining weights, on the system performance. Some simulation results using discrete optimum combining and discrete equal ratio combining is given.In chapter 6, the retrodirective ability of the electrically small antennas with two ports has been studied. Using the phase conjugation mixer the compact wire antenna with two isolated ports presented in chapter 2 is simulated , and the results show that the antenna can follow the incoming signal with the main beam and has 4-8dB gain improve against the standard monopole in the incoming signal direction. The gain of the retrodirective antenna in the incoming signal direction fluctuates with ?dB as the incident angle increases.In chapter 7, the summery of the whole dissertation is given.