Research Onmuti-polarzition Antennas Technology

The radio spectrum is a limited and valuable natural resource. In order to make the most of its utility,a bounch of advanced communication techniques have been proposed.Among them, antenna diversity, including space diversity, polarization diversity, pattern diversity and frequency diversity, is the one this thesis focuses. With the polarization diversity antennas, not only significant increase of the channel capacity,but also radiator or frequency multiplexsing can be achieved. Therefore, polarization diversity has attracted increasing attention in recent years. In the open literatures are usually dual-linearly-polarized and dual-circularly-polarized antennas, but multi-polarization(e.g. three and four polarization states) antennas have seldom been reported. In this thesis, we mainly study muti-polarization antennas based on microstrip patch antennas.In chapter 1, research background is introduced. History and recent development on muti-polarization antennas have been reviewed.Chapter 2 includes the basic concepts and principles of the thesis. First, working mechanism and methods of analysis for microstrip patch antennas, i.e. the transmission-line model, the cavity model and the full-wave simulation, have been addressed. Then, design procedure of microstrip patch antennas have been summarized.Finally, principle and applications of antennas have been given.In chapter 3, a novel low-profile dual-polarized antenna for 2.4GHz applications has been proposed. The proposed antenna consists of a circular patch with four curved T-stubs and a differential feeding network. Due to the parasitic loading of the curved T-stubs,the bandwidth has been improved. Good impedance matching and dual-polarization with low cross polarization have been achieved within 2.4-2.5 GHz,which is sufficient for WLAN application. The total thickness of the antenna is only 0.031?, which is low-profile when compared with its counterparts.In chapter 4, an antenna with switchable quadri-polarization has been studied. The antenna consists of the radiating patch and the feeding network. The feeding network is composed of two Wilkinson power dividers, two slow wave transmission lines, two Schiffman shifters, two branch-line hybrids and a wideband crossover. With differenct feeding signals through the feeding network, four differenet polarization, i.e. ±45° linear polarization and left/righ-hand circular polarization, have been achieved. Corresponding results have been verified by both simulation and measurement.In chapter 5, a summury of our work in the thesis has been given and some drawback and future work have been discussed as well.