Broadband Multi-Polarization Reconfigurable Antennas

With the development of wireless communication technology,wireless communication systems are required to be muti-functional,high-capacity and ultra-wideband.By loading electronic devices to change the antenna current distribution,reconfigurable antennas can operate in different modes.As the superposition of multiple antennas,reconfigurable antennas not only meet the needs of the development of wireless systems,but also reduce the number of antennas on communication platform and simplify electromagnetic environment,which have become the hotspot of the current research of antenna theory and technology.Depending on the different reconfigurable purposes,reconfigurable antennas can be divided into frequency reconfigurable antenna,polarization reconfigurable antenna,pattern reconfigurable antenna.By employing the technology of polarization reconfigurable antennas,it is possible to realize frequency reuse,improve the capacity of the communication system,and mitigate the signal loss caused by multipath fading.Therefore,the research of polarization reconfigurable antennas is valuable and may find wide applications.The mian focus of this paper is on the polarization reconfigurable antennas.The major contributions of this work are summarized as follows.1.A simple circular polarization reconfigurable planar antenna is presented.The antenna consists of a pair of rectangular loops with four PIN dinodes.By switching the states of the four PIN dinodes,the current can flow over different paths in the antenna structure,forming two types of dual off-center-fed dipoles.Each of the off-center-fed dipoles can obtain a 90° phase difference required for either left handed circular polarization(LHCP)or right handed circular polarization(RHCP).Thus the antenna can be reconfigurated to generate LHCP or RHCP radiation patterns.Two parasitic loops are used to enhance the bandwidth of the circularly polarized antenna.Measured results show that the polarization reconfigurable CP antenna achieves a bandwidth of 31%(2.05-2.8 GHz)for return loss>10 d B and a bandwidth of 16%(2.3-2.7 GHz)for axial ratio(AR)<3 d B.The antenna gain is about 7 d Bi with stable radiation pattern.2.A broadband multi-polarization reconfigurable antenna is presented.The antenna consistsof two similar linearly polarized dipole antennas which are orthogonally nested together and fixed on the reflector.Each dipole antenna is composed of a half-wave dipole,a coplanar microstrip line and a L-shaped microstrip feed line,which are all printed on the same substrate.The dipole antenna has wide arms,which adopts a broadband balun to achieves broadband performance.The reconfigurable feeding network is located on the back side of the reflector.Nine PIN diodes and a DC bias circuit are soldered on the feeder network.By controlling the switching states,the antenna is able to operate in four different polarization states including ± 45o line polarizations and left and right circular polarizations.The measured results show that the antenna can achieve a bandwidth of 37% for return loss>15 d B(0.69-1.0GHz)and a bandwidth of 34%(0.65-0.92GHz)for AR<3 d B.The antenna gain is about 6 d Bi for all polarizations.3.An improved broadband multi-polarization reconfigurable antenna is developed.By adding a pair of parasitic elements above the half-wave dipoles,the impedance bandwidth of the antenna is enhanced and the L-shaped microstrip feeding line with three-band impedance matching achieves better performance.The measured bandwidth is 55%(0.66-1.16 GHz)for linear polarization and 43% for circular polarization.Experimental results show that the antenna has a AR bandwidth of 57%(0.62-1.11GHz)for RHCP and 36%(0.66-0.95GHz)for LHCP.The antenna gain is also about 6 d Bi.These multi-polarization reconfigurable antennas may find applications in radar and communication systems.