Research On The Frequency-reconfigurable And The Polarization-reconfigurable Antennas

Reconfigurable antennas with characteristics-tunable capability have attracted extensive attention in modern wireless communication system due to their advantages of miniaturization and multifunction. The reconfigurable antenna can acquire different current distribution by changing its physical structure or size, and which can acquire different frequencies, pattern and polarization mode. Such antenna can realize the faction of multiple antennas, which is equal to that multiple antennas share an antenna aperture.At present, the research of this field has had a lot of achievements since reconfigurable antennas were presented, and which can be used widely. Because there is no mature methods to design and analysis it, the field is difficult to be explored. In this paper, after reading the related literature at home and abroad, and understanding the related principles and methods, some kinds of frequency reconfigurable antenna and polarization reconfigurable antenna are presented, and the major work and contributions of the author are as follows:1. A frequency-reconfigurable coplanar-waveguide(CPW) fed monopole antenna using switchable stubbed ground structure is presented. Compared with the traditional method of slotting in the ground plane, the design of adding stubs is more flexible. Four PIN diodes are employed in the stubs stretching from the ground to change the length and shape of the stubs, which can make the antenna reconfigurable in three operating modes: a single-band mode(2.4-2.9 GHz), a dual-band mode(2.4-2.9 GHz/5.09-5.47 GHz) and a triple-band mode(3.7-4.26 GHz/5.3-6.3 GHz/8.0-8.8 GHz). These frequency bands cover a number of wireless communication systems, including WLAN, WIMAX, C-band, and ITU. This antenna is especially suitable for multiple /single band communication system. Furthermore, an optimized biasing network has been integrated into this antenna, which has little influence on the performance of the antenna. This paper presents, compares and discusses the simulated and measured results.2. A wideband circular polarization reconfigurable antenna with off-centered fed is designed. By controlling the loading voltage of a single-pole double-throw switch(SPDT) in feed line, the antenna can work in left-hand circular polarization(LHCP) mode or right-hand circular polarization(RHCP) mode with the bandwidth of 5-5.9 GHz. This design uses the method of off-centered fed which is the one of the perturbation methods to separate the two orthogonal modes, and make them produce a 90 degree phase difference, which can form a circular polarization(CP) wave. Because the implemented switch has good performance, and there is no need to design complex bias network, the simulation and measured results are agree well with each other. The antenna patterns of left-hand circular polarization mode and right-hand circular polarization mode are symmetrical, and their S parameter and gain curves are basically identical, which reflects that the performance of the antenna is stable, and it achieves the goal.