Design Of The Reconfigurable Antenna And Broadband Circularly Polarized Antenna

with the fast development of high capacity,multifunction,multi-band frequency/UWB(ultra wide band) technique, Single platform multi antenna in modern communication system is getting more and more common. more antennas not only means a rise of cost and weight,but also have a bad inflence of EMC. Reconfigurable antenna and ultra wideband antenna is an effective solution to the problem.This paper study on the design method of reconfigurable antenna and ultra wideband antenna, The research results have great practical value and application prospect of multifunctional broadband wireless communication. The main contexts of this paper are as follows:Frist research on the switchable polarization of slot antenna. On linear polarization annular slot antenna as the foundation, through open rectangle slot at a reasonable position outside the annular slot and connect them with a very narrow slotline section,slot antenna presents circular polarization characteristics.Antenna’s polarization characteristics can be cotrolled by pin diode’s on and off. In addition, annular slot antenna can aslo achieve circular polarization at other frequency point by open rectangle slot inside the annular slot.Two antennas allowing switching either between linear and circular polarization or between frequency and linear and circular polarization are designed.Then a reconfigurable antenna is proposed based on the different feeding locations of the linear-polarized and circular-polarized microstrip patch antennas fed through the bottom of the antennas. By introducing two reasonable slots on the patch and switching them by pin diodes, the proposed antenna can work as circular polarization at the high frequency and linear polarization at the low frequency. In addition, through introducing a miniaturization 1/4 wavelength stub with its terminal grounded, diodes can be directly controlled by the voltages between the patch and ground, which will not affect the radio frequency character of the antenna. Thus, this proposed antenna can be reconfigured easily by the bias tee on the feeding port of the antenna, which eliminates the complexity of the additional complex direct current(DC) biasing circuit and its effect on the RF signal. The simulation and measured results show that the operating states of the antenna can be switched between the circular polarization at 3GHz and the linear polarization at 2.75 GHz with good return loss and axial ratio.Finally Study on the design method of ultra wideband Sinuous antenna. Design a Sinuous antenna working at 2~14GHz.Using the exponential gradient balun as the feeding system for its broadband characteristics.The simulation results show that the antenna has a good return loss,axial radio and gain.