Research On Pattern Reconfigurable Antennas In Communication Systems

With the rapid development of wireless communication technologies in recent years,the requirements of the antenna performances are becoming higher and higher.Traditional antennas are hard to meet the requirements in many occasions because of the fixed performances.The pattern reconfigurable antennas can adjust the radiation patterns to adapt to the different surrounding conditions,so the signal to noise ratio and the system capcity could be improved.The pattern reconfigurable antennas have broad application prospects.The following three subjects are included in this dissertation.Firstly,a wideband pattern reconfigurable tapered slot antenna is proposed.By changing the bias voltages of four p-i-n diodes,four endfire radiation patterns are realized with a simple bias circuit.The measured common impedance bandwidth of reflection coefficient less than –10dB is 71.3% which covers from 1.57 to 3.31 GHz.The gains of the four modes are all higher than 6.4 dBi at the center frequency of 2.4 GHz.The zero-index-metamaterial?ZIM?units are designed and loaded in the tapered slot.The simulation results show that extra gains of 1.4 to 1.7dBi can be obtained within the bandwidth of 2.2GHz-2.6GHz.Secondly,a pattern reconfigurable patch antenna is proposed with complementary split ring resonator?CSRR?loaded on the ground.Two different kinds of radiating elements are adopted in this design which provides a new way to realize the beam switch characteristic.By changing the states of the p-i-n diodes installed on the CSRRs,the main radiation directions can be switched both in the E-and H-planes.Nine and six patterns are realized for the coaxial fed and the microstrip line fed patch antennas,respectively.The corresponding sizes are 0.82?₀×0.78?₀ and 0.73?₀×0.78?₀,respectively.A four-element linear phased array is designed by the proposed reconfigurable antennas.The simulation results show that it has wider scan range,less gain fluctuations and lower side lobe level comparing with the ordinary microstrip phased arrays.Thirdly,the differential evolution?DE?algorithm is proposed to design a planar electronically steerable parasitic array radiator?ESPAR?.The main beam can be steered in the azimuth plane by changing the reactive loads on the parasitic elements.The antenna is analyzed using equivalent network model and the loaded reactance values are optimized by the DE algorithm.There is no need for a large number of full wave electromagnetic calculations during the procedure and the optimization efficiency is improved significantly.The impacts of the network parameters on the antenna performances are analyzed theoretically.The measured results show that the optimization design method is accurate and efficient.