| Recent years,with a rapid development in the field of wireless communication,communication systems'requirement for antennas'performance has been higher and higher.Traditional antennas'performance is stable,but it has a single-function feature,making it hard to meet all needs in different circumstances.Directional pattern reconfigurable antenna can reconstruct the antenna,change direction pattern to adapt to the changes in the environment surrounded,improve antennas'SN ratio,and decrease antennas'energy consumption,thus smart antennas have practical market value.This essay introduces a novel practical plane miniaturized electronically steerable phased array radar?ESPAR?,intending to realize the reconstruction of antennas'direction patterns.According to the theoretical analysis about the electric fields of orthogonally crossed dipoles in different phase,it is discovered that the crossed dipoles radiate linearly polarized wave in the azimuth plane.Furthermore,when the dipoles are in phase quadrature,antennas can radiate average linearly polarized wave in the azimuth plane,thus we design the planar crossed dipole according to this feature above.Inspired from Yagi antenna,we can control antenna radiation pattern by making orthogonal crossed dipoles the antenna incentive element and taking advantage of leading element and reflective element structure at the same time.Meanwhile,this essay also comes up with a simple but practical impedance matching method which suits this kind of antennas well——control the antenna capacitance through controlling the rectangular patch area of top layer and bottom layer of the substrate.In this way,antenna impedance matching can be controlled.To verify these theoretical analysis,we design,simulate,create and test an antenna resonated at 2.45GHz with using a microstrip antenna structure.Practically,two kinds of driven elements which suit this band have been come up with——sector and windmill structure.Since the gain of sector structure is relatively low,the windmill structure is the one that is chosen to be used after simulation.At the same time,the cost can be reduced using PCB production.As for the antenna,it is a low-profile plane antenna with the size of0.61?0?0.61?0?0.013?0.Through the switch on and off to PIN diode,the antenna 3dB main lobe width can be 90?and 180?.Also the direction pattern can be reconstructed.The measured results indicate that the proposed antenna achieves more than 27.7%impedance bandwidth when the antenna 3dB main lobe width is 180?and more than 7.7%impedance bandwidth when the antenna 3dB main lobe width is 90?.Owing to its planar thin structure,compact size,electronically beam-switching ability,low power,and low cost characteristics,it is promising for applications in wireless communications. |
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