Research On Magnetic Toroidal Dipole And Circular Polarization Antenna

Electric,magnetic and toroidal dipoles constitute the family of elementary electromagnetic sources.Electric and magnetic dipoles can be visualized as a pair of opposite charges and a circular current,respectively.The magnetic toroidal dipole(MTD)is created by the following two mechanics:(1)A set of magnetic dipoles,which are produced by currents flowing on the surface of a torus along the meridians,form a circle.(2)The toroidal response comes from the near-field coupling hybridization effect among magnetic dipoles,which is characterized by a head-to-tail distribution of magnetic field within magnetic resonators.Compared with the normal multipoles,dynamic toroidal dipole has the ability to confine time varying electric and magnetic field in a small circular region,and has high Q.This property has bright application prospects on sensor,and an ultrasensitive sensor is designed based on the toroidal dipole.In addition,wireless communication is a common electromagnetic technology.In this era of high informationization,a stable wireless communication system with high channel capacity is particularly important.The circularly polarized antenna has the advantages of mitigating multipath interference and advoiding multipath fading,and has good stability.Broadband technology and orbital angular momentum(OAM)technology can effectively improve the channel capacity of communication systems,and have great research value.In this thesis,two circularly polarized antennas are designed based on broadband technology and orbital angular momentum technology,respectively.The main works of this paper are as follows:1.A novel open-drum shaped cavity based on an electromagnetic toroidal dipole with resonance frequency 860 MHz is proposed.Inside the cavity,a vortex magnetic field distribution and field focusing effect and a high Q factor up to 573.3 have been obtained.This structure has ultra-high sensitivity to permittivity and permeability perturbation,which is very suitable for the application of ultrasensitive sensors.2.A novel miniaturized broadband circularly polarized slot antenna is proposed.The circularly polarized characteristics is realized by the asymmetry of the ground and off-center feeding techniques.The parasitic unit further broadens the circularly polarized bandwidth of the antenna and achieves miniaturization of the antenna.The circular polarization bandwidth and size are 100%(2.15-6.44 GHz)and 0.32×0.31×0.006?~3(?is the wavelength of the lowest operation frequency),respectively.3.In this paper,a reconfigurable OAM reflective metasurface(MS)array with high gain and low profile is proposed.The OAM circularly polarized wave is excited by rotating feed technology.Two reconfigurable OAM modes l=±1 can be achieved by switching four pin diodes in the feed network.