Research On Design And Implementation Of Orthogonal Polarization Diversity Antenna

With the development of wireless communication technology,the dual-polarized antenna,due to its good properties such as the ability to combat multipath fading and its increasing capacity,has been put int o wide use in the fields of mobile communication,navigation,radar,remote sensing and telemetry for both military and civilian purposes.Under the background of different applications,various types of antennas,of wide impedance bandwidth,high gain,low cross-polarization,wide-angle scanning and high port isolation,have been developed and applied.Although most of these antennas are of fine properties,the polarization orthogonality of two ports in the whole space is rarely focused on.With orthogonal polarization diversity antenna as the main research object,the major contents of this research are as follows:Firstly,by using cross-placed electric dipoles,a kind of layered dual-polarized line-dipole antenna is designed.The cross-polarization is discriminated by introducing an irregular structure reflect panel for the dipole on the top layer.By optimizing the bend-dipole to meander-line structure,a dual-polarized bend-dipole antenna is proposed to reduce the longitudinal dimension of dipoles,and the cross-polarization,port isolation,and the longitudinal dimension of dipoles are compared under two kinds of schemes.Secondly,by using the magnetic dipoles,a type of L-probe fed dual-polarized patch antenna with layered structure is designed,which has slots in the radiation patch and a reflector is added above the patch to improve its impedance band width.In addition,in order to obtain high impedance bandwidth,with jumpwire technology,a wideband Log Periodic Dipole Antenna(LPDA)is proposed.The longest dipoles of the dual-polarized antenna are in a meander-line structures to reduce the antenna size.Thirdly,to meet the requirements of the antenna in wide-scanning dual polarized phased array radar systems,a polarization-diversity method,with the electric field vectors orthogonal in the whole space,based on magneto-electric dipole,is proposed.By using electric-dipole and patch as radiation elements,a type of magneto-electric dipole dual-polarized antennas is designed,with the electric vectors orthogonal in the whole space in theory.To improve the im pedance bandwidth,the magnetic-dipole is optimized to slot structure,a kind of electric-dipole and slot antenna is presented.The magnetic-dipole is fed by microstrip balun to broaden the impedance bandwidth further.Besides the high port isolation and low cross-polarization,the electric vectors for the two ports of the proposed dual-polarized antennas are semi-orthogonal in a large space.The dual polarized phased array radar systems,equipped with this type of antennas,don't need more complicated post-processing algorithm,and thus their real-time processing ability is improved.Furthermore,based on a square horn antenna with Ortho-Mode Transducer(OMT),with the electric field vectors orthogonal in the whole space,a novel polarization-diversity method is proposed.By using OMT to separate equipower TE10 and TE01 modes of horn antenna,a mono-layered waveguide fed dual-polarized array antenna with super high port isolation and extra ordinarily low cross-polarization is presented,and the detailed design procedures are given about the OMT.A metal grid structure is introduced into the horn array aperture to suppress antenna sidelobes.The simulated and measured results show the port isolation of the antenna is high and the cross-polarization is low.Apart from the traditional antenna performance criteria,the gain,cross-polarization and especially the electric vectors orthogonality of the two polarization ports in the whole space is researched in detail.The gain of the proposed dual-polarized horn array antenna is high,and the cross-polarization is extraordinarily low in the seven typical planes.Even more importantly,the electric field vectors of the proposed horn array antenna are orthogonal in a large space.The orthogonality achieves its theoretical limit in the plane when ?=90o.The proposed polarization-diversity method,with the electric field vectors theoretically orthogonal in the whole space,provides a good reference for antenna design in wide-scanning dual-polarized phased array radar systems.