Research On The Design Of Broadband Circularly Polarized Antenna And Broadband Reconfigurable Antenna

Due to their advantages in improving receiving sensitivity,enhancing channel capacity,and overcoming multipath interference,circular polarization antennas(CPAs)and reconfigurable antennas(RAs)have been widely used in modern wireless communication systems.This dissertation systematically summarizes the research status of broadband CPAs and broadband RAs,and conducts in-depth research on some new design methods.In terms of the key technical difficulties faced in design process,such as compactness,wideband,good radiation characteristic,multi-polarization selection,and multi-radiation selection,some innovative ideas and techniques origining from basic radiation structures and working mechanism have been proposed.The main research contents can be summarized as follows.(1)In view of requirements of CPAs such as broadband,low-profile,high aperture efficiency,etc.,two broadband low-profile directional CPAs are studied and designed.Firstly,based on the slow-wave characteristics of the two-dimensional periodic structures,a novel miniaturized broadband artificial magnetic conductor(AMC)reflector is proposed.And it has been applied to four orthogonal dipole arms to achieve broadband high-efficiency CP.Secondly,a meta-surface loading method was used to design a stacked dual CP patch antenna.The improvement on radiation gain and port characteristics of the patch element after loading the meta-surface is analyzed.By using two-stage 3-d B coupling bridges,a dual-port feed network is designed to complete broadband low-profile and high-gain dual CP,which has high-efficiency and good engineering application values.(2)For the purpose of directional ultra-wideband(UWB)CP application,a compact UWB directional CP antenna is introduced.Starting from the miniaturization design of the tapered slot element(TSE),an impedance matching enhancement technique based on parasitic shorting patches loading is proposed,and its equivalent circuit is modeled and analyzed.A broadband coupled-line phase shifter and a multi-stage Wilkinson power divider are utilized to design a feed network,which feeds crossed TSEs to achieve UWB CP.A top loaded dial-shaped parasitic metal strip is designed to improve the the front-to-back ratios(FBRs)at the low band significantly.The proposed antenna not only has UWB directional CP capability,but also has a compact structure and stable patterns.Compared with others,the proposed one has obvious advantages in bandwidth and size.(3)To meet the demands of broadband multi-polarization applications,two quadpolarization reconfiguration(QPR)antennas are put forwared by using multi-feed technique.Firstly,a dual-port wideband linear polarization(LP)element is proposed.Due to the inherent 180° phase difference(PD)of radiated fields between two ports,the design complexity of feed network can be reasonably simplified.A switchable feed network containing 6 PIN diodes is designed to feed a crossed three-port radiation structure,which realizes directional QPR of more than 80%,and the radiation patterns are stable within a compact structure.Secondly,for broadband omnidirectional multi-polarization,the dual-mode work of four-printed dipole based on square patches loading is introduced,from which the embedded design concept of horizontal polarization(HP)element and vertical polarization(VP)element are taken shape to heavily reduce the profile height.An advanced feed network which just contains four direct current(DC)voltages is designed for achieving omnidirectional QPR.The proposed antenna has the advantages of compact size and low DC power consumption.(4)For broadband multi-beam coverage,two pattern-reconfigurable antennas are designed.On one hand,the circular patch loaded with shorting pins with broadside radiation mode and conical radiation mode are refered.The suspended pins loading and gap-coupled feed techniques are introduced to improve port isolation and radiation features.For the broadside mode,a T-shaped feed branch is proposed to enhance impedance matching and broaden bandwidth.Four PIN diodes are used to design a switching network,which realizes the desired low-profile pattern diversity.On the other hand,for widebeam coverage,a broadband multi-beam reconfigurable antenna is proposed based on PEC-loaded printed rotating dipoles.By arranging the bias line,controlling the parasitic metal strips,and optimizing the rotation angle of dipole arms,a wide impedance bandwidth within a compact size is realized,and the half-power beam-width can cover the entire upper space.These antennas mentioned above have potential to be applied in some systems,such as vehicle global position system(GPS),satellite communications,microwave imaging,wide-angle scanning phased array,etc.