Design Of Dual-polarized Antennas And Low RCS Antennas Based On Characteristic Mode Theory

With the development of wireless communication and the demand on stealth in the field of national defense,the properties of antenna structures,especially in the miniaturization,low profile,wide bandwidth,and low scattering,have become a hotspot in antenna's research.While some problems have been solved by the simulation and optimization of antennas,these conventional methods cannot fully meet current urgent needs.Therefore,it has become a new challenge that how to use new research methods to design antennas meets the requirements mentioned above.In recent years,the Theory of Characteristic Mode?TCM?has been widely applied into antenna engineering.It has attracted a great attention owing to its clear physical insight into the antennas'resonant and radiating property through modal decomposition without any external excitaton sources.In view of this,the research in this thesis uses TCM as an analysis instrument to design single-polarized and dual-polarized antennas,simutaneously owning the properties of low profile,wideband and directional radiation.Besides,a planar slot antenna's Radar Cross Section?RCS?is reduced based on this theory.The main contributions are summarized as follows:1.The design of single-polarized metasurface antenna.This antenna is based on 5×5metasurface rectangular patch unit cells.The results of TCM for this structure show that it owns a pair of orthogonal dominant modes.By introducing a suspended dipole antenna,designing active-matching network and differential feeding network,feeding at the center of the dipole,the co-operation of dipole mode and metasurface dominant mode in the same polarization direction is realized.The test results show that in the 4.2-5.5 GHz band,the reflection coefficient of the antenna is less than-10dB,and the relative bandwidth is 26%.At the same time,the maximum of the gain is 9dB.The height of this antenna profile is only0.09?₀??₀ is the wavelength in free space at 5GHz?.2.The design of dual-polarized metasurface antenna.This work is based on the metasurface proposed in part 1.By introducing two orthogonal dipoles,designing two power-divider differential feeding networks and feeding in the edges of the dipole center can successfully excite the horizontal and vertical polarization modes respectively.After the fabrication and the measurement of the antenna,the maximum of insolation of the horizontal and vertical polarization ports can achieve 30dB;the reflection coefficient less than-10dB of the horizontal polarization port is the frequency from 4.16GHz to 5.46GHz?26%of relative bandwidth?,whereas the vertical port is from 4.11GHz to 5.43GHz?26.4%?in terms of the bandwidth;both of the peak realized gains are 9dB.Similarly,the height of the dual-polarized antenna profile is only0.09?₀??₀ is the wavelength in free space at 5GHz?.3.The design of low RCS antenna.Using a improved H-shaped planar slot antenna as the prototype and the TCM as the analysis tool,the scattering modes of the antenna in the cross-polarization direction are judged by the Modal Weighting Coefficient?MWC?,and the characteristic currents of the scattering modes are suppressed by the slot loading,thus reducing the RCS of the antenna in the cross-polarization direction.The simulation results show that the antenna can achieve the maximum RCS reduction of 10 dB in the working frequency band while keeping the original radiation characteristics nearlly unchanged.