Antenna Design And Optimization Research Based On Eigenmode Analysis

Characteristic mode theory(CMT),which is convenient for helping designers to understand the working mechanism of antennas and guiding antenna design works,can describe the resonant characteristics of various antennas and scatters,and give the accurate results of numerical analysis while revealing physical conceptions.Therefore,characteristic mode theory can be widely used to solve various antenna problems.Based on CMT,this paper mainly studies the realization of UWB antenna pattern stability,beam steering of reactance loaded array and bandwidth broadening of antenna unit,respectively.1.The design of UWB omnidirectional antenna based on CMT.The broadband characteristics of the elliptical ring are first analyzed with classical characteristic mode theory.To realize the miniaturization of the antenna structure,the resonant frequency of the basic modes is reduced by adding the periodic rectangular slots.Then the rotating symmetric dipole feeding structure is designed and introduced to excite various modes in turn in the target frequency range.After that,the coupling inner ellipsoid ring is introduced to enhance the coupling effect and add new modes having patterns similar to basic modes.Satisfying the stability of multi-mode electric field pattern in broadband,a compact ultra-wideband omnidirectional antenna for TV white spectrum is finally proposed.The realized bandwidth is480～1028 MHz,the relative bandwidth is about 72.68%,and the gain in band is about1.84～3.63 d Bi.2.The design of beam steering of reactance loaded antenna array based on N-port characteristic mode theory(NPCMT).Multiple ports are first added to special-shaped Yagi-Uda antenna.After extracting the impedance matrix which characterize its port features,we establish generalized eigenvalue equation of PCMT and then obtain characteristic currents and eigenvalues.After obtaining network parameters such as total port currents,taking reactance values as optimal parameters and using differential evolution algorithm to optimize these values.Finally,the maximum angle of the special-shaped Yagi-Uda antenna’s far field pattern varies from-55° to 55° independently under the limits of certain maximum side-lobe level,half power beam width,gain and port reflection coefficient.3.The research on bandwidth broadening of antenna based on NPCMT.The integral structure of slotted elliptical ring and rotating symmetric dipole is analyzed by classical CMT at first.According to the distribution of the maximum characteristic current of the main mode in the target frequency band,the position of the loading port for motivating the mode with low weight coefficient or secondary modes is determined.After adding ports at analyzed locations,the optimal inductance /capacitance value is optimized by the differential evolution algorithm.Finally,the relative bandwidth of bandwidth broadened antenna unit increase from 4.28% to23.89%,the reflection coefficient is lower than-10 d B in 800～1017 MHz frequency band while the working band of realized gain expand.