Research On Microstrip Patch Antenna Based On The Theory Of Characteristic Mode

In the rapid development of wireless communication technology,the antenna occupies an important position.Among the many antenna types,the microstrip patch antenna has attracted the attention of many researchers because of its small size,easy processing,easy conformal and low cost.With the demand of engineering,the structural complexity of microstrip antenna gradually increases,from a single patch to multi-unit,from single feed to multi-point feed,from single-layer medium to multi-layer medium.Although antenna's performance has been significantly improved,the difficulty of antenna analysis and design has also increased.In recent years,the theory of characteristic mode has become the focus of research again.It can study the characteristic modal and radiation characteristics of the patch without feeding,by selecting the appropriate characteristic mode and exciting it effectively,the antenna which radiation characteristics consistent with these characteristic modes can be obtained.Therefore,this method fast and efficient,and can provide a clear physical image for the antenna radiation mechanism.Based on this,this paper adopts the characteristic mode theory to study the high performance circularly polarized microstrip antenna.The main contents are as follows:1.The development status and fundamental theories of the characteristic mode theory are introduced,and the theory and design method of the circularly polarized antenna is summarized.At the same time,the distortion of antenna radiation pattern and its improvement method is described.2.A low profile broadband circularly polarized microstrip patch antenna is designed.The antenna patch is composed of subwavelength square patch elements.The characteristic modal analysis of the patch is carried out by using the theory of characteristic mode,two modes with the same resonant frequencies and orthogonal current distributions are chosen as operation modes.Besides,the microstrip meander-line is used as the feeding device to excite the selected operation mode to obtain preset radiation performance.Based on this,the antenna is simulation analysis,the results show that the relative impedance bandwidth of the antenna is 33.6%(4.7-6.6 GHz),3-dB axial-ratio bandwidth is 20.2%(4.9-6 GHz),and the in-band gain of the antenna is 6.8-9.7 dBic.The overall performance of the antenna is good.At the same time,the antenna is fabricated and tested,and the measured results have good agreement with the simulation results.3.A high-performance circularly polarized antenna with a wide band and stable radiation pattern is studied by using the characteristic mode theory.Take a microstrip circularly polarized antenna with a distorted radiation pattern as an example,by analyzing the characteristic mode of the antenna patch,and the distribution of modal current on the patch is observed to find out the mode that causes the radiation pattern distortion.Further,the patch at the outermost is truncated corner to cut off the current pattern that causes the radiation pattern to split.Finally,the antenna is fed by a sequential rotation feed network.The results show that this method can improve the splitting of the radiation pattern at high frequency.And the antenna radiation pattern stability is realized in the whole frequency band.