Researches On Multi-Band Circularly Polarized Planar Antennas

With the rapid development of the wireless communication technology and the emergence of a growing amount of various application scenarios,including the satellite communication,the mobile communication,the wireless sensor,and the wireless local area network,the communication system is promoted and needs to obtain the characteristics of stability,high performance,and multiple functions.As a key component of the communication system,the antenna is constantly facing new challenges.In the urban environment with a lot of skyscrapers and complex and diverse indoor scenes,the multipath fading and the polarization mismatch will disturb the transmission of the signal.The circularly polarized(CP)antenna can effectively alleviate such problem.Compared with linearly polarized antennas,CP antennas have the following outstanding advantages.It can not only counteract the multipath interference from the reflected signal,but also alleviate the Faraday rotation effect when the signal passes through the ionosphere.Moreover,there is no strict requirement on the relative placement between the receiving antennas and the transmitting antennas.However,the current researches on CP antennas are mainly focused on the single-band and dual-band antennas.The dual-band CP antennas are usually based on the stacked patches or based on the symmetric reactive loadings along the diagonal lines or the axis lines.In addition,there are few studies on tri-band CP antennas.Some design methods and examples of CP multi-band patch antennas are presented in this dissertation.The dissertation is arranged as follows:I.Design of dual-band CP antennas based on loading stubs.Firstly,the first two modes of the circular patch,namely the TM₁₁ mode and the TM₂₁ mode,are excited by loading only one stub on the patch which is fed by a microstrip line through the aperture on the ground plane.The antenna obtains the dual-band linear polarization and broadside radiation characteristics.Then,the antenna can achieve the dual-band CP performance by loading another stub of the same dimensions.These two pairs of the orthogonal modes and the way how they can realize dual-band CP performance,are analyzed and described.The frequencies of these two frequency bands can be adjusted by changing the dimensions of the circular patch and the stubs.Adjusting the position of the loading stubs,the senses of CP in these two frequency bands can be changed.Furthermore,a dual-band filtering CP antenna is designed by using a combined dual-band resonator to excite the dual-band CP patch.II.Design of multi-band circularly polarized antennas based on etching slots.Firs of all,the first two modes of the circular patch,namely the TM₁₁ mode and the TM₂₁ mode,are excited by etching only one slot on the patch.The patch is excited by a microstrip line through the aperture on the ground plane.The antenna obtains the characteristics of dual-band linear polarization and the broadside radiation.After that,the antenna can achieve the dual-band CP performance by etching another slot of the same dimensions.This slotted circular patch antenna obtains the feature of a small ratio of the upper frequency to the lower one.These two pairs of the orthogonal modes and the way how they can realize dual-band CP performance,are analyzed and presented.The frequencies of these two frequency bands can be altered by modifying the dimensions of the circular patch and the slots.The senses of CP in these two frequency bands can be changed by modifying the position of the etching slots.On the other hand,the resonant frequencies of these two pairs of the orthogonal modes can be closer by choosing the proper dimensions of the slots.Hence,a tri-band CP antenna with the small frequency ratios is designed by using only two pairs of orthogonal modes of a single slotted circular patch.III.Design of tri-band circularly polarized antennas based on loading stubs and etching slots.Three pairs of orthogonal modes of the rectangular patch,namely the TM₀₁ mode/TM₁₀mode,the TM₀₂ mode/TM₂₀ mode,and the TM₀₃ mode/TM₃₀ mode,are utilized to realize tri-band CP performance by loading stubs and etching slots on the single square patch.The patch is excited by a microstrip line through the aperture on the diagonal line of ground plane.Analyzing these three pairs of the orthogonal modes,the mechanism of CP of the antenna is shown.The antenna,utilizing a single radiation patch,can realize the tri-band CP performance.Moreover,the antenna has a high degree of design freedom.Altering the dimensions of the stubs and the dimensions and position of the slots,the resonant frequency and sense of CP in each frequency band can be controlled relatively independently.To sum up,three types of planar multi-band CP antennas are proposed with their working mechanism,design process,experimental results.The summary of the research on planar multi-band CP antennas is described in the last part,including the advantages and disadvantages of each type as well as the prospect.