Investigations On Microwave And Milimeter Wave Circularly Polarized Antennas And Arrays

With the development of new wireless communication technologies,novel customized antenna with high performance is an essential parts of wireless system and has a great impact on wireless system.Especially in microwave and millimeter-wave systems such as mobile communications,radar,radio astronomy and microwave imaging fields,it is of great significance to design low cost and high performance antennas and arrays.And circular polarized?CP?antenna has obvious advantages over the linearly polarized antenna in suppressing multipath reflection and reducing polarization mismatch.Therefore,based on the substrate integrated waveguide?SIW?technology and microstrip patch technology,a series of wideband CP antennas and arrays,wideband feed networks and phase-shifting devices have been designed for microwave and millimeter-wave bands,they have the character of light weight,low profile,low cost,high performance,easy planar integration,etc.The dissertation is organized as follows:1)Low profile wideband CP microstrip antenna is studied.Based on a microstrip wideband phase shifter,a wideband sequential rotating?SR?feeding network is designed.A coplanar parasitic patch loaded CP antenna structure is proposed to meet the requirements of low profile structure.The SR feeding network and radiating patches are located on both sides of the ground plane,the feeding probe is disconnected from the middle ground using a circular slot,and connected between the two sections based on inductive coupling.The circular driving patch and four coplanar square parasitic patches are effectively coupled by the conformal slot loading method,and the gain and its flatness are improved.By analyzing the current distribution,two resonant modes are introduced to explain the radiation mechanism,and some key parameters are optimized for reflection coefficient,axial ratio?AR?and gain bandwidth.The proposed antenna exhibits excellent performance on AR bandwidth of 69%and easy to process with PCB technology.2)Wideband low profile CP antenna with omnidirectional conical beam radiation is studied and discussed.Two omnidirectional CP antennas are proposed and designed by using SIW and microstrip patch technique.Firstly,a cavity-backed SIW patch antenna is studied,a monopole circular patch with high-order mode is introduced as driving patch to broaden the impedance bandwidth.An annular array consists of slot coupled sector patches and a SIW cavity loaded with radial stub are introduced to realize wideband dual-resonant omnidirectional CP radiation.Operational principle and CP characteristic of the antenna are explained in detail by using current distribution and corresponding equivalent circuit model.Then,a microstrip patch antenna with omnidirectional conical beam CP radiation is studied,instead of introducing other auxiliary structures,this antenna adopts the narrow-band annular array to broaden the AR bandwidth for maintaining a simple structure and easy optimization.At last,measurement and simulation results show that the two proposed antennas achieve low profile and omnidirectional conical beam CP radiation,and they also have large ground compatibility.3)With the development of 5G communication system towards millimeter waves,SIW technique has been used in millimeter-wave device and CP antenna,exhibiting advantage of planar circuit integration.A novel microwave phase shifter combined with power divider based on SIW structure is proposed,which has advantages of compact structure,wide phase shifter and flexible topology.Its operational principle is explained by equivalent circuit model.Then,SIW-based SR feeding network and grounded coplanar waveguide feeding network are designed,a stacked patch antenna element and its sub-array are implemented.Finally,a 4×4 CP antenna array is achieved,which shows a good performance such as impedance bandwidth,AR bandwidth and gain bandwidth.This scheme solves a problem that using antenna element with narrow AR bandwidth realizes an array with broadband performance.4)Slot CP antennas based on SIW cavity-backed is studied for supporting Q-LINKPAN of China.Two cavity-backed slot CP antennas are designed and implemented by using SIW technique as its high Q-factor and low mutual coupling.Firstly,a CP slot antenna with circular SIW cavity is proposed,which uses two degenerated high-order mode TM₁₁₀ in the circular cavity.The two mode can be slightly separated by four unequal length shorted via array and shorted probes in the cavity.Then,another scheme is presented to broaden AR bandwidth by loading U-shaped slot in a square SIW cavity.This scheme utilizes two orthogonal degenerated modes TE₁₀₂ and TE₂₀₁ and TM₁₀ and TM₀₁ modes coming from square patch in the center of the cavity to implement wide impedance bandwidth.The U-shaped slot on the patch is equivalent to two patches with different sizes,so that two frequencies working at CP mode is achieved.And at last,this scheme maintains a compact antenna structure and broadens impedance bandwidth and AR bandwidth of antenna.