Multi-Mode Printed Circularly Polarized Antennas

As frontend devices for receiving and transmitting electromagnetic wave,antennas directly affect the performance of entire wireless systems.Circularly polarized(CP)antennas have been widely applied in wireless systems such as satellite navigation,satellite communications and mobile communication because of their greater flexibility in orientation angle between transmitter and receiver,better mobility and weather penetration,and reduction in multipath reflections.Printed CP antennas based on PCB technology become a hot issue because of their excellent features including light weight,compact size,low cost,simple structure and easy to assemble.Thus,studies on printed CP antennas adapted to modern wireless systems are of great significance.In this dissertation,through the analysis of the antenna resonant mode and construction,multi-band CP antenna,multi-mode broadband CP antenna and low-profile omnidirectional CP antenna have been studied.The contribuations of the author can be summarized as follows:1.The multi-mode multi-frequency CP printed antennas are studied,and novel multi-band CP antennas are designed by constructing multi-mode resonators.We propose a design method of compact single-feed CP slot antenna for dual-broadband operation.Two folded concentric annular slots with reduced size are employed as radiators to realize radiation in two different bands,and stepped microstrip feeding line are applied and optimized to achieve good impedance match in both bands.Two design examples aim to different applications are given to verify the design method.For dual-band wireless energy transmission system which demand dual CP band performance and harmonic suppression,a slot-loaded dual-band CP mircrostrip patch antenna with second harmonic suppression are designed.By adjusting the parallel branch and spur-line on microstrip feed line,a good impedance match at 2.45 GHz and 5.8 GHz and their second harmonics suppression are achieved.A low profile dual-band dual-mode CP antenna combining slot and microstrip modes and a tri-band tri-mode CP antenna combining slot,microstrip,and mono-pole modes are proposed.The method of constructing radiating resonant modes,the working principle and method of tuning the resonant frequencies are studied.The proposed low-profile dual-band antenna for GPS application covers GPS L1 and L2 band,and the proposed triband antenna with radiation pattern diversity covers not only the GPS L1/L2 bands with unidirectional radiation but also CDMA communication bands with omnidirectional radiation.The prototypes of all the designs are fabircated and measured.2.The multi-mode broadband CP antennas are studied,and three wideband CP antennas with different bandwidth enhancing mechanisms are designed.By employing a branched microstrip feedline to excite odd and even modes of a CPW,which works as a quarter-wavelength slot radiator for odd mode and a transmission line for even mode,two orthogonal linearly polarized radiations are realized and the combining radiation results in a broadband CP radiation within 47%operational band.Based on the dual-mode microstrip antenna design in chapter third,a wideband dual-mode CP antenna is proposed with the benefit of the electromagnetic coupling between two modes,and 21%working band is abtained.HIS,a kind of meta-surface,is applied as a radiator to design a broadband CP antenna covering a 17%working band with extremely low profile(only 2mm)and unidirectional radiation.Meanwhile by using the CP antenna with HIS as an element,2×2 antenna arrays designed with different feeding network structures result in a gain of 13-16 dBic.The realization mechanisms,configuration and tuning methods of these broadband CP antennas are studied and the prototypes of proposed antennas are measured and analyized.3.Low-profile wideband CP omnidirectional antenna design and polarization reconfigurable techniques are studied.A low-profile omnidirectional CP antenna is proposed.And it consists of a vertically polarized microstrip patch antenna working in TM01/TM02 modes and sequentially bended slots etched on the ground plane for radiating horizontally polarized electric field.The combined radiation from both the microstrip patch and the slots leads to a CP omnidirectional radiation pattern.The polarization reconfigurability is realized by introducing PIN diodes on the slots.By electronically controlling the states of the PIN diodes,the effective orientation of the slots on ground plane can be changed dynamically and the polarization of antenna can be altered between left-hand circular polarization(LHCP)and right-hand circular polarization(RHCP).The design method and energy coupling between radiators are studied.The DC biasing circuits on polarization reconfigurable antenna is analysis and simplified.Only a single voltage is used to switch the polarization of antenna.The prototypes of proposed antenna are assembled and measured.The measurment of proposed antennas validate our design concept.