Study On Improved Circularly Polarized Microstrip Antennas With Rotationally Symmetric Slots

In wireless communication system, research and development efforts areaimed at improving performance while reducing size. Microstrip antennas havebeen considered as potential circularly-polarized antennas as a result of severalattractive features including having low profile, being lightweight, conformabilityto various mounting structure and compatibility with integrated circuit technology.Circularly polarized microstrip antenna can receive any linear polarized waves, andbe more anti-fading to enhance the wireless system capacity. Recently the bandwidth enhancements of antenna are becoming more and more exigent forexpanding capacity of wireless communication too. Circularly polarized microstripantennas are classified as single-feeding type or dual-feeding type, depending onthe number of feeding points required to generate the circularly polarized waves.The single-fed type circularly polarized antenna is simple and small and it doesn’trequire an external polarizer such as a90hybrid coupler, and the truncated edgepatch is one of the simplest circularly polarized antennas. The objective of this thesis is to study and design the circularly polarizedantennas with wider impedance bandwidth, better axial ratio and high gain. The CPantennas are designed by combining the truncated edges patch, the Swastika slots,L parasitic elements, L slots and the central vacuum in the patch, which showsbetter CP performance than the basic truncated edge microstrip antenna. Twodifferent types of feeding technology are used in the design, one is a50coaxialSMA connector and the other is a50coaxial SMA connector followed by theround microstrip line. The50coaxial SMA connector followed by the roundmicrostrip line is used for feeding the CP antenna and further improve the-10dBbandwidth and axial ratio of the proposed antenna.The Swastika slot just looks like a rotator, in which the resistance is smallenough to rotate in the fluid field. If the Swastika slot is introduced into the patch,some current may be distributed along the curved slot. The rotational symmetry ofthe Swastika slot may improve the CP performance of the antenna, if the phaseperformance is better. Accordingly, reducing the unrelated linear polarization isanother good method to improve the circular polarization, especially in the regionnear the feeding point.Results show that, by introducing the rotationally symmetrical Swastika slots into the patch, the impedance band, AR band and gain is increased by about6.99%,3.233%and0.88dBi respectively. Similarly, by introducing the rotationallysymmetrical4-L slots and4-L parasitic elements into the patch, impedance band,AR band and gain is increased by about9.5%,5.49%and1.7dBi respectively. Themaximum obtained gain is8.7dBi for antenna with4-L elements and4-L slots. Thedetailed information of the proposed antennas are discussed in chapter3and4.