Circularly-polarized annular-ring patch antennas with size reduction

Abstract

The demand of antenna elements is rapidly increasing recently due to varieties of wireless communication systems launched into the market; for instances, 2G/3G mobile services, marine or land vehicle navigations (GPS), wireless LANs access, remote sensor with monitoring systems, and many small devices embedded with Bluethooth, UWB, Zigbee, DVB and etc. Among many types of antennas, they can be classified into two categories which are linearly-polarized and circularly-polarized elements. For majorities of wireless applications, the linearly-polarized antennas are good enough for transmitting as well as receiving the RF signals. However, for satellite communication and high sensitivity systems like as GPS, satellite phone and the space-to-earth communication, then the circularly-polarized antennas must be used in order to maintain a good capability of signals strength. Therefore, in this project, a study of development of new circularly-polarized (CP) microstrip antenna elements is carried out. The aims of this project are to design a small CP annular ring patch antenna (ARPA) which targets to use in satellite communications. A novel techniques for size reduction in the microstrip ring patch is proposed. Firstly, a comparison between the annular-ring patch with conventional square / circular patch antennas is shown. Then, a technique for exciting CP radiation of the annular-ring patch by adding an L-sharp strip is introduced. Furthermore, a novel size reduction by employing “compact microstrip resonant cells” (CMRC) into the microstrip antenna is described. Finally, a bandwidth enhancement for the small antenna, with CMRC embedded, by using an L-probe fed and metallic wall are inaugurated. All antenna designs are studied by IE3D and HFSS simulation, and then confirmed by measurements. In the finalized design, it is found that the size reduction of patch is around 40~50% when compared with a conventional antenna with the same center frequency. And the impedance bandwidth (BW) and 3dB axial ratio BW are above 10% and 1.5%, respectively. And the gain of this antenna is 6.8dBi. These result are meet the specified requirement and in good agreement.