Radiation and polarization diversities of compact Archimedean spiral antennas
Loading...
Date
2014-12-03
Authors
Momen Mehrabani, Ali
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
In this thesis, four-arm Archimedean spiral antennas are investigated, which are low profile and have compact structure. The operating frequency bands can be designed for any microwave and millimeter frequency ranges and the antenna may be utilized in any desired applications such as Global Positioning Systems, radars, navigation systems, modern satellite communications, adaptive nulling, beam shaping, and direction finding. The concept of cavity backed absorber-filled structure along with a small ground plane embedded inside, as an inexpensive and wideband balun, is employed to reduce the axial size of the antenna. The antenna can generate broadside and boresight-null radiation patterns at the dominant and higher order modes, respectively. The study demonstrates that the proposed compact structure successfully supports the excitation of higher order modes.
Polarization diversity of spiral antennas is mathematically described for an N-arm spiral antenna along with the required feeding networks. Realization of circularly-polarized broadside radiation patterns, with both senses of polarization, is then elaborated for a center-fed low-profile four-arm Archimedean spiral antenna. The radiation active zones, for generating both right- and left-handed circular polarization waves, are determined and the antenna performance in a frequency band, shared by both senses of polarization, is investigated.
The developed antennas can be utilized in frequency reuse applications to enhance the wireless channel capacity and as primary feeds in high gain reflector antennas. Their performance in small front-fed parabolic reflector antennas is numerically investigated. It is shown that excellent circular polarization performance, with a remarkable radiation pattern symmetry and axial ratios below 0.5dB, low cross polarization components, and reflector total efficiencies, as high as 77.8% can be attained. Moreover, backward radiation properties of center-fed four-arm Archimedean spiral antennas are also explored, and their possible applications in reflector antennas are presented.
Finally, the proposed dual-polarized spiral antennas are further investigated by dielectric loading, for size reduction purposes and frequency tuning applications. Both full and partial dielectric loadings are considered and investigated for the spiral antenna performance. A grooved dielectric substrate is also utilized to enable generating low-contrast dielectric permittivities. The spiral antenna performance, etched on such a grooved substrate, is similarly investigated.
Description
Keywords
Antennas