Degree Granting Department
Thomas M. Weller, Ph.D.
Self-complementary, Archimedean, Equiangular, Balun, FSS, Helical
Advances in technology have placed a great emphasis on the design of broadband antennas as well as antenna miniaturization to cope with the demands of making electronic and handheld communication devices smaller and more efficient. In this thesis, the design and fabrication of a frequency independent antenna and a narrow-band planar microstrip Balun are presented. An analysis of frequency selective surfaces is also introduced in order to demonstrate their capability to miniaturize antenna thickness. Lastly, s-parameters measurements and efficiency characterization are performed to determine the radiation properties of surface mount chip inductors in order to determine the feasibility of using them as electrically small antennas.Two types of frequency independent antennas are considered due to their planar geometries, the Equiangular and Archimedean spiral antennas.
Frequency independent antennas are radiating devices that have frequency independent impedance and pattern properties because their shape is specified only in terms of angles.The Balun is designed to meet the need of a feeding element for the Archimedean spiral antenna. A Balun is a three port device that connects an unbalanced transmission line such as a coaxial line to a balanced feed line such as the one required by two-arm spiral antennas. The Balun discussed in this work is designed to operate at 2.4 GHz with a 200 MHz bandwidth and to transform the antenna input impedance to a 50-ohm reference impedance. The main characteristics from this device that distinguish it from commercially available structures are its low cost, planarity, and compact footprint. The balancing capability of this Balun is shown by the close agreement between the measured and simulated results.
Antennas can be potentially miniaturized in the z-direction by replacing the PEC ground plane separated from the antenna by a lambda /4 thick substrate with a frequency selective surface (FSS) structure that allows the ground plane conductor to be in close proximity to the antenna without affecting its radiation performance. The FSS layer operating at 2.4 GHz presented in this thesis is static (not tuned) and thus the overall bandwidth reduces approximately to the bandwidth obtained with the narrow-band Balun.
Scholar Commons Citation
Aristizabal, Diana P., "Electromagnetic characterization of miniature antennas for portable devices" (2006). Graduate Theses and Dissertations.