Compact-Size Wideband Antennas and Arrays for Wireless Communications

Polarization is an important parameter for characterizing antenna systems. Dual-polarized and circularly-polarized wideband antennas with compact size are very useful for mobile communications and satellite communications. Due to the multipath propagation and shadowing in urban environment, radio signals received by mobile terminals can become very weak. Dual-polarized antennas can achieve better signal quality in mobile communications by using polarization diversity. Wideband circularly polarized antennas are very important for mobile satellite communications as circularly polarized signals are immune to Faraday rotation effects. Circular polarization also enables mobile satellite communications without strict alignment between transmit and receive antennas. Therefore, dual-polarized antennas and circularly polarized antennas have been drawn increasing popularity in the wireless communication systems.

In this thesis, several novel designs of compact, wideband, and specially functioned antennas and arrays are developed for wireless communication applications. First, wideband antennas and arrays are investigated for base station applications with different appealing features, such as compact radiator size, enhanced upper out-of-band suppression, or low pattern sidelobes. They are designed with different novel design concept, such as shared-dipole, electromagnetic dipoles, shorted dipoles, and fourth-order coupling structure. Then, to directly match to the newly emerged differential circuit systems, several wideband differentially fed dual-polarized antennas are proposed for base station applications. They are designed for high common mode suppression, high harmonic suppression, or compact radiator size by using the idea of orthogonal six-port power divider, multi-resonance structure, and crossed open loop resonators. The final designs are two circularly polarized antennas, which have the wide overlapped impedance and axial ratio bandwidth, or dual circularly polarized radiations realized by using crossed open slot-pairs, orthogonal power diver, and phase shift unit cells.

The working principles of these different antennas are extensively illustrated with the relevant design theories and detailed structure studies. The performances of these antennas and arrays are evaluated first by the full-wave electromagnetics simulations, and followed by the measurements of the corresponding fabricated prototypes. Good agreements between the simulated and measured results are obtained. With these different features to accommodate different requirements, these antennas and arrays can be the good candidates for the wireless communication systems.