| The evolution of wireless communications at the dawn of the third millennium decade has entered a new era in which convergence and worldwide standardization of communication systems is experiencing fast growth than ever before. In the pursuit of better spectral efficiency, higher data rates, higher capacity and overall enhanced system performance in wireless communications, advanced technologies such as LTE (Long Term Evolution), IEEE 802.16 WiMAX (worldwide interoperability for microwave access) and IEEE 802.11n Wi-Fi (Wireless Fidelity), together define the roadmap growth of current and emerging 3G (Third Generation of Mobile) and 4G (Fourth Generation of Mobile) systems and the entire future of wireless communication industry. In this evolution, antennas which serve as connection interface between wireless communication devices and free space propagation of information signal waves play a unique role as they make possible, in the first place, the existence of wireless communications.Over the years, wideband and multiband antenna solutions have been proposed to keep pace with the upgrade of wireless systems for which new bandwidth specifications are defined in time. Antenna design and implementation can be regarded today as a mature technology, accounting for the breakthroughs that have been made thus far. Notwithstanding in as much as technology maintains a continuous evolution, much research effort is still needed in new antenna architectures featuring wideband, multiband performance and excellent radiation characteristics.Antenna miniaturization, design simplification and deployment cost effectiveness for current and emerging wireless systems remain a challenge. Secondly, compact size antenna elements have low gain whereas those integrated in many wireless devices are often customized for specific bandwidth applications and feature irregular shape complex geometries which make them difficult to scale to different frequencies and bandwidths of operation. Thirdly, MIMO systems with beamforming as described in smart antenna techniques in the current state-of-the-art are much complex and their real world deployment have mostly remained expensive especially for implementation in wireless consumer products. There is therefore a need to develop new antenna solutions with comprehensive geometries for easy scalability over different frequency bandwidths as allocated in wireless systems. Likewise, it is desirable that beamforming be simplified by employing new antennas and arrays that maximize MIMO capabilities first at antenna level by means of optimal exploitation of diversity techniques. Developing multiband multi-polarized compact arrays with directional antenna elements to implement promising hybrid adaptive-switched smart antenna techniques is one such solution.In this dissertation, we explore frontiers of wireless communication systems innovation in the field of antenna technology with particular emphasis on compact antennas and arrays for wireless devices. The dissertation, as a whole, targets new antenna solutions in consideration of the aforementioned desirable performance characteristics. A key methodology employed in the research work is the semi-analytical approach in most of the antenna designs by describing geometries mostly in terms of wavelength units, accounting for the fact that antenna operation is wavelength dependent.Among the contributions of the dissertation, we introduce a new hybrid antenna element which is a hybrid between a balanced dipole antenna and a monopole antenna above ground. The new hybrid dipole-monopole (HDM) element with broadband and high radiation efficiency characteristics has simple geometry, simple feed mechanism and can be configured for directional gain and dual polarization operation. Secondly, we propose a method for the design of miniaturized suspended plate multiband antennas along with an illustrative design of a periodic plate suspended plate antenna (PSPA) which has multiband performance essentially independent of ground plane size.The dissertation thirdly proposes a new class of traveling wave antennas, namely, the damped harmonic traveling wave antennas class (DHTWA). The new traveling wave antennas, with geometric shapes defined by truncated periodic and exponentially damped function products, feature easy modeling and efficient control of the traveling wave behavior for high gain, broadband and multiband response. Forth, we present a design technique for directional gain enhancement in low profile tapered slot antennas; we study along a yagi-like dual tapered slot antenna (DTSA) which features high gain, high front-to-back ratio and broadband characteristics with a short taper profile. The closing contribution in this dissertation is a miniaturized dual band dual polarized array (DBDPA) design consisting of directional antenna elements for beam selection MIMO systems. The new DBDP array with hexahedral topology exhibits high port-to-port isolation and low envelope correlation among the elements and can be used to achieve concurrently array gain, diversity gain and spatial multiplexing as well as interference rejection for implementation of high performance MIMO access points (APs) in wireless networks.The overall objective of the dissertation is to contribute in the state-of-art advance of antenna technology with some new design methods, new elements and array architectures having wideband and multiband characteristics, with preferential directional gain in radiation pattern. Particular emphasis is put on compact antennas able to operate in frequency bands within the 700 MHz～6 GHz spectrum which covers most of the 3G and 4G systems currently in use and under development such as Wi-Fi (Wireless Fidelity), WiMAX, HSPA (High Speed Packet Access) and LTE technologies.
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