The recent rapid advancement in wireless communication has created a tremendous need for miniature, high performance, low profile printed antennas. It is well known that miniaturization and high performance does not go hand in hand. The degree of design difficulty increases greatly when antennas are printed and integrated within the mobile device platform. The focus of this dissertation is to explore, design, and develop miniaturized, low profile antennas and arrays for application in future high-capacity wireless communications.

Currently mobile handheld wireless devices are available with integrated internal antennas which require substantial separation from the printed circuit board to operate efficiently. This increases the device size and creates problems for other components and circuit elements nearby. In this work we propose a novel concept where the printed circuit board of the mobile device is modified in the form of a slow-wave structure which helps achieve antennas that require half the separation distance than conventional antennas. The underlying principle applied is the proper utilization of the printed circuit board which works in tandem with the antenna, specifically in the lower 900 MHz frequency band. A laboratory prototype antenna is developed and measured to demonstrate performance at 900/1900 MHz.

Arrays of printed dipoles are widely used in ground-based, vehicular, and air-borne applications. To achieve directional patterns and hence high directivity such antennas are operated against a metallic ground plane, which results in severe performance degradation when the antenna height from the metal ground is small. To alleviate this problem printed dipoles require about a quarter wavelength separation from the metal ground plane. However, such a height for low dielectric constant substrates and at the lower GHz frequencies can be substantially large in volume, weight and radar cross-section, which will also generate undesirable surface wave losses. In this work, a new methodology is introduced based on the self and mutual impedance concepts of dipole antennas which can be used to design ultra-thin (one hundredth of the wavelength) printed antennas on electromagnetic bandgap (EBG) structures. A comprehensive study is conducted to understand the effects of the frequency dependent reflection phase characteristics of an EBG structure on the input impedance of a dipole antenna. Optimum EBG phase profiles that help achieve wide impedance bandwidths are generated for a number of antenna heights. Finally a printed dipole antenna on an EBG structure is fabricated and tested (antenna height of 0.03l) to validate performance at 3 GHz.

The above extremely promising results are based on 3D mushroom type EBG structures. The complexity and cost of fabrication associated with a 3D EBG structure motivated us to explore planar EBG structures. For operation in the lower GHZ frequencies, traditional planar EBG structures, such as the UCEBG will require larger unit cells that pose two problems: (1) many handheld or portable devices do not have enough space to accommodate them and (2) material cost is higher due to the large unit cell required. Recently we have designed, fabricated, and developed a new class of planar EBG structure that has a stopband frequency half of that of the UCEBG. We have also designed and developed thin printed antennas, such as dipoles and slots with such EBGs which will have significant impact on compact diversity and MIMO antenna arrays for wireless applications.