Wireless communication systems are everywhere in today's modern world. The number of mobile devices has grown to be larger than the number of people on the planet. Alongside this growth there is an increase in the demand placed on these communication networks. Users expect to be able make calls and send texts while at the same time being able to stream high quality video seamlessly while on the move. New technologies have made all of this possible and newer technologies will push the limits further. This thesis presents a body of work that developed antennas designed to work with the high data throughput wireless networks that are necessary to make this modern communication possible. Several antenna elements were designed over the course of this thesis. Their development, fabrication, and analysis is presented in this thesis. All antennas use or build off a planar inverted-F antenna (PIFA) design. This base design was chosen for its near omnidirectional pattern, high efficiency, ease and cost of fabrication, and dual-band nature. These elements include a dual-band 4G/LTE antenna operating in the 700-800 MHz and 1850-1990 MHz bands; a dual-band WLAN antenna operating with bands 2.4-2.5 GHz and 5.725-5.85 GHz; two single-band elements designed to operate on a large ground plane with widened bandwidths of 2.2-2.4 GHz and 4.4-5.0 GHz; and a novel design which combines the 2.2-2.4 GHz and 4.4-5.0 GHz elements into one that operates as a dual-band radiator. The ultimate goal was to design dual-band antennas to be used in MIMO antenna systems. MIMO systems are antenna systems using multiple antennas at the transmit and receive ends along with encoding and decoding algorithms in order to achieve high throughput data connections while maintaining robust data links in complex urban environments. This document includes an introduction to MIMO systems, details parameters used as figures of merit to describe and assess MIMO systems, and shows the development, fabrication, and measurement of these MIMO antennas. The MATLAB code used to calculate MIMO figures of merit such as envelope correlation coefficient, total active reflection coefficient, capacity loss, and mean effective gain is included with this work.