Multiple-Input-Multiple-Output (MIMO) is effectively a radio antenna technology as it uses multiple antennas at the transmitter or receiver to enable a variety of signal paths to carry the data by grabbing more than one signal, choosing separate paths for each antenna to enable multiple signal paths to be used. Giving benefits of reflected signals to provide improvements in channel robustness and throughput. Many wireless and RF technologies are using the new MIMO wireless technology to provide increased link capacity and spectral efficiency combined with improved link reliability. This book represents a design and investigation of 4-port multiple-input-multiple-output (MIMO) antenna with tri-band applications covering GSM, WiMAX and WLAN bands of modern wireless broadband communication.