Beam-steering antennas are the ideal solution for a variety of system applications including traffic control, regulation and collision avoidance radars (S-band 3 GHz) installed on most ocean going ships to provide better detection of ships in rough sea and heavy rain condition. Beam-steering is most commonly achieved through phased arrays, where phase shifters are used to control the relative main-beam of antenna array. Many antenna system applications require that the direction of the beam's main lobe be changed with time, or scanned. This is usually done by mechanically rotating a single antenna or an array with fixed phase to the element. For this reason, electronic scanning antennas which are known as phased array antennas are used. A phased array antenna is composed of lots of radiating elements each with a phase shifter. Beams are formed by shifting the phase of the signal emitted from each radiating element, to provide constructive/destructive interference so as to steer the beams in the desired direction. This book will greatly help in doing research on the above mentioned technology.