Electromagnetic (EM) emission from substrate edges is increasing significantly when the communication systems move from the first generation to the fifth generation using millimeter waves. It is reasonable and very interesting to utilize the substrate edge to design antennas. For example, H-plane horn antennas are implemented in commercial substrates using the substrate integrated waveguide (SIW) technology. H-plane SIW horns have the advantages of low profile, good gain, and little EM interactions due to the closed structure. In addition, radiation from the substrate edges also can be in leaky waves, which features simple feedings, good impedance matching and high gain. Substrate edge antennas (SEAs) are easy to form arrays with multiple beams or steering beams, and also very suitable to be employed together with packaging technologies. SEAs and the arrays are very promising in the next generation communication systems, like in handset terminals.