The influence of substrate height on the radiation efficiency should be described by two stages. Stage 1: When the height is small, dielectric loss (and maybe together with conductor loss) dominates. In this stage, the radiation efficiency increases with substrate height, since larger height leads to smaller dielectric loss and stronger radiation. Stage 2: When the height is large, surface-wave loss dominates and this loss increases with substrate height. Thus keeping increasing the substrate height cannot improve the radiation efficiency infinitely.