The authors study the different types of wave components that comprise the total aperture field of a planar leaky-wave antenna, and show how each influences the radiation pattern. The two main components of the aperture field are the radiation (continuous-spectrum) field and the surface-wave field. The radiation field is further decomposed into the ,leaky-wave field and the space-wave field. The authors also study how a finite-size aperture affects the radiation from the different aperture field components, and thus influences the total radiation pattern. The effects of scan angle, in particular, on the radiation from the different aperture field components is investigated. The authors also study the accuracy of two different simple formulas for determining the finite-aperture radiation pattern, one based solely on the radiated pattern of the leaky wave, and the other using an improved formulation called the subtraction method. >