Field patterns arise in wave equations with a space-time microstructure. They occur when the microstructure has the interesting feature that a disturbance propagating along a characteristic line, and subsequently interacting with the microstructure, does not evolve into a cascade of disturbances, but rather concentrates on a pattern of characteristic lines. This pattern is the field pattern. Here we focus on the appearance of field patterns in one spatial dimension plus time. In such a case, the field patterns occur when the slopes of the characteristics and the space-time microstructure are in a sense commensurate.