The zigzag antenna grew out of a study of the well-known helical antenna. The zigzag antenna is a special type of travelling wave antenna. It radiates end-fire if it is fed with respect to a reasonably sized ground plane (which functions as a reflector). Without a ground plane or reflector the zigzag antenna radiates back-fire. (Antenna Magus designs for an end-fire zigzag antenna)
The section lengths and the spacing between the sections are crucial to achieve the desired pattern.