The result of interference from reflections off surfaces surrounding the antenna. This interference changes the target's return signal strength: sometimes it is stronger and sometimes weaker than expected. The degree of lobing depends on the type of reflective surface; smooth ground or water produces the strongest effects. The formation of maxima and minima of target signal strength at various angles of the vertical plane antenna pattern caused by the reflection of energy from the surface surrounding the radar antenna. These reflections reinforce the main beam at some angles and detract from it at other angles producing "fingers of increased probability of detection" called "lobes". Between the lobes are "nulls" which are areas of decreased probability of detection. The strengths of the lobes and nulls are dependent on the type of reflective surface. Smooth ground or water produces the strongest effects.

A vertical array of two or more drivers will beam energy in a series of vertical lobes, over a portion of the frequency band. Probably more than you want to know about lobing can be found by following this link.

The tendency of a speaker system that consists of more than one driver to produce a lobed frequency response in space with in-phase reinforcement (lobes) from the various drivers occurring at some elevations and out-of-phase opposition (nulls) at points between the lobes.