Ever wonder why diffraction order exist only at discrete angles?

Check out the visualization below – it can help explain why diffraction orders, or grating lobes, exist only at discrete angles. Waves that are reflected from (or transmitted through) a periodic structure take on the same period as the structure. The field must also be continuous. Only certain discrete angles allow the field to be both periodic and continuous. These are the diffraction orders. The angles depend on the period of the array as well as the wavelength of the wave.