What can happen if inappropriate element spacing is introduced in a phased array antenna?

Ideally, the spacing (Dx) between radiating elements in a phased array should be as follows:

Dx < l/(1+sinqs)

Where qs is the maximum scan/look angle e.g. for qs = 90 degrees, Dx < l/2

Scanning above this angle will cause grating lobes which is an artifact where strong radiation occurs in an unintended direction.

With l/2 spacing between radiating elements, we have the following when scanned to 50 degrees:

1. Full Field of View (qs = 90 degrees)



2. Main Lobe at 50 degrees



3. 2D Antenna Gain Contours shown



4. 3D Beam Pattern shown



With 0.7l spacing between radiating elements, we have the following when scanned to 50 degrees:

1. Limited Field of View (qs = 25.3769 degrees in elevation angle)

2. Main Lobe at 50 degrees with grating lobe 



3. 2D Antenna Gain Contours shown



4. 3D Beam Pattern shown with grating lobe