What type of antenna array has elements aligned in a straight line with no radiation at the ends?

A collinear antenna array features elements that are arranged in a straight line, and its radiation pattern is designed to minimize or eliminate radiation at the ends of the array. This type of configuration enhances the gain and directing capabilities of the antenna by focusing the energy in a specific direction, typically away from the ends. The vertical stacking of elements creates constructive interference for signals emitted from the center while canceling out radiation at the ends, resulting in a more efficient directional radiation pattern.

In contrast, end-fire and broadside arrays produce unique radiation patterns; end-fire arrays radiate primarily in a direction parallel to the antenna line, while broadside arrays radiate perpendicularly to the antenna line. The doublet, usually being a dipole, does not align elements in a collinear manner, nor does it fulfill the specific requirement of having no radiation at the ends as specified in the question. Understanding these distinctions is crucial for selecting the appropriate antenna configuration for specific communication needs.