What is the main characteristic of a collinear antenna array?

The main characteristic of a collinear antenna array is that the elements are arranged in a straight line. This linear arrangement contributes to specific radiation patterns, gain characteristics, and improved directivity. Such configurations are commonly used in applications where focused signal direction is beneficial, as they can enhance performance by creating higher gain in the desired direction of transmission.

In the context of antenna design, the spacing and orientation of the elements are crucial to achieving the desired radiation pattern and operational efficiency. While other options touch upon various aspects of antenna design and functionality, they do not correctly define the defining feature of a collinear arrangement. The straight-line configuration is what sets it apart from other types of antenna arrays, which may have different formations and spacing options.