An antenna does not radiate an electromagnetic (EM) wave uniformly in all directions due to its physical design and properties. Several factors contribute to the directional radiation pattern of an antenna:
Antenna structure: The physical structure of an antenna, such as its size, shape, and arrangement of elements, affects the radiation pattern. Different types of antennas, like dipole, monopole, yagi, or parabolic antennas, have distinct radiation patterns based on their design.
Antenna orientation: The orientation of the antenna elements and the direction of current flow impact the radiation pattern. Antennas are designed to optimize radiation in specific directions or within certain angular ranges. For example, a dipole antenna oriented vertically radiates more effectively in the horizontal plane, while a horizontally oriented dipole has better radiation in the vertical plane.
Antenna gain: Antenna gain refers to the ability of an antenna to focus its radiated power in a particular direction. High-gain antennas concentrate energy in specific directions, resulting in a narrower radiation pattern. Low-gain antennas, such as omnidirectional antennas, radiate more uniformly in many directions but with lower overall power in any specific direction.
Antenna impedance: The impedance of the antenna and its matching with the transmission line or the impedance of the surrounding medium influence the radiation pattern. Mismatches can lead to reflections and changes in the radiation pattern.
Ground effects and reflections: The presence of nearby objects, the ground, or reflecting surfaces can affect the radiation pattern by causing reflections, interference, or blocking certain directions.
By carefully designing and shaping the antenna elements, engineers can control the radiation pattern to suit specific application requirements. Different antenna designs are chosen based on factors like desired coverage, directionality, gain, and interference considerations.