Relationship between Antenna Gain and Directionality

Antenna gain and directionality are two closely related concepts in antenna engineering.

Antenna gain refers to the ability of an antenna to direct or concentrate the radiated power in a particular direction compared to an isotropic radiator (a theoretical antenna that radiates power equally in all directions). Directionality, on the other hand, describes how the antenna radiates power differently in different directions.

A high – gain antenna typically exhibits strong directionality. This is because in order to increase the gain, the antenna is designed to focus the radiated energy in a specific direction. For example, a parabolic dish antenna has a very high gain. It achieves this high gain by reflecting and concentrating the electromagnetic waves onto a small area in front of the dish. As a result, the directionality of the parabolic dish antenna is very pronounced. The main lobe of its radiation pattern, which represents the direction of maximum power radiation, is very narrow. This means that the antenna is highly effective in transmitting or receiving signals in the direction of the main lobe but has much lower performance in other directions.

Conversely, an antenna with low gain generally has less directionality. A simple dipole antenna, for instance, has a relatively low gain compared to a parabolic dish. Its radiation pattern is more omnidirectional, meaning it radiates power more or less equally in all directions in a plane perpendicular to the dipole axis. While it can receive or transmit signals from a wide range of directions, it does not concentrate the power as effectively as a high – gain antenna.

The relationship between gain and directionality can be quantified through the antenna’s radiation pattern. The gain in a particular direction is related to the ratio of the power radiated in that direction by the antenna to the power that would be radiated by an isotropic radiator. The shape of the radiation pattern, which shows the distribution of power in different directions, clearly illustrates the directionality of the antenna. By understanding this relationship, engineers can design antennas to meet specific requirements for applications such as long – distance point – to – point communication (requiring high gain and strong directionality) or wide – area coverage (requiring lower gain and more omnidirectional characteristics).