Very simply put, antennas transfer the power, energy from voltage and current, from an antenna feed into electromagnetic radiation (EMR) in the form of Electromagnetic waves. These electromagnetic waves form patterns that can be controlled.
A highly directive antenna will radiate a number of beams, or lobes, with one ‘main lobe’, a number of ‘sidelobes’, and a ‘back lobe’.
Conversely, an Omni-Directional Antenna will radiate a Donut Pattern with equal energy being distributed in every direction. Below are some common antenna types and typical applications for each.
This Omni-directional antenna is typically used for mobile radio communications as it has a low directivity but radiates in a broader range to more easily pick up signals as a receiver. The gain is typically between 0 and 2 dBi. Figure 3 illustrates a radiation pattern of a quarter wavelength whip antenna, also known as a monopole antenna.
GPS patch antennas are similar to whip antennas in that they have a low directivity to function best as receivers. This is due to the fact that GPS systems are able to calculate location from a variety of GPS signals coming in all directions.
Dome antennas also have a low directivity and a gain that stands around 3 dBi. Often used in passive distributed antenna system (DAS) installations these dome antennas serve as a mobile signal booster in environments that would normally not have connectivity. In these applications, the dome antennas amplify the signal that is hardwired in to connect to phones and devices in the vicinity.
The Yagi antenna is highly directional and offers gains around 11 dBi typically. The high gain and directivity of this antenna serves telemetry applications such as supervisory control and data acquisition (SCADA) applications to supervise and control plant equipment and machinery. This necessitates a concentrated transmit signal to focus on a target.
The waveguide horn antenna’s radiated beam also has high directivity from the flare of the horn. The horn antenna can come in a variety of waveguide sizes to function all the way into the W-band with gains ranging from 10 to 20 dBi. Horn antennas are often used as feed horns for larger satellite antenna to increase performance of the system.
Typical radiation patterns of these antenna types are shown below
In essence, an increased directivity corresponds to a more centralized beam in one direction whereas an antenna with no directivity can radiate evenly in all directions.