What Is the Difference Between Directional and Omnidirectional Antennas and What Are They Used For?

Directional Gain Horn Antenna

Antennas are the basic components and devices used to convert electromagnetic signals traveling through free space to a conductive environment via waveguides and transmission lines. Antennas can be as simple as a single exposed conductor or as complicated as modern active/advanced antenna systems (AAS) with hundreds of individual antenna elements and active electronics driving each element. Two basic distinctions among types of antennas are directional antennas and omni-directional antennas. Simply put, directional antennas are antennas with an antenna radiation pattern that is less than 360 degrees along the azimuth, while omnidirectional antennas have a 360-degree azimuth radiation pattern. This distinction doesn’t differentiate between antennas that have varying elevation radiation patterns, purely along the horizontal.

Omnidirectional antennas are used in applications where the direction of target systems or incoming signals is unknown or could be from multiple directions. For instance, in a wireless mesh network that can be actively/automatically reconfigured, the nodes in the mesh could be in any location in relation to nearby nodes. Hence, using omnidirectional antennas for these mesh networks would likely make deploying the nodes and general mesh operation easier. Many communication systems that broadcast over long distances use omnidirectional antennas, such as AM/FM broadcast and early cellular telephone systems.

Directional antennas focus the antenna radiation along a more targeted area than omnidirectional antennas. The benefit of this is that the directional radiation pattern can contain higher RF energy than if an omnidirectional antenna were used. The caveat to this, is that a directional antenna can only sense and send signal energy within the direction of the radiation pattern, so must be pointed in the direction of a target or receive signal. However, the increased signal energy available in the directional pattern, i.e. antenna gain, allows for the same amount of RF energy to cover longer distances or offer improved the signal-to-noise/bit-error-rate (SNR/BER)  at the same distances and with the same input energy as an omnidirectional antenna.

Modern AAS used multiple antenna elements and electronics to generate extremely directional antenna patterns that can be steered. Additional electronic systems can be used to allow for multiple-input and multiple-output (MIMO) spatial multiplexed signals sent and received by these complex antennas. Though many of the latest Satellite Communication (Satcom), radar, RF sensing, and cellular antennas are complex highly directional systems, omnidirectional antennas are still widely used for any application that doesn’t require high directionality. There are many omnidirectional antenna systems built as antenna modules or even on to PCBs as trace structures or solderable modules for Internet-of-Things (IoT) devices used in medical, industrial, and consumer applications.