Do you know the difference between omnidirectional verses directional antennas and which you should be using for your situation? The right choice for your application can make the difference between great system performance and just marginal results.
The main difference between the two types is in their acceptance/radiation pattern or how they emit and receive signals. RF loss, also known as signal loss or attenuation, is the reduction of signal strength that occurs as a signal travels. RF loss can be caused by a variety of factors, including absorption, reflection, scattering, diffraction, and refraction, as well as the frequency of the signal. When an RF signal is transmitted, it loses power as it travels. Signals with higher frequencies tend to experience more RF loss than signals with lower frequencies. Getting into specifics as to the differences:
An (practical) omnidirectional antenna radiates or accepts RF energy equally in all directions, creating a 360° donut shaped radiation pattern. This shape allows the antenna to receive signals from any direction in the lateral plane for antennas with vertical polarization, making it ideal for use in situations where there is no specific directionality required, such as when the required coverage area surrounds the antenna position. The advantage of omnidirectional antennas is that they are easy to install and require little to no alignment.
Omni-directional antennas have some disadvantages, including:
- Limited Range: Omni-directional antennas have lower gain compared to directional units and thus can have a limited range.
- Interference: Omni-directional antennas are vulnerable to interference from other sources of RF energy coming from any lateral direction as they don’t have any nulls in the lateral plane. This can cause signal degradation or loss of signal altogether. Some systems may benefit from in-line filters such as our PF 25 or PF 50 or filter/amplifiers, such as our UFM144, in order to keep strong interfering signals to a minimum – i.e. TV transmissions
- Susceptible to Multipath Propagation: Due to their wide radiation pattern, omnidirectional antennas are more susceptible to multipath propagation, which is the interference caused by the reflection of radio waves off buildings, cars, and other metal surfaces.
- Inefficiency: Omni-directional antennas can be less efficient than directional antennas when used with transmitters because they radiate energy in all directions, including into space where it is wasted.
In contrast, a directional antenna radiates or accepts RF energy in a specific direction, creating a cardioid or hyper-cardiod pattern in the lateral plane Directional antennas may be used with transmitters to direct the signal to a specific location and focus it, so that more of the energy arrives at the intended destination. Directional antennas are the most effective for point-to-point connections - where two antennas are used to transmit data. A hotspot is broadcast using one antenna and a second antenna is used to connect to the same hotspot that was communicated using the first. Because of this, a near-perfect link may be established between the antennas, resulting in higher signal reliability. For receivers, these antennas are often used in situations where the signal needs to be focused on a specific area or direction, such as film or TV work where the set is in a specific location. One of the main advantages of directional antennas is that they have a higher gain in the forward direction, which allows them to cover longer distances and provide better signal quality in many situations. Directional antennas, when used correctly, can be used to improve signal to noise (s/n) ratios by being positioned to block unwanted sources. They should be affixed above head height (10 ft is a good rule of thumb), with a clear line of sight to the receiver. By orienting them so that their null sides are “pointing” at unwanted sources of RF (local TV or public safety signals) the RF s/n ratio is further improved. We published a list of common antenna combinations for our equipment in Wire List #12. If you're using coax cables to bridge distance between antennas and receivers, inspect them before use, as wear and damage can cause a loss of signal. All coax cables result in losses of signal strength, depending on the cable material and length, as shown in this handy online table. As mentioned earlier, some systems may benefit from in-line filters. A powerful tool for many systems is the directional ALP690 active/passive antenna with selectable amplification, attenuation, and filtering. We explain why this antenna is an important tool when using digital wireless mic systems in Wire List # 57.
There are several disadvantages of directional antennas, including:
- Limited Coverage Area: Directional antennas are designed to focus or accept the signal in a specific direction, which means that they have a limited coverage area. This can be a disadvantage in situations where a broad coverage area is desired, such as in a large public space or a densely populated area.
- Reduced Signal Strength: Because directional antennas focus the signal in a specific direction, the signal strength in other directions may be reduced. This can be a disadvantage in situations where the signal needs to be strong in all directions, such as when the antenna is in the center of the operating area.
- Signal Interference: Directional antennas can be more susceptible to signal interference than omnidirectional antennas in cases where strong interfering sources are on-axis, while the desired signals are off-axis.
- Difficult to Align: Directional antennas need to be aligned with the source of the signal for optimal performance. This can be difficult to achieve, especially in situations where the antenna is mounted at a height or in an area that is difficult to access.
- Cost: Directional antennas can be more expensive than omnidirectional antennas, especially those that are designed for long-range or high-performance applications. This can be a disadvantage for individuals or organizations with limited budgets.
In summary, the main difference between omni and directional antennas is that omni-directional antennas radiate or accept energy in all directions, while directional antennas radiate or accept energy in a specific direction. The choice of antenna depends on the specific application and the desired coverage area. You may also choose to improve your signal through filtering and attenuation. We cover this topic in our video with Dr. Audio as well as some of our prior Wire-Lists:
Wire-List #11: Transmitter Antenna Combos
Wire-List #12: Recever/Antenna Combos
Finally, various techniques can be employed to minimize RF loss, such as using high-quality, low-loss coax cable between antennas and receivers, minimizing the distance between the transmitters and receivers, using signal boosters or amplifiers when needed to overcome coax cable losses, and yes, optimizing the type of antennas used and their placement. A convenient primer to all of these options is covered in our Wireless Side Chat video #1 – Introduction to RF Spectrum for Wireless Microphone Use.
Have questions about what type of antenna to use for your application or how to improve the quality of your RF signal? Email us at our Ask The Experts box (link to: