Directional (Yagi/LPDA) or Omni Antenna - Which one is right for you?

Deciding between Yagi- and Omni Directional Antennas

Written in conjunction with The Poynting Group.

The choice of omni-directional and directional antenna is not always simple. We will try to explain the key differences experienced by using a uni-directional (aka ‘directional’) antenna vs. an omni-directional (aka ‘omni’) antenna.

The essence is that a directional antenna focuses its gain (reception) in one direction and reduces the gain (reception) in the other directions, much like a flash light does to a light bulb. The omni antenna provides similar reception in all directions (like a normal round light bulb). This can be both an advantage and disadvantage, for which a few points are listed for consideration.

Omni Antenna:

• Benefits are that it can receive signal from virtually all directions. I.e. the mobile or LTE enabled router can roam across various cellular mobile base stations in any direction. If the one cellular base station (tower) is congested or faulty, then the possibility of receiving another site is better than when compared to a directional antenna. You will therefore have a better probability to maintain good connection stability in these situations.
• A disadvantage is that you will also potentially receive interference from all directions, which could degrade your experience. So, the benefit above could also be a disadvantage in higher interference areas (interference is the reception of unwanted signals that can degrade your experience).
• The overall gain of the omni antenna is lower, so the peak throughput is lower when generally compared to the directional antenna.
• An omni antenna is easier to install than a directional antenna and it does not require realignment/adjustment when the network changes (new sites, network problems, etc.).

Directional Antennas:

• When you are far away from cellphone towers and only have marginal signal reception from a single site, then a directional antenna is often a better choice.
• The benefit is that the signal from the target direction is improved through the directivity gain (like amplification). The gain from other directions is reduced as a result and hence the interference (unwanted signals) is suppressed. This can improve the Carrier to Interference Ratio (C/I) where a higher C/I is beneficial in cellular and other radio frequency (RF) systems reception. The signal reception stability is better for this reason, but only while the target base station (tower) is not congested nor faulty.
• When the site to which you have directed the antenna starts performing poorly, you may need to re-align the antenna. Implementation of the antenna may be more complicated as the antenna must be directed towards the target base station or transceiver. Selecting which site to direct the antenna towards is not always easy.
• When the cellular base station (tower), which your antenna is directed towards, becomes congested or faulty, then the impact will become more severe when compared with an omni antenna. From a general stability perspective, the omni-directional antenna might be a better choice.
• When the ability to receive a signal where there is virtually no signal, or an area with high interference, then a directional antenna can be considered.

In Essence:

Omni – better reliability overall (especially in cellular site outages and congestion scenarios) but slower throughput and less efficient in difficult areas. Better option for urban/suburban areas with sufficient cellular base station sites.

Directional – better throughput, but when the cellular base station is congested or out of service, then the experience can become terrible. This is where the omni will perform better.

However, in difficult areas (mostly distant rural areas) the directional antenna does reduce interference from other sites which are not in the same direction as the target site – this is what improves the C/I and thus the throughput.

Implementation of both directional and omni antenna in a MIMO router:

As the above scenarios have their advantages and disadvantages; it is also possible to combine them both in a MIMO configuration which would reduce each option’s disadvantages.

This article was brought to you in collaboration with The Poynting Group. For more information on Poynting Antenna's contact 012 657 0050 or email.

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