The gain of an antenna could change the radiation pattern, and it reflects what the maximum range is going to be for the FPV antenna. In this article we will discuss how antenna gain affects range, and the pro’s and con’s of high gain antennas.
For a more complete overview of FPV system and antenna, make sure to check out our guides:
- The complete guide to FPV
- How to choose the best FPV antenna
- How polarization affects antenna performance
There are normally 2 ways to increase the range of your FPV system, either to increase the power of video transmitter or use a higher gain directional antenna.
As RC hobbyist we should avoid blindly increasing the power of video transmitter to achieve longer range, simply because: 1. it’s heavier; 2. it might not be legal; 3. it will consume more power and generate more heat. So that leaves us with one only option – to use higher gain antennas.
Understand Antenna Gain
Antenna gain is the measure of antenna power in decibel (dB), which is equal to 10*log(Pout/Pin).
FPV antennas will usually have a dB specification by manufacturers. This value gives you an idea of how the antenna will alter the radiation pattern. However it’s more often used by directional antennas, and often ignored on omni-directional antennas.
Every 3dB increase in gain doubles the range of the Antenna. However, the longer range is achieved by focusing power toward one direction in a narrower beam width.
Pretty much like a water balloon. The volume is the power of your VTX (or total signal coverage area) which doesn’t change, an antenna of different gain and radiation pattern can change the shape of the balloon. The longer you stretch it, the narrower it becomes.
A different analogy is bulb vs torch, which represents omni antenna and directional antenna.
Although signal reception becomes narrower with increased antenna gain, a common technique is to use diversity receiver to have multiple antennas working together. This way we have more range and also covers a wider angle.
Every antenna has a different radiation pattern, and you can clearly see the effect of antenna gain in these examples.
A radiation pattern of the hypothetical isotropic antenna at 0db gain. It’s a nearly perfect sphere in both vertical and horizontal axis.
This is a standard omnidirectional 3dB rubber duck antenna. Notice it has significant signal loss on the top and bottom. Similar radiation pattern applies to most omni-directional antennas out there.
In 3D it would look like a doughnut. :)
And here we have an even higher gain Patch directional antenna at 8dB. As you can see majority of the signal are focus on 1 direction to the right just as we expected from a directional antenna.
By using antennas with higher gain do not magically create extra power in your FPV system, it simply focus the radio waves into narrower space, so the signal coverage can reach out further in the required direction. It’s important to remember that by gaining distance, the effective angle will be lost.
So when choosing antennas for mini quad FPV (or drone racing), unless you know what you are doing, you should choose low dB omni antennas since the aircraft could be flying around yourself.
It’s common to pair an omni antenna with a high gain directional antenna in a diversity system. The directional antenna allows you to fly further in front of you, and the omni antenna allows the copter to fly behind without losing signal immediately.
- Oct 2013 – article created
- May 2017 – article revised