Everything today has antennas, including our drones. But do we understand how they work? Polarization, connectors, gain, all these things play into the performance of your system and directly impact your range and signal penetration. Today we’ll go over what to look for and how to choose your antennas for any drone.
What is an antenna
Taken from Wikipedia : “In radio engineering, an antenna is an electronic device that converts an alternating electric current into radio waves (transmitting), or radio waves into an electric current (receiving). In transmission, a radio transmitter supplies an electric current to the antenna's terminals, and the antenna radiates the energy from the current as electromagnetic waves (radio waves). In reception, an antenna intercepts some of the power of a radio wave in order to produce an electric current at its terminals that is applied to a receiver to be amplified.”
Long story short, an antenna takes electrical variations and amplifies it into magnetic waves that can be interpreted by a receiver.
Polarization
JEM engineering defines polarization as : the direction of the electromagnetic fields produced by the antenna as energy radiates away from it. These directional fields determine the direction in which the energy moves away from or is received by an antenna.
In RC, linear and circular polarizations are the two readily available types of polarization. The standard video frequencies used are 5.8Ghz, 5.2GHz, 3.3GHz and 1.3GHz. Linear is often used for smaller drones at higher frequencies like 2.4GHz and 5.8GHz and for 1.3GHz video, whereas circular polarization is preferred for larger aircrafts on high frequency bands like 5.8GHz.
Linear polarization refers to the oscillation of an antenna’s electrical field on a linear plane.
Circular polarization refers to a radio wave that rotates as the signal propagates. When it rotates to the right, the polarization is referred to as Right-Hand Circular Polarization (RHCP); when it rotates to the left, it’s referred to as Left-Hand Circular Polarization (LHCP).
Connectors
Antennas need to interface with the transmitter or receiver, and so you’ll need to choose the right connector. Usually, FPV equipment comes with either, uFl, MMCX, SMA or RP SMA. When using adapters and connectors, you need to remember that at every connection you’re incurring a loss of signal strength, usually between 0.5 to 1.2 dB per connection.
Antenna Gain
Antenna gain measures how efficiently an antenna focuses radio waves in a specific direction, compared to an ideal isotropic antenna that radiates equally in all directions. A higher gain means a more focused signal, but also a narrower coverage area. Antenna gain is measured in dBi, which is on a logarithmic scale, similar to noise level measurements. Every 3dB the “power” is doubled. Most omni directional antennas are around 2.5dB, and directional patch antennas are anywhere between 7 to 18dB.
When shopping for antennas, keep in mind the polarization, to make sure it matches your system standard, or what you plan to use. Then make sure you pick the right connector for your build, and try to have as little adapters as possible to retain as much of the gain as possible. And finally, make sure you have the appropriate antenna for your flying style, higher gain results in higher range.