2024.9.23 13:43
By 김민준
Antennas and RF is what allows us to have wireless communications and what allows remote control. Antennas have many designs and they impact their performance, and RF has many different characteristics that are good to know.
Antennas have many designs. Simple to complex, and they also have different usecases. In a nutshell, antenna acts as a way for RF power to get radiated and dissipated. Without antennas RF power generated from a transmitter will not be able to get dissipated properly, and for receivers to not be able to receive signals properly.
Antennas are tuned to specific frequencies. RF is essentially just electromagnetic radiation at specific wavelengths. Antennas are designed to essentially resonate at specific frequencies so at that frequency, it can receive signals properly. For example, 2.4GHz signals, commonly used for wifi and RC links, has a wavelength at 12.5cm. With this, if you have a piece of wire that is cut to 12.5cm you will be able to receve 2.4GHz signals properly. However, typically antennas are cut to be 1/4 or even 1/8 the wavelength, so 2.4GHz antennas are usually 28.8~32mm long(for RC links, cut to 31.23mm). This means that the lower the frequency, the larger the antenna is. However, by using 1/4 or 1/8 wavelength, the antennas can be smaller while sacrificing rf reception.
The main 2 types of antennas. Omnidirectional and directional antennas. As the name implies, omnidirection antennas receive signals in a 360 degree pattern, and directional antennas receive signals in a certain direction. Typically, the antenna on the drone is a omnidirectional as you want good transmission or reception despite whatever position the drone is at, and the antenna on the ground is a directional as you want good transmission/reception.
A important concept is antenna gain, measured in Db. This is essentially how sensitive the antenna is and can also be used to determine the directionality of said antenna.
Here are some of the more common types of antennas.
Dipole antennas are the simplest antennas, and are widely used. Their construction is extremely simple, just a straight piece of wire. They are normally encased in a plastic housing, or for RC link receivers, they are sometimes just a wire.
Source - Amateur Radio Stack Exchange
Source - Aloft Hobbies
Dipole antennas are used as they’re simple to make, yet they offer decent omnidirectional performance. Dipole antennas are used in practically everything from wifi routers to receivers, to transmitters.
Dipoles can come in a plastic housing with the exposed active element(white cable) and a crimped on metal tube which is the ground plane. This method offers decent reception while being protected, so it’s a favored method to create antennas
What is more commonly used in RXs and for drones is ‘whip’ antennas. They’re essentially dipole except the crimped on ground plane. This type of antenna is extremely simple to make as it’s just a coaxial cable that has been stripped to reveal the inner cable, which is then used as the antenna.
Omni antennas have a slightly unique structure. They offer better omnidirecitonal reception than dipole antennas but they do cost a little extra due to the added complexity in their construction.