Antenna polarization of FPV drone
There are two types of antenna polarization: linear polarization and circular polarization. The key difference between linear polarization and circular polarization is how their radiation modes propagate. A linear antenna projects waves along a single plane (vertical or horizontal). This polarization allows more energy to be transferred, because the waves only move in one direction. However, due to the difficulty of linear wave sailing around the object in its propagation plane, its penetration ability to obstacles is reduced. Circularly polarized antennas emit waves in a helical manner, which periodically spirals in the vertical and horizontal planes. Therefore, circularly polarized antenna is a more skilled competitor’s application and needs to penetrate obstacles; for example, typical FPV Park flight.
LHCP / RHCP
There are two other types of circular polarization, left-handed circular polarization and right-handed circular polarization. LHCP and RHCP can be considered as screw like threads. When the radio waves emitted by circularly polarized antennas rotate towards the waiting receiver, they tend to rotate clockwise (right) or counterclockwise (left). The signal transmitted by RHCP antenna can only be successfully captured by other RHCP antennas, and vice versa.
FPV drone antenna uses a special type of wire to transfer current to the active part of the antenna. This kind of wiring is called coaxial cable. Coaxial cable is mainly composed of four parts: sheath, central conductor, shield and insulator. The central conductor is usually a thick single stranded copper wire surrounded by an insulating layer, usually a thin plastic tube. Shielding shrinks the insulation, a network of thin wires that completely cover the outer surface of a coaxial cable. Occasionally, a layer of insulating plastic (sheath) is added on the shielding surface. The purpose of coaxial cable is to keep very close to the center conductor and shield to suppress the formation of harmful magnetic field, because each opposite charged wire around the formation of opposite magnetic field will cancel each other.
There are various connectors for the temporary matching of FPV drone antenna and video transmitter or receiver. The most commonly used antenna connectors are SMA and RP-SMA connectors. The second most popular connector is the micro UFL. Although UFL is much more compact than SMA, it is easier to separate from the video transmitter and the connecting elements degrade faster. Recently, MMCX style connectors have gained wide attention, providing a suitable middle ground between SMA and UFL.
Different types of antennas
There are many different antennas available, each more suitable for a particular task. The selection of common antennas for FPV flight is discussed in detail below.
The monopole antenna consists of a singular straight wire perpendicular to the ground. Monopole antenna is a kind of omnidirectional antenna, which is linearly polarized. Monopole antenna is commonly used in radio transmitter and receiver. Occasionally, monopoles are used with video transmitters in micro helicopters because of its low profile and light weight, which is good for racing applications.
A dipole is similar to a monopole in that it is an omnidirectional linear antenna. The structure of dipole is that two monopoles intersect end to end. Dipole is usually used in the transmitter or receiver of remote radio control system.
Inclined plane / clover
Inclined plane antenna or clover antenna is omnidirectional circularly polarized antenna, which is composed of a group of leaves connected to the top of a section of coaxial cable. These antennas are almost exclusively used for video transmitters or as video receiving antennas.
Pagoda antenna is a newly developed omnidirectional circularly polarized antenna. Compared with the inclined plane / clover leaf design, the cost is relatively low, and the PCB structure is simple. It is also most commonly used as a video transmission antenna, or a video receiving antenna.
The spiral antenna is designed as directional circularly polarized antenna. Spiral antenna is the best use of video receiving antenna during long-range flight, and its penetration must be maximized. However, the large volume of spiral antenna brings difficulties to the safe transportation of antenna and the installation of video receiver.