Antenna
An Antenna can be used either as a transmitting antenna or a receiving antenna. In the field of communication systems, whenever the need for wireless communication arises, there occurs the necessity of an antenna.
Frequency
Antennas used in FPV are always tuned to a particular radio frequency. The two most commonly used frequencies in FPV are 2.4GHz and 5.8GHz
5.8G
2.4G
Directional
Based on the directivity of the beam divided into two categories:
Directional antennas are optimized for beaming a signal over long distances and in a very specific direction.
Omnidirectional antennas are best suited for the radiation of a radio signal in as many directions as possible, but over a relatively shorter range.
A bulb without a lampshade will emit light at an angle of 360 degrees. It works well to illuminate the area in close proximity, but doesn’t have great range in terms of distance.
A good analogy to explain.
Torch light is much more directed, and thus has a further coverage range – But we don’t see light outside of the ‘sides’. The smaller the angle, the further the reach.
Antenna Polarization
There are two main categories:
Linear and Circular polarized antennas.
Linear polarization refers to an antenna system that is operating with Horizontal and Vertical polarization
Circular Polarization
It is possible to transmit a signal where the polarization appears to rotate while the signal travels from the transmitter to the receiver. This is referred to as a circular polarization (CP).
Circular polarized signal always overlap no matter what orientation or angle your mini quad is flying at relative to your receiving antenna (no signal loss regardless the antennas alignment is).
LHCP vs RHCP
Two different directions that the signal can rotate is expressed as either
Right Hand Circular Polarization (RHCP), or Left Hand Circular Polarization (LHCP).
Transmitter and receiver need to have matching RHCP or LHCP antennas otherwise it could result in significant signal loss.
Gain
Gain is an indicator of directional antenna’s range and angle of coverage.
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Gain is measured by the unit “dBi”.
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Higher gain have a very concentrated and narrow beam.
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Lower gain will have a rounder radiation pattern, excel at high quality short range transmission and reception.
Radiation pattern (radiation chart) shows the shape of the radiation emitted by the antenna. These charts can tell where the weak spots are and how likely it is to lose signal.
Omni-directional antennas usually has signal loss on the top and bottom, and the radiation pattern would look more like a doughnut in 3D.
SWR
Stands for “Standing Wave Ratio.”
It's the ratio of how much output power reaches its destination versus how much is reflected back. We aim for a VSWR value as close to 1 as possible. At 1 VSWR, it means we can transfer 100% of the energy into the antenna.
MMCX
SMA
RP-SMA
U.FL
Connectors
Different in design and not compatible with each other, so make sure you buy the right one.
