Circular polarized antenna is the most popular antenna for FPV flying with 5.8Ghz FPV system, such as skew planar (four-leaf) or cloverleaf antenna (three-leaf). Although they do allow better range and reception, there are situations where you are better off using simple linear polarized antenna, such a dipole antenna.
Linear polarized antenna can be made very small and light weight, especially useful for weight-critical application, such as on a micro quadcopter.
It’s funny everybody talks about how to make CP antenna, theory how the length are calculated etc, but rarely mention the basic 5.8Gghz video transmission antenna like whip or dipole. Hope I I got this right here and actually help someone who wants to DIY this. I am using this antenna on my DIY 5.8Ghz FPV combo with good result.
What’s inside a whip antenna
If you open a whip antenna that comes with every 5.8Ghz video transmitter or receiver, you will find it’s just a simple Coaxial Cable inside.
But what we really need to know is, the length of the exposed wire affects the signal frequency that it receives. If the wire is 12.92mm then it’s tuned for 5.8Ghz, but only a little shorter e.g. 12.70mm, and it’s now tuned to 5.9Ghz.
For example this one is not very well made for 5.8Ghz, could be a little longer. For 2.4Ghz system, it’s the same such as radio receiver.
Calculation of wire length for antenna
If the antenna is a quarter wave monopole antenna, then its length should be a quarter of the signal wavelength.
Length (m) = c / frequency / 4
Where c is the speed of light.
The more precise wire length is, the better signal you should get ideally. If you are using Coaxial Cable, it doesn’t matter how long the shell is, all that matter is the exposed wire (the part that is without the shielding). Alternatively if you are using a wire like copper wire, just cut it to the calculated length.
Further reading: 5.8Ghz Frequency Bands For different FPV brands.