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I've seen many references saying that mushroom antennae (like the one shown below) are excellent at receiving and transmitting omnidirectionally. I have them on my drones' video transmitters and one paired with a patch antenna on my FPV goggles.

What makes them so good at this?

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  • $\begingroup$ I think this question requires clarification; i.e. what do you mean by "are excellent at receiving and transmitting omnidirectionally". I can see several parameters you may be referring to: - the omnidirectionality itself, i.e. why do mushroom antennae transmit as uniformly in all directions as they do - The quality of signal in general, when compared to other omnidirectional antennae (possibly not only circularly polarized ones). - Possibly their good efficiency or something? etc. I think you should clarify this. As it is the question is too generic. $\endgroup$
    – FlashCactus
    Apr 16, 2020 at 10:40

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Most omnidirectional antennae have two factors that work well for them.

1) They have fairly symmetrical and uniform RF profiles. This means that you are less prone to sudden drop-outs in the video as you change the orientation of the antenna as it is less likely that you will line up well with an area of lower RF intensity.

2) They are often circularly polarised, as the mushroom is. This means that that the correct Rx / TX combination effectively cuts out interference from signals reflected from various obstructions, making for a more clean and reliable reception.

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The primary purpose of using circularly polarised antennas is the rejection of out of phase video reflections. They tend to have lower gain compared to linear antennas but linear need the antenna alignment to be maintained. On aircraft that flip and roll in all axis and also fly near buildings ETC circularly polarised antennas with the analogue transmission is very advantageous however with digital transmissions reflections can help.

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  • $\begingroup$ Note that while more gain sounds nice, it doesn't actually describe how "good" an antenna is in general but rather it's directivity. So for an omnidirectional you are trying to get your gain as low (= close to 1) as possible. $\endgroup$
    – id -un
    Apr 17, 2020 at 18:11
  • $\begingroup$ (close to 1 means close to 0 dB) The lowest possible gain is actually archived with a linear antenna, but that changes drastically when transmitter and receiver aren't perfectly aligned. $\endgroup$
    – id -un
    Apr 17, 2020 at 18:20

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