Circular polarized antennas (CP) are far more popular for FPV setups, but why most radio transmitters still use linear polarized antennas (LP)? In this post we will explore the differences and explain the advantages of CP and LP antennas for radio transmitters.
LP and CP antennas performance are similar at the ideal conditions. However things get a bit different when you change antenna orientation.
If you put the receiver antenna at an angle to the transmitter antenna, the signal will be weakened. This is especially worse for linear antennas, you could get as much as 20.7dB in signal loss at 90 degree alignment, that’s over 90% reduction in range!
Further Reading: How to calculate range with dB?
It’s true that circular polarized antenna has much less signal loss due to antenna misalignment – only 0.33dB at 90 degree compared to the 20.7dB of LP.
But why do we still prefer to use LP antennas on radios?
First of all, linearly polarized antennas are smaller and lighter than circularly polarized antennas.
Also antenna size is related to the signal frequency, lower frequencies normally require larger antennas. Radio transmitters normally use lower signal frequency such as 2.4GHz and 900MHz, and so the antennas will be larger than those in 5.8GHz.
This is how big a 2.4GHz CP antenna is.
Transmitter and receiver should have matching antennas, i.e. both sides should have either CP or LP antenna, because mixing them will result in at least 3dB signal loss.
As you can imagine, having a large CP antenna on the drone will be highly inconvenient, and easy to damage it in a crash, therefore the more compact LP antennas are a far more popular choice. To match that, LP antenna should be used in the radio.
To mitigate signal loss from antenna misalignment, diversity receiver can be used. Diversity receiver has two LP antennas, and when you place them at 90 degree to each other, they are always in good alignment with the transmitter antenna, and therefore signal loss can be reduced.
With all that said, you can use CP antennas on the radio transmitter, but you should also have matching CP antenna on the receiver, the size and weight might not be a good idea.
Here are some good aftermarket antennas for your radio:
- VAS Diamond: https://oscarliang.com/product-strm
- Frsky Infinity: https://oscarliang.com/product-1u2h
900MHz (Crossfire / R9M):
Before placing your order, make sure they have the correct SMA or RP-SMA connector.