Antennas are a critical part of any drone system -- whether for RF remote control or for telemetry & control. The cloverleaf antenna is a popular option owing to its reasonable gain pattern in the lateral directions and because of its circular polarization. But it's always important to evaluate your antennas to make sure their performance is inline with specifications -- sometimes a simple little change in the antenna geometry can have massive ramifications.
A buddy of mine is an antenna engineer who has worked at Google and Apple on some of their iconic devices. He recently acquired some of the 3D Robotics cloverleaf antennas and performed an analysis. Some of the specs are a little off -- there’s no way a cloverleaf design achieves 18dBi gain (as mentioned in their specs); it’s more like 2dBi. But the gain is still pretty respectable for a cloverleaf design; the radiation pattern is nice and isotropic (on the lateral plane); and the polarization is reasonably circular (axial ratio of 3.8dB means its a bit more elliptical, but good enough).
All too often, antennas seem like a “black box” to those of us who specialize in electronics, computer science, or mechanics.... so I was really excited when my buddy posted an approachable theoretical explanation behind the cloverleaf antenna (as well as others) over on his Antenna Theory website.
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Also, a 4-leafed antenna is commonly called a 'skew planar antenna', and a 3-leafed antenna is called a clover leaf antenna'. It's also most common that the "cloverleaf" is used for TX and the "skew planar" is used for RX ( as the cloverleaf as a slightly higher gain ( good for a tx) , and the skew-planar is slightly better at rejecting cross-polarised signals. ( better for rx ). .... but the differences are so marginal that it barely makes a difference much either way.
I think that was typo its more like 1.8dBi
It is sort of black magic when it comes to antenna design and manufacturing. A lot of time theory and design would show one dimensions and once produced antenna would be resonant on other frequency. Same thing goes with impedance. It is all based on type and dimensions of used material. Some time just different batches of material can produce different results. This is seems to be exponential with higher frequencies.
- There is nice book (HAM Bible) for people who like to start digging more in antenna design by "Karl Rothammel"
- Than mostly based on previous book there is "ARRL antenna book"
- And I would like to point out to this seasoned HAM radio antenna designer YU1AW
For all those that would like to squeeze extra distance on 2.4Ghz radio transmitter ( Taranis, Spectrum, Futaba, Solo ... ) I would like to suggest obelisk or 3d corner