Spedix Pagoda 2 5.8ghz Antenna, RHCP, SMA (By Maarten Baert)

The Pagoda 2 antenna is an omnidirectional circularly polarized antenna design that Maarten created. Main design goals were:

-Good omnidirectional radiation pattern.
-Good axial ratio.
-Reasonably small.
-Easy to manufacture within fine tolerances at low cost, even for a hobbyist.

Specs
Center frequency: 5.8 GHz
Bandwidth: 500 MHz (5.55 – 6.05 GHz)
Matching: S11 < -20 dB, VSWR < 1.22 (at center frequency)
Axial ratio: < 1.3
Radiation efficiency: 95%

http://www.maartenbaert.be/quadcopters/antennas/pagoda-antenna/