Specifications

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%

Originally the radiation efficiency was listed as 92%, this was a mistake. These values are based on simulation, actual measurements are below (they are very similar). The center frequency may shift a bit between batches as a result of variations in the dielectric constant of FR4. Also, not all brands of FR4 have the same dielectric constant. Frequency shifts up to 100 MHz are normal.

Radiation pattern

3D radiation pattern. Look at the 2D version if you actually want to see the numbers.

Simulation model.

Best case, vertical cross-section taken at various angles.

Worst case, vertical cross-section taken at various angles.

Simulation model.

Best case, vertical cross-section taken at various angles.

Worst case, vertical cross-section taken at various angles.

The 'best case' and 'worst case' correspond to different assumptions about what happens to signals that travel along the outside of the coax. In the 'best case' simulation, these are completely absorbed at the other end of the coax. In the 'worst case' simulation, they are completely reflected back towards the antenna. The latter case usually results in standing waves on the outside of the coax, which causes the coax itself to radiate and interfere with the radiation pattern of the antenna. This is why the radiation pattern isn't smooth anymore. The reality will be somewhere between these two extremes.

Measurements

VNA measurements.

EMAX Pagoda 2 Antenna 5.8G 80mm 8cm RHCP Red Omnidirectional Omni FPV Flat Panel SMA(2pcs)