"eggbeater" antenna for the 868 MHz ISM band

I made the antenna of an insulated copper wire with a diameter if 1.8mm (3.5mm with insulation).

The centerfrequency of the 868 MHz ISM band (863 MHz - 870 MHz) is 866,5 MHz. 

The circumference of one loop is: 27295 / 866,5 MHz => 31.5cm

The lengh of 1 radial for best swr is: 11264 / 866,5 => 13cm

The distance between the lower edge of the loop and the Radials are 3412 / 866,5 MHz => 4 cm

In my case, these values ​​gave the best results. 

Using a different wire will likely result in different values.