This pattern is an adaptation of a center fragment from a vintage round tablecloth pattern that can be found all over Pinterest, for example:
https://www.pinterest.ca/pin/1196337402468023/
https://www.pinterest.ca/pin/1122663013356496820/
also on Ravelry:
https://www.ravelry.com/patterns/library/calolo

I do not know who the designer is.
Please, feel free to add / tag the name in the comments if you do.

As I was struggling to make out how many crochets and chains that pattern suggests, I realized it will be easier to recreate it in my own polar coordinates as the last few rounds had to be adjusted to make it work for a hoop.

So, here it is:

1) full circle diagram (chart)
2) general description, instructions for fitting into the hoop, and diagram for a fraction of the crochet circle

Please, note that there is NO written pattern provided

Supplies:
• Metal hoop 20 inches in diameter.
• 1/2 lb (227 grams) of 10/2 Linen Yarn, 100% Unbleached Linen (1500 yards/1 lb).
• Crochet hook, 1.75 mm
• Double sided tape 6 mm wide if the hoop is to be wrapped with yarn

The entire pattern is done with two basic crochets: chain and treble, using 1.75 mm hook.

The pattern will work for other yarn or hook size, but the diameter of finished product will most likely be different, and a smaller or larger hoop may be needed.
Stiffer yarns are preferable. Softer yarns give more stretch.