The antenna is built on a separate substrate, I'm guessing a spread glass such as Rogers RO1200. You can do the aperture calculation here, which for a square a

The antenna is built on a separate substrate, I'm guessing a spread glass such as Rogers RO1200. You can do the aperture calculation here, which for a square aperture at 100% efficiency is 18x18 mm. It's probably more like 75% efficiency. https://www.everythingrf.com/rf-calculators/effective-antenna-aperture-calculator https://www.everythingrf.com/rf-calculators/effective-antenn...