Antenna design with 'Air Substrate'

I read a variety of articles that air substrate used instead of such as FR-4 to improve antenna parameters. Are there real 'air substrate' sold out by any company? How to realize them? or it's just for visual?

Plastic spacers (which are just plastic posts surrounded by air) are often used, but I've found that styrofoam has close enough properties to air to be reasonable substitute.