Aperture and microwave antennas

At microwave frequencies the wavelength shrinks to centimetres, which changes what an efficient antenna looks like.

Apertures and reflectors

A horn flares a waveguide open to launch a clean beam — a great feed and reference. Put that feed at the focus of a parabolic dish and the dish collimates it into a high-gain pencil beam; gain grows with the square of the dish diameter in wavelengths.

Printed and compact

A microstrip patch is just a metal rectangle on a circuit board — flat, cheap, and easy to array, which is why it is everywhere in GPS, Wi-Fi, and phones.

Circular for space

An axial-mode helical delivers circular polarization off the end of a coil — perfect for satellite links. At these frequencies, big gains are easy because even a modest antenna spans many wavelengths.