Antenna aperture

Okay, imagine your hand is an antenna. The antenna aperture is the size of your hand that can actually pick up signals. When you hold your hand out to catch a ball, you have to make sure you have a big enough surface area for the ball to land in your hand. In the same way, an antenna needs to have enough surface area to "catch" signals from the air.

The bigger your hand is, the more likely you are to catch the ball. Similarly, the larger the antenna aperture, the more likely you are to catch signals.

So, to summarize: antenna aperture is the size of the surface area on an antenna that can "catch" signals. The bigger the aperture, the better the antenna can receive signals.