Antenna types

Antennas come in many forms, each shaped by the frequency it must work at and the pattern of radiation required. The most basic is the dipole, two collinear conductors fed at the centre, typically a half wavelength long and radiating broadside to its axis. Removing one half and working it against a conducting surface gives the monopole or ground-plane antenna, widely used for vertical, omnidirectional coverage on vehicles and base stations.

For directional performance, several designs concentrate energy into a beam. The Yagi-Uda antenna adds a reflector and one or more director elements to a driven dipole, producing forward gain that made it the classic rooftop television aerial. Loop antennas, from small magnetic loops to larger resonant loops such as the quad, offer compact size and useful directivity. Helical antennas wound as a coil radiate circular polarization in their axial mode, which suits satellite and space communication where the relative orientation of the link keeps changing.

At higher frequencies, aperture antennas dominate. The horn is a flared waveguide that radiates a clean beam and is often used as a feed or as a reference standard. The parabolic dish uses a reflecting surface to focus microwave energy into a very narrow, high-gain beam, the form familiar from satellite reception and radar. Choosing among these types is a trade-off between gain, beamwidth, bandwidth, polarization and the physical space available.

Frequently asked questions

What is the simplest antenna type?

The half-wave dipole, two equal conductors fed at the centre, is the basic building block from which many other antennas are derived.

Why are dish antennas used at microwave frequencies?

Short microwave wavelengths let a reflector of practical size focus energy into a very narrow, high-gain beam, which is hard to achieve with wire antennas.

What makes a helical antenna useful for satellites?

In its axial mode a helical antenna produces circular polarization, which keeps a link working even as the relative orientation of the satellite and ground antenna changes.