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Biquad

Directional Antennas

Two square loops over a reflector—an easy, effective microwave beam.

Band: SHF (e.g. 2.4 GHz)
Gain: ~10-12 dBi
Polarization: Linear

Photos

Real-world photo of a Biquad in use — Real-world example. Source: Wikimedia Commons (CC BY-SA 3.0; John Bradley).

Radiation / wave patterns

Idealized radiation pattern of the Biquad — Idealized azimuth radiation pattern (illustrative, generated). Radial scale in dB.

How & why it works

A biquad is built from a single wire bent into two side-by-side squares (each side about a quarter wavelength) mounted a fraction of a wavelength above a flat reflector plate. The two loops together form a full-wave radiator whose currents add in phase, and the reflector throws the pattern forward into a moderately directional beam. Its forgiving dimensions and 50-ohm-friendly feed make it a popular do-it-yourself antenna for 2.4 GHz.

Real-world uses

Wi-Fi links, drone control/video, and amateur microwave experimentation.