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Biquad

Directional Antennas Microwave Directional 🔧 Buildable at home

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

New to these diagrams? How to read a radiation pattern →

Radiation pattern of the Biquad
Faces its target with a moderately wide forward lobe; the reflector plate kills the backward radiation.

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.

Make one at home

A practical starting point — always trim and check SWR for your exact frequency.

See the finished antenna pictured above ↑.

A biquad is a famous 2.4 GHz DIY antenna — two wire squares over a reflector, great for Wi-Fi links.

You’ll need

  • Stiff copper wire (~1.2–2 mm), e.g. from house wiring
  • A copper-clad board or a CD-case-sized metal reflector plate
  • A short piece of coax + connector

Dimensions (2.4 GHz)

  • Each of the 8 sides: 30.5 mm (a quarter wavelength)
  • Reflector: ~110 × 110 mm
  • Element-to-reflector spacing: ~15 mm.

Build

  1. Bend the wire into two adjacent squares (a ‘bowtie of squares’); the centre is where it feeds.
  2. Mount it ~15 mm above the reflector on the coax: centre conductor to one square, braid to the other.

Tune

Dimensions are forgiving; keep the 15 mm spacing close. Verify with an SWR/return-loss meter if you have one.

Safety

  • Keep antennas well clear of power lines — never put one where it could fall onto or contact mains wiring.
  • Don’t transmit while anyone is close to the antenna; mind RF-exposure limits and your local licensing rules.
  • Ground masts and use coax surge protection where appropriate.
  • Cutting/soldering: eye protection and a ventilated space.