How does a far-field antenna range work?
A far-field range illuminates the antenna under test (AUT) with a source antenna far enough away that the incident wave is approximately planar across the AUT, conventionally R ≥ 2D²/λ (phase error ≤ 22.5°), also with R much greater than D and λ. Outdoor elevated, slant and ground-reflection ranges, and indoor direct-illumination chambers, are the main types.[1][2]
What range length is needed?
For an AUT of largest dimension D: R ≥ 2D²/λ. A 30 cm antenna at 10 GHz needs 6 m; a 3 m reflector at 10 GHz needs 600 m, which is why large antennas are measured on compact or near-field ranges.[1]
What are the outdoor range types?
- Elevated range: source and AUT on towers, with low-gain-toward-ground source antennas and absorber or diffraction fences to suppress ground reflection.
- Slant range: AUT on a tall tower, source near the ground, aimed upward.
- Ground-reflection range: deliberately uses the ground-reflected ray to form a smooth interference lobe at the AUT, useful at VHF/UHF.[1]
What limits accuracy?
Amplitude taper across the AUT, phase curvature, multipath reflections, weather and interference outdoors, and alignment. Range qualification maps the field over the test volume.[1]
Frequently asked questions
Can the source be closer than 2D²/λ?
With larger phase error; low-sidelobe antennas often need longer ranges.
Why do outdoor ranges still exist?
Very large or low-frequency antennas may not fit any chamber.
What is amplitude taper?
Variation of the incident field across the AUT caused by the source pattern.
See also
References
Online sources accessed October 21, 2026; printed works cited by edition. See all sources.
- “IEEE Recommended Practice for Antenna Measurements (IEEE Std 149-2021)”. IEEE Antennas and Propagation Society. 2022.
- “Antenna Theory: Analysis and Design, 4th ed.”. C. A. Balanis, Wiley. 2016.