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New for July 2026. A compact range uses a parabolic reflector to convert a near-field, spherical antenna pattern into a far-field, plane wave, for testing antenna designs. It is called "compact" compared to normal antenna ranges as the distance needed to ensure a plane from an illuminating antenna is can be quite long and often impractical without the trick of a parabolic reflector. A compact range is often configured inside a walk-in anechoic chamber. Today, as we move up to millimeterwave and sub-terahertz frequencies, compact ranges can be even more compact, as we will show you.
The compact range was first submitted for patent in 1964 by Rlchard C. Johnson, of Georgia Tech Research Institute (GTRI). US patent 3,302,205 was granted in 1967 and contains some excellent images and a description of how it works. We cribbed Figure 1 from the patent and pasted it below.
In the figure, "M" is the illuminating member, comprising the emitter and its mounting structure.
"11" s the parabolic reflector. It is large enough so that very little of the emitted wave hits its edge or passes around it.
"12 is the emitter, a standard gain horn. It has very low back radiation and provides a nearly perfect spherical wave. Its pattern is smaller than the surface of the reflector. It is placed at the focal point of the parabolic reflector, but well off-center. The reflected wave passes entirely above it so that the radiated field is unaffected.
"A" is the antenna under test (AUT), on a mast "22". Although this is not mentioned in the patent, it will have means for rotation azimuth and elevation. Transmission is measured between the emitter and the AUT so that antenna patterns can be plotted versus these spherical coordinates. Further, the antenna can be rotated normal to the plane wave to evaluate polarization.
Table-top compact range
At IMS 2026, a table-top compact range was on display at Millibox. Here is a photo of the antenna mount and the reflector. Read about the system on Millibox's website. the antenna under test is on a gimbal on the right, and the emitter is below it, closer to the reflector.
The parabolic reflector has to be machined to tight tolerances, maintaining the its shape within tolerances of a small fraction of a wavelength at the frequency of operation. This tolerance deserves a full-page explanation, maybe someone could help us explain it?
We asked Millibox where their reflector was made. It turns out that it was fabricated by Eravant, using CNC machining. Below is a photo we took of an Eravant reflector at IMS 2026, it is not part of a compact range.
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