IEEE URSI AP-S

The Fraunhofer boundary r = 2D²/λ is the IEEE standard definition. Below this distance, wavefronts are not yet planar and far-field measurements become invalid. This is precisely why near-field measurement techniques exist.

At 1 mm, we are in the immediate reactive near-field region. The individual radiating elements are still spatially resolved. This is one of the key strengths of near-field measurements: you can literally "see" inside the antenna.

This rotational phase signature is characteristic of a circularly polarized spiral antenna. It is a classic example of an antenna "fingerprint" in the near field—and a textbook diagnostic case for Anyfields.

A Rat Race hybrid coupler provides two excitation modes. Feeding the sum port (Σ) drives both patches with equal amplitude and phase, producing a symmetric field distribution. Feeding the difference port (Δ) drives the patches with equal amplitude but a 180° phase shift, creating a characteristic two-lobe near-field pattern. Near-field measurements therefore allow the active excitation mode to be identified directly, without requiring a vector network analyzer.

Directivity and beamwidth are inversely correlated. A narrow beam means the radiated energy is concentrated into a smaller angular region, resulting in higher directivity.

Approximate relationship for aperture antennas:

D≈32000θEθHD \approx \frac{32000}{\theta_E\theta_H}D≈θE​θH​32000​

Electronic beam steering is the defining signature of phased-array antennas. In the near field, this steering appears as a lateral displacement of the field maximum—directly visible on an Anyfields map without requiring an anechoic chamber.

The simulation/measurement overlay acts as an RF engineer's "diff tool." A localized discrepancy can immediately reveal a misaligned layer, a poorly drilled via, or a substrate discontinuity. What once required days of debugging can now be diagnosed in seconds.

Anyfields addresses four major use cases:

• Teaching electromagnetic phenomena through visualization
• Rapid antenna troubleshooting
• In-line quality control during AIT and manufacturing
• Prototyping with simulation-to-measurement comparison

One technology, four applications.

Far-field testing requires several meters of separation distance (according to the Fraunhofer criterion) and a reflection-free environment. In a manufacturing setting, this is often impractical. Near-field measurements performed a few millimeters from the device can be integrated directly into a production line without heavy infrastructure.

A frequency shift in a patch antenna is typically caused by variations in substrate thickness or dielectric permittivity. At the nominal operating frequency, the Anyfields map will show a weaker field than expected. By sweeping frequency, the field maximum appears at a different frequency, enabling diagnosis in less than a minute.