MPAC OTA Test From protocol testing to full 3D beam analysis

In over-the-air (OTA) testing, “multi-probe” refers to a chamber setup that uses an array of fixed probes, typically antennas, placed around the device under test. Instead of rotating the device or a single measurement antenna to capture performance in different directions, the probes can simultaneously or sequentially capture radiation patterns, throughput, or other metrics from multiple angles.

This approach significantly reduces measurement time compared to mechanical scanning systems, since a large portion of the spatial field is covered at once. Multi-probe setups are particularly useful for evaluating devices that rely on complex antenna arrays or beamforming, where rapid changes in direction and phase must be captured accurately.

A 2D MPAC system arranges probes in a single plane around the device under test. This configuration is effective for measuring performance metrics such as total radiated power, total isotropic sensitivity, and throughput under simplified spatial conditions. It provides a balance between speed and accuracy and is often used for conformance or pre-compliance testing.

A 3D MPAC system extends probe placement to cover a full sphere around the device, allowing characterization of antenna patterns in all directions. This is critical for modern devices that use sophisticated beamforming or adaptive antenna techniques, since their performance can vary significantly depending on orientation and angle of arrival. The 3D configuration provides more complete data for evaluating coverage, efficiency, and spatial diversity, but requires a larger number of probes and more complex calibration.

At millimeter-wave (mmWave) frequencies, wavelengths are very short, meaning antennas and beams are more narrowly focused. To capture these sharp variations in radiation patterns, probes in the chamber must be spaced closely enough to resolve the fine angular detail of the beams. If probe density is too low, narrow lobes or sidelobes may be missed, leading to incomplete or inaccurate characterization of antenna performance.

Higher probe density ensures the chamber can resolve the true behavior of phased arrays and beam-steering systems, which are central to 5G and 6G designs. However, increasing density comes with trade-offs in terms of cost, chamber complexity, and calibration effort. Engineers must balance these factors depending on whether the goal is high-resolution characterization or faster, lower-complexity functional testing.

Calibration is critical in any OTA chamber, as it ensures the measured results represent the true performance of the device under test rather than artifacts of the test setup. In multi-probe systems, calibration aligns the relative gain, phase, and position of each probe so that measurements across the array are consistent and comparable.

Calibration accounts for factors such as probe placement errors, cable delays, chamber reflections, and frequency-dependent characteristics of the antennas. Without proper calibration, small inaccuracies can accumulate, especially at higher frequencies where tolerances are tighter, leading to misleading results. Regular calibration allows engineers to trust that changes observed in device performance are due to the device itself and not the test environment.