Industry standards require Over-The-Air (OTA) characterization of cell phones (handsets) before they are used in the US. OTA measurements require measuring the radiation characteristics of the handset in a spherical coordinate system. OTA test systems must contain a two axis positioning system that allows the orientation of the handset to be varied in the phi and theta angles of a spherical coordinate system.
The Howland Company wireless test labs were developed in collaboration with Motorola engineering. The first priority was to design products that would set the industry standard for accurate measurements. With this goal in mind, it became apparent that how one mounts the handset to the positioning system is critical if the measurement uncertainty is to be minimized. The classical approach would have been to mount the handset on a two-axis positioner. However, if this is done, then the positioner structure, even if it is plastic, perturbs the electromagnetic field and dramatically increases the measurement uncertainty and creates 'gravity vector' problems which contribute additional measurement uncertainty.
The Howland Company's wireless test labs employ a distributed axis positioning system. The handset sits on a low dielectric foam block which rotates in phi (Φ); this arrangement eliminates gravity vector problems. The measurement antenna is mounted to a low dielectric mast which moves in theta (θ). As a result, the measurement uncertainty contribution due to quiet zone ripple of The Howland Company wireless test labs is the lowest in the industry, typically less than 0.28dB at 95% confidence.