Open Area Test Site

Description

An Open Area Test Site (OATS) is a type of test facility defined in 3GPP specifications (notably TS 38.113 for NR) for performing standardized Over-The-Air (OTA) testing of radio equipment. It consists of a large, flat, open area with a highly reflective ground plane (typically metal), free of obstructions and reflectors within a specified distance. The core principle is to create a free-space propagation environment to measure the true radiated characteristics of a device under test (DUT). How it works: The DUT (e.g., a UE) is placed on a non-conductive turntable at a fixed height above the ground plane. A measurement antenna, connected to a receiver or signal analyzer, is placed at a far-field distance (e.g., 3m, 5m, 10m, or 30m) on an antenna mast. The DUT is rotated, and the measurement antenna height is scanned to capture radiation patterns. Key measurements include Total Radiated Power (TRP), Total Isotropic Sensitivity (TIS), and Effective Isotropic Radiated Power (EIRP). The reflective ground plane creates a predictable image antenna, allowing calculations to simulate free-space conditions. Its role is to provide a reproducible and controlled environment for mandatory regulatory testing (e.g., for FCC, ETSI) and 3GPP RF conformance testing, ensuring devices do not cause harmful interference and can perform adequately in real networks.

Purpose & Motivation

OATS exists to provide a foundational, standardized method for evaluating the radiated RF performance of wireless devices in a controlled, repeatable manner. It solves the problem of inconsistently measuring a device's antenna performance, which can be severely affected by nearby objects, walls, and other reflections in an ordinary environment. Prior to standardized test sites, it was difficult to compare results between different labs or ensure devices met strict regulatory emission limits. The creation and standardization of OATS specifications were motivated by the need for fairness in certification, ensuring all devices are tested under equivalent conditions to prove compliance with international electromagnetic compatibility (EMC) and radio equipment directives. It addresses the limitations of ad-hoc testing setups by defining precise geometry, site validation procedures (e.g., site attenuation measurement), and measurement methodologies, forming the baseline against which alternative test methods (like reverberation chambers or anechoic chambers) are often correlated.

Key Features

• Standardized geometry with defined separation distance between DUT and measurement antenna
• Large, flat metallic ground plane to create a predictable reflective surface
• Requirement for a clear, obstruction-free area to minimize unwanted reflections
• Defined procedures for site validation using normalized site attenuation (NSA) tests
• Support for measurement of radiated emissions (spurious and out-of-band) and radiated RF performance (TRP/TIS)
• Foundation for regulatory compliance testing (e.g., EMC directives) and 3GPP conformance testing

Evolution Across Releases

Defining Specifications