What is DFF?
DFF (Direct Far Field) is an over-the-air (OTA) test method used in 5G device and antenna testing. It involves mounting the device under test (DUT) on a positioner that rotates in azimuth and elevation while a measurement antenna located at far-field distance captures the radiated signal. DFF is the most straightforward OTA test approach and produces highly accurate results, but at mmWave frequencies, the required far-field distance becomes impractically large, making alternative methods like CATR and NFTF more common for FR2 testing.
How Does DFF Work?
The far-field distance is defined as 2D²/λ, where D is the largest dimension of the antenna under test and λ is the wavelength. At this distance, the radiated electromagnetic field is essentially a plane wave, and the angular radiation pattern is independent of distance. In a DFF setup, the DUT is placed at or beyond this distance from the measurement antenna inside an anechoic chamber. The DUT is rotated through a full sphere of angles to capture the complete 3D radiation pattern, from which metrics like EIRP, TRP, EIS, and TRS are derived. At FR2 frequencies (e.g., 28 GHz), the far-field distance for a typical smartphone-sized array exceeds several metres.
Use Cases
5G NR FR1 device OTA conformance testing, antenna pattern measurement for small antennas, EIRP and TRP validation, reference measurements for CATR and NFTF calibration, and legacy 4G LTE device testing.
3GPP / Standards Reference
3GPP TS 38.141-2 (NR BS conformance testing — radiated), 3GPP TR 38.810 (Study on test methods for NR)
Related Terms
OTA | CATR | NFTF | IFF | EIRP
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This glossary entry is part of the 5GWorldPro Complete 5G Glossary. To go deeper into 5G architecture and technology, explore our 5G Training courses.
