B.2.2 Direct far field (DFF)
38.508-13GPP5GSPart 1: Common test environmentRelease 17TSUser Equipment (UE) conformance specification
B.2.2.1 Description
The DFF measurement setup for FR2 is capable of centre and off-centre of beam measurements and is shown in Figure B.2.2.1-1 below.
Figure B.2.2.1-1: DFF measurement setup
The key aspects of the DFF setup are:
– Far-field measurement system in an anechoic chamber
– The criterion for determining the far-field distance is described in B.2.2.4.
– A positioning system such that the angle between the dual-polarized measurement antenna and the DUT has at least two axes of freedom and maintains a polarization reference.
– A positioning system such that the angle between the link antenna and the DUT has at least two axes of freedom and maintains a polarization reference; this positioning system for the link antenna is in addition to the positioning system for the measurement antenna and provides for an angular relationship independently controllable from the measurement antenna.
– For setups intended for measurements of UE RF characteristics in non-standalone (NSA) mode with 1 UL configuration, an LTE link antenna is used to provide the LTE link to the DUT. The LTE link antenna provides a stable LTE signal without precise path loss or polarization control.
– For setups intended for measurements in NR CA mode with FR1 and FR2 inter-band NR CA, test setup provides NR FR1 link to the DUT. The NR FR1 link has a stable and noise-free signal without precise path loss or polarization control.
The applicability criteria of the DFF setup are:
– The DUT radiating aperture is D ≤ 5 cm
– Either a single radiating aperture, multiple non-coherent apertures, or multiple coherent apertures DUTs can be tested
– If multiple antenna panels that are phase coherent are defined as a single array, the criterion on DUT radiating aperture applies to this single array
– D is based on the MU assessment in Annex B.1.1.3 of TR 38.810 [24]
– A measurement distance larger than the far-field criteria defined in B.2.2.4 is not precluded
– If the uncertainties can be further optimized, the MU may be reduced or D may be increased
– A manufacturer declaration on the following elements is needed unless the entire DUT size is contained in a sphere of diameter of ≤ 5 cm:
– Manufacturer declares antenna array size
For RRM testing, an example baseline system with two simultaneously active AoA (NMAX_AoAs = 2) as defined in Clause 7.1.3 using a DFF setup is illustrated in Figure 2.2.1-2. Implementations of the RRM baseline system with only a subset of the probes are possible as long as the system can satisfy the relative angular relationships outlined in Clause 7.1.3.2.1.
Figure B.2.2.1-2: Example RRM baseline system with two simultaneously active AoA using a DFF setup.
B.2.2.2 Quiet zone dimension
In order to allow testing of DUTs of different sizes and to allow for flexibility in test chamber implementations, there will be various defined quiet zone dimensions. The smallest quiet zone shall have a radius of 100mm to accommodate DUTs such as smartphones. The next larger quiet zone shall have a radius of 150mm to accommodate larger DUTs such as tablets. To test even larger devices, e.g., larger tablets and laptops, quiet zones with 200mm and 275mm are defined The device types are listed as examples and other device types are not precluded.
The radiating portions of the device have to be fully enclosed within the quiet zone, but the non-radiating portions of the device can be located/placed outside the quiet zone if a vendor declaration with positioning reference points and the minimum QZ required to contain all active antennas within the quiet zone (per band) is provided. This grey-box testing approach where the declared reference point is aligned with the centre of the QZ is further illustrated in Figure B.2.2.2-1.
Figure B.2.2.2-1: Grey-box test approach
In the absence of a vendor declaration, the geometric centre of the DUT shall be aligned with the centre of the QZ and the DUT shall be fully contained within the QZ. This black-box testing approach is further illustrated in Figure B.2.2.2-2.
Figure B.2.2.2-2: Black-box test approach
B.2.2.3 Quality of the quiet zone
The quality of the quiet zone shall be measured for the frequencies defined in FFS. The measured quality of the quiet zone performance is used in uncertainty calculations for the appropriate quality of the quiet zone dimension utilized for the DUT.
B.2.2.4 Measurement Distance
For far-field measurements, the distance R between the DUT and the measurement antenna shall be calculated by the following equation.
where is the largest wavelength within the frequency band of interest and D is the diameter of the smallest sphere that encloses the radiating parts of the DUT.
For DFF, free space path loss is calculated by applying the Free Space Loss formula with R equal to the far field distance: 
.
The minimum range length of a DFF system, i.e., the minimum distance between the centre of the quiet zone and the measurement antenna, needs to take into account the unknown offset of the antenna aperture from the centre of quiet zone in order to guarantee far-field conditions for any antenna array integrated inside the DUT. The distance between the centre of the quiet zone to the measurement antenna is referenced as RDFF, while the radius of the quiet zone is RQZ as illustrated in Figure B.2.2.4-1. The minimum distance between the antenna array integrated anywhere within the DUT and the measurement antenna needs to meet the far-field distance, RFF = 2D2/.
Figure B.2.2.4-1: Illustration of DFF System for range length definition
The setup in Figure B.2.2.4-2 is used to derive the minimum range length for NR FR2 DFF systems where the sphere enclosing the DUT matches the QZ and the DUT antenna with radiating aperture diameter D located in the corner of the DUT. With this setup, the minimum range length, RDFF, can be determined as
RDFF = RQZ – D/2 + RFF = RQZ – D/2 + 2D2/
which is tabulated in Table B.2.2.4-1 for two different QZ sizes assuming D=5cm.
Figure B.2.2.4-2: Illustration of DFF System for minimum range length definition
Table B.2.2.4-1: Minimum Range Length of DFF System for D = 5cm
|
f [GHz] |
24.25 |
30 |
40 |
50 |
52.6 |
|
20 |
0.48 |
0.58 |
0.74 |
0.91 |
0.95 |
|
30 |
0.53 |
0.63 |
0.79 |
0.96 |
1.00 |
The influence of measurement distance on measurement uncertainty is discussed in Annex B.2.1 of TR 38.903 [XX].