A.3 Anechoic chamber constraints

37.5443GPPConformance testingRelease 16TSUniversal Terrestrial Radio Access (UTRA) and Evolved UTRA (E-UTRA)User Equipment (UE) Over The Air (OTA) performance

A.3.1 General

The main objective of this section is to define basic parameters of the anechoic chamber suited for the Tx and Rx measurement of UMTS and E-UTRA UEs.

The chamber should be equipped with an antenna positioner making possible to perform full 3-D measurements for both Tx and Rx radiated performance. Two main measurement set-ups are presented for this purpose:

a) A so-called spherical scanner system implies that the DUT is placed on a positioner that rotates in a horizontal plane. The probe antenna is rotated physically in the vertical plane. Alternatively, multiple probe antennas can be placed along an arch in vertical plane and electronically switched in order to get the full 3-D radiation/sensitivity pattern (see Figure A.3.1-1). Alternatively a multiple probe system, which has a set of probes located on the full spherical surface may be used [21]. In this case the DUT does not have to be rotated.

b) A dual axis system implies that the DUT is placed on a positioner that is able to rotate around two different axes. The signal is transmitted/received by a fixed probe (see Figure A.3.1-2). It is noted that many conventional two-axis systems (i.e. many commercially available systems built for a more general use) are built for the support of rather heavy test objects (with narrow antenna beam), which by their mechanical size may disturb the measurement of nearly omnidirectional antennas. Note that such systems are equipped with a positioner that may disturb the measurement of nearly omnidirectional antennas.

Figure A.3.1-1: Example of a spherical positioner system with a moving probe antenna (left), and with multiple probe antennas (right)

Figure A.3.2-2: Example of a dual axis (roll-over-azimuth) positioner system

Figure A.3.3-3: The coordinate system used in the measurements

In both cases the measurement antenna should be able to measure two orthogonal linear polarizations (typically theta () and phi () polarizations).

Note that for an anechoic chamber, horn antennas are usually used as probe antennas. There are two kinds of horn antennas: single-polarized and dual-polarized. The dual-polarized horn antenna has advantages of a major importance in comparison with the single-polarized. In fact, it is possible to measure two orthogonal polarizations without any movement of the probe, and this will:

a) Reduce the cable antenna uncertainty contribution

b) Improve the measurement stability

c) Reduce the time delay between the acquisitions of each polarized signal due to the electrical RF relay.

If using single-polarized probe antenna, it is possible to perform the measurements by turning one linear polarized antenna by 90 ° for every measurement point. However, this technique has a major drawback: the cable of this antenna is subjected to numerous bendings and rotations, which brings some measurement instabilities. The various positions of the cable have an effect on the repeatability of measurements, and the stress applied to the cable can reduce its performance. The use of a "stress cable", or a rotary joint, connected to the main low-loss cable that is connected to the BTS simulator is recommended if using a single-polarized probe.

A.3.2 Quiet zone dimension

Quiet zone has to be large enough to contain DUT attached to a phantom head and shoulders. The dimensions have to be slightly larger than the phantom dimension due to the fact that the rotation axes are not passing through the symmetry plane of the phantom, but through the phase centre of the DUT. Thus minimum radius of the quiet zone has to be 150mm, which is the approximate distance from a UE to the edge of the head and shoulders phantom while the phone is placed in an "intended use" position.

A.3.3 Minimum distance between the DUT and the measurement antenna

For far-field measurements, the distance r between the DUT and the measurement antenna should be calculated by the following equation.

where  is the largest wavelength within the frequency band of interest and D the maximum extension of the radiating structure. Then the phase and amplitude uncertainty limits and the reactive near field limit are not exceeded. The influence of measurement distance is discussed in Annex E.

A.3.4 Reflectivity of the quiet zone

Reflectivity of the quiet zone must be measured for frequencies used with method described in Annex G. Measured reflectivity level is used in uncertainty calculations.

A.3.5 Shielding effectiveness of the chamber

In order to be able to measure sensitivity all external radiation has to be eliminated. Depending on the conditions at the test site in question, different values of shielding effectiveness of the measurement chamber might be required. The only general requirement on the shielding effectiveness of the chamber is that the measured level of external signals at the frequency of interest (UMTS, E-UTRA frequency band) has to be 10dB below sensitivity level of the UE. See Annex G for more details on shielding effectiveness validation.

When specified in a test, the manufacturer shall declare the nominal value of a parameter, or whether an option is supported.