How do I perform over-the-air testing of a millimeter wave 5G device in a shielded environment?
5G mmW Over-the-Air Testing
OTA testing is mandatory for 5G mmW devices because the antenna is integrated into the device and cannot be separated from the radio. This means all RF performance metrics must be measured wirelessly, through the air, in a controlled chamber environment.
| Parameter | SOLT Cal | TRL Cal | eCal |
|---|---|---|---|
| Accuracy | Good | Excellent | Good-very good |
| Standards Needed | 4 (S,O,L,T) | 3 (T,R,L) | 1 (module) |
| Bandwidth | Broadband | Band-limited | Broadband |
| Setup Time | 5-10 min | 10-20 min | 1-2 min |
| Best For | Coaxial, general | On-wafer, waveguide | Production, speed |
- Performance verification: confirm specifications against the application requirements before finalizing the design
- Environmental factors: temperature range, humidity, and vibration affect long-term reliability and parameter drift
- Cost vs. performance: evaluate whether the application demands premium components or standard commercial grades
- Interface compatibility: verify impedance, connector type, and mechanical form factor match the system architecture
- Margin allocation: include sufficient design margin to account for manufacturing tolerances and aging effects
Frequently Asked Questions
What chamber size do I need?
For direct far-field testing of a smartphone-sized device (array approximately 50 mm) at 28 GHz: R_ff approximately 0.5 m. A small anechoic chamber (1.5 × 1.5 × 1.5 m) is sufficient. For a fixed wireless access CPE (array approximately 200 mm) at 28 GHz: R_ff approximately 7.5 m. A large chamber or CATR is needed. For near-field testing: the chamber can be smaller (the probe is placed 0.5-2 wavelengths from the DUT), but the scan area must cover the full antenna aperture plus margin.
How do I handle beam steering during OTA testing?
Two approaches: 1) Fixed DUT, measure each beam command: the DUT is held stationary, and the base station emulator commands the DUT to steer its beam to different directions. At each beam command: measure the EIRP at the measurement antenna position. This tests the beam steering accuracy and EIRP vs. beam direction. 2) Rotating DUT, fixed beam: the DUT transmits at its maximum EIRP beam, and the DUT positioner rotates to measure the beam pattern in the far field. This tests the antenna pattern quality.
What are the 3GPP OTA test requirements?
3GPP TS 38.521-3 (for handsets) and TS 38.521-4 (for fixed terminals) specify: EIRP measurements at specific beam directions (the device must meet minimum EIRP at beam peak), EIS measurements (minimum receive sensitivity at beam peak), EVM (error vector magnitude when transmitting modulated signals), ACLR (adjacent channel leakage ratio), and beam correspondence (alignment between transmitted and received beams). The test must be performed in an anechoic chamber meeting the quiet zone requirements specified in TR 38.810.