How do I select an antenna measurement system for testing millimeter wave antennas?
Antenna Measurement for mmWave
Antenna measurement at mmWave is one of the most specialized and expensive areas of RF testing, driven by the growth of 5G, automotive radar, and satellite communications.
- 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
CATR or near-field for mmWave?
CATR: simpler setup, direct far-field measurement, no NF-to-FF transformation. Best for: single-beam antenna pattern measurements, EIRP testing, and production OTA testing. Near-field (spherical): captures the complete 3D pattern (including all sidelobes), provides phase information, and enables mathematical beam steering analysis. Best for: R&D characterization, phased array diagnostics, and beam management validation. For 5G device OTA conformance: both CATR and near-field methods are accepted by 3GPP (TS 38.141-2).
How big does the anechoic chamber need to be?
For CATR at 28 GHz: the chamber must be large enough for the reflector (1-2 m diameter) and the quiet zone (test region where the plane wave is uniform). Typical chamber: 3 × 3 × 5 m (minimum). For far-field at 28 GHz (50 mm AUT): R = 0.5 m, so a small chamber (1.5 × 1.5 × 2 m) is sufficient. For far-field at 77 GHz (100 mm AUT): R = 5.1 m, requiring a 6+ meter chamber. The chamber walls are lined with RF absorber (pyramidal foam or ferrite tiles) to prevent reflections that corrupt the measurement.
What about phased array testing?
Phased array antennas (5G base stations, radar) require special testing: beam scanning: measure the pattern at every beam state (codebook entry). For a 64-element array with 100 beam states: 100 separate pattern measurements. Active array testing: the phased array is actively powered and steered during measurement (not passive antenna testing). OTA EIRP and EIS: measured at each beam direction. The test time is proportional to the number of beam states × angular points × frequency points. Automated rotation + fast switching reduces test time from days to hours.