What is the beam correspondence requirement in 5G NR and how does it affect antenna calibration?
5G NR Beam Correspondence
Beam correspondence is specified in 3GPP TS 38.101-2 and TS 38.802. It is a requirement for the gNB (base station) and is a capability declared by the UE. If beam correspondence holds: the beam management procedure is simplified, reducing latency for initial access and handover.
- 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
Frequently Asked Questions
How often must calibration be performed?
Calibration frequency depends on: temperature drift (the PA and LNA gain and phase change with temperature. For SiGe or CMOS beamforming ICs: phase drift of approximately 1-2° per °C. At 10°C temperature change: 10-20° phase error. Calibration must be updated every few minutes during temperature changes). Aging (components drift slowly over months/years. Periodic full calibration at maintenance intervals). Power-on calibration (full calibration at boot-up using the internal calibration network). Run-time calibration (continuous or periodic updates using over-the-air measurements or internal calibration network). For 5G base stations: continuous background calibration is typical (the calibration runs concurrently with traffic, using dedicated calibration time slots or spare resources).
What is the internal calibration network?
The internal calibration network: a passive RF network built into the antenna array that provides a known coupling path from each antenna element to a calibration port. Implementation: each antenna element has a weak coupler (approximately -20 dB) connected to a common calibration bus. To calibrate element i: inject a known signal at element i's TX path and measure it at the calibration port. Compare the received amplitude and phase to the reference. The difference is the calibration coefficient for element i. This is repeated for all elements (sequentially or using orthogonal codes). The calibration network adds: approximately 0.1-0.3 dB of loss per element (from the coupler), and cost/complexity (additional RF components and routing). But: it enables real-time calibration without external equipment.
Does the UE need beam correspondence?
For the 5G NR UE (handset): beam correspondence is a declared capability (the UE reports whether it supports beam correspondence or not). If the UE supports beam correspondence: the base station can use a simplified beam management procedure (less measurement overhead, lower latency). If not: the base station must perform separate TX and RX beam sweeps for the UE, doubling the beam management overhead. Most modern 5G mmWave smartphones (iPhone, Samsung Galaxy, Pixel) implement beam correspondence using: calibrated phased array antenna modules (Qualcomm QTM545/547), which maintain consistent TX/RX beam patterns through internal calibration.