Insights > RF + Microwave

VNA Best Captures 5G Amplifier EVM

2022-05-12  |  4 min read 

Ultra-reliable low latency communication (uRLLC), massive MIMO, phased arrays—the implementation demands of 5G FR2 are propelling revolutionary transformation in communication technology. While normalized loads and linear behavior are every amplifier designer’s dream, massive MIMO and beamforming architectures experience highly variable load conditions in practical applications. Further complexity is added with 5G FR2’s millimeter wave (mmWave) carrier frequencies, wide bandwidth signals, and complex modulation schemes which impose stringent component error vector magnitude (EVM) qualification. Designers face increasing challenges in generating accurate device models, minimizing design cycles, and certifying their device’s 5G conformance with a traditional EVM measurement signal analyzer set-up. 

In part 1 of webinar series, VNA Active Device Characterization Essentials, Keysight PNA Product Manager, Nizar Messaoudi, and Focus Microwave Executive Vice President, Vincent Mallette, discussed how using a vector network analyzer (VNA) instead of a signal analyzer to capture EVM simplifies the measurement set-up, enables measurement repeatability, and allows component characterization under realistic load conditions. Nizar describes the critical importance of accurate, repeatable EVM measurements for power amplifiers (PAs), as well as the need for designers to subject their PAs to as realistic conditions as possible when gathering EVM data. 
Although measuring a mmWave power amplifier’s EVM can be complex and error prone, using Keysight’s VNA with modulation distortion analysis software allows for faster EVM measurements with increased signal-to-noise-ratio (SNR) while under a modulated signal stimulus. Nizar shows how 5G’s complex modulation signals can be generated by the vector signal generator (VXG), and in conjunction with the VNA’s arbitrary load control application and a passive tuner,  EVM under variable load conditions can be measured. This provides designers with realistic power amplifier performance measurements under beamforming conditions.
Expanding on Nizar’s comments, Vincent Mallette provides an in-depth review on load pull measurements, how to perform load pull measurements with a passive tuner, and what the benefit of load pull measurements is for power amplifiers. Both illustrate how modulation distortion analysis plus load pull on a VNA with a passive tuner is the best way to gain insight into how a PA would perform in a beamforming phased array application. 

Spurred by the demands of 5G, the pace of technological transformation in communication system architecture  introduces a variety of design and test challenges. Achieving the lowest residual EVM is crucial for implementing power amplifiers in massive MIMO phased arrays with wide bandwidth signals and complex modulation schemes. For more information on the VNA solution mentioned above, please visit:  High Accuracy EVM Measurements for a Power Amplifier Using the PNA-X Series Network Analyzer