mmWave Signal Analysis Test Challenges - Boldly Go Where Nobody's Gone Before
2021-12-07 | 4 min read
Previously, conducted measurements, predicated on wired device-under-test (DUT) probe points, were feasible test methods given lower frequency technology. However, over-the-air (OTA) tests are required for 5G New Radio (5G NR) mmWave spectrum technologies because components designed for mmWave devices are compact with no place to probe. Unfortunately, measuring performance via OTA methods increases difficulty achieving accurate, reproducible results. These complexities are exacerbated by high frequency path loss and wideband noise, as well as high frequency and wideband’s impact on frequency response.
At these higher frequencies, increased path loss between instruments and DUTs often results in low signal-to-noise ratio (SNR). In turn, this induces difficulty in acquiring signal analysis measurements including error vector magnitude (EVM). Additionally, wideband also negatively impacts SNR. While wideband enables advantages such as higher throughput, faster data rate, and lower latency, it comes with a cost: more noise is introduced to the system. Transmitted signals must now compete with a channel’s higher noise floor in order to be accurately detected. Finally, high operation frequency and wideband also make DUT isolation and characterization more arduous. Test system components such as cables, connectors, and fixtures between the signal analyzer and DUT contribute to erroneous frequency responses in amplitude and phase, degrading modulation quality.
Dr. Akhshi addresses mmWave complexities by discussing several RF signal paths — such as default path, microwave preselector bypass, low-noise path, and full-bypass path — to reduce noise, improve sensitivity, and achieve higher SNR. Additionally, Dr. Akhshi elaborates on how to improve signal condition with an optimized mixer in the system setup.
Boldly going into the new frontier of mmWave technology promises revolutionary advancements in everyday life and fundamental alterations to society’s infrastructure. With these massive changes come new challenges, most immediately including excessive path loss, wideband noise, and convoluted frequency response. For more information on the signal analyzer solutions mentioned above, please visit: https://www.keysight.com/us/en/assets/7121-1035/white-papers/Tackling-Millimeter-Wave-Signal-Analysis-Challenges.pdf