How do I select a signal generator for testing a receiver at millimeter wave frequencies?
mmWave Signal Generator Selection
Testing at mmWave frequencies adds significant complexity and cost compared to sub-6 GHz testing, primarily due to the higher cable losses, connector challenges, and phase noise requirements.
- 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
Can I use a sub-6 GHz generator with an upconverter?
Yes. A common lower-cost approach: use a mid-range VSG (6-20 GHz) with an external frequency upconverter (mixer + LO) to reach mmWave. Advantages: lower instrument cost ($30,000-60,000 total). Disadvantages: higher EVM floor (the upconverter adds phase noise and distortion), additional complexity (two instruments), and limited output power. For R&D prototyping: this is a viable approach. For production or conformance testing: a direct mmWave VSG is preferred.
What about 77 GHz automotive radar testing?
Automotive radar at 77 GHz requires: a signal generator at 76-81 GHz (W-band). Options: VDI or OML frequency extenders driven by a 20-40 GHz generator, or dedicated automotive radar signal emulators (Keysight E8740A, R&S AREG100A). The radar test also requires: FMCW chirp generation (specific to automotive radar), target simulation (delay, Doppler shift, RCS), and antenna pattern characterization (OTA in anechoic chamber).
How important is phase noise at mmWave?
Phase noise is often the limiting factor for EVM at mmWave. At 28 GHz: the generator phase noise is approximately 9 dB worse than at 10 GHz (20 log(28/10)). For 5G NR 256QAM: the required EVM is 3.5%. The phase noise contribution to EVM must be < 1% to leave margin for other impairments. This requires integrated phase noise < 1° RMS (100 kHz to carrier/2). Only high-end generators achieve this at 28+ GHz. For 64QAM testing (EVM 8%): the phase noise requirement is 6 dB more relaxed, and mid-range instruments suffice.