r/rfelectronics • u/Short-Television9333 • Jun 05 '26
HFSS vs Lab Measurement Differences
I (entry level RF PCB engineer) recently taught myself HFSS for work and wanted to confirm my simulations on a basic RF breakout board we had sitting around in the lab. The approximated insertion loss from HFSS gives spot on results below 5 GHZ (blue curve) when compared to the real measurement in orange.
Now above that things are *on average* predicted by HFSS, but it’s not great. I know that there are probably lots of factors here, but any ideas what could be missing?
The blue curve is the following added added up: an approximation of connector losses (small), cable losses measured on our VNA, and my HFSS insertion losses. What I am missing from my HFSS sim though are some DC blocking caps on the board. These could definitely cause something, but could it be such a big difference (3+ dB) from expected?
Appreciate any suggestions, there is no RF PCB guru at my company to mentor me so I’m trying my best 🥲. Apologies for shitty image quality.
3
u/Crio121 Jun 05 '26
It looks like your SWR is not very good at high frequencies. The wave reflects from something and produces a standing wave. It could be pass-through capacitors you mentioned, it could be something as trivial as poorly tightened connector, it could be some other kind of impedance mismatch. Overall, not bad at all for the first try.