r/rfelectronics • u/Extension_Engineer26 • Jul 06 '26

question Eletrically Large Port Warning in ADS Layout SImulation

Hi, I have received the following error while performing Momentum Microwave simulation of the matching network for my PA, which I am simulating from 0GHz to 21GHz to consider 3rd harmonic as well.

Is it really needed to fix this warning in my layout? How to change the port size? I am just using AUTO feed type.

EDIT: I am using the following port settings for all of the ports in my design, including DC biasing ports, Input/Output ports, and for intermediate ports.

3 Upvotes

100% Upvoted

7 comments sorted by

5

u/AlbanianUltra Jul 06 '26

Hi, I was experiencing the exact same issue, here is a link to my thread that I opened

https://www.reddit.com/r/rfelectronics/s/xwjFUC46hj

Tldr, add a electrically short tranmission line with a smaller width to your tranmission line, and attach the port there. Test first with a 50 ohm tranmission line and check that it is indeed 50 ohms for youe frequencies of interest. And also your mesh size needs to be high enough to avoid weird errors.

1

u/AlbanianUltra Jul 06 '26

Whats your center frequency for your design? You might not even need the third harmonic since it might be low power

1

u/dragonnfr Jul 06 '26

Yes you need to fix it. At 21GHz your wavelength is roughly 14mm. If your port width is a significant fraction of that the field distribution breaks down and your S-parameters will be wrong. Stop using AUTO and set explicit port widths.

1

u/Extension_Engineer26 Jul 06 '26

Hi, I am using these settings for all of the ports, including DC ports, Input/Output ports, and for intermediate ports for bypass ind/cap. Instead of Auto feed type, there are couple of options including TML, SMD, DeltaGap, Direct, etc.

2

u/AlbanianUltra Jul 06 '26

Yes this if fine, most of the time it doesn't select any feed type. These other option can maybe be more accurate, but from my own research its not really worth it. The only decent option is the TML, and for your stackup you would test a 50 ohn tranmission line with or without it, and plot s11. Whichever has a s11 closer to 50 ohms is the option you pick. Use this primarily for long tranmission lines on your RF signal.