PCB Antenna

I am trying to tune an antenna as seen above, using this wonderful Smith Chart Tool. It needs to match 35 + 10j characteristic impedance.

I have found a tool like the Microstrip Impedance Calculator to determine the impedance of the transmission lines.

However, i am unsure how to determine the characteristic impedance of the stubs that don't have a ground plane (green area) behind them. Does anyone know how that impedance is calculated?

  • \$\begingroup\$ I heard on another forum that my notion of what a stub is, may have been incorrect. I presumed that the antenna could be modeled with stubs, but in fact, stubs are a different thing, used to tune the antenna. Does the antenna etching itself maybe have zero theoretical impedance when modeling with the link included? \$\endgroup\$ – Lammy May 4 '20 at 3:00

Given stubs over air, with unknown parasitics and RF return paths(unknown phase shifts), your tuning task becomes cut_and_try.

Stub tuning tends to be predicted, with AIR above and a KNOWN dielectric spaced a KNOWN distance above an smooth (uncut, no slits, no nearly Vias) GROUND plane.

  • \$\begingroup\$ I don't know anything about antennas but how come the stubs being over air suddenly makes everything unknown? Free space or something around the stub can't be used in the calculations? \$\endgroup\$ – DKNguyen May 3 '20 at 4:20
  • \$\begingroup\$ Most of the PCB trace antennas I have looked at explicitly say not to have the ground under the stubs lines. The Smith Chart Tool I linked seems to think there's a way to calculate the open and short stub impedances, but I haven't found any examples off the net for that. \$\endgroup\$ – Lammy May 3 '20 at 6:11

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.