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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?

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  • \$\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
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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.

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  • \$\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

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