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I have a 50Ohm impedance source at 800Mhz and a coil with complex impedance Z = 0.0028 + j3973.9121 Ohms at 800Mhz.

I would like to maximize the current through the coil and protect the source. I cannot change the properties of the coil.

What is the best way to connect the source and coil? From my understanding impedance matching network will not be a good choice because the load impedance is mostly reactive. Should I just add some resistors either side of the coil to increase the resistance (maybe 25Ohms total?) and then use an impedance matching network with that or would that impact my requirement to maximize current too much?

Should I not impedance match and use a circulator with a terminator between the source and coil load?

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  • \$\begingroup\$ "...and protect the source" - protect the source from what? \$\endgroup\$ Apr 14, 2020 at 1:39
  • \$\begingroup\$ @BruceAbbott Protect source from RF reflection because of impedance mismatch. \$\endgroup\$
    – axawire
    Apr 14, 2020 at 2:33
  • \$\begingroup\$ If you want to maximise the current through the coil, then you tune out the reactive part with a capacitor, and transform the resistive part to 50 ohms. However, transforming over that large ratio will be impractical. If you want to minimise the reflection, tune out the reactive part with a capacitor, and then pad up to 50 ohms. That will waste practically all the input power. So now you need to arrive at a compromise between practical matching, and maximising of current. \$\endgroup\$
    – Neil_UK
    Apr 14, 2020 at 6:53

1 Answer 1

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I don't know what's the "best" way for connecting this coil to the source, but here is a tuning proposal for 50 Ohms matching of this antenna to a 50 Ohms source impedance.

enter image description here

The smith-chart used for tuning looks like this:
enter image description here

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  • \$\begingroup\$ Thank you, what is the name of the software you are using? \$\endgroup\$
    – axawire
    Apr 14, 2020 at 12:29
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    \$\begingroup\$ Smith V4.1. You can get it here: fritz.dellsperger.net/smith.html \$\endgroup\$ Apr 14, 2020 at 14:17

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