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I am into RF design and I have some queries related to impedance matching and trace. We had an RF module and the module was connected to an antenna through a single trace with no LC components in between for additional matching. But the trace width was set such that its characteristic impedance was set to 50 ohm. But in real time testing it was seen that the antenna feed impedance when measured from the RF module it was only 19 ohm, and after additional tuning I could achieve only up to 40 ohm.

Even thought the RF trace impedance was set to 50 ohm why did the impedance vary?

So is there any way in which the impedance can be improved by varying the RF trace impedance alone such that we can improve the 19 ohm to a value such that after additional tuning we can make it 50 ohm.

Also if we can set the trace impedance to the characteristic impedance why do we do we provide additional LC tuning and how is the matching done using the LC tuning?

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  • \$\begingroup\$ What kind of antenna (Datasheet if applicable)? What frequency? And how long is the trace? \$\endgroup\$ – The Photon Oct 30 '17 at 15:03
  • \$\begingroup\$ Actually i haven't used an antenna as such, a pad was given and i could get only 19 ohm for a frequency about 2 ghz just in the path from the module to the antenna pad. can the pad width to trace width ratio cause an impedance mismatch? because in some i have read and seen that in some places trace width will be almost equal to the pad width ,and somewhere else the trace width will be smaller but the impedance mismatch is nominal only. So does this have to do anything with antenna only because almost most losses occur at the antenna feed ryt? It would be kind if you could help \$\endgroup\$ – Vishak Oct 31 '17 at 5:22
  • \$\begingroup\$ Were you measuring the trace looking in to the pad where the antenna would attach, or looking out from where the amplifier(?) drives the line? Was the amplifier still present when doing the measurement (are you sure you weren't just measuring the output impedance of the amplifier)? Was the amplifier powered up during the test? \$\endgroup\$ – The Photon Oct 31 '17 at 5:35
  • \$\begingroup\$ A picture of how you connected your network analyzer to the circuit would probably help make clear what exactly you were measuring. \$\endgroup\$ – The Photon Oct 31 '17 at 5:35
  • \$\begingroup\$ we where measuring the impedance at the antenna feed or antenna pad. \$\endgroup\$ – Vishak Oct 31 '17 at 5:41

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