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I'm currently trying to match some SMD antenna breakout boards. These boards have one type of SMD antenna, footprints for an SMD pi network and a 50 Ohm cable as connection to my VNA.

Now the problem is, I'm reading a real value of 0 ohms on the desired frequency of 2.45 GHz. I tried to match it, and (more a tolerance problem) got a nice result on 2.3 GHz, but 2.45 is still at 0 ohm. I'm stuck at the moment since the values I'd need are very small or very big if I try to calculate a matching network with these parameters.

This is the result with a 0ohm resistor in series with the antenna.

enter image description here

Also the result with a matching network (lowpass, 12nH P/N(LQP02HQ11NH02), 24.5pF P/N(GJM0225C1C120GB01) at 2.4 GHz).

enter image description here

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2 Answers 2

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Your plots look they're for return loss, RL. This is measured in dB, not ohms. So you're reading 0 dB of return loss at 2.45 GHz, not 0 ohms.

Note, 0 dB return loss is very bad, and means you have a very poor match.

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  • \$\begingroup\$ Yeah, I understood the fact that its bad, but I don't know how to combat this, or if it is possible. Also the 0Ohms are the measured impedance at the cursors, in the tables below the plot. \$\endgroup\$
    – Sibelius
    Commented Dec 12, 2019 at 10:49
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You need to educate yourself a bit in antenna matching theory and procedure.

Very short: Find impedance Z in mid frequency of the plain antenna with 0E jumper. Use smith chart to transform this Z into 50 Ohms. Get component values of the filter from smith chart. Measure and re-iterate until your return loss is at least below -10dB over the entire band of interest.

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