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Problem: S11 of LCR circuit through directional coupler

Problem: S11 of LCR circuit through directional coupler

Problem: S11 of LCR circuit through directional coupler

I am building a circuit to measure the S11 characteristics of an LCR tank circuit. The LCR tank circuit is connected to the next stage, so in order to probe the LCR circuit, I am using a directional coupler. The circuit is shown in the attached pdf. As shown there, S11 of the tank circuit shows the resonance by a dip. Even after the bias tee, the resonance is clearly there. However, when I measure via the coupler, the resonance is present but there are several attenuation throughout the S11 spectrum. When I measure the S11 of the coupling port of the coupler separately (shown in the right upper corner) with out port floating and in port terminated.

The coupling is close to 12 dB of the coupler, so maybe that explains -22 dB in S11. But I should still obtain the resonance dip superimposed on this S11 characteristics. Can anyone explain why do I not find the resonance of LCR circuit through the coupler?

Note: All components are from Mini-Circuits

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