Not detailed here is that series inductance would also increase as frequency increases but we can see how if the capacitance relative to the inductance is significantly larger that the trajectory would move down faster than up and to the right resulting in the minimum as the OP is seeing. As we move off resonance upward in frequency, the resonator adds a shunt capacitance that in this case brings us closer to the center origin (where Z=50 ohms, perfect match), providing a lower S11 as it maximizes the net impedance of the resonator's connection to ground essentially the resonator is tuning out the series inductance as it becomes capacitive. In the first plot where we have no parasitic inductance in series with an exaggerated parasitic resistance in the resonator (reducing the input impedance at resonance when the reactive inductance cancels the reactive capacitance). ![]() The Smith Chart visual provides immediate insight of a shunt L-C resonator (tank circuit) to ground. This can occur with a series parasitic inductance or capacitance in the resonator the case with a series inductance is demonstrated below.
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