Filter w/ seemingly higher output voltage than input?
That is common behavior for a resonant LC circuit.
Near resonance, the input impedance nears zero, because the capacitive reactance is equal and opposite from the inductive reactance (\$X_C\approx-X_L\$). Therefore even a small input voltage can produce a large current through the LC series combination. However the voltage across each individual element in the circuit is still \$V=jIX\$, so the voltage across each element can be larger than the input voltage.
It may be more accurate to model the source in your antenna as a current source rather than a voltage source, and to include a loading effect due to whatever circuit the antenna is feeding.