Your circuit should work as drawn, but don't have an earth. The dipole is balanced. Earth is in the middle of the feed, not at one end. You don't need it.

Connect the source across the capacitor.

Malcolm White Thank you so much for your reply. The ground in CST does not always mean the "real" ground. (Note that the common ground does always exist, even if the design does not contain any ideal ground block - CST HELP). It is needed for the software to measure the voltage across the port.

When I remove the ground and connect the source across the capacitor as shown in the figure below, it practically produces the same result.

Anyway, as you said the circuit should work as drawn. However, when I vary the matching capacitor, the best value tends to 0, say C_1 = 10^-15 F. When I increase its value, it will unmatch the dipole as S_11 increases towards 0 dB. That's why I was wondering whether I did the schematic right

A half-wave thin dipole should not need a capacitor. That is why it is a half wave. The impedance across the gap should be almost completely real when the length is a half-wave.. If the dipole is shorter than a half-wave then you will need the series inductors. I'm not sure if you will need the shunt capacitor. perhaps if the dipole is too long you will need series capacitors.

So sorry for not providing a complete scenario. I am learning to design dipoles for ultra-high field MRI scanners. So the human head and body parts will detune/unmatch the dipole. That's why the shunt (matching) capacitor is needed. I just follow the design in the paper: "Unshielded bent folded-end dipole 9.4 T human head transceiver array decoupled using modified passive dipoles"

Malcolm White Thank you for your answer. I figured out what was missing. As you said, the dipole by itself doesn't need a shunt capacitor to match. Actually, this matching and tuning circuit only works when the human body/head is present. When I loaded the human voxel model in CST, I can now match the dipole using the shunt capacitor :D