A bottom feed cavity aperture antenna is provided. The bottom feed cavity aperture antenna includes a patch and a ground structure. The patch feeds a signal to the bottom feed cavity aperture antenna. The ground structure includes a continuous wall, and a top end and a bottom end, wherein the continuous wall surrounds the patch, a thickness of the ground structure is formed between the top end and the bottom end, a patch height is formed between the patch and the bottom end, and a ratio of the patch height to the thickness is substantially lower than 1/2, and a magnetic field is formed at the top end, and magnetic resonance directions of the magnetic field are parallel to a first axis.