As much as I know the major advantage of patch antenna over dipole antenna is it's directivity.
So if the planar dipole antenna can achieve the same directivity then why we use patch antenna? Are there any other advantages of patch antenna over dipole apart from directivity and ease of fabrication.
A patch antenna radiates efficiently when it is very close to a ground plane, whereas an electric diploe parallel with the ground is shorted out and has very poor radiation if it is close to a ground. The patch radiates as two magnetic dipoles, which are not shorted out by the ground plane and radiate well.
Can you explain, exactly how dipole antenna is shorted? If the dipole is not in contact with the ground? How in patch antenna they are not shorted out?
Saying it is shorted out may be inexact. The currents on the ground plane radiate the same as a reflection of the dipole under the ground, but with the opposite currents in it. If the dipole is very close to the ground the radiation cancels entirely. It may be correct to say the antenna is shorted out.
Ok. Why doesn't the same happen in case of patch? In case of patch also the currents on the ground plane are in opposite direction. Then why doesn't the radiation cancel in case of dipole?
It is not the currents that radiate in a patch antenna. It radiates as a magnetic dipole from the ends, where the electric field oscillates, not much from the sides where the current is. The changing electric field across the slot at the ends radiates in phase with the image of the electric field in the ground.
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