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Why in planar dipole antenna current is perpendicular to the feed while in patch antenna the current is parallel to the feed line? Is the direction of current dependent on the input supply terminals? What are the differences between patch antenna and dipole antenna? enter image description here

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  • \$\begingroup\$ Remember that these can only be momentarily "snapshots" of what happens and not representative for the whole period of your signal, and also not snapped at the same phase of the input signal. Also, as said in Tim's answer that's not how things look like in a patch antenna. \$\endgroup\$ Jun 15, 2022 at 7:48

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Feed direction is fairly irrelevant, as long as it doesn't interfere with the antenna element(s) themselves.

Also the patch diagram is somewhat erroneous, but it depends on what size the patch is. A resonant patch of square geometry will have several resonances at nearby frequencies (due to different patterns of charge between its edges/corners), and therefore be more difficult to tune, or to use over a wide bandwidth (certainly, there are better designs when bandwidth is desired). Electrically-short patch antennas have a largely uniform charge density and achieve resonance through internal structures (e.g. high-K dielectric substrate) or matching components.

As for contrasting with the dipole, suppose the patch antenna is longer (in the direction of current flow) than wide. Then suppose the ground plane (not shown, but implied under the substrate) was brought up to the same level (top surface), opposite the patch shown. Basically mirroring the structure. Now bend the feedlines out at an angle, and finally remove the ground plane (somewhat optional), et voilà, the left diagram has been transformed into the right diagram. In the course of this transformation, of course impedance and radiation pattern have changed

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