antenna-theory.com

[rem1473]

I was just reading the information about slot antennas. I watched the youtube video on the page as well. The video states that the circumference of the slot needs to be 1 wavelength. What happens if the slot were a perfect circle? At what points on the circle, is the feed point 50 ohms? My intuition tells me the feed point will be on a chord of the circle, but how is the length chord calculated?

I am still not understanding the radiation polarization of the slot. In figure 2 on the Slot antenna page, the explanation states that the dipole antenna in the figure has vertical polarization, while the slot antenna is opposite and has horizontal polarization. In what plane is the polarization horizontal? Is the horizontal polarization parallel to the plane of the metallic surface? Or is the horizontal polarization perpendicular to the plane of the surface with the slot?

What is the radiation polarization of a slot antenna that is a circle? Assuming that I am correct and the feed point is on a chord, how does changing the location of the chord change the radiation pattern and/or the polarization?

[slk23]

Sorry, I can't answer your questions about a circular slot antenna.

To picture the radiation pattern and polarization of a linear slot antenna, visualize the slot and dipole antennas placed next to each other with the slot and the dipole parallel. The radiation pattern is the same with nulls at the ends of the slot and dipole. The dipole's polarization is parallel to its length. However, the slot's polarization is 90 degrees to its length. In this picture the slot polarization is horizontal and the dipole polarization is vertical.



Or flipping the picture 90 degrees, imagine the polarization from this slot as if there were a phantom dipole on the Z axis:



So the polarization is perpendicular to the plane of the surface with the slot.

I hope that helps.

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