# Circular patch antennas

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Here's a tip on an easy way to calculate the radius of a circular patch antenna from a rectangle patch antenna, from Dan:

Lately I've been working on a dual band dual polarized AESA for a mobile weather radar for those guys who like to chase tornadoes. Anyway, I found a clever way to calculate a conversion from a standard rectangle patch antenna to a circular patch antenna. It's fairly accurate as I have reverse engineered several research papers on the subject into a usable formula and it seems to work fairly well, at least for my application.

First use a online patch antenna calculator, for which there are several, utilizing dielectric constant, dielectric height and center frequency. Your results will be the height and width of the corresponding rectangular patch antenna.

Now take the Height, Width, and Dielectric height of your rectangle patch in millimeters and plug them into this formula.

Take the square root of (W+Dh) x (H+Dh), then divide that subtotal by two.

Now you have your radius in millimeters for a circular patch antenna driven by a Quad Hybrid for the same freq as the rectangle patch antenna.  I know what you're thinking! It couldn't be that easy! I don't need my network analyzer???

Initially I performed the conversion utilizing a 1.6mm dielectric height with Teflon Er of 2.23. I have noticed that in further calculations utilizing thicker dielectric heights that the radius was a bit undersized and that multiplying the Dh by 1.5 gives a more accurate result.So the formula would now be: