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I was wondering what the relationship is between a patch antenna's gain and its physical size is. If I wanted to say double a patch antennas gain (add an additional 3 dB), by how much do you increase its physical size. In other words, to add an additional X dB gain to the antenna, you take the current dimensions of the antenna and multiply them by a factor of Y. My question is how do you find Y given how much additional gain you want.

This where the confusion comes in. I know it isn't as simple as doubling the dimensions to double the gain because this is what you do to chance the antennas operating frequency. For example, if you multiply the dimensions of the antenna by two, you do not increase its gain, you decrease its operating frequency by half (ex. 2.4 GHz to 1.2 GHz for an antenna twice as big). So my question is what is the underlying theory behind a patch antennas size and its gain?

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So my question is what is the underlying theory behind a patch antennas size and its gain?

The physical size affects the gain. But, the size is based on the materials used and the operating frequency. Merely increasing the dimensions would decrease performance. Sort of a catch-22.

For example, if this was a traditional PCB patch antenna, that used circuit board construction, the physical size would need to be smaller due to a different dielectric constant. So the gain would be less. The GP Patch project uses an air dielectric which allows for the largest possible dimensions for the desired resonant operating frequency. This trickery gives it higher gain (up to a couple of dB).

If you want a higher gain patch then you have to build a "patch array." This is two or more patch antennas with phase matched connections. They are VERY difficult to design. Even more difficult to build correctly.

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I had not realized a patch antennas size is determined by its dielectric. Now that I think about it, I guess it does make sense. Darn, I thought making the antenna bigger would increase its gain. I should have known something that simple would be too good to be true.

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