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Fall 2004 Issue |
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ANTENNAS 2.4-GHz Patch Antennas By Kent Britain, WA5VJB |
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This time I’m going to show you some simple-to-build 2.4-GHz patch antennas. My styrofoam wall-board designs don’t work well above 1500 MHz or so, as the material is just too thick. Thus, we will be building this one “DeadBug” style. The ground plane can be almost any sheet metal. I like to use a sheet of PC-board material, but you can use sheet aluminum, brass, copper, tin, or even steel. If you do use PC-board material, there are a few things to watch out for. With single-sided PC board make sure the copper side is toward the patch. If you’re using double-sided PC board, make sure you have a good ground to the ground plane closest to the patch. The size of the ground plane somewhat affects gain, but going much more than an inch beyond the edges of the patch doesn’t add much gain. As it is, the round and rectangular patches will have 9 to 9.5 dBi gain. The circular-polarized version has about 6 dBi vertical gain and 6 dBi horizontal gain for 9 dBiC (dbi circular). The patch needs to be something to which you can solder. Sheet brass or tin works best. It doesn’t have to be square, and as you notice from the photographs, none of the three featured patch antennas are square. The first patch is round. There are few advantages to a round patch, though. It can be a bit harder to build using hand tools, and it tends to be narrower in bandwidth than a square or rectangular patch. There are some tricks such that the circle is really an oval; it’s fed slightly off center and develops circular polarization. Many of the VHF and UHF patch antennas on AO-40 use this technique, but when using hand tools, this antenna is more of a novelty. I found the bottom of a Campbell’s soup can was about the right size and used it to mark my circle on sheet brass. The point of attachment was found experimentally using a network analyzer. Maximum gain is perpendicular to the patch. Looking at the example shown in photo 2, the maximum signal would be directed right at you.
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