Spring 2004 Issue

Building materials for the Cheap Patch antennas.

 By Kent Britain,* WA5VJB

Previously we have covered Cheap Yagis. I’ve wanted to expand into Patch antennas, but I never quite figured out how to solder the coax to aluminum foil on styrofoam.

This project starts at your local building-supply store. You’re going to need a sheet of 1/2-inch insulating siding. Look at it very closely. You need aluminum foil on both sides for the 900-MHz and above antennas. On most versions, one aluminum-foil side is obvious, but the other side has the aluminum foil between a layer of plastic and a layer of cardboard. Next, you need a roll of aluminum-foil tape. The aluminum tape is often found in the air-ducts section. Last, you need some sheet tin or sheet brass. I get mine at a local hobby shop, and .010-inch to .032-inch thickness can be used, along with a length of coax, of course.

The electrical connection between the coax and the patch is almost as much a capacitive connection as a resistive connection, but keep the tin tabs wide and the coax will couple well.

Square vs. Rectangle

Most Patch antennas are square, but you can increase their bandwidth a bit by making the patch a rectangle. The wider the rectangle, the wider the bandwidth. Don’t get too carried away, however, as you can excite some bazaar high-order modes in the patch. A 1-to-1 (square) ratio makes the most compact antenna. A 1.5- to-1 has good bandwidth, and a 2-to-1 ratio should only be used if you have the test equipment to make sure it’s really working on the frequency you think it is.

Ground Plane

A Patch antenna likes a big ground plane. All these antennas would benefit from an even larger ground plane behind the patch, but the performance improvement would be small. Hey, if you have the room and the extra styrofoam, go ahead. If space is tight, you can trim a bit off the four sides of the ground plane, but you’re on your own.
 

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