Tamara Wilhite is a technical writer, industrial engineer, mother of two, and published sci-fi and horror author.
What Is a Planar Disk Antenna?
A planar disk antenna is made from two disks stacked one above the other, close to each other without touching. Coax is soldered at the gap between the two disks/antennas. The lowest frequencies they can receive are based on the size of the disks. The gap between the disks acts like the exponential slot of a Vivaldi antenna at high frequencies. The wide frequency range that planar disk antennas can receive makes them a common type of ultra-wide band antenna.
Planar disk antennas are more sensitive to long distance signals than sources close by, making them ideal for receiving a wide range of signals like multiple ham radio bands.
How to Build Your Own Planar Disk Antenna
How can you build your own planar disk antenna? Pizza plates are one low cost solution.
Two pizza plates can be used to make a broad banded vertical antenna, a type of ultra-wideband antenna. Ultra wide band antennas are notable for being able to work on a frequency span of 10:1 or more. A planar disk UWB antenna could handle 1 MHz to 10 MHz signals if not a wider range, for example.
How do you make your own planar disk antennas out of pizza plates? Buy two pizza pans that are 16” to 18” across. If you use smaller 14” plates, the SWR is high for the 2 meter frequency band. 12” pans are so small they work on the broadcast FM frequencies. Steel pizza plates work better than aluminum ones.
The antennas will be mounted flat against a rod or support, one above the other with a 1/8” to ¼” gap between them. You can put construction adhesive or other non-conductive glue in this gap to help make sure they don’t touch.
You can attach the antennas to a wooden rod by screwing them in place with solder lugs; the objective is to screw them into a plank long enough to hold both without them touching. Or you can solder a steel pizza place directly to a coaxial connection. Note – aluminum coax shield won’t solder to stainless steel. If you’re having problems soldering the copper core to the plates, you can scratch the surface to help it stick.
The central conductor goes to the top pizza plate. The shield will be mounted to the lower pizza place. If this antenna is going to be used outside, silicone sealant or putty needs to be put on the feed-point. Use the same materials to seal the open coax braid.
You can spray paint the antennas with non-metallic spray paint to offer some protection from rust.
Then you can hang the antennas by hanging the mount from a cord or tying it to a support so it points the direction you want.
If you use 18” steel pizza pans, at a roughly -10 dB return loss, it will have a 2:1 SWR, and a -20 dB loss results in a 1.2:1 SWR. This means the SWR is 2:1 or better for frequencies from the 2 meter ham band (144-148 MHz) to 2 GHz frequency range.
Given these numbers, this homemade ham antenna can be used with multiband amateur radio rigs or a scanner.
My thanks to Kent Britain, WA5VJB, for his advice regarding for this article. He is also the designer of the antennas shown here.
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.
Questions & Answers
Question: Does it matter if the pizza pans are perforated when building a planar disk antenna?
Answer: As long as the perforations are small, less than a quarter of an inch, it doesn't matter. WA5VJB also makes good planar antennas.