The Delta Loop Antenna is another design of beam antenna, that is designed to concentrate the output of your radio transmitter in a particular direction and pick up received signals from that same direction. And, at the same time, like all beam antenna designs, it cuts down or attenuates your reception of radio signals from either side, and usually from behind as well. The exact characteristics of forward gain and side and back rejection all depend on the tailored design of each individual delta loop antenna.
The photo ar right shows a group of Ham Radio Operators helping to assemble a 3-band delta loop beam antenna, which will be hoisted to the top of an antenna tower for use. This beam delta loop antenna has three sets of spreaders, which appear to be for the 20m, 15m and 10m Amateur Radio HF bands. There is a separate pair of spreaders for each of the bands, since a mono-band delta loop beam would only have one pair of spreaders.
This is a tri-band HF delta loop antenna. It has 12 thin poles attached to the one thicker pole below, while the horizontal part at the top of the loop is made from wire. This allows for easier tuning adjustments and much less weight than a delta-loop or triangle antenna would be if constructed with metal tubes on all three sides.
The video clip below shows a ham with a simple triangle antenna that works on exactly the same principle as a delta loop antenna. Both types are one full wavelength in perimeter size. This means that a triangle shaped antenna or delta loop would have three roughly-equal sides which all about 1/3 a wavelength and which add up to one full wavelength. A quad antenna has 4 sides, each of which are 1/4 wavelength (or 0.25 wavelength long).
The triangle antenna below is not a beam antenna, because it has no director or reflector element. But it will show some directivity to the front and back. The antenna shown in the video below appears to be built around a 10 meter-long fiberglass pole. And if constructed for the 20-meter Amateur band, the total wire length would be around 69 feet. (The formula for the wire in the driven element is 984/frequency (in MHz). Therefore for a 20m antenna, it would be 984/14.2 = 69.296 feet; and for an 11 meter band (27 MHz CB) triangle, loop or quad antenna, the wire would be 984/27.2 = 36.1765 feet.)
To turn a delta loop antenna, or a triangle or quad antenna into a beam antenna, you can add one reflector element at the back and a director element in front. Make the reflector length 5% longer than the driven element; and make the director element 4% shorter. Spacing between the two (or three) elements should be about 1/8th wavelength (or 0.125 the wavelength).
As always, you need to adjust the lengths of the wires to make the antenna resonant. An antenna analyzer is strongly recommended, but a VSWR meter or a grid-dip meter (GDO or grid dip oscillator) can also help you tune your loop antenna.
Picture Credit: Wikimedia Commons.
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