An Introduction to Quagi Antennas
What Is a Quagi Antenna?
A quagi antenna combines a yagi antenna design with a cubical quad antenna; the quad-yagi hybrid antenna is simply called quagi out of convenience. The first quagi antennas were reported on at the 1972 West Coast VHF Conference. This is five decades after the first square (quad) antennas were patented.
Quagi antennas attempt to capitalize on the benefits of quad antennas while sharing the benefits of yagi antennas.
What Is a Quad Antenna?
A quad antenna is an antenna that forms a square, in contrast to helical and loop antennas made from circles of wire. Cubical quad antennas are made from two quad antenna elements. Quad antennas typically have sides one or more wavelengths in length; the design can be seen as two bent half wave elements or one full wavelength of wire folded into a square. Quad antennas give you wide coverage with a single coax feedline. Quad antennas have a light wind load.
Quad antennas offer better gain than yagi antennas on average. They tend to have better performance than a yagi antenna at a lower boom height and operate more efficiently when close to the ground. Quad antennas are internally stackable. Lengthening the director elements sacrifices gain but allows you to receive a broader bandwidth. Some of the most commercially successful quad antennas were designed for CB radio.
Quad Antennas versus Yagi Antennas
Quad antennas consistently deliver two dB or more than yagi antennas when they have the same boom length and element count. Quads give you a better front to back ratio. Quad antennas offer better reception and more side rejection due to their cophased pattern. Quad antennas may be larger in three dimensions but have a smaller turning radius than yagi antennas.
Quad antennas aren’t as affected by ground reflection as yagi antennas, and the voltage standing wave ratio of a quad antenna won’t change as the antenna is lifted or lowered. Quad antennas are typically more sensitive than yagi antennas. The quad style element and reflectors provide immunity to noise from static buildup and good gain.
Yagi antennas have stronger side lobes and better beamwidth, and yagis beat quad antennas when it comes to almost interference free reception of a signal over a narrow frequency range. And yagi antennas are structurally stronger. Quagi antennas attempt to combine the better performance of quad antennas with the relative advantages of the yagi antenna.
An Overview of Quagi Antennas
Quagi antennas are made from a long yagi antenna with quad antenna reflectors and deflectors on the back. The original quagi antennas were designed for moon-bounce communications, combining low cost with high gain. Quagi antennas, like yagi antennas, are directional antennas.
A long yagi antenna with parallel elements are enhanced by the cubical quad antenna on the back in place of the reflector on Yagi-Uda antennas. The cubed reflector adds several decibels of forward gain and more than a standard reflector element. The typical quagi antenna design has one square reflectors and a square director element centered on the same central line as the yagi elements.
Quagi antennas frequently have between eight and fifteen elements. One sixteenth inch brass welding rods can be used as directors on a quagi antenna. Any non-conductive boom can be used to hold the elements. If you use an aluminum boom, the antenna elements need to be mounted on insulators so they don’t touch the aluminum.
Quagi antennas are occasionally used for VHF and UHF ham radio contests. They aren’t used as often as other types of antennas due to the complexity of tweaking the design and the ease of buying and/or making either a yagi or quad antenna to specification.