A quagi is a directional antenna that uses a combination of quad and yagi elements. Normally the quad section is used at the back end of the antenna, from the driven element to the reflector elements. The front end of the antenna uses short yagi directional elements that take up less space than a full-on quad antenna. While not as efficient as a straight-forward quad, it is a reasonably efficient and directional antenna that can be used by ham radio operators to get a signal out and to reel in the weak replies.
Quagis are easy to construct. The driven and reflective elements do require spreaders to make a large square of wire, which tends to be the toughest thing to buy or build. Fiberglass works great if you coat it and protect it from UV radiation. I always had great luck using cheap fiberglass shorecasting fishing poles designed for saltwater ocean environments. Cabela's carried them for twelve bucks each, and I used eight of them for a reflector element and a driven element.
The yagi portion is normally made out of aircraft aluminum tubing, which is cheap and can be purchased in different diameters to allow tapering the elements. This reduces weight and helps to strengthen the overall directional elements.
The directional capabilities are excellent, allowing one to focus in a particular direction with little interference from signals off of the main lobes. Of course, to use the quagi in this manner one must use some form of rotating system.
Iron Noder 2017