History
The quad antenna is a development of several inventions.
In 1924, Moses Jacobson patented a loop antennas with rhombic shape.
In 1938, George Brown et al. patented a loop antenna with rhombic shape and quarterwave sides.
In 1951 Clarence C. Moore, W9LZX, a Christian Missionary and engineer at HCJB (a shortwave missionary radio station high in the Andean Mountains) developed and patented a two-turn loop antenna that he called a "quad". He developed this antenna to resolve issues caused by large coronal discharges while using a beam antenna in the thin air of higher altitudes. This is not the antenna termed "quad" today. Moore describes his antenna as "a pulled-open folded dipole" and describes the time when it was developed:
We took about one hundred pounds of engineering reference books with us on our short vacation to Posoraja, Ecuador during the summer of 1942, determined that with the help of God we could solve our problem. There on the floor of our bamboo cottage we spread open all the reference books we had brought with us and worked for hours on basic antenna design. Our prayers must have been answered, for gradually as we worked the vision of a quad-shaped antenna gradually grew with the new concept of a loop antenna having no ends to the elements, and combining relatively high transmitting impedance and high gain.Moore's design eliminated interference from coronal discharge. "End effect", which is inherent with the Yagi, is absent in a quad because its elements have no ends. But other advantages appeared. The higher impedance mentioned in the quote above translates to lower current and thus lower loss on the transmission lines, and gain is higher than that of a Yagi.
In 1957 James Sherriff McCaig patented what we now as a "cubical" (two-element) multi-band quad antenna.
In 1960 Rudolf Baumgartner patented the swiss quad
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