TABLE OF CONTENTS The 1:4 unbalanced-to-unbalanced (unun) transformer can be said to have had the most attention in the literature from an analysis standpoint (refs 9-27). [1] Credit is given, in large measure, to Ruthroff, who published his classic paper in 1959 (ref 9). The 1:4 unun finds extensive use in solid-state circuits and in many antenna applications when matching ground-fed antennas such as shortened verticals, vertical beams, slopers and inverted Ls, where impedances of 12 to 13 ? have to be matched to 50- ? coaxial cable. Even very short verticals, which are used for mobile operation, can approach impedances of 12 ? because of losses in the loading coils and the less-than-perfect ground systems.
These 1:4 transformers can be designed basically in two ways: (1) the Ruthroff method, which uses a single, coiled transmission line and a feedback (or "boot-strap") connection in order to sum two voltages, and (2) the Guanella method, which sums two voltages by using two coiled transmission lines (and thus equal delays) in a parallel-series connection. The Guanella transformer, which is basically a balun, requires extra isolation as an unun and was discussed in Sec 2.3 of Chapter 2.
Besides these two different methods, the transformers can also come in many forms. These include large and small rods and toroids; transmission lines of wire, coaxial cable or stripline; beaded lines; and low- and high-impedance versions. In all of these cases, several rules of thumb concerning design can be stated: (1)...
