Real frequency design of 1～30 MHz transmission line transformer

The principle of Guanella-type transmission line transformer (TLT) is presented, and its characteristics of impedance transformation and balance to unbalance transition are analyzed by using the telegraph equation. To obtain the best input impedance at the low impedance terminal of the balun, the characteristic impedance of the transmission line is chosen according to the measured load impedance. Two 9∶1 baluns, which can operate at 1～30 MHz, are designed for 450 Ω to 50 Ω, 600.0 Ω to 66.7 Ω transformations, respectively. Because of the narrow interval between windings, the transmission line’s characteristic impedance of the 600.0 Ω to 66.7 Ω balun can hardly achieve the required value by simulation. However, the difference between the measured and the simulated input impedances o