An Interesting Impedance Matching Network (Correspondence)

A simple stepped‐impedance transmission line load network for inverse Class F power amplifiers

“…In this case, the stepped‐impedance transmission line with equal section lengths of 30° loaded by the short‐circuit quarter‐wavelength line and λ 0 /12 open‐circuit stub creates an open circuit at the second harmonic and short‐circuit at the third harmonic seen by the 20‐Ω source at its input. A short‐length transmission line as an element of the fundamental frequency output matching circuit is required to compensate for the reactive part of the modified source impedance (any source impedance can be transformed to a real load impedance using a λ 0 /8 transformer whose characteristic impedance is equal to the magnitude of the source impedance [9]) followed by the quarter‐wavelength transmission line that provides the transformation of the real part of the modified source impedance to the standard load of 50 Ω. The frequency response of such a transmission‐line load network with harmonic tuning is shown in Figure 5(b), which demonstrates the fundamental‐frequency impedance matching at 2 GHz and corresponding second and third harmonic tuning at 4 GHz and 6 GHz, respectively.…”