Automated Design of Nonuniform Transmission Lines for Practical Microwave Circuits

This article presents an automated design method for nonuniform transmission lines (NTLs) for broadband complex impedance matching. The approach is inspired by, and compatible with, the simplified real frequency technique (SRFT). In contrast to tapers like the Klopfenstein, the presented method enables matching between complex impedances, such as required in interstage matching circuits for multistage amplifiers. A microstrip implementation of a NTL matching network is likely to require bending in circuit layout, which is not usually done for tapers. Therefore, an analytical technique is demonstrated for meandering microstrip lines with a continuously varying impedance, allowing compact integration in a circuit, particularly useful in monolithic microwave integrated circuits (MMICs). Practical applications of this method are demonstrated for several circuit designs with predetermined physical constraints, including an octave-bandwidth band-stop filter, a resonator for an InGaAs MMIC oscillator, hybrid single-stage 1–4 GHz amplifier, and distributed GaN MMIC with five sections designed from dc to 40 GHz. Comparisons with more common broadband matching techniques are also shown.