A generalized 90° impedance transformer with improved spurious suppression for arbitrary real terminated impedances

摘要

A generalized impedance transformer for arbitrary real terminated impedances is proposed in this article. This transformer mainly features 90 phase shifting at the operating frequency, matching for arbitrary real terminated impedances, and improved spurious suppression. It consists of two-section transmission lines and three parallel transmission-line stubs. By equating the ABCD matrixes of the proposed impedance transformer and conventional quarter-wavelength impedance transformer, closed-form design equations are obtained as a final analytical design approach. Several numerical and measured microstrip transformers with improved spurious suppression are presented. Finally, experimental performances verify this generalized structure and the proposed rigorous design equations.