Design of Microstrip Dual-Mode Impedance Transformers

New four-port component, dual-mode impedance transformer for wideband matching of two microstrip lines with equal characteristic impedance and a coupled microstrip line with general even-and odd-mode impedances, is proposed. Practical realization problems are discussed and a new dimension correction approach is derived. Two transformers between 50-Ω microstrips and microstrip coupled lines with even/odd impedances 100 Ω/68 Ω and 36 Ω/27 Ω, respectively, were built. The concept was experimentally verified at the frequency band 0.01-16 GHz.