A broad-band quarter-wavelength impedance transformer with three reflection zeros within passband

A new impedance transformer employing a transmission line and a coupled-line section is presented in this paper. It is physically a quarter-wavelength long, but can achieve three reflection zeros within the passband. Therefore, broad bandwidths can be obtained for a wide range of impedance ratios. The location of the reflection zeros can be synthesized through the transmission line and coupled-line parameters. Design curves for the transformer synthesis have been obtained by solving the design equations directly. Using these results, a stripline impedance transformer has been implemented. This 50-110-Ω impedance transformer achieved over 25-dB return loss from 0.6 to 1.6 GHz.