Enhancement impedance transforming ratios of coupled line impedance transformer with wide out-of-band suppression characteristics

This article presents the design of an impedance transformer (IT) with wide out-of-band suppression characteristics. The wide out-of-band suppression characteristics can be obtained by loading several transmission zeros in the lower and upper out-of-bands. For experimental validation, a 50-to-10 Ω IT was implemented at a center frequency (f₀) of 2.6 GHz for the long term evolution signal. The measured results are in good agreement with the simulations, showing a return loss higher than 20 dB over a passband bandwidth of 0.35 GHz (2.35-2.7 GHz) and out-of-band suppression better than 18 dB from DC to 1.78 GHz and from 3.45 to 6.97 GHz.