Ultra-High Transforming Ratio Coupled Line Impedance Transformer With Bandpass Response

An impedance transformer (IT) with a ultra-high impedance transforming ratio (UHITR) is presented in this letter. The UHITR is obtained by controlling coupling coefficients of cascaded open-circuited coupled lines. Two transmission poles have appeared in the passband for an under-matched region. For the validation, the IT with impedance transforming ratio of 10 was designed at a center frequency (f₀) of 2.6 GHz. From the experiment, insertion and return losses at f₀ were determined as 0.55 dB and 21.47 dB, respectively. Within the operating band from 2.515 to 2.73 GHz, the insertion and return losses were better than 0.8 dB and 18 dB, respectively. The out-of-band suppression characteristics are higher than 20 dB from dc to 1.92 GHz and better than 18 dB from 3.28 to 7.2 GHz.