This study presents a novel miniaturized dual-band coupled-line impedance transformer. This dual-band matching technique uses the characteristics of coupled-line and dual-band stubs to realize matching arbitrary complex impedance to arbitrary complex impedance at two arbitrary uncorrelated frequencies. Especially, it satisfies the demand of dual-band matching at two relatively closed operating frequencies (n= f2 / f1 ≤ 1.2), and occupy a very small circuit area with inherent DC-Block function. The proposed synthesis approach is validated by the design and fabrication of a 30 W gallium nitride (GaN)-based class-AB power amplifier (PA) for GSM and WCDMA at 1800 MHz and 2140 MHz. The PA's output matching network based on the proposed structure can accurately match 50 Ω to the ideal load impedances of the transistor at two designed frequency simultaneously and has 20% and 15% bandwidth for which the reflection coefficient magnitudes are less than 0.1, respectively.
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