Compact Dual-Passband Doherty Power Amplifier Based on Stub-Loaded Stepped-Impedance Transformer

In this paper, a dual-band Doherty power amplifier (DPA) is proposed that can operate over two wide passbands, which is realized by multiple transmission zeros (TZs) in an all-pass response. The short/open stub loaded stepped-impedance transformers act as the output matching networks (OMNs) in both carrier and peaking paths. The shunted stubs not only generate TZs but also perform impedance conversion, simultaneously satisfying the load-pull requirements at both output back off (OBO) and saturation. This is achieved over two wide frequency ranges. The combination between the OMNs in the two paths realizes a dual-passband response, even though the number of TZs at saturation is one less than that at OBO. A prototype DPA is implemented based on two 10-W GaN transistors to validate the methodology. Measured lower and upper frequency bands are from 1.35 to 1.75 GHz and 3.05 to 3.45 GHz, respectively, with both having 400 MHz operating bandwidths. Measured results demonstrate a maximum saturated gain of 9.2 dB and an output power of 43.8 dBm. Maximum 6-dB OBO and saturated efficiencies ( $\eta$ ) are 58% and 72%, respectively. The circuit occupies a very compact size with an area of $0.5\lambda _{g} \times 0.43\lambda _{g}$ .