Generalized Theory and Design Methodology of Broadband Outphasing Power Amplifiers Employing Low-Order Bandpass Networks

In this article, a general theory and associated design methodology for outphasing power amplifier (OPA) is proposed. The design theory leads to the conclusion that, compared to previous OPAs, the proposed conjugation network of an OPA can be a much more flexible structure by satisfying input reflection coefficient conjugate, namely, impedance matching and phase compensation. Then, based on this theory, this article proposes a low-loss bandpass network of the power combiner in a wide operating band for the OPA. For verification, a broadband OPA operating at 2.2-2.8 GHz is designed and tested. Experimental results show that the saturation output power can be maintained between 43.78-45.47 dBm. The drain efficiencies are 65.5%-79.4% and 51.5%-87.5% at saturation output power and 6-dB power back-off points, respectively. For the down-link long-term evolution (LTE) signal with a channel bandwidth of 20 MHz and a peak-to-average power ratio (PAPR) of 8 dB, the average adjacent channel power ratio of the fabricated OPA is better than 49.1 dBc after digital pre-distortion at the target frequency band with average output power back-off (OBO) efficiency of above 36.3%. The reported experiments confirm the validity and effectiveness of the proposed design methodology.