A new design methodology for wideband analog predistorter with the characteristics of frequency-dependent gain and phase conversions

A novel design method, which can transform the nonlinear circuits design to the impedance matching network (IMN) design, is proposed for wideband analog predistoter (APD) with the characteristics of frequency-dependent gain and phase conversions in this paper. First, the design method for the desired gain and phase conversions is introduced. The ABCD parameters of the IMN can be computed. To simplify the design, the obtained parameters are transformed to the IMN terminal impedance. Then we can only need to design the IMN terminal impedance to obtain the desired transfer characteristics. In the meanwhile, an APD with 4.5 dB gain conversion and 50° phase conversion is designed and simulated to validate the design method for specify gain and phase conversions. The simulated results show good effectiveness of the design method. Second, for wideband application, the complex gain and phase conversions surface design is transformed to the IMN terminal impendence curve versus frequency design. This gives the designers a well-defined strategy for wideband APD design focusing on frequency-dependent phase conversion as well as gain conversion. To validate the proposed method, a wideband APD operating at K-band (17-20 GHz) is designed, fabricated and measured. A linearized 100W K-band TWTA is shown to achieve a noise power ratio (NPR) >20 dB at 3 dB output power back-off, and phase change <6.5° among the operating band.