A Design Approach for Compact Wideband Transformer With Frequency-Dependent Complex Loads and Its Application to Wilkinson Power Divider

In this article, a new design approach for the wideband transformer with frequency-dependent complex loads is proposed, which is based on the least-square method and the generalized modified small reflection theory (MSRT) with proper electrical parameters. Compared with the wideband transformers based on other approaches such as the generalized MSRT and transmission line theory, the proposed ones feature easy design, compact size, and wide bandwidth. For validation, several wideband transformers with frequency-dependent complex loads are designed, simulated, and measured. The measured results are consistent with the calculated and simulated results, and a wideband transformer with a fractional bandwidth of 68.5% (defined by 15-dB return loss) and an overall size of 0.025λg2 is achieved. In addition, when applied to the design of wideband Wilkinson power divider, a fractional bandwidth of 110% ( defined by 25-dB isolation) and an overall size of 0.069λg2 are attained.