Ultra-wide stopband miniaturised Wilkinson power divider for application in Doherty power amplifiers

This paper presents the design of an ultra-wide stopband Wilkinson power divider (WPD) based on the two bandpass filters (BPFs) and a rectangular-shaped resonator. The design process of the BPFs includes several steps: first, a structure based on the coupling effect between four resonators is presented; then, by modifying it, the coupling effect between the resonators has increased, which has led to an increase in transmission zeros. Utilising the interdigital structure, using only four resonators, and increasing the coupling effect between these resonators, the final dimensions have been effectively reduced. Resonators based on rectangular stubs with coupling effects have increased the number of transmission zeros and the upper stopband of the proposed power divider (PD). The operating centre frequency is 2.52 GHz with a fractional bandwidth (FBW) of 24.1%. The upper stopband can suppress harmonics more than the 8th harmonic, and the DC signal is eliminated between two output ports. The feature of DC signal elimination between two output ports provides the advantage of utilising this PD in Doherty power amplifiers (DPAs), which reduces the number of DC block capacitors.