Abstract: This paper proposes an improved 1:8 power divider based on radial waveguide at ka-band. To widen the bandwidth ofthe divider/combiner, an axially symmetric oversized coaxial waveguide is used to transform input to the radial waveguide, and atthe bottom of the radial waveguide, stepped-impedance technology is used to realize the impedance match. According to EMsimulations, the simulated -20dB return loss bandwidth is approximately 28.57% (ranging from 30 to 40 GHz), and goodamplitude imbalance and phase imbalance are observed in the band. This structure has properties of not only a wide band, low insertion loss and high output power, but also a small size, a high power combining efficiency and efficient heat sinking, and haspotential for illimeter-wave broad-band high power combination.