Abstract: A 2～18 GHz Wilkinson power divider is discussed in this paper, which can meet ultra-wideband and multi-band applications. A mutual coupling coil, which is formed by winding the inductors on the two power divider paths, to replace the independent inductances in the traditional lumped parameter Wilkinson power divider as an inductive device, reducing the layout area while utilizing the mutual inductance effect between coils to broaden the bandwidth of the power divider. The chip is implemented in IPD GaAs process. Within the nine octaves frequency band, the chip has an insertion loss of 3.65 dB to 3.88 dB (additional passive loss 0.65 dB to 0.88 dB), passband ripple is less than \pm 0.12\text dB , isolation is greater than 11 dB, input and output return loss are both greater than 10 dB, the core layout area without pad is only 780 μm×430 μm (0.0000149 λ² at 2 GHz), demonstrate excellent broadband characteristics.