In this letter, we derive an analytical model for trans-capacitances in Junctionless Nanowire Field Effect Transistors (JL NW FET). As for static operation, we show that a complete small signal capacitance network can be built upon an equivalence scheme recently pointed out between JL NW FET and its double gate counterpart for which such a model has been proposed. This approach is validated by 3D Technology Computer Aided Design simulations and bridges the gap between the nanowire junctionless device and its application in circuits.