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Rotman lens is widely used to feed a phased array antenna to implement a beam forming network. In designing Rotman lens, one of the most important challenges is the phase error. In recent years, Rotman lens has been designed by using a non-focal idea whereas the position of ports are only optimised to reduce the phase error. Because of the unsuitable location of the ports, which causes mismatching and coupling, the previous non-focal method cannot be constructed easily. To implement the lens, a new scheme, converting three-focal Rotman lens to non-focal, is presented. By using a simple procedure, the phase error is properly reduced. To evaluate the proposed method, the non-focal Rotman lens has been implemented at 10 GHz. The simulation and measurement results illustrate that the method is implementable. Furthermore, the average improvement of the maximum phase error in the proposed lens, with five beam ports and five array ports with overall lens size of 15 × 15 cm 2 , is 36% better than the previous reported work.