In this work, a wide banded planar multi-input/output port Rotman lens for phase array antennas is investigated by simulation. The Rotman lens consists of lens and delay lines. With essential parameters, the outline of the lens is calculated by Matlab, in this way we can design a Rotman lens with certain functions, also the model is constructed by simulation software with the data imported from Matlab. The lens consists of the lens and the delay line. A useful segmented design of the delay line is applied to improve the transmission efficiency. A principle for dumpy port design is raised to improve the output characteristics. By this way, the magnitude error of different frequency is limited within 3 dB and below 5 dB when the port is changed. The lens offers a phase shift from -70 degree to +70 degree with a changeable step.