Nowadays multiple antennas are very popular. However embedding many antennas closely in a compact printed circuit board will raise the issue of mutual coupling between them, which will decrease their performance. The research described in this thesis, concerns enhancing the isolation in a dual port antenna. The general approach is to design a four-port feed network to be connected to the antenna to fulfil this task. The sample antenna that the approaches were applied to is an already designed by a member of Antenna and Applied Electromagnetics Laboratory. The feed-network that has been designed consists of a coupler and a phase shifter. Different kinds of couplers have been designed and implemented. The simulation and measurement results are compared and the conclusions are drawn.