Nowadays they liked to use Unmanned Aerial Vehicle (UAV) equally for military uses, field reconnaissance or observation. However, problem can occur when these flying vehicles plying in group relatively close to each other because the probability of a collision is higher if there are more of them in a given compartment. A GPS-based distance measuring system tried to solve this problem but a previous paper showed that even in precise measuring mode, the standard deviation is too large, so this method don't provide any reliable distance information between two aircrafts. As a result of this, a demand has come up in order to develop a system which is able to measure the displacement of UAVs relative to each other more accurately completing the GPS-based system. So another method should be used to measure the displacement which in our case is based on phase measurement. Thereby, my task is given, thus the goal of my paper is to realize a system that measuring the phase and define the displacement of two UAVs relative to each other. Henceforward the theoretical background of the displacement measurement, as well as the design, the construction and the operation of the device will go into details.