A new simple system of 3-D radars-the system of height finding by comparing phases of two beams radiated by a single doubly-curved antenna-is presented. The principle of producing phase difference of two beams and its algorithm are studied. A brief description is given to the effect of S/N on the height finding accuracy. The problems of height finding starting point of low elevations and dual values are analyzed and the corresponding solutions given. The trials of prototypes and the practical tests with aircrafts have proved that the system is feasible and completely fulfils the requirements of indicating radars with targets. This system is simple in structure

easy to realize and low in cost.