In order to miniaturize a microwave passive component carrying out the function of circulation, several structures were considered. Among those, the stripline Y-junction circulator was the solution adopted and design rules of this component were established. Thus it is possible to size this circulator according to circulation frequency and material parameters. Several series of simulations using Ansoft HFSS simulator software were made to estimate the behaviour of the component. Evolution of transmission parameters and electromagnetic fields through the structure were studied in order to quantify the effect of each parameter on circulator performances. The material used is barium hexagonal ferrite which is deposited at DIOM Laboratory by using an RF sputtering system. A new design method based on the second Bessel's solution of the first order resonance mode was developed. That aims to use micrometer thin films of non reciprocal magnetic material for the miniaturization. Evolution of transmission parameters and electromagnetic fields were examined for the second design. A stripline Y-junction circulator using 10 /spl mu/m thick barium hexagonal thin films and operating around 40 GHz was simulated. For this microwave passive component destined for military applications of telecommunication or low power radars, the isolation is 22.51 dB at 40.20 GHz and the insertion losses are 2.85 dB.