Recently, the finline ferrite devices have attracted people’s attention. Beyeretal. have done theoretical and experimental researches for a finline isolator.1,2In order to make it convenient for theoretical design and experimental adjustment of this device, we have developed a synthetical theory and have carried out the experimental research successfully.3In this paper, we have done the further theoretical analysis and experimental researches for the finline ferrite isolator, such as the impedance matching, the effects of device structure on performances, and the transplantation of a waveguide isolator to a finline isolator problem. Good agreement between design and experiment is obtained. The performances of aX‐band finline isolator are as followsA+<1.5 dB,A−≳18 dB, VSWR<1.5 in a 8% bandwidth, and the bia‐field is lower (about 1000 Oe).<ks>