The authors propose a new method of controlling the isolation of an RF splitter. In the proposed method, a bias current is superimposed on an RF signal to change the permeability of the ferrite core used in the splitter's transformer. By doing this, the splitter isolation can be controlled. Experimental results have shown that superimposing a bias current of 500 mA improves device isolation by about 5 dB without affecting the loss characteristics.