Abstract This paper is intended to describe the properties of nonreciprocal microwave ferrite devices from the four-terminal network analysis. First, the impedance and the scattering matrix of an X-band rectangular waveguide containing a transversely magnetized ferrite post are measured as a function of the (1) diameter of the post, (2) position of the post in the waveguide, and (3) applied d. c. magnetic field. Then, the T-equivalent circuits are obtained from the scattering matrix measurements. Results prove that when a thin ferrite post is placed near a side wall of the guide, it acts essentially as a shunting capacitance. The susceptance decreases with d. c. mangetic field. As far as the impedance is concerned, the post itself behaves like a tuning screw. Finally, the equivalent circuit of a waveguide containing two or more ferrite posts is studied. It is found that when the distance between the two nearest posts is greater then λ/2, the equivalent circuit is simply the "single post" circuits connected in cascade. A phase shift network is used to illustrate the application of the principle of the circuit analysis.