Various methods are described by which the usual TEM coaxial-line mode can be distorted to produce a region of circular polarization in which the non-reciprocal properties of ferrites can be exhibited. Three basic designs of isolator are given:(a) A coaxial-line construction with stub arms. Simple theory is given for this, as well as performance details. Information is given on models of two differing line sizes, together with a method of broad-banding the isolator.(b) An isolator in which the line is split and crossed in such a manner as to produce time and space quadrature of the r.f. fields. Performance figures of a practical model using printed-circuit techniques are given.(c) An isolator construction using a half-dielectric-filled coaxial line. The method of taper calculation and construction is described, and performance figures for the isolator are given.Gyrators and circulators have also been constructed:(d) A 90° gyrator using a partially dielectric-filled coaxial wave-guide. The method of mode transformation is described, together with results for a practical model. The performance of a 4-port circulator using this gyrator is predicted.(e) A compact triplate 3-port circulator is described. Attention is given to the important parameters, and the dependence of performance upon them is discussed.