Experimental study of unidirectional ferrite microstrip lines

An experimental study of unidirectional ferrite microstrip lines was made, for the purpose of determining their characteristic and input impedances as well as the effect of insertion of a lumped inhomogeneity on the unidirectional properties. The characteristic impedance was determined by comparison of a known lumped load impedance along the line with the input impedance near the free edge of the upper conductor, after measurement of the complex reflection coefficient as the ratio of output-to-input complex voltage amplitudes over the 1 to 3 GHz frequency range with a DK1-5 instrument and a 50 ohm standard S6-2A resistor (ceramic cylinder with absorbent coating layer of thickness equal to that of the ferrite substrate). The characteristic impedance was found to be low, within 3 to 5 ohms for the 60SCh ferrite material, and to thus limit the range of insertable amplifying or control elements. The data are useful for design optimization of rectifiers, circulators, attenuators, modulators and other nonreciprocal devices on microstrip lines.