A broad-band Smith-diagram display unit has been developed by using a new waveguide circuit called a phase-directional coupler. Among the interesting features of this new display unit are its broad-band capabilities, high precision and simple construction. A "vibrating-dummy method" has been developed as a perfect termination in contrast with the well-known "sliding-load method." The Smith-diagram display unit of small reflection coefficients was achieved by combining this new method with the above display unit. Included in this paper are the experimental results obtained at 6 Gc and 11 Gc.