Comment on "A quasi-optical isolator" [and reply]

For the original article see ibid., vol. 6, no.5, p. 205-6 (1996). In the aforementioned article, the authors describe the design of a linear-to-circular polarizer. The commenter considers their use of six cascaded printed gratings as a practical way to realize this type of quasi-optical isolator and their use of a resistor loaded grid as a good way to absorb the reflected wave. However, the commenter points out that there have been earlier demonstrations of nonferrite quasi-optical isolators. The use of a linear-to-circular polarization transducer to isolate the input port from reflections from the output and to do so in quasi-optics dates from the mid-50's. Millimeter and submillimeter versions were demonstrated in the 1960's. Also the basic idea was briefly described by Skolnik (1962). In reply the authors express gratitude for being made aware of this earlier work and briefly discuss the four references cited by the commenter.