The Smith Chart was published in 1939 by Phillip H. Smith in the USA. It was developed independently in 1939 by A. R. Volpert in the Soviet Union. It was also invented and published in 1937 by T. Mizuhashi in Japan. Apparently, George Ashley Campbell (of filter fame) also published it circa 1912. Does anyone know of a reference to a G.A.Campbell publication on the subject ?