William Webster Hansen (May 27, 1909 - May 23, 1949) was a US physicist who was one of the founders of the technology of microwave electronics.

Hansen's father was a hardware store owner in Fresno, California and encouraged his son's early talent in mathematics and enthusiasm for electronics. Entering Stanford University at the age of 16, he received his doctorate in 1933.

He went on to become interested in the problem of accelerating electrons for X-ray experiments, using oscillating fields, rather than large static voltages. At the University of California, Berkeley, Ernest Lawrence and David H. Sloan had worked on an accelerator driven by a resonant coil. Hansen proposed replacing the coil with a cavity resonator. However, in 1937, the brothers Russel and Sigurd F. Varian came to Stanford to work on the foundations of what was to become radar. Hansen exploited some of the Varians' work to develop the klystron and during the years 1937 to 1940, along with collaborators such as John R. Woodyard , founded the field of microwave electronics.

In 1941, he moved his team to the Sperry Gyroscope Company where they spent the war years employing their expertise in radar applications and in other problems.

Returning to Stanford in 1945 as a full professor, he embarked on the construction of a series of linear accelerators based on klystron technology and of GeV performance. Sadly, he was never to see the completion of the project, having been exhausted by his extreme wartime schedule, he died in Palo Alto, California. His wife Betsy, the daughter of P. A. Ross , committed suicide a few months later.

The Hansen Experimental Physics Laboratory at Stanford was named for him.

Honours

• Liebman Prize of the Institute of Radio Engineers - (1945)
• Presidential Certificate of Merit - (1948)
• Member of the National Academy of Sciences - (1949)