Stewart, J.A.C.: 'Magnetic tuning of coaxial IMPATT oscillators', Electronics Letters, 1968, 4, (24), p. 526-527, DOI: 10.1049/el:19680409
IET Digital Library, https://digital-library.theiet.org/;jsessionid=3dnua1pvtj6qp.x-iet-live-01content/journals/10.1049/el_19680409