In-situ characterization of spurious modes in HE11 transmission lines with a 5-port coupler B. Plaum, W. Kasparek, C. Lechte, J. Ruiz, D. Tretiak and H. Idei EPJ Web of Conferences, 32 (2012) 04010 Published online: 06 September 2012 DOI: 10.1051/epjconf/20123204010