US Patent 9929471 Very compact TM01 mode extractor

A mode extractor for extracting TM01 mode from an electromagnetic signal, including a first and second turnstile junction, each of the turnstile junctions having first port, four second ports of rectangular waveguide which are mutually orthogonal and orthogonal to first port and matching section provided at least partially in center region of respective turnstile junction, center region being located at intersection of first port and four second ports wherein first and second turnstile junction are arranged so that longitudinal axes of their first ports are aligned with each other and their first ports are facing in opposite directions, each of the second ports of first turnstile junction is electromagnetically coupled to corresponding one of second ports of second turnstile junction, and a coaxial coupling device is inserted into matching section of first turnstile junction so that a portion of coaxial coupling device extends into first port of first turnstile junction.