From email:

C Band interference : Waveguide Microwave Filter.

This filter protects the extended C-band of 3.625-4.8 GHz from potential interference originating below or
above the band.

...

MICROWAVE FILTER CO., INC.
6743 KINNE STREET, E. SYRACUSE, NY 13057
E-Mail: mfcsales@microwavefilter.com
800 - 448 - 1666 • 315 - 438 - 4700
Web: www.microwavefilter.com