An improved SCR system for controlling NOx levels in internal combustion engine exhaust, comprising a least one ammonia sensor disposed at an intermediate longitudinal location in an SCR catalyst and in communication with a System Control Module. A coil wound around the bobbin has a rectangular cross section which on a short axis side includes a width W. A first display device is coupled to the color transformer. If the infected data is repairable, the data is repaired and an out-of-band target data notification is generated and sent to the target computer system. The stacked waveguide circulator may also comprise a a first port and a second port on the first side.