VIEW BEAM [PLANE|FIELD Kn]
View some sub-cube of the (up to 4-D) dirty Beam.
The 2nd argument indicates whether VIEW shows dirty beams of all Fields
for a given frequency plane (PLANE keyword), or all Frequency-dependent
beams for a given Field.
The 2nd and 3rd arguments are optional if the beam is only 2-D or 3-D,
which occurs for a single field or a frequency-independent beam in Mo-
saics (narrow band approximation).