Among the most
important features of a radiotelescope there are its sensitivity and its
resolving power.
The sensitivity represents how a radiotelescope is “reactive”
to extremely faint and/or distant sources, and it directly depends on
the radio waves collecting surface
().The
resolving power, instead, represents the instrument capability to distinguish
two sources which appear near in the sky.
It is linked to the antenna beam width (degrees), which depends on the
dish diameter (m).In particular: ,
that is the
aperture angle is given by the ratio between 57.3 and the antenna diameter
measured in wavelengths. If the dish diameter increases,
grows and so lowers.
The system becomes more directive, so being able to distinguish the two
targets (1 and 2). The resolving
power is strictly linked to the antenna physical dimensions, which cannot
be increased beyond certain limits. Fortunately it’s possible to
exploit a well known Optics law and obtain a large virtual antenna by
means of two smaller dishes separated by the wanted distance. The greater
this distance, the smaller the resulting antenna beam.
).The
resolving power, instead, represents the instrument capability to distinguish
two sources which appear near in the sky.
It is linked to the antenna beam width (degrees), which depends on the
dish diameter (m).
In particular: 
,
that is the
aperture angle is given by the ratio between 57.3 and the antenna diameter
measured in wavelengths.
grows and so 
lowers.
The system becomes more directive, so being able to distinguish the two
targets (1 and 2).