Rewrite (174) as

Re-arrange (176), we have

which represents a set of circles on plane. Note that for a given noise figure *F*,
i.e., a given , the circle provides the corresponding values of source reflection coefficients
.

For each value of *F* or , we have a corresponding *F* circle with

Note that the centers of *F* circles are always on the line drawn between and the origin of the
plane. The radius of *F* circle is getting bigger for a larger *F*. When
, the *F* circle becomes a point on .