Noise figure circles

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 .