A four-phase and an eight-phase signal constellation are shown in the figure below.
For the constraint that the minimum distance between pairs of signal points be $d$ for both constellations, the radii $r_1$ and $r_2$ of the circles are
- $r_1=0.707 d, \; r_2=2.782 d$
- $r_1=0.707 d, \; r_2=1.932 d$
- $r_1=0.707 d, \; r_2=1.545 d$
- $r_1=0.707 d, \; r_2=1.307 d$