Reflection coefficient T1

in input terminal plane of a two-port

linear

reciprocal microwave network is a linear fractional transformation of reflection coefficient T2 in output terminal plane. The constants of the linear fractional transformation are related to scattering coefficients of the network. A linear fractional transformation maps circles and straight lines in one plane into circles and straight lines in another plane. A Weiss-floch proved that between two straight lines

there exist two perspective centers and a straight line AB

from which image point on straight line in one plane can be located graphically if point on straight line in another plane is given. By means of theorem of cross ratio the paper proves that between two circles or between a circle in one plane and a straight line in another plane there also exists two perspective centers and a straight line AB from which the scattering coefficients of a microwave network may be evaluated graphically by several ways. In this paper four examples are given. They are short-circuit method

variable resistive-load method

scattering coefficients combination method and scattering coefficients division method. The result obtained by short-circuit method is same as that given by G. A. Deschamps.