PO analysis procedure for the FYST beam simulations. The PO analysis follows a time-reversed process. A Gaussian beam produced by the receiver's feed horn illuminates the secondary reflector (M2), inducing surface PO currents (step 1). These currents, in turn, radiate toward the primary reflector (M1), where they induce PO currents on the M1 surface (step 2). Finally, the PO currents on M1 generate the field in the distant source region (step 3).