Effelsberg Gregorian telescope. Left: Cross section x_fz_f – plane primary reflector (parabola) and subreflector (ellipse). Right: Aperture plane or x_fy_f – plane projection. The dashed area corresponds to the support struts and the subreflector (part of the blockage distribution, see Fig. 1); see Table B.1. The receiver or feed antenna is placed in the secondary focus near the paraboloid vertex V_p. The primary focus is near the subreflector and can be seen in Fig. D.1.