The shadow boundary integral technique for Cassegrain subreflectors

The paper formulates the PO radiation integral from a hyperbolic subreflector, illuminated by a focal feeder, in the form of GO plus a line integral along its contour. This representation provides a quite simple and efficient procedure to observe the field from the near to the far field region, with an obvious advantage in terms of computation time. Furthermore, the method is well suited to be improved by more sophisticated diffraction methods. The basic idea of the proposed approach resembles the representation of the radiated field from a finite aperture in terms of incremental contributions arising from its rim. An elegant formulation in this concern is due to A. Rubinowicz, who re-elaborated earlier works via a simple and physically appealing derivation based on the Huygens' principle (see J. Opt. Soc. America, vol.52, no.6, p.717-18, 1962). Following Rubinowicz's philosophy, a line integral representation has been presented for the problem of PO radiation from a parabolic reflector antenna (Infante L. and Maci, S., IEEE Antennas and Wireless Propag. Lett., 2003). The proposed approach extends the work of Infante and Maci to the case of a hyperboloid subreflector, to compute efficiently the field radiated by the whole Cassegrain antenna system.