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Retrofitting an antenna that was originally designed without a beamwaveguide (BWG) introduces special difficulties because it is desirable to minimize alteration of the original mechanical truss work and to image the actual feed without distortion at the focal point of the dualshaped reflector. To obtain an acceptable image, certain geometrical optics (GO) design criteria are followed as closely as possible. The problems associated with applying these design criteria to a 34-m dualshaped Deep Space Network (DSN) antenna are discussed. The use of various diffraction analysis techniques in the design process is also discussed. The geometrical theory of diffraction (GTD) and fast Fourier transform (FFT) algorithms are particularly necessary at the higher frequencies, while physical optics (PO) and spherical wave expansions (SWE) proved necessary at the lower frequencies.

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