Analysis of 3-D offfocus fed and asymmetric dual antenna systems  Equivalent paraboloid antenna and equivalent feed techniques  Radiation pattern calculations for asymmetric Cassegrain and Gregorian antenna systems Off-focus fed reflector antennas are preferred to prevent loss due to aperture blockage effect of secondary reflector and feed in the reflector antenna system. For this reason, it is important to calculate the radiation pattern in the direction of the main beam, especially for single and double reflector antennas with feeder antennas or antenna arrays shifted from the focal point. In this study, a new formulation is given for the acceleration of the calculation by applying the Physical Optics method is modeled by using and equivalent paraboloid reflector antenna and equivalent feed techniques in 3-D off-focus fed and asymmetric structures of dual antenna systems used in satellite-earth stations. Figure A. Application of Equivalent feed and Equivalent Paraboloid Techniques for 3-D off-focus fed and Asymmetric Cassegrain and Gregorian Antennas Purpose: Aimed to increase the speed of calculation by combining two different techniques which helps to obtain the radiation patterns of off-focus fed and asymmetric Cassegrain and Gregorian reflectors. Theory and Methods: It is possible to find an equivalent model for the radiation patterns of a Cassegrain or Gregorian antenna fed by an array, using equivalent feeding and equivalent paraboloid antenna methods. Results: Optimization methods and genetic algorithms for estimating the parameters required for the feed and reflector parts in calculations can be easily applied for different structures Conclusion: In the study given in detail above, two methods are combined to provide an easy and fast solution for the calculation of the radiation pattern in the complex physical structures for Cassegrain and Gregorian reflector antenna systems. This method saves time for calculating the radiation pattern in the main beam direction and for making the necessary optimizations, especially in using the PO integral.