Optimized Cassegrain Antenna with its Feed Placed Behind the Main Reflector and investigating the Effects of the Feed Slant Ratio on its Characteristics

In this paper, a method is presented to design the Cassegrain antenna dimensions and feed antenna in order to optimize antenna blockage efficiency. The special case in which the feed antenna is placed behind the main reflector  is investigated and conical corrugated horn antenna is used as the feed antenna. A mathematical equation is extracted to obtain optimum value of the angle of incident waves from the feed antenna to subreflector edge. This equation is then rewritten as an error function and optimization Toolbox of MATLAB software is used to minimize this error function. After solving this equation, by using the governing relations, the other physical parameters of the antenna can be extracted and a design example is presented to further illustration of the problem in 20 GHz at K-band. In this example, slant factor of the horn is assumed arbitrarily equal to 0.32 and optimum dimensions of antenna are calculated. In continue, this design example is solved for different slant factor values and the effects on various parameters of antenna such as subreflector diameter, antenna magnification factor and horn slant radious are investigated.