Analysis and experiment of near field of a monopulse shaped ring-focus antenna with arbitrary polarization

A monopulse ring-focus antenna with arbitrary polarization is modeled to evaluate its near-field distribution. To overcome the limitations of the principles of geometrical optics (GO), the physical optics (PO) method is employed to derive a general expression. A feed pattern with arbitrary shape and arbitrary polarization is expressed as a combination of two non-coherent functions, namely, f/sub 1/(/spl theta//sub f/) and f/sub 2/(/spl phi//sub f/). An equivalent focus technique is presented to simplify the expression of the incident field of the main reflector. Furthermore, the dual shaped reflector is fitted with polynomials. By use of the Fourier series expansion, the integral with respect to the /spl phi/ axis of the sub-reflector is analytically evaluated. Through a series of operations, the radiation integral is simplified from four dimensions to three dimensions for near-field distribution. To test the formulae, a C-band monopulse shaped ring-focus antenna, with dual circular polarization and 3.5 m diameter, has been designed and manufactured. Comparison between experimental results and calculations shows good agreement.