Relaxing the Small Facet Size Requirement for the Far-field Calculation of Large Reflector Antennas

The accurate calculation of the far-field of a large reflector antenna based on the set of discrete reflector points resulting from a structural analysis of the antenna is one of the key problems in the integrated structural-electromagnetic optimization of such antennas. In this study, the classical method that extends the discrete set of points into flat triangular facets on the basis of which the far field is calculated is considerably upgraded. The innovation is that the proposed method makes full use of the exact knowledge of the systematic error between the ideal reflector surface and its faceted counterpart, and uses this known systematic error to upgrade the calculation of the mechanically deformed reflector, whose surface is composed of corresponding planar facets. Two versions are introduced, the single grid version and the double grid version. The double grid version makes use of a double grid to even further refine the description of the systematic error. Based on this, the dichotomy method is used to quickly obtain the maximum size of the facets that still results in the required precision of the far-field calculation. In the examples given, concerning 50-m standard and 33-m offset reflector antennas operated at 60 GHz, the size of the small facets can be relaxed considerably, yielding much larger facets (such as more than 200 times the operating wavelength for the 50-m standard antenna) for a required far field accuracy of -60 dB with respect to the main lobe level.