Study of the Interaction Between the Feed and the Subreflector and its Impact On Antenna Performance

In the dual offset reflector antenna design where the feed is close to or even intrudes into the enlarged caustic zone due to subreflector shaping, the feed may block the field from the subreflector to the main reflector. In such a case the interaction between the subreflector and the feed should be analyzed to determine the severity of the blockage, and to evaluate the blockage impact on the antenna performance. A simple scattering analysis method, where the feed aperture is modeled as a disk scatterer and its interaction with the subreflector is included in the field calculations employing Physical Optics (PO) algorithm, has been used in the past in the antenna community, yet its effectiveness and accuracy has not been established and verified. This study tries to validate the simple scattering analysis method, by performing more rigorous near field interaction analysis using HFSS, a commercial Finite Element Method (FEM) software, and comparing the results of both analyses to Near Field Range (NFR) measurements. The numerical example shows that the results from both analyses agree with that of the measurement, and it demonstrates that this simple scattering analysis method can be used to analyze this type of scattering almost as well as a very complex method that involves much greater effort and computing resources.