Integrated analysis of a finite array of open-ended waveguides based on a multimode equivalent network.

In this paper we present a hybrid and efficient method for the analysis of open-ended waveguide arrays on top of finite support structures. In space borne vehicles, arrays of open-ended waveguides often find their application in multi-beam feeds for reflector antennas or as tracking radars in the noses of aircraft or missiles. Especially in these cases, the antenna is of limited dimensions due to packaging and aerodynamic constraints. Because of the finiteness of the antenna and its mounting platform, the edge effects play an important role in the generation of side lobes and back scattered energy. In complex environments, stringent demands must be given to the side lobe levels, and the back scattering effects must be properly taken into account to be able to control the negative effects on the antenna performance. Via the Uniform Theory of Diffraction (UTD) approach the truncation of the ground plane can be modeled [2], [3]. In this approach the elements of the array give rise to singly diffracted rays which sum up with doubly diffracted rays excited at the edge of the structure. In particular, these latter are excited by the singly diffracted grazing rays impinging on the edges of the mounting platform. These phenomena can have a significant impact on both the radiation characteristics of the antenna and the input impedance of the radiating waveguides. Therefore, the availability of an accurate and efficient tool for the analysis of arrays, where the finite number of the array elements, the finiteness of the supporting structure, as well as the covering radome are included, is an essential requirement for a complete antenna design CAD tool. The presented model is based on a Multi-mode Equivalent Network (MEN) [1] representation of the radiating waveguides and a high frequency approach for the external region. The accessible ports given by the MENs connecting the antenna and feeding waveguides offer the possibility of optimising the structure looking both at the antenna’s radiation characteristics and the matching network inside the waveguides, rendering very efficient in the design of arrays. Moreover, the MEN method offers the possibility to include more complex structures as building blocks in the array design, structures which are probably best simulated via FEM or FDTD methods. These building blocks are precalculated in a commercial software tool like HFSS and subsequently cascaded in the system at impedance matrix level. This extends the flexibility of the developed CAD tool and creates a more realistic analysis of waveguide arrays.