MakeR
MakeRA contoured beam is often required, particularly for satellites with a specification for well-defined but irregular coverage over a particular region of earth. MakeR is a powerful program operating under Windows 95 which can achieve a synthesis in a few minutes. It allows the entry of a start geometry and adapts this geometry using well-proven techniques to provide a shaped reflector design which meets the input specification.
MakeR generates a dual offset reflector antenna with a single feed. Both reflectors are shaped under assumptions of Physical Optics to produce a prescribed radiation pattern. This version (3.1) is most suitable for contoured beam antenna design. The program can generate an antenna with elliptical aperture and perform multi-frequency optimisation (up to 3 frequencies).
MakeR uses fast synthesis techniques developed by B.S.Westcott and A.A.Zaporozhets. The well-established Geometrical Optics (GO) methods are based on solution of the Monge-Ampère equation [1-2]. They provide a good starting point for the Physical Optics (PO) synthesis, which uses analytical gradient optimisation procedures [3].
The program is written in C for Windows 95 / Windows NT 32-bit PC operating systems, which provide efficient flat memory model and common graphical interface.
The synthesis procedure is split in 4 parts, as shown in Fig.1. After each stage the user has a complete antenna system with certain properties. For example, a GO-generated focused beam antenna with an elliptical aperture is available after Part 2.
At any time it is possible to inspect different antenna characteristics like the shape of main or sub-reflectors, the field on the antenna aperture, etc. and observe what is happening with the antenna system during the synthesis. All the data is available within one program and can be saved into a file or restored from a file at any time.
The synthesis procedure starts with conic system Setup (main reflector - parabola, sub-reflector - hyperbola or ellipse). During the conic system setup it is possible to specify parameters like distance between foci directly or let the program to compute them from some general requirements like clearance between the main and sub-reflector, total system lengths, etc [4]. A conic system has a circular aperture, the aperture power distribution is almost identical to the feed taper.
Reflector GO synthesis reshapes the conic system (which is used as a starting point) to a system with an elliptical aperture and given aperture taper. Then the far-field GO synthesis generates a beam with a given contour in the far field. This gives a good starting point for the PO optimisation.
Figure 1. The synthesis procedure
In order to generate an antenna the user has to follow the items from menu Run (Fig.2). At each stage the required parameters can be modified within a dialog box, which is invoked by pressing right mouse button. The user has full control over the iterative optimisation process which can be stopped (Space key) or continued (PgDn key) after each iteration, if required.
The GO part usually takes just a few seconds on a Pentium PC. The PO part depends on the antenna size in terms of wavelengths. As an example the program generates 60 wavelengths diameter antenna for Eutelsat II European coverage in about 10 minutes (single frequency).
The program outputs the reflector surfaces, far-field radiation pattern and the aperture field functions into files in ASCII format.
Figure 2. The program layout