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A compact splash-plate fed antenna(Figure 1) was designed using a modal matching program(AXIAL). The design aim was to achieve -20 dB near-in sidelobe levels for a reflector antenna with a small aperture diameter of approximately 10 wavelengths at 8.4 GHz. The design procedure takes into account multiple reflections between the main reflector and the splash-plate. A small splash-plate with a matching structure, supported by a dielectric cone made of PTFE, is fed from a circular waveguide. The modal matching technique employed in this design is capable of modeling such a structure accurately even when dielectrics are present. Measured and predicted far-field radiation patterns are shown in Figure 2. In the final analysis, an improved match between the measured and predicted patterns was obtained(thick solid line) by including in the electromagnetic model a small depression at the vertex of the main reflector.

Figure 1

FIGURE 1: Splash-plate Feed and Antenna Geometry.

Figure 2

FIGURE 2: Measured and Predicted Radiation Patterns at 8.4 GHz.

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