We present design, analysis and test results of a dual-aperture coaxial multiband feed horn that operates at S, Ku, K and Ka bands. The design objectives are to achieve aperture efficiencies of 85% for S and Ku bands and 60% for K and Ka bands and cross-polarization level of À20 dB within 30 degree off-boresight for all bands. These values are deduced primarily from the reflector geometry, À10 dB reflector edge taper and moderate cross-polarization requirements for the secondary patterns. In our design the Ku, K and Ka bands are launched through a multiflared circular horn while the S band is launched through a coaxial horn. A method of moment based software is developed to analyze the structure including mutual coupling between the apertures. It is found that the aperture impedance significantly affects the S-band performance. For the high frequency bands, the mutual coupling between the circular and coaxial apertures plays an important role. The simulated results including mutual coupling effects agree well with the measured data. The multiband feed design allows a compact, low weight, single offset reflector configuration as opposed to a Cassegrain antenna system that requires two separate feeds and a dichroic subreflector to accommodate such widely separated bands.

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