Septum feed revisited - Ok1dfc.com

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FIG.15The resulting dish antenna efficiency for the RX port with various choke positions wascalculated using FEEDPATT software. These results are shown in FIG’s 12 through 15. Thesecalculations are based on average values from vertical and horizontal polarization
measurements for the appropriate plane with adjustments made for variations in symmetry,since both software programs assume symmetrical radiation patterns. From these figures it isapparent that the ring choke improves the efficiency of a dish of this size. Additionally, the useof a choke gives us the opportunity to tailor the feed’s beam width appropriately for a givendish. For very deep dishes, good efficiency may be achieved, but with some associateddegradation of circularity.The dish antenna’s directivity, S a and resulting radiation pattern were calculated usingANT-PC and PARPACUP.for software. The PARPACUP.for program does not use actualmeasured values, but calculates the approximate radiation pattern using cos Ν θ. The exponent,N, is based on dish edge illumination. FIG 16 shows calculated results for the bare feedconfiguration where the dish aperture is partially blocked by the square waveguide supportedby four 14 mm diameter struts. In FIG 17, calculated results for the feed configuration havingthe choke 30 mm back and the same dish aperture blockage are shown. The program does notperform calculations using feed efficiency.FIG.16
Page 1 and 2: Septum Feed Revisitedby Rastislav G
Page 3 and 4: The following measurements have bee
Page 5 and 6: FIG 4Impedance Match Changes agains
Page 7 and 8: Normalized radiation patterns at th
Page 9 and 10: FIG.12
Page 11: FIG.14The resulting dish antenna ef
Page 15 and 16: FIG 18Radiation Pattern, TX Port, F
Page 17 and 18: Very good isolation between ports,

Septum feed revisited - Ok1dfc.com

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