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FDTD Analysis of the Ultrawideband Performance of Flared-Horn Antennas


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In this work, the FDTD technique is employed to analyze and improve the UWB pulse performance of flared-horn antennas. The transverse feed and the inline-balun feed are compared as methods of transitioning from coaxial transmission lines to parallel plates, and flared-horns fed with the inline-balun are found to have superior UWB performance. The radiation characteristics of standard flare-taper functions such as the linear taper are compared with taper functions that curl behind from the aperture plane. Untreated aperture discontinuities present standard taper functions constrain UWB radiation performance. By contrast, the tapered-back flare functions provide enhanced UWB performance primarily through the avoidance of the sharp aperture discontinuities. UWB radiation performance improves as the flare length is increased from one quarter wave length that the lowest UWB frequency to lengths exceeding one half wavelength, albeit with a decreasing rate of performance improvement. As the aperture size grows from one-quarter wavelength at the lowest UWB frequency to one wavelength, UWB pulse radiation performance is enhanced, again with a decreasing rate of performance improvement. E-plane energy pattern symmetry can be improved by thickening or widening the plates in the flare region, or by increasing the flare length or aperture size. Finally, the array behavior of one of the tapered-back elements fed with the inline balun is studied with a waveguide simulator, and the VSWR is shown to be very low across the bandwidth.



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