Achieving low cross-polarization levels in antennas is important in applications where polarization diversity is employed. However, obtaining extremely-low cross-polarization levels is not easy. In addition, measuring the cross-polarization level is even harder due to lack of ideal probes which have "purer'' linear polarization than that of the antenna under test (AUT).
In this dissertation, the difficulties of achieving lower cross-polarization EM field transmission (or receiving) and accurately measuring very low cross-polarization levels are addressed by employing wideband electromagnetic polarization filters (EMPF). Planar polarizers were designed by first understanding the sources of cross-polarization in rectangular horn antennas. These EMPFs are applied as add-on screens to reduce the cross-polarization levels of standard gain horns (SGH) and diagonal horns (DH). Cross-polarization level reduction as much as 18 dB is presented for diagonal horns with add-on screens. Similarly, more than 9 dB cross-polarization reduction is shown for standard gain horns across the operational bandwidth. This approach is general enough to be applied to other aperture antennas as well. The add-on screen approach is desirable because it provides substantial cross-polarization reduction without changing the original horn antenna design and makes the proposed method easy to apply to existing horn antennas.
Later, an alteration is done on the add-on screens by making use of Ludwig's 3rd coordinate definition. This modification results in further cross-polarization suppression in the vicinity of boresight direction. For instance, on X-Band SGH, near boresight angular region where cross-polarization level keeps below -60 dB increases by 26% with use of this modified add-on screen.
Furthermore, the errors associated with full polarimetric measurements are investigated using Monte Carlo approach. Rules of thumbs are provided for keeping the effects of these error terms on the measurement accuracy within a certain level. The EMPF itself was used a calibration target in full-polarization scattering measurements. This new polarization calibration target is superior to conventional dihedral reference targets commonly used in such measurements. The advantages of EMPF over dihedrals are its low-weight, low-cost and ease of storage and mounting.
|Commitee:||Burkholder, Robert J., Lee, Robert|
|School:||The Ohio State University|
|Department:||Electrical and Computer Engineering|
|School Location:||United States -- Ohio|
|Source:||DAI-B 78/11(E), Dissertation Abstracts International|
|Keywords:||Cross-polarization, Diagonal horns, Polarizers, Standard gain horns|
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