ECM AEROSPACE ANTENNA STUDIES. VOLUME 2.
Final technical rept. 1 Aug 65-31 Aug 66,
SPERRY GYROSCOPE CO GREAT NECK NY RADIATION DIV
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Measurements have been made of the effects of a conical plasma about an azimuthally slotted cone excited in the first higher order mode. The antenna was tested in the center of its 100-Mc bandwidth at about 750 Mc. Antenna pattern measurements show distortion of the initially omnipattern or - 3 db into primarily a forward and rear lobed pattern. Implications for actual re-entry conditions are discussed as are recommendations for future work in this area. An expression is derived for the admittance of a circumferential slot in an infinite cylinder covered by a set of coaxial dielectric of plasma layers. The slot is fed by the dominant TEM mode in a narrowly-spaced, parallel-plate, radial waveguide. Numerical computations are presented for a multiple layer model of a lossy inhomogeneous plasma and for a dielectric layer which supports surface waves. These computations are compared with previously obtained admittance measurements of a gap-excited cylinder surrounded by an annular pulsed discharge. The measurements are in fair agreement with calculated values based on a three-layer model of the plasma and the discharge tube. Calculations were made on the pattern distortion of plasma-covered slotted wedges appropriately phased to have forward coverage. The numerical results for the two-dimensional wedge are illustrative of the pattern distortion in the forward hemisphere of a similarly excited cone. Both infinite and finite two-dimensional geometries have been considered. The finite wedge is treated by an integral equation technique and the corresponding infinite geometry by a modal expansion method. In the latter analysis, the plasma layer is approximated by a linearly varying impedance sheet.
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