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IEEE Transactions on Antennas and Propagation
Volume 47 Number 1, January 1999

A Curved Spiral Antenna Above a Conducting Cylinder

Page 3.

Abstract:

A curved spiral antenna above a finite hollow conducting cylinder is analyzed using the method of moments. The effects of cylinder length 2{ {H}} and cylinder radius { {r_{cy}}} on the radiation characteristics of the spiral are evaluated. As 2{ {H}} increases, the cross-polarization component of the radiation field in the broadside direction decreases to a constant value (approximately {{-}}18 dB). When 2{ {H}} is greater than one wavelength ({ {\lambda}}_{{0}}), the input impedance of the spiral above a cylinder of radius { {r_{cy}}}{{ = }}{{0.25}}{{\lambda}}_{{0}} is almost constant ({ {250 -}}{{j}}{{20 \Omega}}) with a gain of approximately 7 dB. The spiral above a cylinder of (2{ {H}}, { {r_{cy}}}) = (2.7{{\lambda}}_{{0}}{{, 0.25}}{{\lambda}}_{{0}}) shows a 3-dB axial ratio bandwidth of approximately 23%, which is wider than a flat spiral antenna above a flat ground plane of infinite extent.

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