A curved spiral antenna above a conducting cylinder

A curved spiral antenna above a finite hollow conducting cylinder is analyzed using the method of moments. The effects of cylinder length 2H and cylinder radius r(cy) on the radiation characteristics of the spiral are evaluated. As 2H increases, the cross-polarization component of the radiation field in the broadside direction decreases to a constant value (approximately -18 dB), When 2H 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-j20 Ohm) with a gain of approximately 7 dB. The spiral above a cylinder of (2H, 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.