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/sub 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 (/spl lambda//sub 0/), the input impedance of the spiral above a cylinder of radius r/sub cy/=0.25 /spl lambda//sub 0/ is almost constant (250-j20 /spl Omega/) with a gain of approximately 7 dB. The spiral above a cylinder of (2H, r/sub cy/)=(2.7 /spl lambda//sub 0/, 0.25 /spl lambda//sub 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.