Range-testing a conical logarithmic spiral antenna for a dual-polarized riometer

The off-axis axial ratios and the radiation patterns of conical log spiral models have been examined experimentally at a single frequency with the objective of finding a circularly polarized antenna of small physical height, suitable for use in decametric dual-polarized riometers. Truncation of a narrow-cone-angle spiral produced rapid axial-ratio degradation below
0.75 \lambda
height in tests performed at 960 MHz. A wide-cone-angle configuration was found, however, with all the characteristics desired, particularly axial ratio
\cong 1.25
out to
50\deg
zenith angle, with height only
0.16 \lambda
.