The log-periodic trapped monopole

The concept is being investigated of an HF monopole constructed of short segments interspersed with antiresonant traps; the segment lengths and trap resonant frequencies follow a modified log-periodic sequence so that the hand-off from section to section through the traps is such that the VSWR does not exceed some predetermined value (3:1 was used in the studies). Two versions were investigated: (1) the 'free' monopole in which the segments and traps are chosen such that the driving point VSWR is at or below the limit and (2) a 'constrained' version in which a nearly arbitrary limit on the height has been imposed such as might be encountered in submarine antennas. In the first case an antenna of perhaps 15 or 20 meters tall results but no special matching network is required; in the second case the driving point impedance exceeds the limits and a matching network is needed.