Low-Profile Multifrequency HF Antenna Design for Coastal Radar Applications

A novel design for an electrically small high-frequency (HF) antenna suitable for coastal radar applications is presented. The principle design objectives were to develop an HF antenna resonant at multiple frequencies that is also compact and easily transportable for deployment to coastal sites and on floating platforms. The compact antenna achieves practical performance values for radiation resistance, bandwidth, and gain while maintaining small values of ka. The design presented in this letter consists of a meandering line antenna composed of helical elements and switchable folded arms. The value of ka ranges down to 0.16 at 5.7 MHz. The antenna is self-resonant at multiple frequencies including 5.7, 16.1, 20.6, and 28.1 MHz for open-circuit mode and 15.1, 18.5, and 26.1 for the short-circuit mode. In all cases, input impedances were easily matched to 50-Ω coaxial feed lines, and the achieved bandwidths ranged from 1% to 12% within the HF band (3-30 MHz). The antenna is 90 cm high with a small ground disk of 60 cm diameter. Simulation results and prototype experimental measurements are presented.