Compact, Backward-Radiating Helical Antenna for Mesoband High-Power Applications

A mesoband, high-power microwave source system is presented that couples a compact standing-wave oscillator operating near 500 MHz to a compact helical antenna. The antenna has a turn length that is on the order of 3λ/4 with a pitch of 46°, and the ground plane that is λ/6 in diameter. The system radiates in the axial mode in the backward direction with a front-to-back ratio of -4.6 dB. Numerical analysis of the antenna is presented to understand the design constraints, and a prototype system is built and tested to verify the numerical results. The source and antenna combination are verified at a charge voltage of 23 kV, and radiated fields in excess of 10 kV/m are measured at a range of 1 m with circular polarization.