Abstract
Currently, shortwave broadcasting in the range of 5.9–26.1 MHz remains a relatively large blind spot within 900 km owing to the limitations of ionospheric characteristics. Reducing the emission frequency is a feasible approach for covering blind spots and improving broadcast performance. Thus, a new type of shortwave broadcasting antenna array capable of reducing the lowest emission frequency to 4.4 MHz is proposed in this paper. An electromagnetic simulation software is used to optimize the design. The simulation analysis shows that for the 4 × 4 multi-mode shortwave broadband transmitting antenna array, the gain obtained is 12–23.5 dB in the 4.4–27.4 MHz frequency band, and the VSWR for each mode is lower than 2.5. The radiation patterns at 5.9 MHz and 4.4 MHz on a vertical plane are compared, and the results prove that the radiation elevation angle of the new transmitting array increases significantly. The larger elevation angle and lower frequency ensure the enhancement of close-range coverage. A scale model prototype is fabricated and characterized, and the results of the measurement agree well with those of the simulations. It provides a theoretical basis and technical support for the improved design of broadband high-power shortwave broadcasting transmitting antenna systems.
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