Novel multi-mode shortwave broadcast transmitting antenna array

Area of Science:

• Electrical Engineering
• Electromagnetics
• Antenna Theory

Background:

• Shortwave broadcasting faces coverage limitations within 900 km due to ionospheric characteristics.
• Existing shortwave frequencies (5.9-26.1 MHz) create significant blind spots.
• Reducing emission frequency is a viable strategy to overcome these broadcasting challenges.

Purpose of the Study:

• To propose and analyze a novel shortwave broadcasting antenna array.
• To enable broadcasting at a lower frequency of 4.4 MHz.
• To enhance close-range broadcast coverage by increasing radiation elevation angle.

Main Methods:

• Electromagnetic simulation software was utilized for antenna design optimization.
• A 4x4 multi-mode shortwave broadband transmitting antenna array was designed and simulated.
• A scale model prototype was fabricated and its performance characterized.

Main Results:

• The proposed antenna array achieved a gain of 12-23.5 dB across the 4.4-27.4 MHz band.
• Voltage Standing Wave Ratio (VSWR) for each mode was below 2.5.
• Simulations demonstrated a significant increase in radiation elevation angle at lower frequencies (4.4 MHz) compared to 5.9 MHz, confirming enhanced close-range coverage.

Conclusions:

• The new shortwave antenna array effectively reduces the lowest emission frequency, improving close-range coverage.
• Measurement results from a prototype validated the simulation findings.
• The study provides a foundation for developing improved broadband, high-power shortwave broadcasting antenna systems.