Efficient Multiple-Tuned Antenna for HF Comms

Antennas for HF communication systems tend to be physically large owing to the wavelengths at these frequencies (i.e. 100 m down to 10 m for 3–30 MHz respectively).

Plextek has made good progress in this area through the creation of an innovative multiple-tuned antenna that is electrically small. While tailored specifically for HF communication systems operating across 10–22 MHz, the technology is scalable from very low frequencies (VLF) through to microwave frequencies.

Design specifications

The multiple-tuned antenna engineered by Plextek has a physical height of only 0.6 m, which corresponds to an electrical height approximately 0.02 to 0.044 wavelengths. This low-profile antenna design provides omnidirectional coverage, particularly at low elevation angles ranging from 10° to 40°. The overarching objective is to achieve radiation efficiency levels that closely approach those of a standard quarter-wave monopole antenna under the same operating conditions, but with comparatively much smaller physical height resulting in a low-profile antenna.

Validation through measurements and simulations

Extensive measurements and simulations have been carefully conducted to validate the performance and capabilities of the multiple-tuned antenna. Key observations include the antenna’s expected predominantly vertical polarisation and omnidirectional coverage. Comparisons between simulation results and measurements of the antenna feed-point impedance and electrical field strength have indicated a high level of consistency, underscoring the antenna’s effectiveness and reliability in practical operating scenarios.

Experimental evaluation

To further assess the practical functionality of the antenna, experimental testing at power levels up to 100 Watts was carried out. Real-time access to global software-defined radios (SDR) operating 24–7 enabled comparative analyses to be conducted against a quarter-wave reference monopole antenna. Comprehensive testing has confirmed the omnidirectional radiation at low elevation angles through establishment of long-distance links via ionospheric propagation. Furthermore, the radiation efficiency of the multiple-tuned antenna approaches that of the reference monopole antenna. Long-term transmissions have highlighted the antenna’s performance under varying environmental conditions.

Prospects and potential applications

The reconfigurable nature of the antenna design, enabling operation over a range of frequencies within the HF band, signals its adaptability to diverse communication requirements. As the antenna aligns with the trend towards developing compact and efficient antennas for HF applications, there is a good opportunity for enhancing communication capabilities in challenging environments and ensuring reliable, consistent data transmission over long distances. It is in the interest of the industry that new antenna designs are in some way reconfigurable, such as in this case with frequency.

Conclusion

Plextek’s development of an efficient and compact multiple-tuned antenna for HF communications represents a valuable advancement in antenna engineering. Through precise research, simulation studies, and practical experimentation, the antenna has shown good performance in terms of coverage, efficiency, and adaptability. This innovation can enable enhanced HF communication systems to meet the evolving demands of our communication networks, ensuring reliable connectivity and data transfer is met with agility within various operational scenarios where electrically small antennas are required.

The support of the Defence Science and Technology Laboratory (Dstl), an executive agency of the Ministry of Defence (MOD), is gratefully acknowledged.