Research On Miniaturization Technology Of HF Antenna

The shortwave (HF) band is from3MHz to30MHz，with wavelength from10m to100m. The shortwave radio system has the advantages of long detection distance, stronginvulnerability，long unrepeated span and so on. However, the HF antennas usually getthe disadvantage of large size, which makes it uneasy for transportation, erection andmaintenance. A major challenge of the development of HF communication equipment isto miniaturize the antenna size. A miniaturized HF antenna means an electrically smallantenna. The bandwidth and efficiency are limited by its size. Therefore it is necessaryto research on the miniaturization of HF antenna while maintaining acceptableperformance. This is also the focus of this research.This paper summarizes the defination of electrically small antenna and theimportant performance parameters including: efficiency, gain, input impedance,bandwidth, quality factor and gain-bandwidth product. Based on the basic principles ofelectrically small antenna, efficiency, gain and bandwidth are the most importantperformance parameters when designsing an electrically small antenna. The anysismethods of electrically small antenna are dicussed in detail, which provides thetheorical basis of designing an antenna. Then the miniaturization technology of antennasis detailed intruduced, which provides the technical reference for miniaturizing the HFantenna.This dissertation proposes a novel miniaturized HF antenna composed ofhemispherical wire grids following the structure of a UWB antenna. With the help ofCST Microwave Studio, the antenna is simulated. The results demonstrate that-10dBimpedance bandwidth of this antenna is20MHz~30MHz. The relative bandwidth is40%and the total efficiency is above90%in the working frequency band. The height ofthis antenna is3.3m and the biggest width is3.6m. The height is33%of its higherfrequency wavelength, and22%of its lower frequency wavelength. The antenna hasmet the requriements of miniaturization. A1/5scale model is manufactured. VSWR andgain are measured. The results are consistent with the simulated ones.Based on this antenna, two methods of broadening the frequency range areproposed, including lump loading and dielectric loading. The VSWR of the antennaloading lump elements is below2.2with gain above-20dB from3MHz to30MHz, which meets the requirements and shows great practical value. The performance of thedielectric loaded antenna is limited by permittivity and medium thickness. The effect ofdielectic loading is not apparent. The antenna presented in this paper can be widely usedin HF communication system, over-the-horizon radar and so on.