A study of the radiation efficiency of a half wavelength dipole

Antenna efficiency directly impacts the efficiency of communications and sensing applications, and the emerging use of high frequencies has renewed interest in its mechanisms and estimation. In this paper, the radiation efficiency of the half-wavelength center-fed circular dipole is calculated for representative metals. Both the approximate and the accurate current distribution models for the wire cross section are used. The current distribution model for along the wire is the usual sinusoidal form. From the modeled current distribution, we calculate the ohmic resistance and the radiation efficiency of the dipole. The results quantify the wire thickness and frequency ranges for which the approximate model for the cross section current distribution holds, and demonstrates the limiting antenna loss at high frequencies. For SHF and EHF, using conductors such as stainless steel means that the ohmic resistance is in the same order as the radiation resistance. When using gold coatings at these frequencies, the situation improves, but a coating much larger than that available from regular sputtering is required to attain the limiting efficiency.