High power very low frequency/low frequency transmitting antennas

摘要

Very-low-frequency (VLF) and low-frequency (LF) transmitting antennas are small with respect to the wavelength and are required to radiate substantial power levels. Design parameters for these antennas are discussed, including the impact of technical advances in high-voltage design and bandwidth enhancement. Most of these antennas are various realizations of electrically small monopoles that can be modeled by a simple series tuned circuit with one resonance. From this circuit, simple formulas are derived for the maximum radiated power (P/sub max/), and intrinsic bandwidth (100% efficiency bandwidth) B/sub wo/. It is shown that P/sub max/ is proportional to the square of the effective topload area, B/sub wo/ is proportional to the volume under the topload, and both are proportional to frequency to the fourth power. A normalized area and volume are defined and used as a figure of merit for comparing antenna designs. These factors are calculated for several existing antennas and for a generalized umbrella toploaded monopole (UTLM). The use of multiple elements in VLF antennas is discussed.