Optimizing the receiving properties of electrically small HF antennas

摘要

Because of the large operating wavelength, receiving antennas in the high-frequency (HF: 3 MHz to 30 MHz) operating band are often electrically small. It is well known that electrically small antennas generally exhibit low radiation efficiency, and are difficult to match over wide bandwidths. In the HF band, external background noise is high, and receiving systems are ideally designed to ensure that the system remains externally noise limited. In this paper, we discuss the properties of the general, electrically small, receiving antenna. We present formulas that can be used to determine, characterize, and compare the performance of the general, electrically small, receiving antenna. We demonstrate that optimization of the small HF antenna's receiving-performance parameters, such as its receiving sensitivity and noise figure, are directly a function of optimizing the antenna's impedance match and radiation efficiency, independently of whether a dipole, monopole, or loop-like design is utilized. We demonstrate that impedance matching for the receiving antenna is often a secondary consideration. We illustrate differences in an antenna's matching-network transfer function for the receiving mode versus the transmitting mode. We present formulas and design guidelines for optimizing the receiving system's noise figure and signal-to-noise ratio performance. Finally, we present design examples for an electrically small dipole, loop, and multi-turn loop.