Optimizing the Receiving Propertiesrnof Electrically Small HF Antennas

摘要

Because of the large operating wavelength, receivingrnantennas in the high-frequency (HF: 3 MHz to 30 MHz)rnoperating band are often electrically small. It is wellrnknown that electrically small antennas generally exhibitrnlow radiation effi ciency, and are diffi cult to match overrnwide bandwidths. In the HF band, external backgroundrnnoise is high, and receiving systems are ideally designedrnto ensure that the system remains externally noise limited.rnIn this paper, we discuss the properties of the general,rnelectrically small, receiving antenna. We present formulasrnthat can be used to determine, characterize, and comparernthe performance of the general, electrically small, receivingrnantenna. We demonstrate that optimization of the smallrnHF antenna’s receiving-performance parameters, suchrnas its receiving sensitivity and noise fi gure, are directly arnfunction of optimizing the antenna’s impedance match andrnradiation effi ciency, independently of whether a dipole,rnmonopole, or loop-like design is utilized. We demonstraternthat impedance matching for the receiving antenna is oftenrna secondary consideration. We illustrate diff erences inrnan antenna’s matching-network transfer function for thernreceiving mode versus the transmitting mode. We presentrnformulas and design guidelines for optimizing the receivingrnsystem’s noise fi gure and signal-to-noise ratio performance.rnFinally, we present design examples for an electrically smallrndipole, loop, and multi-turn loop.