A Study of Low-Noise Broadband VLF Receiving Techniques

摘要

The basic difficulty in optimizing the noise performance of receiving systems which must use an electrically small antenna is the lack of a complete noise theory for a reactive source. This report attempted to add to this theory in three areas: First, the various types of small antennas were put on a common basis of comparison. The parameters of effective length, effective area, effective volume, and intrinsic bandwidth have been defined for antennas sensitive to electric fields and for those sensitive to magnetic fields. These parameters were evaluated for a number of common antenna structures. Second, a general method of describing the noise performance of any amplifier was developed in both of its dual forms. This particular characterization, based on complex-correlated input noise voltage and current generators, was chosen out of many possibilities because it is easily applied to the problem of determining noise performance with an arbitrary source. These noise parameters were evaluated for several types of amplifying devices. Third, the ultimate theoretical limits on sensitivity were explored, and a general method of determining the bounds, in terms of the parameters introduced in the previous sections, was developed. These bounds were evaluated in several examples. (Author)