Theory of Broadband Noise Matching for HF/VHF Receivers With Electrically Small Antennas

A general theory on noise matching performance of receivers with electrically small antennas (ESAs) emphasizing HF (3MHz to 30MHz) and VHF (30MHz to 300MHz) applications is presented through theoretical analyses, discussions, and circuit simulations with practical device models from a state-of-the art semiconductor technology. The theory considers all the noise sources and their interplay. The impact on the noise performance from both the physical constraint of the ESA in terms of its radiation quality factor and the scaling of transistor technology and periphery such as gate resistance, gate cutoff frequency and transition frequency has been discussed. Two receiver examples, one with electrically small dipole and the other with electrically small loop are studied with full-wave simulations. The antenna equivalent models are then connected to low noise amplifiers designed with the state-of-the-art Gallium Nitride (GaN) transistor models to evaluate the noise performance of the systems and compared against the theory. It is demonstrated that both the noise figure and its bandwidth can be significantly improved over traditional matching strategy when optimized active direct matching is applied at the price of increased device periphery and power consumption. In particular, the bandwidth of such low noise matching can be orders of magnitude wider than the antenna’s conjugate impedance matching bandwidth that is defined by Harrington-Chu’s limit.