Noise figure characterization

Abstract

Introduction Noise is one of the most critical issues in wireless systems because it is a fundamental limiting factor for the performance of microwave receivers. Industry requirements for increasingly higher performing communication systems require tighter noise specifications that make the noise figure measurement a critical step in the characterization of modern microwave circuits and systems. Noise figure measurements of circuits and sub-systems have been traditionally performed with noise figure meters specifically developed for that purpose. A paradigmatic example is the HP8970 (and associated family) that was considered for years as the reference meter for noise figure characterization. This instrument, as well as other modern equipment, uses the popular Y-factor technique to compute the noise figure from the ratio of two power measurements (“cold” and “hot”). The scalar nature of the measurements allows an easy and straightforward characterization process. This simplicity is undoubtedly part of its large success. However, its accuracy is limited by the match properties of the device under test and measurement setup. There are two factors that have been driving an evolution in the noise figure characterization schemes. One factor is a growing tendency in microwave instrumentation to integrate different types of measurements into a single instrument box. As a result, noise figure characterization is now available as an option in modern vector network analyzers (VNA) from different manufacturers. The other factor is that the accuracy requirements in environments that are not perfectly matched (millimeter wave and beyond, on-wafer setups, etc.) demand a noise figure characterization that takes advantage of vector measurements to improve scalar results.