Users of Vector Network Analyzers (VNAs) often need to estimate and strive to optimize their instrument’s measurement speed. Many RF Engineers are interested in the tradeoffs between speed, accuracy and resolution in VNA measurements, especially those striving to achieve optimal automation of the instrument integrated in a larger measurement system or production environment. This application note details the determining factors for measurement cycle time in Copper Mountain Technologies VNAs. Generally speaking, the measurement cycle for any VNA consists of three major components: the per-point tuning and settling time of the generator, the per point measurement time, and a per-sweep time needed to process and transfer results, switch the generator between output ports, and return the generator to the start frequency. An additional, user-programmable delay between points is available in CMT instruments, which may be useful for integration with external equipment or DUTs with settling times of their own. As will be seen, some of the delay components are effectively fixed, while others depend upon the measurement parameters and thus may be optimized by the user.

A VNA measures reflection coefficients of RF devices and systems. To be very meticulous, each measurement should be accompanied by an uncertainty with a specified statistical confidence interval. To understand the measurement uncertainty, or accuracy, it is important to understand the contributing factors, which are explored in this application note.

The R60 1-Port VNA was used for this application of materials measurement. See the abstract of the IEEE paper below. Abstract: Accurate determination of soil complex-dielectric-permittivity spectrum is important for various applications, especially for the development of soil moisture sensors that can be used, e.g., in agriculture and for environmental monitoring. Wideband measurement of soil dielectric spectrum requires the use of large-diameter coaxial transmission-line cells connected to a vector network analyzer (VNA). We present a new method for soil dielectric-spectrum characterization in the frequency range of 0.05-3 GHz. Our methodology is based on a wideband one-port VNA measurement of a soil sample inserted into a large-diameter coaxial cell. The key part of our approach is the use of a variable load terminating the coaxial cell to extract the scattering parameters of the sample, which are then fed into a dielectric permittivity extraction algorithm. The system provides quick and repeatable measurements without the use of flexible microwave cables. Also, application of a portable one-port VNA significantly lowers the cost of the system in comparison to two-port setups. We verify our methodology based on measurements of reference materials-polytetrafluoroethylene, isopropanol, and ethanol-and then apply it to characterize the soil samples with different moisture content and salinity. Experimental results confirm the validity of our approach.