This paper describes a new type of primary reference standard for coaxial line impedance measurements at millimetre-wave frequencies. The standard can be used to calibrate vector network analysers (VNAs) and other forms of reflection/transmission measuring instrument. The standard is intended for use in the 'small' precision coaxial line sizes-i.e. 1.85 mm and 1 mm. Fabrication and the subsequent use of the standard to calibrate a VNA in the 1.85 mm line size are described. The standard consists of an air dielectric open-circuit offset by a known length of precision coaxial line. This type of device is considered to be a primary reference standard since its electrical characteristics can be predicted from fundamental electromagnetic theory and can be traceable directly to SI base quantities (i.e. the metre and the second).
This paper discusses RF calibration schemes for coaxial one-port vector network analysers other than the traditional short-open-load approach. Before use, the calibration standards are characterised by fitting polynomials to measured voltage reflection coeflcient values. Simulated uncertainty profiles and example measurement uncertainties are presented for various calibration schemes. Examples of non-SOL schemes and a method of adaptively choosing the best calibration scheme, based on minimising the uncertainty of measurement, for a particular device at a particular frequency are also presented.
Increased student use of the Internet and declining reference desk statistics are factors encouraging academic reference librarians to look for new ways to reach patrons. Web-based customer contact center software gives librarians the tools to provide interactive, 24/7 reference service to Internet users. This article describes how the library at California State Polytechnic University, Pomona developed its live/web reference service. We discuss the factors that encouraged us to launch the service, the challenges that we encountered along the way, and examples of our experiences to date.
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