Robert W. Beatty

Impedance measurements and standards for uniconductor waveguide

A tutorial review is presented of the measurement of impedance and reflection coefficient in uniconductor waveguide. Normalized impedance in a waveguide operating in a particular mode is defined and related to measured quantities such as the reflection coefficient and the VSWR. Emphasis is given to the rectangular waveguide operating in its dominant mode and to the tuned reflectometer as an instrument for achieving the most accurate results. The evolution of the tuned reflectometer at NBS is outlined and recent techniques are discussed. Different types of standards of reflection coefficient are described and the advantages and limitations of each are mentioned.

Development and evaluation of a set of group delay standards

Group delay standards of 15,30, and 60 ns have been developed at JPL. Calibration data provided by NBS and others are presented and compared. Calibrations were performed at microwave frequencies of 2113,2295, and 8415 MHz as well as at a baseband modulation frequency of 500 kHz. The uncertainties of the measurement and effects of dispersion and cable reflections are discussed.

Effects of Connectors and Aiapters on Accurate Attenuation Measurements at Microwave Frequencies

A source of error in microwave attenuation measurements, not previously evaluated, is treated in an original analysis. The error is caused by effects of deviations of connectors or adapters from standard specifications. For example, if the coaxial connector at the insertion point in an attenuation measuring system deviates from standard specifications, the measured attenuation of a coaxial pad inserted in this system may differ from the measured attenuation of the same pad when inserted in a system having a standard connector at the insertion point. In the analysis, an attenuator installed in a system is represented by three cascaded two-ports, the central one representing the core or kernel of the attenuator, and the others representing connector pairs. Three general cases are considered: the waveguide component under test has 1) either sexless or mating connectors, 2) nonmating connectors of the same type and sex, or 3) nonmating connectors of different types. The results indicate that significant errors are possible with present connectors, such as the type N, but that these types of errors become negligible when high-precision connectors are used. The analysis permits one to tell how good a connector must be for a specific attenuator application.

Microwave Standards and Measurements, A Progress Review 1960 to 1963

Rather than a comprehensive survey of the field, highlights of the progress in microwave standards and measurement methods are given. Power, attenuation, impedance or reflection coefficient, noise, phase shift, and field strength are covered. Microwave frequencies are assumed to start at 1 Gc and extend upwards, including coherent electromagnetic energy in the spectrum of visible light, approximately 400-800 Tc. A discussion of the intercomparisons of power standards of different nations is followed by a report on newly developed power measuring devices and techniques. Some methods of measuring the power of lasers are given. The present status of attenuation measurements and standards is indicated, giving ranges and accuracies of calibrations at the National Bureau of Standards, Boulder, Colo. New types of standards for millimeter and submillimeter waves and for attenuation of laser beams are mentioned. Impedance standards and measuring techniques are discussed, as well as 2-port measurements and the development of greatly improved coaxial connectors. The recent development of phase shift standards and measurement techniques in the United States is summarized. The essential lack of microwave field strength standards is noted and small progress is reported.

Cascade-Connected Attenuators

Two or more calibrated attenuators are often connected in series (cascade) in order to obtain a desired reduction in power level. The total attenuation of the combination is usually obtained by adding the attenuation of each unit. In general, this will not give the correct result because of reflections due to mismatch at the attenuator junctions. It is shown how the correct value of attenuation can be obtained in terms of reflection coefficient measurements at the attenuator junctions. A nomogram of mismatch error for two cascade-connected attenuators is given.

An attenuation and phase shift divider circuit

An attenuation and phase shift divider circuit is described. The theory is presented for accurate division of small attenuation and phase shift changes by arbitrarily selected ratios, and the procedure is given for adjusting the circuit. The circuit is useful for accurately producing small attenuation changes such as 0.0001 dB and small phase shift changes such as 0.02°, which are outside the capabilities of most commercially available instruments.