Norris S. Nahman

Continuous and discrete Fourier transforms of steplike waveforms

A steplike waveform which has attained its final value is converted into a duration-limited one which preserves the spectrum of the original waveform and is suitable for discrete Fourier transform (DFT) computations. The method, which is based upon the response of a time-invariant linear system excited by a rectangular pulse of suitable duration, is first applied to continuous waveforms and then to discrete (sampled) waveforms. The difference (errors) between the spectra of a continuous waveform and a discrete representation of it are reviewed.

Methodology for Standard Electromagnetic Field Measurements

Establishing standards for electromagnetic (EM) field measurements is a multifaceted endeavor which requires measurements made (1) in anechoic chambers, (2) at open-sites, and (3) within guided-wave structures, and the means to transfer these measurements from one situation to another. The underlying principles of these standard measurements and transfer standards fall into one of the two categories: (1) measurements and (2) theoretical modeling. In the former a parameter or a set of parameters is measured, while in the latter a parameter or set is calculated employing established physical and mathematical principles. In the following discussion, the three measurement topics and field transfer standards mentioned above will be discussed with the guided-wave structures being restricted to the TEM cell. Throughout the discussion the interplay between measured quantities and predicted (modeled) quantities will be seen. The frequencies considered here range from 10 kHz to 18 GHz (and upward) and are dependent upon the physical constraints imposed by our ability to implement an actual measurement, subject to the conditions imposed by rigorous electrodynamic theory in a given analytical model.

Picosecond-domain waveform measurements

A review of the state-of-the-art of picosecond time-domain measurements is presented which draws together techniques from the electrical and optical regions of the electromagnetic spectrum. Measurement methods are listed in categories which exhibit the commonality between electrical and optical methods. State-of-the-art values for temporal resolution are presented with reference citations to specific methods and related technical topics.

Reference Waveform Flat Pulse Generator

The NBS Reference Flat Pulse Generator (RFPG) is used to transfer dc voltage and resistance standards to the nanosecond domain. It provides a step amplitude of 1.000 V (open circuit) from a source impedance of 50.0¿. The transition duration is 600 ps, and all perturbations are damped out to less than ±10 mV within 5 ns. It can also be used as a time interval transfer standard.

Picosecond-Domain Waveform Measurement: Status and Future Directions

A review of the state of the art of picosecond time-domain waveform measurements is presented which includes measurements in both the electrical and optical regions of the electromagnetic spectrum. This review is the latest edition of a series of reviews on high-speed pulse measurements compiled by the author commencing in 1967 [1]; specifically this review updates the 1978 review, [2]. The significance of the IEEE Pulse Standards 181 and 194 (or the identical IEC Standards 469-1 and 469-2) are discussed briefly. The classification of time-domain measurements from the 1978 review is summarized and augmented with basic instrumentation block diagrams. The advances in the present-day capabilities from those in 1978 are presented via temporal resolution state-of-the-art charts using the 1978 format; however, the only entries in the charts are those that have changed since 1978. Also, presented are some opinions as to the future directions of electrical and optical picosecond domain measurements. Fifty-six references are cited.

Application of the homomorphic deconvolution for the separation of TDR signals occurring in overlapping time windows

The homomorphic transformation is used to separate a time domain reflectometry (TDR) signal into its rapidly and slowly varying components, respectively. The separation (deconvolution) technique is successful in the case where the multiple reflections cannot be viewed in nonoverlapping time windows as is required by the conventional TDR method.

Coaxial-Line Pulse-Response Error Due to a Planar Skin-Effect Approximation

The time-domain error introduced by the planar skin-effect approximation is examined by comparing the approximate response with the cylindrical skin-effect response. Expressions are developed for the cylindrical skin-effect response and applied to line outer conductor ID sizes ranging from a 0.1-mm microminiature size to 10 mm. For 50-air dielectric lines (including 3.5 and 7 mm) curves are given for the cylindrical skin-effect response transition (rise) time (0 to 50 percent and 10 to 90 percent) versus line length (0.01-100 m). Step responses are given for a 1-m length of 0.1-mm 50-? microminiature line with relative dielectric constants of 1, 2, and 3.

A Solid-State Reference Waveform Standard

A solid-state reference waveform filter has been developed which uses the Maxwell-Wagner capacitor effect. This filter is realized in a stripline configuration with a lossy dielectric consisting of a thick (5-¿m) layer of SiO2 on Si. The equivalent circuit of this filter is equivalent to that for previously developed filters which used a lossy liquid dielectric. A preliminary design has been completed and a filter fabricated for which the design characteristic impedance, 38 ¿, and transition duration (rise time), 300 ps, agree with measured values to within 2 and 17 percent, respectively. The temperature dependence of the filter transition duration has been estimated from the temperature dependence of the filter conductance to be about 1 percent/° C.

A causal skin-effect model of microstrip lines

A complete transmission line model including skin effect is derived to show the effects of conductor skin loss on the attenuation and phase factors. The frequency-dependent behavior of a microstrip line is included in the model. Distortions of a short pulse due to the skin effect, including attenuation dispersion, and propagation delay, are investigated. Simulation results indicate that the skin effect cannot be neglected in the phase factor in low-conductivity transmission lines.<<ETX>>

Shielded Balanced and Coaxial Transmission Lines - Parametric Measurements and Instrumentation Relevant to Signal Waveform Transmission in Digital Service

Abstract: A method is presented for determining the impulse and step responses of a shielded cable using time domain terminal measurements and a physically based mathematical model for the transmission line properties of the cable. The method requires a computer controlled time domain measurement system and was implemented using the NBS Automatic Pulse Measurement System (APMS). Data are also developed for the frequency domain complex propagation function (attenuation and its related minimum-phase shift). The method is applied to 12 shielded paired-conductor (balanced) cables and 5 coaxial cables. Time domain responses are presented for three nominal cable lengths, 60 m (200 ft), 150 m (500 ft), and 300 m (1000 ft). The time domain responses are applied to the estimation of bit error rate increases due to the insertion of the cables into a digital signaling system employing a balanced polar NRZ waveform. Also discussed is the application of the time domain responses to time domain reflectometry techniques for cable acceptance tests and field-site testing of installed cables.