In this study, a coupled-line coupler was evaluated for its potential to shape sub-nanosecond ultra-wideband (UWB) pulses. The coupler was shown to exhibit a natural tendency to differentiate sub-nanosecond pulses, owing to its bandpass nature. Next, a Schottky detector diode was applied to confirm that the small parasitic reactance in the coupler gives rise to the differentiation behavior. The unconventional application of a coupler and Schottky diode towards signal differentiation culminated in the development of a novel UWB generator that simultaneously produces: a square waveform that has a 20%-80% rise time of 850 ps, a Gaussian waveform that has a pulse duration of 100 ps, and a monocycle waveform that has a 80 ps rise time between its peaks. These waveforms were obtained by taking advantage of the dc isolation of the coupled line structure and using step recovery diodes to compress the edges of a 14 MHz sinusoidal source. The resulting multiport circuit for simultaneous shaping of sub-nanosecond pulses (MCS 3 P) showed good agreement between measured and simulated results.

Quantifying and characterizing isolated tumor cells (ITCs) is of interest in surgical pathology and cytology for its potential to provide data for cancer staging, classification, and treatment. Although the independent prognostic significance of circulating ITCs has not been proven, their presence is gaining clinical relevance as an indicator. However, researchers have not established an optimal method for detecting ITCs. Consequently, this Ph.D. dissertation is concerned with the development and evaluation of dielectric spectroscopy as a low-cost method for cell characterization and quantification. In support of this goal, ultra-wideband (UWB), microwave pulse generator circuits, coaxial transmission line fixtures, permittivity extraction algorithms, and dielectric spectroscopy measurement systems were developed for evaluating the capacity to quantify B16-F10 tumor cells in suspension. First, this research addressed challenges in developing tunable UWB circuits for pulse generation. In time-domain dielectric spectroscopy, a tunable UWB pulse generator facilitates exploration of microscopic dielectric mechanisms, which contribute to dispersion characteristics. Conventional approaches to tunable pulse generator design have resulted in complex circuit topologies and unsymmetrical waveform morphologies. In this research, a new design approach for low-complexity, tunable, sub-nanosecond and UWB pulse generator was developed. This approach was applied to the development of a novel generator that produces symmetrical waveforms (patent pending 60/597,746). Next, this research addressed problems with transmission-reflection (T/R) measurement of cell suspensions. In T/R measurement, coaxial transmission line fixtures have historically required an elaborate sample holder for containing liquids, resulting in high cost and complexity. Furthermore, the algorithms used to extract T/R dielectric properties have suffered from myriad problems including local minima and halfwavelength resonance. In this dissertation, a simple coaxial transmission line fixture for holding liquids by dispensing with the air-core assumption inherent in previous designs was developed (patent pending 60/916,042). In addition, a genetic algorithm was applied towards extracting dielectric properties from measurement data to circumvent problems of local minima and half wavelength resonance. Finally, in this research the capacity for using dielectric properties to quantify isolated B16-F10 tumor cells in McCoy’s liquid medium was investigated. In so doing, the utility of the Maxwell-Wagner mixture formula for cell quantification was demonstrated by measuring distinct dielectric properties for differing volumes of cell suspensions using frequency- and time-domain dielectric spectroscopy.

This paper presents a pulse-duration tunable ultra-wideband (UWB) generator that is developed using a variable edge-rate signal. Edge-rate variability is introduced by applying a step recovery diode (SRD) to compress the edges of the source and then employing a simple RC network to adjust the edge-rate. Afterwards, the compressed signal is differentiated using microstrip transmission lines in a short circuit stub configuration. The tunable generator resulting from this approach demonstrates Gaussian and monocycle pulses with: good symmetry and low distortion over the tunable range; pulse width variation from 800 to 1150ps over a 1-20pF capacitance range; and good agreement between simulated and measured results

The most recurrent pulse generator design approach described in literature employs a series step recovery diode (SRD) and pulse-duration tuning subsequent to Gaussian pulse formation. Although this conventional approach is advantageous in fixed pulse-duration designs, it leads to relatively complex designs for tunable generators. This paper presents a variable edge-rate compression (VERC) approach, to tunable ultra-wideband (UWB) generator design, that entails tuning prior to Gaussian pulse formation and a shunt configuration of forward and reverse biased SRDs. Compared to the conventional approach, VERC offers performance advantages that include broader tuning range, improved tuning sensitivity, increased design simplicity and reduced cost. A comparison of the series and shunt SRD configurations reveals that input-signal slew rate has a dominant effect on pulse-duration tuning for an SRD in a shunt configuration. As slew rate may be modified using frequency, rise time or voltage, the VERC approach also offers greater design flexibility and is more advantageous for tunable UWB generator design

The most recurrent pulse generator design approach described in literature employs a series step recovery diode (SRD) and pulse-duration tuning subsequent to Gaussian pulse formation. Although this conventional approach is advantageous in fixed pulse-duration designs, it leads to relatively complex designs for tunable generators. This paper presents a variable edge-rate compression (VERC) approach, to tunable ultra- wideband generator design, that entails tuning prior to Gaussian pulse formation, and a shunt configuration of forward and reverse biased SRDs. Compared to the conventional approach, VERC offers performance advantages that include broader tuning range, improved tuning sensitivity, increased design simplicity and reduced cost. A comparison of the series and shunt SRD configurations reveals that input-signal slew rate has a dominant effect on pulse-duration tuning for an SRD in a shunt configuration. As slew rate may be modified using frequency, rise time or voltage, the VERC approach also offers greater design flexibility and is more advantageous for tunable UWB generator design.