Performance evaluation of S-parameter extraction techniques for time-domain optoelectronic vector network analyzers

• Main Author: Ruo, Russell L.
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/8226

The objective of the thesis is to evaluate the performance of two methods recently proposed for scattering parameter (S-parameter) extraction using time-domain optoelectronic vector network analyzers. Model-based simulations of an electro-optic sampling experiment for a typical high-speed bipolar transistor were used to investigate the accuracy of the techniques in the presence of experimental non-idealities. In particular, the investigation focused on the effects of finite time window, drift and noise. The methods use step-like signals and digital filtering techniques to extract the S-parameters for one of two situations where signals are either temporally overlapped or not. From the simulations, it was determined that the approach for overlapping signals is not feasible. The experimental impairments of drift and noise interfere with the separation of overlapping signals and result in inaccurate S-parameter computation. Fair results may be obtained within a limited range of frequencies for extracting the S-parameters with the approach for non-overlapping signals. Although feasible, the latter method was not recommended over existing optoelectronic methods which use pulse-like input signals for S-parameter extraction. The digital filtering technique common to both methods was validated by an experimental measurement of signal propagation on a coplanar stripline fabricated on a multilayer S1O2/S1 substrate. The attenuation and effective dielectric constants were measured over a range of frequencies between 20 and 150 GHz. Elecromagnetic simulations of the structure performed by a collaborator were found to be in excellent agreement with the experimental results. The results show high losses and dispersive effects at low frequencies, which are attributed to the conductive substrate used.