Distributed six-port reflectometer based vector network analyzer with multiple measurement techniques and applications for microwave imaging

Abstract

This thesis presents the design and measurement of a distributed six-port reflectometer-based vector network analyzer. The design has been proven to operate with two independent RF power sources. This novel approach makes our system the first-of-its-kind in the world having the capability for accurate phase measurements of distant antennas and other devices which previously required long coaxial cables incurring high-cost and loss of accuracy due to resulting long cable losses. The specific distributed network analyzer reported on herein has a bandwidth of 0.6-1.2 GHz. The study also evaluates three characterization-based measurement techniques, and two calibration-based measurement techniques reported in the literature and draws a comparison based on their performance when used with the current hardware. A test case has been proven for applications of the current hardware to measure the path characteristics in Microwave Imaging applications. A novel approach for determining the reflection and transmission coefficients of the device under test (DUT) has been introduced and validated, utilizing two characterization-based techniques based on non-linear optimization and a geometrical solution. The results were confirmed using a simulation software (ADS) as well as full experimental results using a custom-built measurement hardware. The novel approach allows accurate S-parameter measurements while increasing computational efficiency and using a lesser number of calibration loads as compared to many previously proposed techniques. Although measurement techniques requiring the full S-parameters of the six-port circuit as well as those not requiring the full S-parameters have been tested, our study found that the characterization-based techniques using S-parameters to be more accurate when performed using our custom measurement hardware.