| Microwave circuits and devices, are commonly characterized using commercially available vector network analyzers (VNA). For an operating frequency up to about 110 GHz, a device under test (DUT) that is usually connected to the VNA through coaxial adapters which facilitate the transition from the DUT's transmission media to the VNA's coaxial cables. A test fixture is usually required for such a transition. Compared to the measurements using commercially available VNAs, In-Situ measurements allow the characterization of a DUT in the same environment where it is designed to operate, with no need of precision connectors or test fixtures. This approach is very attractive, particularly for those circuits operating at the upper portion of the microwave spectrum (100--300 GHz) and at the submillimeter-wave region (300--3000GHz), where planar transmission lines are frequently used and precision coaxial or waveguide adapters are largely unavailable.; A variety of non-contacting probing methods have been proposed and demonstrated for microwave circuit in-situ measurements. Most of them are focused on electromagnetic field-mapping. However, these techniques suffer from drawbacks. Some of them require quantification of the Pockels effect and require sophisticated laser instrumentation that is typically not found in standard microwave electronics laboratories. The others utilize coaxial probes which can present over-moding problems for high frequency operation and can be cumbersome to implement and align.; In this work, a new approach for non-contacting in-situ measurements of microwave circuits is investigated and its concept demonstrated. This new approach is a combination of a planar non-contacting probing structure and a six-port reflectometer architecture. The approach described in this work is a stand-alone instrument that has the potential to be monolithic integrated and hence may benefit from low-cost compared to other noncontacting in-situ measurement systems. In addition, a new calibration method based on null double injection technique is demonstrated and studied as an alternative six-port calibration method that does not require sliding terminations. This technique can be implemented and potentially automated using only a few widely-available microwave components, resulting in a more convenient and frequency-scalable system solution. |
