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This article presents a novel transmission-only calibration technique for free-space quasi-optical material characterization, based on rotating the sample around its axis to vary the angle of incidence under which the sample is illuminated. In contrast to common time domain approaches, each frequency point is evaluated individually. Thus, no minimum bandwidth is required and artifacts due to time gating are prevented. In this article, two methods are presented: the first is based on self-calibration, such that all error terms are obtained by the measured sample itself. The second one, which is tailored for thin samples, requires two known standards. Since plane-wave illumination cannot be assumed for highly-focused beams, an analytical model for the coupling of arbitrary paraxial beams is developed, accounting for the lateral beam shift in case of angled samples. Thus, the presented methods are not restricted to free-space beams with high Gaussicity, allowing to employ a variety of feed antennas. Measurements in the frequency range from 220 GHz to 330 GHz of a well-known alumina sample verify the different calibration methods.

Driven by the increasing demand for high-throughput communication links and high-resolution radar sensors, the development of future wireless systems pushes at ever greater operating frequencies. By analogy, high-performance computing (HPC) systems with high-bandwidth I/Os have become a mainstream solution to address multi Gbit/s data rates. Heterogeneous integration technologies play a vital role here in enhancing the performance and functional density, along with reducing the size and costs of such RF systems. In line with this trend, many passive components, which have once been monolithically integrated, are now implemented on ceramic or polymer-based packages. Besides these long-established material and process technologies, considerable efforts have also recently been devoted to the development of RF components on glass and glass-ceramics. Spurred by their low dielectric losses, extremely smooth surfaces, and excellent dimensional stability, glass technologies are emerging as a promising alternative for high-volume and high-performance RF applications. In this article, relevant glass materials and key enabling technologies are reviewed and put into context with well-established RF substrate technologies. Another focus is set on the latest glass-based packaging and interposer solutions ranging from MHz-to-THz frequencies. To showcase the development activities and practical accomplishments of the RF glass technology, also a large variety of key components is presented. Finally, the paper concludes by discussing future research and development directions of RF glass devices.