We seek to increase sensitivity of antenna-coupled infrared detectors by an order of magnitude. We will gain understanding of relevant design parameters, and subsequently design impedance-matched antenna-sensor combinations. We utilize our newly developed high-spatial-resolution, three-dimensional probe techniques to measure electric fields in the vicinity of the infrared antennas. This enables us, for the first time, to determine the infrared-frequency impedance as a function of position. Combined with an iterative design-fabrication-test approach, this will enable development of infrared impedance-matching components. Intellectual merit: We scale up the concept of a radiofrequency network analyzer by nine orders of magnitude in frequency. This proven advance yields experimental tools needed to extend the performance of antenna-coupled sensors by a similar scale in frequency, making the entire field of passive low- 5 frequency electronics operational in the infrared range. Infrared antennas have been proposed for a wide range of applications, including nanoscale chemical and photon sensors, nearfield microscopy, and optical rectennas for energy-harvesting. Such devices would transform the field of optics, enabling sensing devices of nano-scale dimensions with order-of-magnitude enhancement in sensitivity, responsivity, and reliability compared to conventional optical techniques. Broader impact: The proposed research greatly extends the frequency range of classical electronics, while serving as the foundation for a dynamic and engaging learning environment at each of the PIs? institutions. All three PIs have an established track record of mentorship of underrepresented students, and all three participate in programs for science and engineering outreach to K-12 students and research participation of undergraduate students.