Photonics for microwave radiometric sensing

Abstract

Microwave radiometric remote sensing has monitored the earth’s ocean and environment for decades to provide data for weather forecasting models. More recently, the wireless communications community has embraced the idea of infusing wireless networks with sensing capabilities to support new applications, such as beam management for millimeter wave communications and autonomous vehicle monitoring. ☐ This dissertation outlines microwave photonic sensing solutions and focuses on two separate sensing systems: a microwave photonic radiometer for atmospheric sensing, and a microwave direction-finder. The radiometer system uses a fiber-arrayed waveguide grating to optically process the microwave spectrum from 50-70 GHz, near the oxygen absorption peak. Unlike previous radiometers, the system densely samples a full spectral band instead of selecting discrete frequency bins. ☐ For beam localization, a microwave photonic direction-finding system is presented. The system detects the angle-of-arrival of active signals, such as individual transmitters. An antenna array receives the signals, which are then up-converted to the optical domain. A photonic integrated circuit (PIC) optically processes the signals to determine source positions. A star coupler replicates the effect of a Fourier transform lens to determine the angle-of-arrival. The architecture is receive-only and has extremely low latency thanks to analog beam processing in the optical domain. ☐ To further enhance the capabilities of the direction-finding system, a second PIC is integrated for the purpose of frequency detection. The arrayed waveguide grating (AWG) PIC, fabricated at Sandia National Laboratory, has a spectral resolution of only 0.97 GHz to enable spectral sensing. By identifying the frequency of received signals, the effect of squint can be mitigated in the direction-finder, allowing the system to operate over the entire Ka-band (26.5-40 GHz). The combined beam localization and frequency detection capabilities show promise for applications in integrated sensing and communications.