Caleb Fulton

Transmit–Receive Duplexing Using Digital Beamforming System to Cancel Self-Interference

A near-field cancellation duplexing system is demonstrated using multiple coordinated transceivers with symmetrically arranged antenna elements and a digital backend for baseband waveform phase and amplitude weighting controls. By adapting weights of multiple transmit elements, coupled interference at receiver elements deconstructively interferes, providing up to 50 dB of additional isolation over the coupling of a single transmitter to a receiving element. Bandwidth considerations of the array are presented. It is shown that uncorrelated transmit noise from multiple transmitters can be removed through tunable filtering or through adaptive beamforming of multiple receiving elements, both providing an additional 30-40 dB of interference reduction that is tunable over the frequency range of the system.

Calibration techniques for digital phased arrays

Several techniques for calibrating and aligning different aspects of a digital phased array are demonstrated using a 16-element, panelized, vertically-polarized S-band subarray with element-level digitization on both transmit and receive. These techniques make use of the element-level functionality not only to expedite the process of initial alignment and calibration but to enhance the ability of the array to maintain and enforce this calibration over time as RF/analog system variations occur. A method for maintaining element amplitude and phase over time in fully digitized arrays is demonstrated as well as a technique for element-level self-calibration of quadrature mismatches.

A digital array radar with a hierarchical system architecture

A digital array radar system prototype is presented that makes use of a hierarchical digital backend coupled with highly-integrated, multi-channel RF transceivers. The general benefits of using such a hierarchical architecture are briefly discussed, along with how this prototype is in line with a vision for future radars that fully embrace the concept of low-cost integration in a panelized platform. A target tracking example is given using the prototype that illustrates some specific advantages to using a hierarchical digital backend.

Calibration of a Digital phased Array for polarimetric Radar

When an active phased array is used for polarimetric radar applications, the system must be calibrated to reflect the fact that polarization of the transmitted and received fields is dependent on the scan angle. This paper discusses the challenges of polarimetric phased array calibration, and demonstrates these techniques using a linear array of eight S-band dual-polarized antennas connected to an active Digital Array Radar (DAR) prototype system. The ability to accurately measure polarimetric scattering matrices is demonstrated after using direct far-field measurements to compensate for polarization errors on receive and target reflection measurements to compensate for transmit polarization errors.

Low-cost, panelized digital array radar antennas

The design challenges associated with the development of the antenna array for a highly-integrated, low-cost, panelized radar system have been presented, and the methodology for the development of a digital array radar (DAR) antenna panel has been detailed. Now that a solution for the maximization of scan range in in the DAR antenna panel has been identified, the next step is to integrate real T/R modules into the antenna panel and interface it with a fully-digital backend to ultimately demonstrate the flexibility and capability of this new, low-cost radar system.

Digital Array Radar panel development

The Army Digital Array Radar (DAR) projects goal is to demonstrate how wide-bandgap semiconductor technology, highly-integrated transceivers, and the ever-increasing capabilities of commercial digital components can be leveraged to provide new capabilities and enhanced performance in future low-cost phased array systems. A 16-element, S-band subarray has been developed with panel-integrated, plastic-packaged gallium-nitride (GaN) amplifiers, multi-channel transceiver ICs, and digitization at the element level. In addition to full digital beamforming on transmit and receive, the DAR subarray has demonstrated efficient RF power generation exceeding 25 Watts per element, in-situ, element-level calibration monitoring and self-correction capabilities, simultaneous transmit and receive operation through subarray partitioning for an indoor target tracker, and more. An overview is given of these results and capabilities.

Calibration of panelized polarimetric phased array radar antennas: A case study

Demand for improvements in the performance and capabilities of new polarimetric radar systems beyond those of their predominantly mechanically-rotated predecessors has led to an effort to realize large, dual-polarized phased array an-tennas. These arrays have changing polarization characteristics with scan angle, requiring calibration and compensation. This paper provides a qualitative discussion of the challenge in meeting polarime-tric weather radar requirements, such as a low bias in differential reflectivity (ZDR) and integrated cross polarization ratio (ICPR). A case study is presented using low-cost, aperture-coupled, stacked-patch antennas, a representative example of what may be used in large polarimetric phased array applications, to predict quantitatively the performance that can be achieved through suitable calibration and size constraints.

Digital Phased Arrays: Challenges and Opportunities

Digital beamforming (DBF) has long been heralded as the next frontier in phased array technology, and not without reason. The digitization of transmit and receive signals at the element level opens the door to new processing and beamforming schemes and promises to deliver maximum flexibility and unprecedented dynamic range in large systems. However, it is not without inherent technological risks and practical challenges associated with the amount of data to process and the use of less sophisticated transceivers. This paper provides broad overviews of several interrelated aspects of the resulting DBF trade spaces for these systems. In particular, emerging concepts are highlighted for the roles and interconnection of distributed beamforming/processing for fixed and adaptive beamforming. These are then related to digital array calibration mechanisms that can potentially reduce the need for data- and processing-intensive beamforming algorithms.

A dual-polarized patch antenna for weather radar applications

An antenna suitable for use in emerging multifunctional phased array weather radar applications is presented. The S-band (3–3.6 GHz), differentially probe-fed, stacked patch antenna features high port-to-port isolation (> 40 dB) and correspondingly good cross-polarization characteristics in addition to high efficiency and good port-to-port matching. The intended application places strict limits on errors introduced in polarime-tric weather radar measurements by antenna array polarization errors that are not corrected by calibration. The fundamental challenge is described, and it is demonstrated herein that this particular antenna element exhibits fairly good polarimetric performance over a wide scan range without excessive calibration requirements. Results from both a single element characterization and a 9×9 planar array of these elements are presented.

Sensitivity of Tornado Dynamics to Soil Debris Loading

AbstractPast numerical simulation studies found that debris loading from sand-sized particles may substantially affect tornado dynamics, causing reductions in near-surface wind speeds up to 50%. To further examine debris loading effects, simulations are performed using a large-eddy simulation model with a two-way drag force coupling between air and sand. Simulations encompass a large range of surface debris fluxes that cause negligible to substantial impact on tornado dynamics for a high-swirl tornado vortex simulation.Simulations are considered for a specific case with a single vortex flow type (swirl ratio, intensity, and translation velocity) and a fixed set of debris and aerodynamic parameters. Thus, it is stressed that these findings apply to the specific flow and debris parameters herein and would likely vary for different flows or debris parameters. For this specific case, initial surface debris fluxes are varied over a factor of 16 384, and debris cloud mass varies by only 42% of this range becaus...