This research focuses on novel self-phasing antenna array technology that allows secure communication within a distributed network of mobile agents that have no prior knowledge of their respective locations. The specific application of this proposal is for covert terrestrial sensor and nanosatellite networks. Despite the need for distributed intelligence systems to maintain reliable, up-to-date, uncompromised intelligence data dissemination capabilities throughout the entire network, they are often targeted by terrorist attacks. In many cases, these systems are easily detected by conspicuous antenna structures or the high concentration of radio-frequency emission in their vicinity. this research is to develop retrodirective antenna arrays to facilitate covert communications between a distributed terrestrial sensor network and an information gathering nanosatellite network. In contrast to conventional phased-array antennas, retrodirective arrays are self-phasing and are capable of providing self-steering, point-to-point radio crosslink. Retrodirective arrays located at the terrestrial sensors are used to autonomously uplink intelligence data to the satellite. Retrodirective arrays aboard the satellite are used to establish secure satellite-to-satellite crosslinks. The broader impacts of the proposed research will result in more secure, efficient data transmission in wireless networks that are of interest to the scientific, defense, and intelligence communities. The research will also support multidisciplinary training of students in areas that are of critical national importance.

Project Report

This research focused on novel, self-phasing, retrodirective antenna technologies for intelligence-gathering sensor applications. This technology adds an additional layer of security to communications within a distributed network of mobile agents that have no prior knowledge of their respective locations. An example scenario is an intelligence-gathering remote sensor located in hostile territory, where the role of the sensor is to eavesdrop on or intercept RF emissions from hostile emitters whose locations are not only unknown, but can also be mobile. In this type of situation, the most obvious eavesdropping method is for the sensor to use an omnidirectional antenna that can pick up emissions from all directions. The inherent disadvantage of an omnidirectional antenna, of course, is its low gain, which places the burden on the receiving electronics to set the minimum detectable signal. A self-phasing receive array would autonomously direct its receive beam toward an RF source, allowing for an improved link budget and extrapolation of the source location. Next, a retrodirective array would transmit the information to a mobile collection vehicle. The collection vehicle establishes communication by broadcasting an omnidirectional, non-data-carrying interrogation signal. The retrodirective array autonomously responds only in the direction of the interrogator, and can also support communication with multiple-allied interrogators or in multipath environments. This adds a layer of physical security preventing interception while enhancing communication with multiple users or in multipath environments. An S-band self-phasing receive array for RF sensing and tracking was designed and demonstrated. Measurements at 2.3, 2.4, and 2.5 GHz showed that the array was capable of selectively steering toward a specific frequency source in an environment with multiple signals of various frequencies. Another type of retrodirective array was demonstrated based on power detection and phase shifting. This array determined the direction of arrival based on the peak-power direction from the measured power levels of a receive beam swath, and was capable of resolving multiple signals of interest and handling nonuniform wavefronts. Though the power-detecting retrodirective array was capable of handling nonuniform wavefronts, it is not suitable for tracking mobile targets as it must constantly rescan the environment to update the interrogator’s bearing. A completely analog, full-duplex architecture based on phase detection and phase shifting was demonstrated to handle nonuniform wavefronts, and maintain a path loss proportional to the square of the distance between interrogator and array. This architecture used phase-detecting blocks between adjacent element pairs to characterize the incoming wavefront, and control circuits connected to phase shifters to steer the beam back in the interrogating direction. This project demonstrated several advances in retrodirective array design and development. In addition to intelligence-gathering applications, the broader impact of these research developments are pertinent to many secure wireless communication situations involving a collection of terrestrial, airborne, and space-borne mobile agents.

Agency
National Science Foundation (NSF)
Institute
Division of Information and Intelligent Systems (IIS)
Type
Standard Grant (Standard)
Application #
0715203
Program Officer
Sylvia J. Spengler
Project Start
Project End
Budget Start
2007-05-01
Budget End
2013-04-30
Support Year
Fiscal Year
2007
Total Cost
$600,000
Indirect Cost
Name
University of Hawaii
Department
Type
DUNS #
City
Honolulu
State
HI
Country
United States
Zip Code
96822