Jonathan D. Young

Ground penetrating radar as a subsurface environmental sensing tool

Ground penetrating radar (GPR) is considered as an environmental tool. The basic concepts involved in GPR are introduced briefly including the antennas, propagation, target scattering, and mapping. Target identification is important when using GPR since the scatterer can only be observed by evacuation. This is discussed in terms of mapping and complex natural resonances. GPR has been used and is being considered as a tool for the detection of a wide variety of subterranean features. A very brief description of the various applications of GPR is presented. In terms of environmental sensing, it has been applied to detect buried tanks, landfill debris, water levels, and contaminated fluids. The detection of various military devices also represent a serious environmental concern including landmines and unexploded ordnance. There are also possible applications involving the detection of buried utilities highway voids, grave sites. It has been used for examining archeological sites. The above list is far from complete because of the ever-expanding use of GPR. >

Application of plane waves for accurate measurement of microwave scattering from geophysical surfaces

The authors utilized the concept of a compact antenna range to obtain plane-wave illumination to accurately measure scattering properties of simulated sea ice. They also made simultaneous measurements using conventional antennas. Measured scattering coefficients obtained with the plane-wave system at 10 GHz decreased by about 35 dB when the incidence angle increased from 0/spl deg/ to 10/spl deg/. Scattering coefficients derived from data collected with the radar system at 13.5 GHz using conventional far-field antennas decreased by about 20 dB over the same angular region. This demonstrates that the far-field properties of a widebeam antenna are inadequate for measuring the angular scattering response of smooth surfaces. They believe that application of the compact antenna range concept for scattering measurements has a wide range of applications and is the solution to the long-standing problem of how to directly measure scattering consisting of coherent and incoherent components. >

Forward-looking radar navigation system for 1997 AHS demonstration

A forward-looking chirp monopulse radar has been developed for road-vehicle guidance and collision avoidance. The radar chirps between 10 and 11 GHz and operates in conjunction with a frequency selective surface stripe laid in the middle of the highway lane. The monopulse guidance concept derives lateral position data from two receive antennas, one left and one right of the transmitter. The radar system is described in detail, and measured performance data are presented. This radar has been successfully demonstrated at the 1997 National Automated Highway System Consortium Technical Feasibility Demonstration on I-15 in San Diego, California.

COMBINED LONGITUDINAL AND LATERAL CONTROLLER DESIGN FOR A VEHICLE WITH RADAR SENSORS

This paper describes a vehicle-roadway system in which the control of vehicle movement is based on the instrumentation located both in the vehicle and the roadway. A radar based system is also used for both cruise control and for providing position information.

Radar retro-reflective patch for vehicle convoying applications

A retro-reflective patch antenna has been developed for radar-based vehicle following. Radar scattering from vehicles is strongly angle dependent at frequencies of practical interest, which complicates tracking. The antenna described here provides a strong, angle independent return that can be used as a stable aiming point. The antenna is a planar Van Atta array of dipoles with a multilayer stripline feed. The antennas size is comparable to a license plate, and it can be directly attached to the back wall of a van or truck. A description of the antennas design issues and measurements of its RCS are presented. The antenna described here is a microwave analog of the optical retro-reflector, and we expect it to find applications in many areas.

Design, fabrication and measurement of an FSS antenna ground plane

It is always a challenge to accommodate the large number of antennas needed to meet desired system goals on aircraft. This is especially true on small vehicles where the number of prime locations is minimal. One way to mitigate this situation is to co-locate as many antennas as possible. This paper discusses a frequency selective surface ground plane that can be place on a radome covering a dish antenna. It is intended to provide minimal transmission loss at the dish antennas frequency and yet provide a good conducting ground plane for the antenna to be placed on the ground plane. This talk will discuss various aspects of the FSS design that is intended to accommodate fabrication issues using a direct write manufacturing method that has recently been developed. The resulting design will be validated by comparing predictions to measurements.

Waveguide studies of soil modification techniques for enhanced mine detection with ground-penetrating radar

Waveguide studies of the effectiveness of soil modification techniques for non-metallic mine detection with ground penetrating radar are described. Visibility improvements for a nylon target buried in sand are considered as varying amounts of water or liquid nitrogen are added to the sand. Experiments are performed in an S-band waveguide (2.6 - 3.8 GHz), and results show that increased water content improves shallow buried target visibility initially due to increased dielectric contrast between the target and background medium, but eventually obscures target responses due to increased loss. Initial tests of the addition of liquid nitrogen show reduced loss in the high moisture content case, so that targets can again be made visible. Analytical model results are also presented for the experimental configuration and found to be in good agreement with measured data, and further studies of soil modification effects with the analytical model are performed. A finite difference time domain (FDTD) electromagnetic model for more complicated geometries involving general target shapes and inhomogeneous water contents is also described.

Unfurlable folded-dipole uwb antenna for Mars Explorer subsurface sensing

A novel but intuitive antenna design to achieve both broad frequency bandwidth as well as good efficiency is presented. This design utilizes unfurlable folded-dipole with its length mechanically tuned to specified operational frequency. Such antenna has been proposed for subsurface sensing on Mars surface and its prototype was built and tested. The test results verified the desired bandwidth and efficiency feature.

Automated highway radar guidance antenna and system testing results

The Ohio State University ElectroScience Laboratory participated along with the Center for Intelligent Transportation Research as one of six teams to demonstrate an automated highway concept at the National Automated Highway Demo at San Diego in August, 1997. The forward looking radar concept which was demonstrated used a FSS highway stripe. This paper begins by describing the (patented) highway stripe and the forward-looking radar guidance concept. The radar system as implemented for automated guidance is described and present measured results on the system antenna array and on the system itself are given. In addition, results of the demonstration in San Diego are discussed. The forward-looking radar guidance concept is intended to be one more application for the wide variety of forward-looking radars which are being investigated by the automobile community. The FSS Highway Stripe provides an inexpensive way to create a strong echo with a unique signature, attached to the highway, so that the forward-looking radar can be used as an all-weather guidance sensor for an automated automobile. The radar used a monopulse guidance architecture. The antenna array used a single transmit horn, and a matched pair of receive horns, all vertically polarized. All three antennas were nestled into the composite front bumper beam. Performance data on the antennas and the steering sensing information are presented. The radar system was a chirp radar covering a frequency spectrum of 10 to 11 GHz. The narrow frequency of the FSS radar stripe occurred at 10.95 GHz, allowing its signature to be distinguished from the return of vehicles and other objects out in front of the vehicle. Radar system measured results in the highway situation are presented.

Convoying Using a Radar Reflective Patch

This study describes the development of a radar reflective patch to be used for look-ahead radar for convoying ground vehicles. Headway and orientation information is provided by the lead vehicle through a radar patch. The follower vehicle receives the information via a radar/transmitter/receiver.