Planar Near-Field Measurements of GPR Antennas and Applications to Imaging

Hans-Rudolph Lenler-Eriksen

Research output: Book/ReportPh.D. thesisResearch

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Abstract

Ground penetrating radar (GPR) systems are used for detection of objects in soil. The objects are detected by transmission of an electromagnetic field in the soil from a transmitting antenna. The transmitted electromagnetic field causes a scattered electromagnetic field by interactions with the objects in the soil, and the scattered field is detected by a receiving antenna. The detected scattered electromagnetic field contains information about the shape and position of the objects in the soil. To obtain a good extraction of information about the objects in the soil as much a priory information as possible should be used. Knowledge about the electromagnetic properties of the soil like the velocity of propagation is necessary. Furthermore, knowledge about the electromagnetic properties of the antennas is desirable. For non-dispersive and linearly polarized antennas it is often sufficient to simulate the antennas as simple Hertzian dipoles. In this thesis GPR antennas are characterized by the transmitted electromagnetic field in the soil. The transmitted electromagnetic field can be written as a superposition of plane waves by means of a plane-wave transmitting spectrum. The plane-wave transmitting spectrum can be calculated using measurements of the voltage transfer function between the GPR antenna and a buried loop antenna in the soil. To perform the calculations, knowledge of the electromagnetic properties of the soil and the loop antenna is necessary. The electromagnetic properties of the loop antenna are described using a plane-wave receiving spectrum that expresses the sensitivity to the transmitted electromagnetic plane waves in the soil. Development of methods for estimation of the electromagnetic properties of the soil is also important. Subsequently, the calculated plane-wave transmitting spectra are used in a method for image reconstruction of objects in the soil. This method gives a possibility to use the GPR system with an arbitrary antenna for imaging provided that the scattered field from the objects in the soil is detectable. In this thesis two types of antennas are measured and used for image reconstruction. These antennas are a non-dispersive linearly polarized bowtie antenna and a dispersive circularly polarized equiangular spiral antenna, respectively. The experimental work shows that both types of antennas are suitable as GPR antennas if the plane-wave transmitting spectrum is used in the imaging reconstruction.
Original languageEnglish
Place of PublicationKgs. Lyngby
PublisherTechnical University of Denmark
Number of pages119
ISBN (Print)87-91184-54-1
Publication statusPublished - Jul 2006

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