Design and Analysis of Bow-tie Antennas for GPR Applications

Ground penetrating radar (GPR) is a non-destructive testing (NDT) technology, which uses electromagnetic (EM) techniques to map the buried structures in the shallow sub-surface. The efficiency of the GPR system significantly depends on the antenna performance as the signal has to propagate through lossy and inhomogeneous media. The GPR antennas should possess a low frequency of operation for more depth of penetration, ultra-wide band (UWB) performance for high resolution, high gain and efficiency for increasing the receiving power, minimal ringing, compact and lightweight for ease of GPR surveying. Bow-tie antennas are widely used as it can provide most of the above mentioned antenna performances. Though a number of researchers have carried out their research work for the design and development of the Bow-tie antennas for the GPR applications, still there is ample of scopes for the improvement of this antenna to achieve compactness and lightweight, reduced end-fire reflections, better gain and directivity, high radiation efficiency, etc. In this work, two improved Bow-tie antennas for the GPR applications have been proposed. A compact resistive loaded Bowtie antenna is designed and investigated which can provide an impedance bandwidth of 167% (0.4 - 4.5 GHz) with reduced end-fire reflections. The compactness is achieved by using a thin sheet of graphite for the resistive loading instead of using volumetric electromagnetic absorbing materials. The end-fire reflections are minimized by blending the sharp corners of the Bowtie antenna. However, the radiation efficiency and gain of the antenna are degraded significantly due to resistive loading which has been in the second proposed antenna by using an improved RC-loading scheme. The improved and compact RC-loaded Bowtie antenna with metamaterial based planar lens is designed and investigated which can operate over a UWB bandwidth of 3.71GHz (0.29 GHz - 4.5 GHz). This provides a maximum gain of 12.4 dB and maximum radiation efficiency of 94 % throughout the operating band. An improvement in the gain of 5 dB in the bore side direction is achieved by using a modified meta-material lens. The performance of both the designed antennas is investigated in the temperature varying environment and GPR scenario at the simulation level. A comparative analysis of the designed antennas with the other reported antennas indicates that the proposed antennas are advantageous for the GPR applications

Wideband and UWB antennas for wireless applications. A comprehensive review

A comprehensive review concerning the geometry, the manufacturing technologies, the materials, and the numerical techniques, adopted for the analysis and design of wideband and ultrawideband (UWB) antennas for wireless applications, is presented. Planar, printed, dielectric, and wearable antennas, achievable on laminate (rigid and flexible), and textile dielectric substrates are taken into account. The performances of small, low-profile, and dielectric resonator antennas are illustrated paying particular attention to the application areas concerning portable devices (mobile phones, tablets, glasses, laptops, wearable computers, etc.) and radio base stations. This information provides a guidance to the selection of the different antenna geometries in terms of bandwidth, gain, field polarization, time-domain response, dimensions, and materials useful for their realization and integration in modern communication systems

Strategies for Time Domain Characterization of UWB Components and Systems

In this work new methods and criteria for the analysis of Ultra Wideband (UWB) components and systems are introduced. This permit to have a deeper insight into the component characteristics like signal distortion, ringing and dispersion, introduced by the non-ideal behavior of the UWB components over the wide frequency band. The developed analyses are the basis for correction and optimization strategies for the features of the UWB components and systems, compensating for their non-idealities

Waveform Analysis of UWB GPR Antennas

Ground Penetrating Radar (GPR) systems fall into the category of ultra-wideband (UWB) devices. Most GPR equipment covers a frequency range between an octave and a decade by using short-time pulses. Each signal recorded by a GPR gathers a temporal log of attenuated and distorted versions of these pulses (due to the effect of the propagation medium) plus possible electromagnetic interferences and noise. In order to make a good interpretation of this data and extract the most possible information during processing, a deep knowledge of the wavelet emitted by the antennas is essential. Moreover, some advanced processing techniques require specific knowledge of this signal to obtain satisfactory results. In this work, we carried out a series of tests in order to determine the source wavelet emitted by a ground-coupled antenna with a 500 MHz central frequency

DEVELOPMENT OF AN UWB RADAR SYSTEM

An ultra-wideband radar system is built at the University of Tennessee with the goal to develop a ground penetrating radar (GPR). The radar is required to transmit and receive a very narrow pulse signal in the time domain. The bistatic radar transmits a pulse through an ultrawide spiral antenna and receives the pulse by a similar antenna. Direct sampling is used to improve the performance of the impulse radar allowing up to 1.5 GHz of bandwidth to be used for signal processing and target detection with high resolution. Using direct sampling offers a less complex system design than traditional lower sample rate, super-heterodyne systems using continuous wave or step frequency methods while offering faster results than conventional equivalent time sampling techniques that require multiple data sets and significant post-processing. These two points are particularly important for a system that may be used in the field in potentially dangerous environments. Direct sampling radar systems, while still frequency limited, are continually improving their upper frequencies boundaries due to more power efficient, higher sampling rate analog to digital converters (ADCs) which relates directly to better subsurface resolution for potential target detection

An Ultrawideband Dual-Linear Polarization Feed for Solar Microwave Observation

The study of Solar Microwave Bursts (SMB\u27s) emanating from the sun is important from several perspectives. SMB\u27s are well correlated to Coronal Mass Ejections (CME\u27s) and therefore can provide insight into the physics of the sun. SMB\u27s and CME\u27s can interfere with microwave communication systems such as cell phones, satellites, and radar, and can adversely affect the accuracy of the Global Positioning System. Furthermore, CME\u27s can be hazardous to individuals and equipment in earth orbit as well as causing power grid blackouts. The rapid detection of SMB\u27s and their subsequent effect on space weather is a key element of responsibility of the United States Air Force (USAF). Identification of the source eliminates the possibility of intentional jamming or a systems failure. When such a determination is made, warnings can be issued so that measures can be taken such as using different communication frequencies or modes, or to place satellites in a safe mode. Currently the USAF operates the Radio Solar Telescope Network (RSTN) consisting of three parabolic dish antennas each at four locations to continuously observe the sun in the microwave spectrum. The 2.4m RSTN dishes have feeds that are single polarization at four discrete frequencies between 1.4 and 8.8GHz. Expanding the capability of these existing dishes with a single ultrawideband feed to cover 1-10GHz would improve observations, while adding a dual polarization capability could facilitate improved monitoring should there be future developments in spectrum usage. A feed with folded diamond-shaped elements in a damped cavity has been designed and constructed, funded under contract FA9453-09-C-0309 from the USAF Solar Disturbance Prediction Program, with a simulated bandwidth of 0.9 - 12 GHz. Subsequent characterization from 2 - 8 GHz showed good correlation between simulation and measurement, and that the feed meets virtually all performance specifications that were tested

Design And Optimization Of Uwb Antenna For Air Coupled Gpr Applications

This thesis presents a novel antenna structure that satisfies the challenging requirements of an air coupled high speed ground penetrating radar (GPR). The desired GPR system is to achieve high spatial resolution and accurate inspection results while scanning at relatively high speed for highway pavement and bridge deck inspection. This work utilizes the Ultra Wide Band (UWB) antenna design to achieve both physical and electrical requirements imposed. The design procedure starts with a short survey to discuss typical UWB antennas used for GPR applications, and various tradeoffs of each type specifically when used for Air Coupled GPR applications. Our structure anatomy is presented, followed by a theory introduction that mainly focuses on achieving good impedance matching throughout the proposed antenna structure. A proof-of-concept MATLAB model is created to evaluate the preliminary physical dimensions that can achieve minimum reflections at antenna\u27s feed point. These dimensions are then used in SolidWorks to create a 3D model that is imported later in HFSS to obtain accurate electromagnetic characteristics. Furthermore, fine tunings are performed to the antenna structure to optimize both gain and impedance matching. The SolidWorks 3-D structural model is finally used for antenna fabrication. The measurements recorded from the field experiments using the prototypes manufactured are compared to the simulation results confirming our initial findings. Both measurements and simulation results demonstrated very small reflection loss across the 700 MHz ~ 6 GHz frequency band with a very high directed gain and radiation efficiency

Low-frequency Antennas, Transparent Ground Planes, and Transponders for Communication Enhancement in Unfavorable Environments

The communication environment has a major influence on the performance of wireless networks. Unlike antennas, receivers, processors, and other components of a typical wireless system, the designer has almost no control over the communication channel. Therefore, it is imminent that the adverse effects of the communication channel such as path-loss, multi-path, lack of a clear line of sight, and interference are among the most limiting factors in designing and operating wireless networks. Recent investments in infrastructures such as cell-phone towers, communication satellites, routers, and networking devices have been aimed at reducing the aforementioned adverse effects. However, wireless ad hoc networks (WANET) cannot rely on pre-existing infrastructures such as access points or routers. In this thesis, a number of solutions are presented to enhance communication and navigation in harsh environments. 1) At lower frequencies, the defects of the communication channel are less prominent, which has led militaries to use UHF and VHF frequency bands for communication. A number of optically transparent UHF antennas are developed and embedded in the windows of military vehicles to reduce their visual signature. 2) Direction finding at low frequencies using baseline method results in an exorbitantly large array of sensors. However, a vector sensor consisting of three orthogonal two-port loop antennas can be used. A simple and accurate circuit model for the two-port loop antenna is developed for the first time that can be used for direction of arrival estimation over a wide range of frequencies and angles. 3) Using a conventional radio repeater with ad-hoc systems requires a communication protocol and decreases the throughput by a factor of two for every repeater in the chain. A full-duplex repeater, capable of simultaneously transmitting and receiving at the same frequency, is developed for the 2.4 GHz ISM band.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/143898/1/manikafa_1.pd

Thermal magnetic resonance: physics considerations and electromagnetic field simulations up to 23.5 Tesla (1GHz)

Background: Glioblastoma multiforme is the most common and most aggressive malign brain tumor. The 5-year survival rate after tumor resection and adjuvant chemoradiation is only 10 %, with almost all recurrences occurring in the initially treated site. Attempts to improve local control using a higher radiation dose were not successful so that alternative additive treatments are urgently needed. Given the strong rationale for hyperthermia as part of a multimodal treatment for patients with glioblastoma, non-invasive radio frequency (RF) hyperthermia might significantly improve treatment results. Methods: A non-invasive applicator was constructed utilizing the magnetic resonance (MR) spin excitation frequency for controlled RF hyperthermia and MR imaging in an integrated system, which we refer to as thermal MR. Applicator designs at RF frequencies 300 MHz, 500 MHz and 1GHz were investigated and examined for absolute applicable thermal dose and temperature hotspot size. Electromagnetic field (EMF) and temperature simulations were performed in human voxel models. RF heating experiments were conducted at 300 MHz and 500 MHz to characterize the applicator performance and validate the simulations. Results: The feasibility of thermal MR was demonstrated at 7.0 T. The temperature could be increased by ~11 °C in 3 min in the center of a head sized phantom. Modification of the RF phases allowed steering of a temperature hotspot to a deliberately selected location. RF heating was monitored using the integrated system for MR thermometry and high spatial resolution MRI. EMF and thermal simulations demonstrated that local RF hyperthermia using the integrated system is feasible to reach a maximum temperature in the center of the human brain of 46.8 °C after 3 min of RF heating while surface temperatures stayed below 41 °C. Using higher RF frequencies reduces the size of the temperature hotspot significantly. Conclusion: The opportunities and capabilities of thermal magnetic resonance for RF hyperthermia interventions of intracranial lesions are intriguing. Employing such systems as an alternative additive treatment for glioblastoma multiforme might be able to improve local control by "fighting fire with fire". Interventions are not limited to the human brain and might include temperature driven targeted drug and MR contrast agent delivery and help to understand temperature dependent bio- and physiological processes in-vivo