Ultra-Wideband Antenna Design for GPR Applications: A Review <s> A. Bow-tie Antenna <s> Presented paper describes results of comparison study on antennas for ground penetrating radar (GPR, undersurface radar) operating in frequency band from 500 MHz to 3 GHz. Typical representatives of elementary antennas, planar monopoles, dipole antennas, tapered slot antennas, TEM horns and frequency independent antennas are firstly optimized for the operation band in CST design environment. Then structures are described and compared from the impedance, radiation and time characteristic point of view to enable a simple choice of suitable structures for manufacture. Selected antennas are prepared for the manufacture and comparison with their models. <s> BIB001 </s> Ultra-Wideband Antenna Design for GPR Applications: A Review <s> A. Bow-tie Antenna <s> Chapter 1 Ultra-Wideband Antenna Arrays Chapter 2 Smart Antennas Chapter 3 Vivaldi Antenna Arrays Chapter 4 Artificial Magnetic Conductors/High Impedance Surfaces Chapter 5 Metamaterial Antennas Chapter 6 Biological Antenna Design Methods Chapter 7 Reconfigurable Antennas Chapter 8 Antennas in Medicine: Ingestible Capsule Antennas Chapter 9 Leaky-Wave Antennas Chapter 10 Plasma Antennas Chapter 11 Numerical Methods in Antenna Modeling <s> BIB002 </s> Ultra-Wideband Antenna Design for GPR Applications: A Review <s> A. Bow-tie Antenna <s> This paper presents a novel wide beam UWB antennae design for Impulse Radio-Ultra Wide Band (IR-UWB) Through-the-Wall detection radar. The design is based on a typical bowtie slot antenna structure with an added reflector in order to achieve unidirectionality and wide beam. The effects of different parameters of the added reflector on the impedance and radiation characteristics are analyzed. The different structural parameters of antenna are optimized by numerical simulations. Simulated and measured results show that the front-to-back ratio is great than 10dB and the beam width is approximately 120° ~145 ° within operation band for |S11|<-10dB (0.8GHz~2.3GHz). <s> BIB003 </s> Ultra-Wideband Antenna Design for GPR Applications: A Review <s> A. Bow-tie Antenna <s> A back-cavity shielded bow-tie antenna system working at 900MHz center frequency for ground-coupled GPR application is investigated numerically and experimentally in this paper. Bow-tie geometrical structure is modified for a compact design and back-cavity assembly. A layer of absorber is employed to overcome the back reflection by omni-directional radiation pattern of a bow-tie antenna in H-plane, thus increasing the SNR and improve the isolation between T and R antennas as well. The designed antenna system is applied to a prototype GPR system. Tested data shows that the back-cavity shielded antenna works satisfactorily in the 900MHz GPR system. <s> BIB004 </s> Ultra-Wideband Antenna Design for GPR Applications: A Review <s> A. Bow-tie Antenna <s> DESIGN OF A BALUN FOR A BOW TIE ANTENNA INRECONFIGURABLE GROUND PENETRATING RADARSYSTEMSR. PersicoIstituto per il Beni Archeologici e MonumentaliConsiglio Nazionale delle RicercheVia Monteroni, Campus Universitario, Lecce 73100, ItalyN. RomanoDipartimento di Ingegneria dell’InformazioneSeconda Universitµa degli studi di NapoliVia Roma 29, Aversa 81031, ItalyF. SoldovieriIstituto per il Rilevamento Elettromagnetico dell’AmbienteConsiglio Nazionale delle RicercheVia Diocleziano 328, Napoli 80124, ItalyAbstract|This paper deals with the design of a reconﬂgurableantenna that resembles a monolithic UWB bow-tie antenna for GroundPenetrating Radar (GPR) applications. In particular, the attentionis focussed on the design of the balun system able to work in thefrequency band 0.3{1GHz; the eﬁectiveness of the design is shown byexamining the behaviour of the scattering parameters <s> BIB005 </s> Ultra-Wideband Antenna Design for GPR Applications: A Review <s> A. Bow-tie Antenna <s> For the non-destructive sounding of the sub-surface for a large range of applications, a coplanar waveguide-fed bowtie slot antenna operating in a wide frequency band [0.4;1.5] GHz has been designed. The main originality of our work is the extension of the operating frequency band of the uniplanar bowtie slot antenna to frequencies lower than 800 MHz. The shape and the dimensions of the antenna have been optimised in the presence of a soil using numerical simulations based on the finite difference time domain approach. For the characterisation of the sub-surface, a transmission link comprising a pair of bowtie slot antennas that are moved along the soil surface has been studied in details to obtain the system performance in the frequency and time domains. First experimental results have been obtained on a sandy soil in the frequency domain using a vector network analyser. The experimental data have been analysed and compared with simulations results. <s> BIB006 </s> Ultra-Wideband Antenna Design for GPR Applications: A Review <s> A. Bow-tie Antenna <s> The ground penetrating radar (GPR) designs demand antennas with ultra wide bandwidths (UWB). Thus the conventional antennas such as dipoles cannot be used effectively. The GPR antennas are expensive. In this paper, the feasibility of building a low cost ultra-wide band bow-tie antenna for GPR using widely available low cost materials such as FR-4 PCB substrates, low cost TV baluns and scrap iron is explored. The objective was to develop the antenna to radiate in the range from 200 MHz to 600 MHz whilst restricting the antenna lobes to the direction of the ground. A cavity backed design is considered to obtain these requirements. The antenna was modeled using Ansoft HFSS (presently Ansys HFSS) software package which is widely used in current industrial domain. The simulations were carried out for different antenna configurations by changing its parameters according to linear programming techniques. Further, electromagnetic interferences (EMI) have been successfully reduced by integrating a metal cavity which acts as a reflector to the antenna. Parameters related to the cavity were tweaked in order to obtain the optimum frequency response. Considering the simulation results the most satisfactory antenna configuration was obtained and implemented. <s> BIB007 </s> Ultra-Wideband Antenna Design for GPR Applications: A Review <s> A. Bow-tie Antenna <s> A new resistively loaded bow-tie antenna which can operate from 300 MHz to more than 3 GHz bandwidth is proposed. The proposed antenna employs a metamaterial lens to improve the forward gain and front-to-back ratio. The antenna radiates pulses with minimal late-time ringing and high peak amplitude. A stable radiation pattern obtained from 300 MHz to 2 GHz, makes it suitable for time domain as well as stepped frequency continuous wave (SFCW) GPR applications. The antenna is characterized by measurements of return loss, transmission scattering parameter, radiation pattern, gain, front-to-back ratio, and GPR B-scan with object buried under soil. The measured results are in good agreement with the simulation results. <s> BIB008 </s> Ultra-Wideband Antenna Design for GPR Applications: A Review <s> A. Bow-tie Antenna <s> Ultrawideband (UWB) antenna is one critical part of the impulse radar system. In this paper, a shallow Vee-cavity shielded planar dipole antenna working at the center frequency of 400 MHz for UWB vital sign detection radar is investigated numerically and experimentally. It consists of two half-ellipse-shape arms tuned with four semicircular slots and a shallow Vee-cavity. The voltage standing wave ratio (VSWR), input impedance, and radiation waveforms are all analyzed. The resistive and slot loading techniques for improving impulse radiation and reducing late-time ringing are adopted. Several important parameters of the designed antenna have been studied. The influence of a shallow rectangular cavity and the proposed Vee-cavity on the antenna characteristics is also under consideration. Finally, one prototype antenna is fabricated and applied to UWB vital sign detection radar system. The experimental results indicate that the proposed half-ellipse antenna with a Vee-cavity works satisfactorily in the radar system. <s> BIB009 </s> Ultra-Wideband Antenna Design for GPR Applications: A Review <s> A. Bow-tie Antenna <s> The efficiency of the ground penetrating radar (GPR) system significantly depends on the antenna performance as signal has to propagate through lossy and inhomogeneous media. In this research work a resistively loaded compact Bow-tie antenna which can operate through a wide bandwidth of 4.1 GHz is proposed. The sharp corners of the slot antenna are rounded so as to minimize the end-fire reflections. The proposed antenna employs a resistive loading technique through a thin sheet of graphite to attain the ultra-wide bandwidth. The simulated results obtained from CST Microwave Studio v14 and HFSS v14 show a good amount of agreement for the antenna performance parameters. The proposed antenna has potential to apply for the GPR applications as it provides improved radiation efficiency, enhanced bandwidth, gain, directivity and reduced end-fire reflections. <s> BIB010
A bow-tie UWB antenna is widely used in the design for GPR applications, as it has the ability to reduce ground susceptibility during GPR operations BIB002 . Fig. 1 shows a simple bow-tie antenna design which consists of two flares connected to a common feed. The length, l and width, w of the flares in bow-tie structure can be determined by (1) and (2) BIB002 BIB005 BIB003 BIB004 : Where λo is the wavelength of the low frequency range in free space. The flare angle is totally dependent on impedance BIB004 . In BIB005 , a monolithic bow-tie UWB antenna for GPR applications is designed by using a total geometric morphing approach with small pads to form an array. The antenna has been fabricated on a glass epoxy FR-4 substrate with a dielectric constant value, Ԑr of 20 and it is fed by a coaxial cable for impedance matching to the balanced current balun. A slot and reflector have been introduced into the antenna structure to achieve a wide beam width and unidirectional radiation pattern BIB003 . The antenna is fed by a coplanar waveguide (CPW). Furthermore, a modified bow-tie antenna with a shielded back cavity for omnidirectional radiation pattern is also proposed for GPR application BIB004 . The antenna is fabricated on a FR-4 substrate with a dielectric constant, Ԑr of 4.6 and centered at 900 MHz. The edge of the antenna is cut to make the antenna to be more compact and study the effect of edges on reflection coefficient. As the research progresses, new designs have been developed with modifications in the shapes and dimensions of the bow-tie antenna. In addition, one of the antennas has been designed by using the finite difference time domain approach BIB006 . CPW is used as the feeding method while metal stubs is introduced for impedance matching. The work in BIB001 introduces the structure of a bow-tie antenna into its dipole antenna to improve the gain for GPR. The ideal performance of a bow-tie dipole antenna can be achieved by feeding the antenna with 100-200 ohm impedance. In BIB008 , a resistive-loaded UWB bowtie antenna is proposed to improve the forward gain from the employment of metamaterial lens. As the signal of the GPR system required propagating through inhomogeneous media, the efficiency of the antenna must also be taken into account. Thus, in order to enhance the efficiency, a compact shape slotted bow-tie antenna is designed BIB010 . The compactness in the shape of antenna is achieved by rounding the sharp corners of the bow-tie structure and triangular stubs with extended arms. The antenna is fed by a CPW and a thin graphite sheet is used to reduce the end-fire reflection of the UWB antenna for GPR application. In  , an elliptical shape of bow-tie antenna is proposed to broaden the bandwidth. A semicircular slotted-tuned halfellipse antenna in a bow-tie formation is designed in BIB009 . The proposed antenna has four semicircular slots in the bow-tie ellipse to further improve its penetration properties for vital signs detection. A low cost UWB bow-tie antenna for GPR is presented in BIB007 . A reflector cavity design technique is used where the model is initially tested with only a bottom reflector followed by a side reflector and both reflectors at the same time. There is also a gap between both flares of the bow-tie where a balun is deployed to match the impedance. Finally, the antenna is equipped with a four-sided reflector to study the gain parameters.