Ultra-Wideband Antenna Design for GPR Applications: A Review <s> INTRODUCTION <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> INTRODUCTION <s> This paper presents the design and optimization of ultra-wideband (UWB) transverse electromagnetic (TEM) horn antennas for ground penetrating radar (GPR) applications. The numerical simulations of electromagnetic wave propagation are performed in the time domain for a preliminary and modified TEM horn antenna. The TEM horn antennas have some reflections and ringing which are not suitable for GPR applications. These effects are reduced by optimization of the antenna structure. The time domain characteristic and voltage standing wave ratio (VSWR) of the antennas are computed. The optimized TEM horn antenna is then modeled with the typical GPR environment with earth, and the hidden object inside the earth. The presented antenna can be used in the GPR systems to detect and image buried objects, and for the characterization of the non-homogeneous layered structure. <s> BIB002 </s> Ultra-Wideband Antenna Design for GPR Applications: A Review <s> INTRODUCTION <s> A novel compact double exponentially tapered slot antenna (DETSA) for GPR applications is presented. To extend the antenna's impedance bandwidth, the antenna arms are rolled back and lengthened, and lumped resistors are used near the ends of the rolled arms. An improved coplanar waveguide (CPW) to coupled stripline (CPS) transition for feeding is also investigated. The measured transmission loss of two back-to-back CPW-to-CPS transitions is less than 2.6 dB in the frequency band of 200 MHz-6 GHz, which agrees well with the simulated result. The measured S11 of the antenna in frequency domain is less than -10 dB in the band of 220 MHz-6 GHz, and it is also verified that the resistors mainly have influence on the antenna's S11 below 1 GHz. The measured reflected pulses show that there are only two reflecting points, and the reflection is weak. The simulated and measured antenna gains at boresight show little variations with loading resistors of different values, and this means that the resistive loadings do not affect the gain characteristics of the antenna. The antenna's transmission re- sponse in time domain is also tested, and its application in GPR detection of a buried target is validated by experiments. <s> BIB003 </s> Ultra-Wideband Antenna Design for GPR Applications: A Review <s> INTRODUCTION <s> In this letter, an ultra-wideband (UWB) bandpasss filter with multiple notch bands is presented. The UWB bandpass characteristic is achieved using a modified distributed highpass filter (HPF) and suppressing higher order harmonics of the HPF by realizing defected stepped impedance resonator. The dual band notches at 5.75 and 8.05 GHz are obtained by embedding two open stubs on the main microstrip line. The in band and out of band performance obtained from fullwave electromagnetic simulation, equivalent circuit model and measurement are in good agreement. <s> BIB004 </s> Ultra-Wideband Antenna Design for GPR Applications: A Review <s> INTRODUCTION <s> A novel microstrip ultra-wideband (UWB) differential filter with narrow notched band based on the transversal signal- interference concept is presented. In order to enhance the interference immunity from undesired signals efficiently, the notched band is implemented by coupling with quarter wavelength shorted-line at input and output ports. By taking advantage of the bandgap characteristic of defected ground structure (DGS), a slot-line DGS is used for improving the common-mode rejection. In this work, at the center frequency of the notched band which is 2.45 GHz, about 7.3% bandwidth (2.35-2.53 GHz) is realized by full-wave simulator. Agreement between experiment and simulation is observed. <s> BIB005 </s> Ultra-Wideband Antenna Design for GPR Applications: A Review <s> INTRODUCTION <s> In this paper we demonstrate the gain enhancement of a semicircular slot antenna using a multilayer frequency-selective surface (FSS). A theoretical analysis of the FSS with a UWB semicircular slot antenna is presented. The multilayer FSS provides an appropriate reflection phase to act as a reflector and is able to enhance the gain of the slot antenna. Simulations show a linear phase response from 3.5 GHz to 12 GHz that is sufficient for ultra wideband operation. A significant improvement of 3 to 4 dB gain over the whole frequency range is demonstrated. The composite antenna has a theoretical gain of 8 dBi and a very small maximum gain variation of ±1.5 dB over the 3.5 to 10 GHz frequency range. Its compact configuration provides flexibility for mounting the reflector close to the slot antenna and makes it more suitable for modern UWB devices. <s> BIB006 </s> Ultra-Wideband Antenna Design for GPR Applications: A Review <s> INTRODUCTION <s> In this article, the design of a ultra-wideband (UWB) monopole antenna with coplanar-waveguide (CPW)-coupled-fed is presented. The antenna is composed of a trapezium patch with a CPW-fed printed on one side of the substrate and an elliptical radiator on the other side. By simply cutting slits on the radiation patch, a single, dual, and triple band notched characteristics can be achieved. Parametric studies on the antenna and slits are carried out by computer simulation. Results show that the notch frequencies can be set by using dimensions of the slits. The antennas are designed and optimized using computer simulation. For verification, the antennas with single and dual band-notched characteristics are fabricated and measured. The simulated and measured results on the return loss, radiation pattern, peak gain, and efficiency of the antenna are presented. Due to the small ground-plane size of the antenna, the feeding cable used in the measurement equipment significantly affects the measured results and leads to large discrepancies between the simulated and measured results at low frequencies. To study this, the simulation model of the feeding cable is also used in simulation and results show that the discrepancies are substantially reduced. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:1017–1027, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27530 <s> BIB007 </s> Ultra-Wideband Antenna Design for GPR Applications: A Review <s> INTRODUCTION <s> Novel planar Vivaldi antenna with better performance compared to conventional TEM horn antenna is introduced. An exponential tapered slot edge (TSE) structure is employed. Electromagnetic band gap structure as seven pair of loop or square shaped defected ground structure is added to the ground antenna plane. The proposed shape has the advantage of extending the low-end bandwidth limit due to improving the antenna matching especially at low frequency and reduced the electrical length of the antenna by 45% compared to the original antenna size. <s> BIB008 </s> Ultra-Wideband Antenna Design for GPR Applications: A Review <s> INTRODUCTION <s> Ultra-Wide Band (UWB) technology in Ground Penetrating Radar (GPR) imaging has been an interested research topic for the last couple of decades. Although there have been a lot of work and research conducted on this subject, there c still interested research matters that has to be studied. UWB directional antennas are one of the critical components for UWB-GPR applications. The parameters of the antennas that are used within the system affect the performance of the application. The horn antenna; for example, can give the focusing ability needed in some applications thanks to its high directivity feature. Although there are many parameters that affect the design of a Horn antenna, aperture size and the feeder type are commonly used parameters to obtain wider frequency operation. In this study, the effect of different feeding structures on frequency bandwidth for a fixed waveguide dimensions are investigated and the results are shared. For this purpose, various feeding structures that are straight wire feeder, spherical feeder, cylindrical feeder and conical feeder are examined and the simulated and the measured bandwidth results are presented. Furthermore, we propose a new feeder type that provides better simulation results in terms of bandwidth is introduced. With this new structure, the horn antenna is optimized using an antenna simulation software; CST-Microwave Studio and the corresponding produced antenna is measured to complete the design. <s> BIB009 </s> Ultra-Wideband Antenna Design for GPR Applications: A Review <s> INTRODUCTION <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> BIB010 </s> Ultra-Wideband Antenna Design for GPR Applications: A Review <s> INTRODUCTION <s> A compact quad-ridged horn antenna (QRH) for the deep ground penetrating radar water detection applications is designed operate in frequency range of 50MHz to 500MHz. Within this contribution the design and simulation of such an antenna is considered for water level detection in Egyptian dessert aquifers. Among the varying horn design parameters, the linear and exponentially tapered walls are studied as well as variations of the curvature of the dielectric waveguide between the two ridges enhancing the matching conditions hence, reducing size and increasing the antenna operational bandwidth. The design goal is to achieve broad bandwidth antenna with maintaining compact dimensions. Two modifications have been introduced on the conventional triangular TEM horn antenna. First multifunction tapering of the horn plates with curvature ending, second inserting perturbing two different ridges between the aperture planes and filling the space between the ridges with high dielectric constant material, in order to lower the operating frequency without increasing the size of the original setup. Replacing the two ridges with four ones, each pair is perpendicular to the other, reduces more the antenna size and improves more its matching. The antenna dimensions are 145 × 102 × 124 cm ::: 3 ::: that resembles improvement in size as compared with similar commercial GPR horn antennas as Satimo Horn model SH 68 with dimensions 2983×1615×2505 cm ::: 3 ::: . <s> BIB011 </s> Ultra-Wideband Antenna Design for GPR Applications: A Review <s> INTRODUCTION <s> Abstract We present a ground penetrating radar (GPR) system, which uses an antenna array for in situ measurements of the thickness and dielectric permittivity of an asphalt pavement layer. We calibrated the antenna array by considering the antenna phase center and the antenna offset. The results of the laboratory measurements demonstrate that the proposed calibration method can greatly improve the accuracy of the velocity and thickness estimations when compared with the conventional method. A field measurement conducted on a highway pavement shows that the error of the thickness estimation of the asphalt layer is less than 6 mm (10%). <s> BIB012 </s> Ultra-Wideband Antenna Design for GPR Applications: A Review <s> INTRODUCTION <s> This letter presents a new transverse electromagnetic flared horn antenna for the demanding requirement of an air-coupled impulse ground-penetrating radar. Structure anatomy is performed focusing on achieving good impedance matching throughout the wide frequency band. The design procedure starts with constructing an analytic model to evaluate the preliminary physical dimensions to achieve minimum reflections. Structural fine tunings are then performed for optimization. The antennas are fabricated and tested. Experimental results validate the design effectiveness. <s> BIB013
The research interest on ultra-wideband (UWB) systems has gained popularity mainly after the year 2002 when the US department of Federal Communications Commission (FCC) allocated a license-free spectrum for Industrial and Scientific purposes. This greater step of FCC has opened new doors of researches for UWB in the field of wireless communications and microwave imaging  , BIB004 . The UWB covers a frequency band ranges from 3.1 to 10.6 GHz that has foreseen the applications in the field of Wireless Local Area Networks (WLAN), Wireless Body Area Networks (WBAN), Wireless Interoperability for Microwave Access (WiMAX), Wireless Personal Area Networks (WPAN) and Ground Penetrating Radar (GPR) technology where wide bandwidth is required BIB005 , BIB007 . GPR is one of the major applications of UWB technology, which is widely used in military and civilian applications such as the detection of land-mines BIB006 . In addition, GPR is also used in remote sensing techniques such as nondestructive testing of concrete and detection of trapped people underdebris or in opaque environment BIB009 . For the implementation of UWB GPR systems, the performance of various antenna designs, such as bow-tie antenna BIB001 , BIB010 , spiral antenna BIB001 , loaded dipole antenna BIB013 , TEM horn antenna BIB002 , BIB011 , tapered slot antenna  , BIB003 and Vivaldi antenna BIB012 , BIB008 have been evaluated. This paper examines the technical and methodological aspects involved during the design of ultra-wideband antennas for ground penetrating radar detection applications. The study has been performed based on antenna gain, directivity, complexity of the design as well as the frequency bandwidth. Later the comparison of results to address the fundamentals of GPR applications, such as penetration depth and resolution has been performed. Finally one of the best suitable antenna design is chosen for further research and future directions. The organization of this paper is as follows: Section II discusses the UWB antenna designs and methodologies suitable for GPR application. Section III presents the results and analysis of the antennas discussed in the previous section. Finally, the paper is concluded in Section IV.