Ultra-Wideband Antenna Design for GPR Applications: A Review <s> F. Dipole, Cone, and Spiral 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> F. Dipole, Cone, and Spiral 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> F. Dipole, Cone, and Spiral Antenna <s> In this letter, an enhanced planar elliptical dipole antenna design for ultrawideband (UWB) communication and impulse radar systems is presented. The printed-circuit-elliptical (PCE) antenna has been investigated to be an effective radiator for UWB applications. To enhance gain and return loss bandwidth of the antenna, elliptical slots are used on the dipole arms. The gain performance of the antenna has been increased by means of elliptical slots in the frequency range from 2.7 to 11 GHz. The standing wave ratio is less than 2 (SWR < 2) along 94.4% of operation bandwidth from 1.1 to 11 GHz. The radiation pattern in E- and H-plane for certain frequencies, the return loss, and the gain performance are presented with the experimental and simulation results. Moreover, the time domain analysis of the antenna is presented. The antenna introduces low-level ringing and pulse distortion. Consequently, the antenna is very useful for impulse and UWB communication systems. <s> BIB003 </s> Ultra-Wideband Antenna Design for GPR Applications: A Review <s> F. Dipole, Cone, and Spiral Antenna <s> In this letter, we demonstrate the gain enhancement of an ultrawideband (UWB) antenna, achieved using an appropriately designed multioctave dual-layer frequency selective surface (FSS) reflector. The proposed novel FSS reflects effectively in phase over a bandwidth of about 120%. Hence, significant enhancement in antenna gain has been achieved with a low-profile configuration without compromising the impedance bandwidth of the UWB antenna. The proposed FSS reflector has a low transmission coefficient and linearly decreasing phase over an ultra-wide frequency band, which is the key requirement for providing an effectively in-phase reflection at the antenna plane. The composite structure is compact, with a total height of λ/4, where λ is the free-space wavelength at the lowest operating frequency of 3 GHz. Experimental results show an impedance bandwidth of 122%. The antenna gain is maintained around 7.5 dBi from 3 to 7 GHz. Between 7-14 GHz, the antenna is more directive with a gain of about 9 dBi with ±0.5 dB variation. Experimental measurements con firm the predicted wideband antenna performance and gain enhancement due to the FSS reflector. <s> BIB004 </s> Ultra-Wideband Antenna Design for GPR Applications: A Review <s> F. Dipole, Cone, and Spiral Antenna <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> BIB005 </s> Ultra-Wideband Antenna Design for GPR Applications: A Review <s> F. Dipole, Cone, and Spiral Antenna <s> We propose a design for the specific class of trans- verse electromagnetic (TEM) horn that can effectively radiate the electromagnetic signals into soil or concrete. The designed horn antenna has the same aperture height and width, resulting in a square-shaped horn aperture. A design guideline for the horn that considers return loss and radiation performance is described in this paper. The proposed TEM horn is constructed and measured to validate the design. The constructed horn has a maximum dimension (including the balun) of 42.9 × 26.8 × 20 cm. Simulated and measured results suggest that the proposed horn is more effective in radiating electromagnetic energy into concrete, compared with existing TEM horn designs. For free space radiation, measured operating bandwidth of the horn is 0.75-12.0 GHz, with a gain of 3-13 dBi. When radiated into a concrete block, measured operating bandwidth of the horn is 1.0-12.0 GHz. <s> BIB006 </s> Ultra-Wideband Antenna Design for GPR Applications: A Review <s> F. Dipole, Cone, and Spiral Antenna <s> A new magneto-electric dipole antenna with a unidirectional radiation pattern is proposed. A novel differential feeding structure is designed to provide an ultra-wideband impedance matching. A stable gain of 8.25±1.05 dBi is realized by introducing two slots in the magneto-electric dipole and using a rectangular box-shaped reflector, instead of a planar reflector. The antenna can achieve an impedance bandwidth of 114% for SWR ≤ 2 from 2.95 to 10.73 GHz. Radiation patterns with low cross polarization, low back radiation, fixing broadside direction mainbeam and symmetrical E- and H -plane patterns are obtained over the operating frequency range. Moreover, the correlation factor between the transmitting antenna input signal and the receiving antenna output signal is calculated for evaluating the time-domain characteristic. The proposed antenna, which is small in size, can be constructed easily by using PCB fabrication technique. <s> BIB007 </s> Ultra-Wideband Antenna Design for GPR Applications: A Review <s> F. Dipole, Cone, and Spiral 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> BIB008 </s> Ultra-Wideband Antenna Design for GPR Applications: A Review <s> F. Dipole, Cone, and Spiral Antenna <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> BIB009 </s> Ultra-Wideband Antenna Design for GPR Applications: A Review <s> F. Dipole, Cone, and Spiral Antenna <s> A printed planar antenna having a compact dimension of 27×23.5 mm2, fed by a microstrip line is proposed in this article. The proposed compact antenna consists of a circular disc radiator and partial ground plane with a rectangular slot on its' top edge. Experimental results show that the antenna has an ?10 dB impedance bandwidth ranges from 3.3 GHz to 20 GHz (193%) which almost covers the entire UWB band. A symmetric and stable radiation pattern with an average realized gain of 5.11 dBi makes the proposed antenna suitable for using in different UWB applications. Details of the proposed antenna design are presented and discussed. <s> BIB010 </s> Ultra-Wideband Antenna Design for GPR Applications: A Review <s> F. Dipole, Cone, and Spiral Antenna <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> BIB011 </s> Ultra-Wideband Antenna Design for GPR Applications: A Review <s> F. Dipole, Cone, and Spiral Antenna <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> BIB012 </s> Ultra-Wideband Antenna Design for GPR Applications: A Review <s> F. Dipole, Cone, and Spiral Antenna <s> A CPW-feed prototype slot antenna for ultra-wideband applications is proposed. The slot is made by etching on the ground plane, the union of two elliptical structures placed at right angles. The fractal shape antenna is excited by two stepped CPW feed. To enhance the gain, a compact ultra-wideband frequency selective surface (FSS) structure is designed and implemented. The measured impedance bandwidth of antenna with and without FSS is nearly same and equal to 9.0 GHz from 3.6 to 12.6 GHz. The measured peak gain varies from 3 to 5 dB without FSS and from 5 to 12.5 dB with FSS. Measured results are found in good agreement with the simulated results. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1498–1502, 2014 <s> BIB013 </s> Ultra-Wideband Antenna Design for GPR Applications: A Review <s> F. Dipole, Cone, and Spiral Antenna <s> Ultrawideband phased array antennas are an enabling technology for many ground-based and airborne communications and radar systems. This book surveys electromagnetic theory and phased array antenna theory and provides examples of ultrawideband phased array antenna technology. It describes some of the research on ultrawideband phased arrays undertaken by the authors and their colleagues at MIT Lincoln Laboratory over the last ten years. The book focuses on experimental prototype ultrawideband phased array technology developed at Lincoln Laboratory for applications in the VHF and UHF bands from approximately 100 MHz to 1 GHz, and addresses dipole, monopole, loop, and other antenna array elements. It offers examples of antennas for both airborne and ground vehicle applications. Most of the examples are developed in the context of rapid prototyping for quick assessment of communications and radar systems feasibility, with measurements and numerical electromagnetic simulation results provided for many prototype examples. The book is intended primarily for practicing antenna engineers, radar engineers, and communications engineers, and for graduate students and researchers in electrical engineering. Readers need no prior knowledge of ultrawideband antennas, although some background in electromagnetic theory, antennas, radar, and communications would be helpful. <s> BIB014 </s> Ultra-Wideband Antenna Design for GPR Applications: A Review <s> F. Dipole, Cone, and Spiral 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> BIB015
Dipole, canonical and spiral antennas are also the potential candidates for GPR applications and are discussed in this section. A dipole antenna can be constructed on either a planar structure or from a wire BIB001 . Various dipole antennas have been designed such as wired dipole, elliptical dipole and short dipole BIB014 for UWB applications. The length, L of a dipole from a simple wire can be calculated as follows BIB007 : The advantage of using a wired dipole is that it ensures high microwave power which is preferable in GPR technology BIB001 . Similarly, cone and spiral antennas are also proposed for UWB applications. To increase directivity, a radiation stub cone or disk cone  has been introduced into the antenna with a fractional bandwidth of 70-80% BIB001 . Spiral antennas are also favorable as the antennas have a balanced feed over the entire frequency band  . The arms of spiral antenna can be defined by using a polar function which is given by (14) BIB002 : BIB011 Where Ro controls the radius of the spiral as it grows exponentially, while a controls the flare rate. In BIB003 , an elliptical-shaped structure is introduced into each of the dipole's arm as shown in Fig. 6 . The proposed design is capable to improve the gain and reflection coefficient for UWB applications. The elliptical slots are used for time domain analysis. Another antenna consists of a 16-port sharedarm dipole array is proposed for radar imaging  . A magneto-electric dipole is investigated in BIB007 . In the design, a greater bandwidth is achieved by introducing two slots in the magneto-electric dipole by using a rectangular box reflector to fix the broadside direction of main beam. Other antenna designs for UWB GPR applications are constructed from the cone and spiral shapes BIB001 . A cone antenna, as shown in Fig. 7 , is an elementary antenna in 3-D structure to improve the impedance bandwidth for GPR systems. The angle of the cone is always related to the impedance, which can be calculated from (15)  : On the other hand, spiral antennas with two uniform width arms with gain are also suitable for GPR applications. Fig. 8 shows the spiral antenna. Fig. 7 . Cone antenna design BIB001 . Fig. 8 . A spiral antenna BIB001 . (IJACSA) International Journal of Advanced Computer Science and Applications, Vol. 8, No.7, 2017 397 | P a g e www.ijacsa.thesai.org III. RESULTS AND DISCUSSIONS Ultra-wideband antenna designs that are suitable for ground penetrating radar applications mainly require greater frequency bandwidth along with the parameter of high gain. Based on the above mentioned parameters, results of antenna designs discussed in Section 2 are presented for the analysis during this section. The operating frequency of the designed antenna, its percentage bandwidth and the maximum value of obtained gain over the entire UWB band are summarized in tabular form. This summarization helps us to develop a better understanding regarding antenna performance for GPR applications. The measured results for bow-tie antennas are shown in Table 1 . From these results, it can be observed that the bow-tie antenna designed by cutting edges has sufficient percentage bandwidth, which is suitable for an UWB GPR system. But there are some significant differences shown in the gain obtained for these antennas. The results of a backed cavity bow-tie antenna designed in BIB008 and bow-tie slotted antenna in BIB015 have a comparatively better gain with the value around 7 dB. But the bow-tie antenna designed using metamaterial lens has the highest gain with the value of 11.52 dB. In addition to this, these designed bow-tie antennas also have a sufficient flares length which is preferable to match the lower frequency band. Because of this reason these antennas are mainly capable of targeting the penetration depth properties for the GPR detection applications. However, the discussion about the ability of these antennas to distinguish among different detectable objects through imaging is difficult because of low resolution properties, as lower frequencies are not suitable for imaging characteristics. In a similar manner, the measured gain and bandwidth obtained for Vivaldi antenna designs are shown in Table 2 . The percentage bandwidth of all the proposed UWB antennas is sufficient to consider Vivaldi shape design for GPR applications. This is due to the fact that Vivaldi antennas offer dimensionality as well as ground optimization to achieve the desired bandwidth. The exponentially tapered slotted edge antenna designed in BIB009 has the least percentage bandwidth and the value of gain for this antenna is 8 dB, due to which this design is also considerable for GPR systems. From the table, it can be deduced that the gain of Vivaldi antennas have considerable values and also they covered the complete UWB frequency band defined from 3.1 to 10.6 GHz. The antipodal Vivaldi antenna designed in  performs better with greater bandwidth of approximately 15.9 GHz and the gain of 9.6 dB. Another antipodal antenna is also proposed in  with Ushaped slots and a mouth opening at the order of λ/4 also gives significant results with a gain of 15.2 dB and a greater bandwidth that covers UWB band. These results shown in Table 2 provides a wider opportunity for the Vivaldi shape antenna designs that makes it one of the suitable candidate for GPR applications with deep penetration and better resolution imaging. Horn antenna designs, discussed in the earlier section possess high gain value mainly because of its directional properties. Measured results of horn antennas in the form of gain and percentage bandwidth are shown in Table 3 . From the table, the performance of the antennas in terms of gain and bandwidth is analyzed and the results showed a significant increase in gain. As such, a TEM flare horn antenna designed in BIB006 can be used in a GPR system for detection as it addresses the requirements of deep wave penetration and better resolution imaging to distinguish among the detected objects due to its high gain as well as greater bandwidth compared to remaining horn designs. While other designed antennas seemed to target penetration depth as their operating bandwidth lies within the lower frequency band. The horn antenna designed in BIB012 has the least percentage of bandwidth even though its gain value is significantly higher due to which it can penetrates up to few feet under the ground. Nevertheless, a horn antenna design is still one of the best suitable candidates for GPR applications because of its highly directional properties, suitable gain, proper impedance bandwidth and less susceptibility to ground effect the performance of antenna. The results obtained from planar antenna designs are shown in Table 4 . From the given table, printed circular patch antennas with the slotted ground are designed in BIB010 , BIB004 . These antenna have sufficient gain value which is approximately 7.5 dB and also have greater bandwidth. This significant increase in the bandwidth of planar antennas can be attributed to the extra electromagnetic coupling between the ground and the radiating patch BIB010 . The performance of a circular patch antenna designed in BIB010 , makes planar antenna a suitable candidate for GPR applications. The performance of the other designed planar antennas is also considerable only for deep penetration as the bandwidth operates in lower frequencies. Tables 5 and 6 shows the results obtained from a tapered slotted antennas, dipole, spiral and cone antennas. From the results shown in Table 5 , it can be observed that the tapered slot antenna (TSA) designed in  , double exponentially tapered slot antenna (DETSA) designed in BIB005 and eye-shaped slotted antenna designed in BIB013 have comparatively high gain with greater percentage of bandwidth. The good performance of tapered slot antennas is mainly due to the coplanar properties of radiator and ground, and tapering characteristics, which is helpful in order to improve the performance of the antennas. Therefore, these tapered slot antennas have the ability to address the problem of deep penetration properties and high resolution imaging in GPR applications. From the results obtained in Table 6 , it can be observed that the magneto-electric dipole antenna designed in BIB007 has significantly high gain value over the entire operating bandwidth. This magneto-electric antenna also cover the complete UWB band which makes this antenna design as one of the suitable antenna that can be designed for GPR detection applications. From the results obtained for different types of antennas, designed specifically for GPR applications for detection purpose, it can be observed that the Vivaldi, horn and tapered slot antenna designs have significantly better performance. However, based on further comparison between these designed antennas, a tapered slot antenna is the best suitable candidate for UWB ground penetrating radar system and it has the potential to be further developed due to significant gain and greater bandwidth.