Ultra-Wideband Antenna Design for GPR Applications: A Review <s> R w S <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> R w S <s> A compact double-ridged horn antenna for ground penetrating radar applications in the frequency range of 1–7 GHz will be presented in this work. Within this contribution the design, simulation and fabrication of such an antenna will be considered. Among the varying design parameters are linear and exponentially tapered walls as well as variations of the curvature of the dielectric waveguide between the two ridges. In addition an absorber structure and a complex shaped metallic back plate have been introduced to further improve the return loss. The primary design goal is a broad bandwidth while maintaining compact dimensions. Two modifications have been introduced in this antenna design in contrast to the standard TEM horn. By protruding the ridges from the aperture plane and filling the space between the ridges with dielectric material it is possible to lower the operating frequency without increasing the size of the original setup. The proposed design has been applied to subsurface radar application in both, field simulations by means of CST Microwave Studio and measurement in a GPR test scenario. The fabricated antenna has been verified by anechoic chamber measurements. The performance of the antenna with respect to the detection of subsurface objects will be verified by various experiments. <s> BIB002 </s> Ultra-Wideband Antenna Design for GPR Applications: A Review <s> R w S <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> BIB003 </s> Ultra-Wideband Antenna Design for GPR Applications: A Review <s> R w S <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> BIB004 </s> Ultra-Wideband Antenna Design for GPR Applications: A Review <s> R w S <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> BIB005 </s> Ultra-Wideband Antenna Design for GPR Applications: A Review <s> R w S <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> BIB006 </s> Ultra-Wideband Antenna Design for GPR Applications: A Review <s> R w S <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> BIB007
Where S is a dimensionless quantity, w is the distance between the horn apertures, R is the length of aperture and λ is the wavelength. A double ridged horn (DRH) antenna is presented in BIB002 . The antenna has a wider bandwidth and is proposed for GPR applications. The reduction in operating frequency will compromise the size of the antenna. Thus, in order to achieve a small size but with lower operating frequency, the ridges have been extended from the aperture plane and the gap is filled with dielectric material. In BIB001 , another DRH antenna is also designed to increase the bandwidth. An UWB quad ridged horn (QRH) antenna is proposed in GPR application for deep penetration by modifying a conventional triangular transverse electromagnetic (TEM) horn BIB005 . First modification is performed by tapering the horn plates with a curvature and the second modification is the addition of double ridges in between the horn aperture BIB002 . A substrate with a high dielectric constant is used to fill the gap. The substrate used is the Rogers RT-3010 with Ԑr of 10.2. The fabricated antenna is then compared with the SH-68 Satimo horn antenna that is commercially available. There are some reflections and ringing effects in the conventional TEM horn antenna that are not suitable in GPR application. Therefore, an optimized design of TEM horn antenna for UWB is proposed BIB003 . The antenna is designed by carving an arc in the two exponentially tapered plates of horn and perpendicular plates are connected at the lower end. In BIB004 , another TEM horn with a flare shape is designed with a balun for proper current balancing. The design consists of two flaring conductors constructed by cutting a brass sheet for the top and bottom flare and combined together with a triangular slab from Styrofoam to secure the conductor in a flare. The antenna is experimentally tested with a concrete to observe the gain when in contact with other materials. In BIB007 , an UWB horn antenna consists of a coaxial feed line and a proper waveguide with a round and tapered-shaped aperture. The antenna is designed by using the D-angle and Wangle methods for the waveguide. The aperture has rounded corners to improve the performance. Various feeding techniques are also discussed in BIB006 other than proposing a new feeding technique. In order to realize the new technique, the waveguide of the antenna is fixed and a screw is added on the opposite side of the feeder to increase the gain.