⋅A p-adaptive discontinuous Galerkin time-domain method is developed to obtain high-order solutions to electromagnetic scattering problems. A novel feature of the proposed method is the use of divergence error to drive the p-adaptive method. The nature of divergence error is explored, and that it is a direct consequence of the act of discretization is established. Its relation with relative truncation error is formed which enables the use of divergence error as an inexpensive proxy to truncation error. Divergence error is used as an indicator to dynamically identify and assign spatial operators of varying accuracy to substantial regions in the computational domain. This results in a reduced computational cost compared to a comparable discontinuous Galerkin time-domain solution using uniform degree piecewise polynomial bases throughout. Numerical results are presented to show performance of the proposed divergence error based p-adaptive solutions. It is shown that an accuracy similar to that of uniformly higher order solutions is obtained in terms of the scattering width, using fewer degrees of freedom.
In this paper, we present an efficient numerical method to calculate the frequency and time responses of the field scattered by an object buried between two random rough surfaces for a 2-D problem. This method is called Generalized PILE (GPILE) method because it extends the PILE method which considers only two surfaces or an object buried under a surface. The GPILE method solves the Maxwell equations rigourously by using a simple matrix formulation. The obtained results have a straightforward physical interpretation and allow us to investigate the influence of the object buried between the two rough surfaces. We distinguish the primary echo of the upper surface, the multiple echoes coming from the lower surface and those arising from the object. The GPILE method is applied to simulate the Ground Penetrating Radar (GPR) signal at nadir. The resulting time response helps the user to detect the presence of the object buried between the two random rough surfaces.
Metamaterials are artificially configured composite materials exhibiting unique characteristics such as negative effective permittivity and permeability. Due to these distinctive characteristics, metamaterials have drawn special attention in designing novel antenna structures and improving antenna performances. The application of metamaterial in antenna technology significantly brings miniaturization to the antenna structure, enhances the impedance bandwidth, gain, and efficiency of the antenna as well as improves isolation between the MIMO antenna elements. The substrate integrated waveguide (SIW) reduces the conductor and dielectric loss, and surface waεve excitations in the antennas. Although an overview of the performance enhancement of microstrip patch antennas under the influence of metamaterial has been incorporated in this article, the authors have put more effort in presenting a detailed study on working mechanism of metamaterial-based SIW antennas. Thus, a detailed review of the novel designs of metamaterial-inspired SIW cavity-backed slot antennas (CBSA), leaky-wave antennas (LWA), aperture antennas, and H-plane horn antennas has been included. The theoretical background of the metamaterials characteristics has been presented. Moreover, the working principles of metamaterial-based SIW CBSAs, SIW LWAs, SIW aperture antennas, and SIW H-plane horn antennas have been thoroughly outlined in obtaining antenna miniaturization, gain enhancement, beam steering through frequency scanning, polarization flexibility, bandwidth broadening, and isolation improvement. Besides this, a study has also been included in eliminating the limitations of SIW on-chip antennas such as narrow bandwidth, low gain, and efficiency by including metamaterial/metasurface in the antenna designs. Although the emphasis has been given to elaborating the attractive antenna performances, some design limitations have also been identified, and those need further investigation. This survey brings up not only the conceptual framework of the attractive characteristics of metamaterial, the design methodology of the non-resonant type metamaterial in the SIW environment, and the working principles of metamaterial-inspired SIW antennas but also the design limitations. Thus, consideration can be given to this article as the potential design guidelines of the metamaterial-based SIW antennas, and possible ideas can be obtained for doing further advanced research on the identified research gaps.
Low-Radar Cross Section antennas attract substantial attention in Stealth Technology. The Radar Cross Section reduction performance of the microstrip antennas should be improved since they contribute to the overall Radar Cross Section. A novel microstrip patch antenna with a polarization converter metasurface is proposed to extend the Radar Cross Section (RCS) reduction bandwidth. The metasurface uses metallic strip structures to obtain the required polarization conversion for Radar Cross Section reduction. The proposed patch antenna shows the overall RCS reduction bandwidth of 7.25 GHz-24.83 GHz (110%) as compared to the metal sheet and the Reference Patch antenna. 10 dB RCS reduction is obtained from 8.33 GHz-9.16 GHz (9.49%) and from 12.81 GHz-18.85 GHz (38.16%) as compared with the Reference Patch antenna. The RCS reduction of the antenna and the antenna radiation patterns are verified by numerical simulations and experimental observations. The main novelty of the proposed design is its wideband RCS reduction for Transverse Electric as well as Transverse Magnetic polarization with enhancement in antenna radiation pattern parameters. Significant RCS reduction can also be obtained for oblique incidence.
With the supersonic growth of mobile data demand, the fifth generation (5G) mobile network would exploit the extensive amount of spectrum in the millimeter-wave (mm-Wave) bands to tremendously increase communication capacity. There are conceptual differences between mm-Wave communications and other existing communication systems, in terms of high propagation loss, directivity, and sensitivity to blockage. These characteristics of mm-Wave communications present several challenges to completely exploit the potential of mm-Wave communications, including integrated circuits and system design, interference management, spatial reuse, anti-blockage, and dynamics control. 5G mobile communication systems with sub-6 GHz and millimeter-wave bands are already replacing 4G and 4.5G systems as an evolution towards higher-speed mobile communication and wider bandwidth. From the hardware perspective, the 5G-band causes the miniaturization of RF components including the antennas. In this article, an overview of recent research is presented that discusses design challenges and measurement considerations for various types of compact 5G antennas.
Compact antenna with good performance characteristics is always preferred for small IoT (Internet of Things) sensor nodes. The novelty of this proposed work is not in terms of design but in terms of application as Log-Periodic antennas has been so far used for UHF/VHF (Ultra High Frequency/Very High Frequency) and TV reception applications, and in this paper, the advantages of Log-Periodic structure have been exploited for IoT applications. This antenna design consists of two Log-Periodic like structured radiating elements on an FR4 substrate of 1.6\,mm thickness. The compact antenna of size of 15 mm×17 mm covers a bandwidth ranging from 2.01 GHz to 4.04 GHz including the WiMAX (2.3 GHz-2.4 GHz, 2.5 GHz-2.7 GHz and 3.4 GHz-3.6 GHz) and WLAN (2.4 GHz and 3.6 GHz) frequency bands. This system employs Defected Ground Structure (DGS) technique to obtain the required range of bandwidth of operation, for improving the isolation and obtaining mutual coupling suppression between the two individual elements. This miniaturized cheap antenna has a very low ECC (Envelope Correlation Coefficient) value and all other MIMO (Multiple Input Multiple Output) parameters in acceptable range. The isolation obtained over the entire range of operation is below -30 dB, and the performance efficiency is as good as 92.8% with a maximum gain of 2.9 dB. The simulated and measured results of the antenna system are also found to be in good agreement. The MIMO system can be considered as a good candidate for medium range IoT applications for its small size and good performance.
This paper reports a novel, cost effective, and compact ultra-wideband (UWB) antenna for applications in an unlicensed-frequency band of 3.1-10.6 GHz. To achieve the UWB operation, a novel concept of annular shapes, circular slot combinations, and partial ground is employed. Furthermore, the proposed antenna with novel configuration occupies an attractive size of only 18×12 mm2 which allows compatibility with portable UWB application devices. This flower-horn shaped UWB antenna is printed on a cost-effective FR-4 substrate, which exhibits a dielectric-constant of 4.4 and a loss-tangent of 0.019. The fabricated prototype is experimentally tested, and measured results validate the design approach of presented UWB antenna. The measured results confirm its UWB characteristics covering 3.1-11.2 GHz with S11 ≤ -10 dB. Also, a maximum peak-gain of 5.05 dBi at 9 GHz and a minimum radiation-efficiency of 94.35% are noted in the full operating-band. A good agreement has been obtained between the simulated and measured results in terms of reflection-coefficient, gain, radiation-efficiency, radiation patterns and group delay which confirm the suitability of suggested small printed antenna for the intended UWB applications.