Antenna Theory And Design

Science and technologies based on terahertz frequency electromagnetic radiation (100 GHz–30 THz) have developed rapidly over the last 30 years. For most of the 20th Century, terahertz radiation, then referred to as sub-millimeter wave or far-infrared radiation, was mainly utilized by astronomers and some spectroscopists. Following the development of laser based terahertz time-domain spectroscopy in the 1980s and 1990s the field of THz science and technology expanded rapidly, to the extent that it now touches many areas from fundamental science to 'real world' applications. For example THz radiation is being used to optimize materials for new solar cells, and may also be a key technology for the next generation of airport security scanners. While the field was emerging it was possible to keep track of all new developments, however now the field has grown so much that it is increasingly difficult to follow the diverse range of new discoveries and applications that are appearing. At this point in time, when the field of THz science and technology is moving from an emerging to a more established and interdisciplinary field, it is apt to present a roadmap to help identify the breadth and future directions of the field. The aim of this roadmap is to present a snapshot of the present state of THz science and technology in 2017, and provide an opinion on the challenges and opportunities that the future holds. To be able to achieve this aim, we have invited a group of international experts to write 18 sections that cover most of the key areas of THz science and technology. We hope that The 2017 Roadmap on THz science and technology will prove to be a useful resource by providing a wide ranging introduction to the capabilities of THz radiation for those outside or just entering the field as well as providing perspective and breadth for those who are well established. We also feel that this review should serve as a useful guide for government and funding agencies.

The 2016 terahertz science and technology roadmap

Before the emergence of ultra-wideband (UWB) radios, widely used wireless communications were based on sinusoidal carriers, and impulse technologies were employed only in specific applications (e.g. radar). In 2002, the Federal Communication Commission (FCC) allowed unlicensed operation between 3.1–10.6 GHz for UWB communication, using a wideband signal format with a low EIRP level (−41.3dBm/MHz). UWB communication systems then emerged as an alternative to narrowband systems and significant effort in this area has been invested at the regulatory, commercial, and research levels.

IEEE Transactions on Microwave Theory and Techniques and Antennas and Propagation Announce a Joint Special Issue on Ultra-Wideband (UWB) Technology

https://calhoun.nps.edu/bitstream/10945/24839/1/singlesidebandtr00elli.pdf

Single sideband transmission by envelope elimination and restoration.

Computational Methods

A novel higher order finite-element technique based on generalized curvilinear hexahedra with hierarchical curl-conforming polynomial vector basis functions is proposed for microwave modeling. The finite elements are implemented for geometrical orders from 1 to 4 and field-approximation orders from 1 to 10 in the same Galerkin-type finite-element method and applied to eigenvalue analysis of arbitrary electromagnetic cavities. Individual curved hexahedra in the model can be as large as approximately 2/spl lambda//spl times/2/spl lambda//spl times/2/spl lambda/, which is 20 times the traditional low-order modeling discretization limit of /spl lambda//10 in each dimension. The examples show excellent flexibility and efficiency of the higher order (more precisely, low-to-high order) method at modeling of both field variation and geometrical curvature, and its excellent properties in the context of p-refinement of solutions, for models with both flat and curved surfaces. The reduction in the number of unknowns is by an order of magnitude when compared to low-order solutions.

https://www.engr.colostate.edu/~notaros/Papers/T-MTT_Mar_2003.pdf

Higher order hierarchical curved hexahedral vector finite elements for electromagnetic modeling

We have observed that the size and shape of the ground conductor of axial mode helical antennas have significant impact on the antenna gain. By shaping the ground conductor, we have increased the gain of a helical antenna for as much as 4 dB. Theoretical results are verified by measurements.

Enhancing the gain of helical antennas by shaping the ground conductor

A novel higher order large-domain hybrid computational electromagnetic technique based on the finite element method (FEM) and method of moments (MoM) is proposed for three-dimensional analysis of antennas and scatterers in the frequency domain. The geometry of the structure is modeled using generalized curved parametric hexahedral and quadrilateral elements of arbitrary geometrical orders. The fields and currents on elements are modeled using curl- and divergence-conforming hierarchical polynomial vector basis functions of arbitrary approximation orders, and the Galerkin method is used for testing. The elements can be as large as about two wavelengths in each dimension. As multiple MoM objects are possible in a global exterior region, the MoM part provides much greater modeling versatility and potential for applications, especially in antenna problems, than just as a boundary-integral closure to the FEM part. The examples demonstrate excellent accuracy, convergence, efficiency, and versatility of the new FEM-MoM technique, and very effective large-domain meshes that consist of a very small number of large flat and curved FEM and MoM elements, with p-refined field and current distributions of high approximation orders. The reduction in the number of unknowns is by two orders of magnitude when compared to available data for low-order FEM-MoM modeling.

Higher Order Hybrid FEM-MoM Technique for Analysis of Antennas and Scatterers

Helical antennas have been known for more than half a century, but it seems that reliable design data for helical antennas do not exist in the open literature. This paper points out some inaccurate data about helical antennas, and presents a new set of data related to the optimum design of helical antennas. The antenna's performance is optimized by varying the antenna's geometrical parameters for narrowband and broadband designs. Based on these results, a set of diagrams is provided to enable simple but accurate design of helical antennas above an infinite ground plane. Finally, the results are experimentally verified

Optimization of Helical antennas [Antenna Designer's Notebook]

An efficient and accurate large-domain higher order two-dimensional (2-D) Galerkin-type technique based on the finite-element method (FEM) is proposed for analysis of arbitrary electromagnetic waveguides. The geometry of a waveguide cross section is approximated by a mesh of large Lagrangian generalized curvilinear quadrilateral patches of arbitrary geometrical orders (large domains). The fields over the elements are approximated by a set of hierarchical 2-D polynomial curl-conforming vector basis functions of arbitrarily high field-approximation orders. When compared to the conventional small-domain 2-D FEM techniques, the large-domain technique requires considerably fewer unknowns for the same (or higher) accuracy and offers a significantly faster convergence when the number of unknowns is increased. A comparative analysis of solutions using p- and h-refinements shows that the p-refinement represents a better choice for higher accuracy with lesser computation cost. In addition to increasing the field-approximation orders, the geometrical orders of elements (where needed) should also be set high for the improved accuracy of the solution without subdividing the elements. However, in general, an arbitrarily high accuracy cannot be achieved by performing the p-refinement in arbitrarily coarse meshes alone; instead, a combined hp-refinement should be utilized in order to obtain an optimal modeling performance.

/pdf/efficient-large-domain-2-d-fem-solution-of-arbitrary-10qypf8xre.pdf

Milan M. Ilic

Papers

Higher order hierarchical curved hexahedral vector finite elements for electromagnetic modeling

Enhancing the gain of helical antennas by shaping the ground conductor

Higher Order Hybrid FEM-MoM Technique for Analysis of Antennas and Scatterers

Optimization of Helical antennas [Antenna Designer's Notebook]

Efficient large-domain 2-D FEM solution of arbitrary waveguides using p-refinement on generalized quadrilaterals