A new antenna, the planar inverted cone antenna (PICA), provides ultrawideband (UWB) performance with a radiation pattern similar to monopole disk antennas , but is smaller in size. Extensive simulations and experiments demonstrate that the PICA antenna provides more than a 10:1 impedance bandwidth (for VSWR<2) and supports a monopole type omnidirectional pattern over 4:1 bandwidth. A second version of the PICA with two circular holes changes the current flow on the metal disk and extends the high end of the operating frequency range, improving the pattern bandwidth to 7:1.

A new ultrawideband printed monopole antenna: the planar inverted cone antenna (PICA)

A high frequency solution for scattering from a thin dielectric slab is developed, based on a modification of the uniform geometrical theory of diffraction solution for a haft-plane, with the intention of developing a model for a windshield of a small private aircraft. Results of the theory are compared with experimental measurements and moment method calculations showing good agreement. Application of the solution is also addressed.

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High frequency scattering by a thin lossless dielectric slab

The method of moments (MM) represents a suitable procedure for dealing with electromagnetic scattering problems of arbitrary geometrical shape in the lower frequency range. However, with increasing frequency both computation time and memory requirement often exceed available computer capacities. Therefore a current based hybrid method combining the MM with the physical optics (PO) approximation suitable for three-dimensional perfectly conducting bodies is proposed in this paper. The hybrid formulation allows a substantial reduction of computation time and memory requirement, while the results are in reasonable agreement with those based on an application of the MM alone. Further improvement can be achieved for flat polygonal parts of the scattering body by a heuristic modification of the PO current density taking into account the effects of edges. As opposed to the physical theory of diffraction (PTD), no additional electric and magnetic line currents along the edges are necessary. >

Improved PO-MM hybrid formulation for scattering from three-dimensional perfectly conducting bodies of arbitrary shape

In this article we describe recent progress on the design, analysis and implementation of hybrid numerical-asymptotic boundary integral methods for boundary value problems for the Helmholtz equation that model time harmonic acoustic wave scattering in domains exterior to impenetrable obstacles These hybrid methods combine conventional piecewise polynomial approximations with high-frequency asymptotics to build basis functions suitable for representing the oscillatory solutions They have the potential to solve scattering problems accurately in a computation time that is (almost) independent of frequency and this has been realized for many model problems The design and analysis of this class of methods requires new results on the analysis and numerical analysis of highly oscillatory boundary integral operators and on the high-frequency asymptotics of scattering problems The implementation requires the development of appropriate quadrature rules for highly oscillatory integrals This article contains a historical account of the development of this currently very active field, a detailed account of recent progress and, in addition, a number of original research results on the design, analysis and implementation of these methods

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Numerical-asymptotic boundary integral methods in high-frequency acoustic scattering ∗

The application scenarios and requirements are more diverse in the fifth-generation (5G) era than before. In order to successfully support the system design and deployment, accurate channel modeling is important. Ray-tracing (RT) based deterministic modeling approach is accurate with detailed angular information and is a suitable candidate for predicting time-varying channel and multiple-input multiple-output (MIMO) channel for various frequency bands. However, the computational complexity and the utility of RT are the main concerns of users. Aiming at 5G and beyond wireless communications, this paper presents a comprehensive tutorial on the design of RT and the applications. The role of RT and the state-of-the-art RT techniques are reviewed. The features of academic and commercial RT based simulators are summarized and compared. The requirements, challenges, and developing trends of RT to enable the visions are discussed. The practices of the design of high-performance RT simulation platform for 5G and beyond communications are introduced, with the publicly available high-performance cloud-based RT simulation platform as the main reference. The hardware structure, networking, workflow, data flow and fundamental functions of a flexible high-performance RT platform are discussed. The applications of high-performance RT are presented based on two 5G scenarios, i.e., a 3.5 GHz Beijing vehicle-to-infrastructure scenario and a 28 GHz Manhattan outdoor scenario. The questions on how to calibrate and validate RT based on measurements, how to apply RT for mobile communications in moving scenarios, and how to evaluate MIMO beamforming technologies are answered. This tutorial will be especially useful for researchers who work on RT algorithms development and channel modeling to meet the evaluation requirements of 5G and beyond technologies.

The Design and Applications of High-Performance Ray-Tracing Simulation Platform for 5G and Beyond Wireless Communications: A Tutorial

The problem of the diffraction of an arbitrary ray optical electromagnetic field by a smooth perfectly conducting convex surface is investigated. A pure ray optical solution to this problem has been developed by Keller within the framework of his geometrical theory of diffraction (GTD). However, the original GTD solution fails in the transition region adjacent to the shadow boundary where the diffracted field plays a significant role. A uniform GTD solution is developed which remains valid within the shadow boundary transition region, and which reduces to the GTD solution outside this transition region where the latter solution is valid. The construction of this uniform solution is based on an asymptotic solution obtained previously for a simpler canonical problem. The present uniform GTD solution can be conveniently and efficiently applied to many practical problems. Numerical results based on this uniform GTD solution are shown to agree very well with experiments.

A uniform GTD analysis of the diffraction of electromagnetic waves by a smooth convex surface

For many years, The Geometrical Theory of Difraction (GTD) has been applied to antenna and scattering problems for which the structure is large in terms of wavelength. GTD solutions have mainly been concerned with pattern computations with little information concerning antenna impedance and/or aperture distributions. This is especially true for wire-type antennas. On the other hand, The Method of Moment (MM) has been applied to such problems for which the structure is small in terms of wavelength. This paper presents a technique which can be used to combine these two solutions such that a whole host of new problems can be handled.

A technique to combine the geometrical theory of diffraction and the moment method

Numerical solutions for the radiation patterns of aircraft antennas provide an excellent means of designing and locating antennas in order to achieve the desired performance. The high frequency solutions presented in this paper are based on fuselage antennas mounted on a general-type aircraft but applied specifically to the KC-135 aircraft. The roll and elevation plane patterns are computed for a monopole, axial slot, and circumferential slot mounted both over and forward of the wings. In each case the calculated patterns compare very favorably with the measured patterns. The precision pattern measurements were taken on a \frac{1}{25} scale model of the KC-135 aircraft at NASA (Hampton, Va.) with special emphasis on reducing the mount and background effects.

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A study of KC-135 aircraft antenna patterns

An asymptotic solution based on the uniform geometrical theory of diffraction (UTD) is proposed for the canonical problem of surface field excitation on a circular cylinder with an impedance boundary condition (IBC). The radius of the cylinder and the length of the geodesic path between source and field points, both of which are located on the surface of the cylinder, are assumed to be large compared to a wavelength. Unlike the UTD based solution pertaining to a perfect electrically conducting (PEC) circular cylinder, some higher order terms and derivatives of Fock type integrals are found to be significantly important and included in the proposed solution. The solution is of practical interest in the prediction of electromagnetic compatibility (EMC) and electromagnetic interference (EMI) between conformal slot antennas on a PEC cylindrical structure with a thin material coating on which boundary conditions can be approximated by an IBC. The cylindrical structure could locally model a portion of the fuselage of an aircraft or a spacecraft, or a missile. Validity and accuracy of the numerical results obtained by this solution are demonstrated in comparison with those of an exact eigenfunction solution.

A UTD based asymptotic solution for the surface magnetic field on a source excited circular cylinder with an impedance boundary condition

The overall capability of an electromagnetic radiating system is dependent on its ability to operate effectively in a complex environment, in that its pattern performance can be adversely limited by pattern distortion effects, such as blockage and structural scattering. In many cases these detrimental effects can be minimized by judiciously locating the antennas. This task is complicated by the large number of systems that are competing for prime locations on, for example, a modern military ship. Without an efficient means to position such systems one normally attempts to use locations similar to previous designs, which may be inexpensive but are certainly not optimum. As a result there is a great need for electromagnetic tools that can efficiently evaluate the pattern performance of radiating systems in their proposed environment.

R.J. Marhefka

Papers

A uniform GTD analysis of the diffraction of electromagnetic waves by a smooth convex surface

A technique to combine the geometrical theory of diffraction and the moment method

A study of KC-135 aircraft antenna patterns

A UTD based asymptotic solution for the surface magnetic field on a source excited circular cylinder with an impedance boundary condition

Antennas on Aircraft, Ships, or Any Large, Complex Environment