Abstract—The attenuation, depolarization, and fluctuation of a microwave signal going through a tree canopy are investigated by developing a Monte Carlo based coherent scattering model. In particular, the model is used to analyze the performance of global positioning system (GPS) receivers under tree canopies. Also the frequency and time-domain channel characteristics of a forest are investigated when a transmitter is outside and a receiver is inside a forest. A fractal algorithm (Lindenmayer system) is used to generate the structure of coniferous or deciduous trees whose basic building blocks are arbitrarily oriented finite cylinders, thin dielectric needles, and thin dielectric disks. Attenuation and phase change of the mean field through foliage is accounted for using Foldy’s approximation. Scattering of the mean field from individual tree components and their images in the underlying ground plane are computed analytically and added coherently. Since tree trunks and some branches are large compared to the wavelength and may be in the close proximity of the receiver, a closed-form and uniform expression for the scattered near-field from dielectric cylinders is also developed. Monte Carlo simulation of field calculation is applied to a cluster of trees in order to estimate the statistics of the channel parameters, such as the probability density function (pdf) of the polarization state of the transmitted field, path loss, and the incoherent scattered power (the second moment of the scattered field), as a function of the observation point above the ground. Index Terms—Channel simulation, propagation, vegetation. I.

Abstract—This paper reports a general Lagrangian formulation for constrained electromagnetic inverse source problems. The formulation is applicable to different forms of inverse source problems having different constraints. Two possibilities are emphasized in the paper. One yields the usual minimum energy solution. The other establishes a new minimum energy solution with the additional constraint that the source has a prescribed reactive power (which can be zero). The latter solution incorporates the important reactive energy issues of an antenna which had not been considered before in the context of the inverse source problem. The new solution is shown to obey a homogeneous wave equation in the interior of the source volume, and expressions for the associated interior field and interaction power are also derived. The derived theory is illustrated for a canonical dipolar source and an alternative approach where the reactive power is minimized for a prescribed maximum functional energy is also presented. Advantage is taken of some of the results to briefly discuss some questions about fundamental antenna limits. Index Terms—Antenna limits, antenna optimization, antenna synthesis, inverse source problem, minimum energy sources, nonradiating sources, reactive energy. I.

Abstract—A new general framework for characterizing scalar and electromagnetic (EM) nonradiating (NR) and minimum energy (ME) sources and their fields is developed that is of interest for both radiation and source reconstruction problems. NR sources are characterized in connection with the concept of reciprocity as nonreceptors. Localized ME sources are shown to be free fields truncated within the source’s support. A new source analysis tool is developed that is based on the decomposition of a source and its field into their radiating and NR components. The individual radiating and reactive energy roles of the radiating and NR parts of a source are characterized. The general theory is illustrated with a time-harmonic EM example. Index Terms—Inverse problems.

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Heron, Patrick Lascelles Modeling and Simulation of Coupling Structures for Quasi-Optical Systems. Under the direction of Michael B. Steer and James W. Mink Sponsored research was directed toward developing millimeter wave power sources utilizing quasi-optical techniques. A system consisting of an array of oscillators that radiated into a quasi-optical resonator was analyzed. Each oscillator was comprised of a solid state device and a radiating structure. A dyadic Green's function was developed for a Fabry-Perot resonator which consisted of a metallic planar reflector and a shallow spherical metallic reflector. The Green's function was applied to determine the driving point impedance matrix for an array of electrically small antennas within the resonator. An experimental X-band resonator was designed and fabricated, then one and two-port measurements were used to validate the theoretical calculations. A technique was determined for simulation of antennas that are not electrically ...

Abstract—Wireless networks can greatly facilitate the communication in underground mines and road/subway tunnels, where the propagation characteristics of electromagnetic (EM) waves are significantly different from those in terrestrial environments. According to the structure of underground mines and road tunnels, two types of channel models can be utilized, namely, tunnel and room/pillar channel models. However, there exists no theoretical model for room-and-pillar channel in underground mines to date, and current existing tunnel channel models do not provide an analytical solution for both near and far regions of the sources. In this paper, the multimode model is proposed, which provides an analytical expression for the received power and the power delay profile at any position in a tunnel. Moreover, the multimode model is extended to characterize the room-andpillar channel in the underground mines after combining it with the shadow fading model. The theoretical models are validated by experimental measurements. Based on the proposed channel models, the effects of various factors on the signal propagation are analyzed. The factors include: the operating frequency, the size of the tunnel or underground mine room, the antenna position and polarization, and the electrical parameters. Index Terms—Wireless networks, underground mine, tunnel, channel model, waveguide, multi-mode model. I.

The electric properties of monolithic microwave integrated circuits can be described in terms of their scattering matrix using Maxwellian equations. The corresponding three-dimensional boundary value problem of Maxwell's equations can be solved by means of a finite-volume scheme in the frequency domain. This results in a two-step procedure: a time and memory consuming eigenvalue problem for nonsymmetric matrices and the solution of a large-scale system of linear equations with indefinite symmetric matrices. Improved numerical solutions for these two linear algebraic problems are treated. Contents 1 Introduction 1 2 Scattering Matrix 2 3 The Boundary Value Problem 3 4 The Maxwellian Grid Equations 5 5 The System of Linear Algebraic Equations 6 6 The Eigenvalue Problem 8 7 Conclusions 9 List of Figures 1 Structure under investigation : : : : : : : : : : : : : : : : : : 2 2 Primary and dual grid : : : : : : : : : : : : : : : : : : : : : : 5 1 Introduction The design of monolithic micro...

The method of moments (MoM) in conjunction with the generalized scattering matrix (GSM) approach is proposed to analyze transverse multilayered structures in a metal waveguide. The formulation incorporates ports as an integral part of the GSM formulation, thus, the resulting model can be integrated with circuit analysis. The proposed technique permits the modeling of interactive discontinuities due to the consideration of a large number of modes in the cascade. The GSM--MoM method can be successfully applied to the investigation of a variety of shielded multilayered structures, iris coupled filters, determining the input impedance of probe excited waveguides, and of waveguide-based spatial power combiners. Index Terms--- Generalized scattering matrix, method of moments, numerical modeling. I. INTRODUCTION T HE generalized scattering matrix (GSM) method has been widely used to characterize waveguide junctions and discontinuities. The GSM is a matrix of coefficients of forward and ba...

Investigation of a DC power delivery network, consisting of a multilayer PCB using area fills for power and return, involves the distributed behavior of the power/ground planes and the parasitics associated with the lumped components mounted on it. Full-wave methods are often employed to study the power integrity problem. While full-wave methods can be accurate, they are time and memory consuming. The cavity model of a rectangular structure has previously been employed to efficiently analyze the simultaneous switching noise (SSN) in the power distribution network. However, a large number of modes in the cavity model are needed to accurately simulate the impedance associated with the vias, leading to computational inefficiency. A fast approach is detailed herein to accelerate calculation of the summation associated with the higher-order modes. Closed-form expressions for the parasitics associated with the interconnects of the decoupling capacitors are also introduced. Combining the fast calculation of the cavity models of regularly shaped planar circuits, a segmentation method, and closed-form expressions for the parasitics, an efficient approach is proposed herein to analyze an arbitrary shaped power distribution network. While it may take many hours for a full-wave method to do a single simulation, the proposed method can generally perform the simulation with good accuracy in several minutes. Another advantage of the proposed 1 method is that a SPICE equivalent circuit of the power distribution network can be derived. This allows both frequency and transient responses to be done with SPICE simulation. I.

Abstract—Heating, ventilation, and air conditioning (HVAC) ducts in buildings are typically hollow metal pipes which can be used as waveguides to carry signals and provide the network access to offices. Knowledge of channel properties is crucial to designing such a communication system. This paper presents a propagation model for a straight HVAC duct terminated at both ends. At high frequencies this duct behaves as a multimode waveguide with a transmitting antenna coupling in and a receiving antenna coupling out. We derive a simple analytical expression for the frequency response of this channel using conventional techniques. Experimental data taken on real circular ducts excited by monopole probe antennas confirm theoretical results. This model represents an initial step toward the development of a tool for planning a wireless distribution system using building HVAC ducts. Index Terms—Indoor radio communication, monopole antennas, multimode waveguides, radio propagation, wireless LAN. I.