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81
Polarimetric Channel Characterization of Foliage for Performance Assessment of GPS Receivers Under Tree Canopies
 IEEE Trans. Antennas Propagat
, 2002
"... 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 tre ..."
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Cited by 13 (1 self)
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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 timedomain 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 closedform and uniform expression for the scattered nearfield 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.
Propagation model for the hvac duct as a communication channel
 IEEE Trans. Antennas Propag
, 2003
"... 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 p ..."
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Cited by 12 (9 self)
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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.
Inverse source problem with reactive power constraint
 IEEE Trans. Antennas Propagat
, 2004
"... 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 ..."
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Cited by 10 (9 self)
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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.
Nonradiating and minimum energy sources and their fields: Generalized source inversion theory and applications
 IEEE Trans. Antennas Propagat
, 2000
"... 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 o ..."
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Cited by 10 (6 self)
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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 timeharmonic EM example. Index Terms—Inverse problems.
Novel mode content analysis technique for multimode waveguides
 in IEEE MTTS Int. Microwave Symp. Dig
, 2003
"... Abstract—This paper presents a novel technique for analyzing the mode content excited by antennas placed in multimode waveguides. The technique is based on measuring the frequency response between the two antennas coupled into a waveguide and using that information to extract the mode content genera ..."
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Cited by 8 (6 self)
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Abstract—This paper presents a novel technique for analyzing the mode content excited by antennas placed in multimode waveguides. The technique is based on measuring the frequency response between the two antennas coupled into a waveguide and using that information to extract the mode content generated by the transmitting antenna. The technique is applicable to cases in which the mode amplitudes are approximately constant over the frequency range of interest. This method is valuable for determining the mode mix generated by arbitrary transmitting antennas in a multimode waveguide propagation environment. An example of such an environment is heating, ventilation, and airconditioning (HVAC) ducts used for indoor communications, where an important antenna characteristic is the mode sensitivity (analogous to the antenna directive gain in free space). We validate our technique with the example of a monopole probe antenna coupled into a multimode cylindrical HVAC duct. Index Terms—Antennas, indoor radio communication, microwave measurements, multimode waveguides. I.
MultiAntenna Capacities of Waveguide and Cavity
 Channels, IEEE CCECE’03
, 2003
"... Abstract—MIMO capacity of waveguide and cavity channels is analyzed in details in this paper. The rationale for this is threefold: (i) waveguide / cavity models can be used to model corridors, tunnels and other confined space channels, (ii) this is a canonical problem; its analysis allows to develo ..."
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Cited by 7 (4 self)
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Abstract—MIMO capacity of waveguide and cavity channels is analyzed in details in this paper. The rationale for this is threefold: (i) waveguide / cavity models can be used to model corridors, tunnels and other confined space channels, (ii) this is a canonical problem; its analysis allows to develop appropriate techniques, which can be further used for more complex problems, (iii) it allows to shed light on the relation between information theory and electromagnetism and, in particular, to establish the limits imposed by the laws of electromagnetism on achievable channel capacity. It is demonstrated that the number of degrees of freedom of the electromagnetic field inside of waveguides, which can be used for MIMO communication, is determined by the waveguide crosssectional area expressed in terms of the wavelength. A system architecture is proposed, which allows using these degrees of freedom.
Channel modeling and analysis for wireless networks in underground mines and road tunnels, 2008 (submitted for publication
"... 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 an ..."
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Cited by 7 (3 self)
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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 roomandpillar 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 roomandpillar 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, multimode model. I.
Modeling and Simulation of Coupling Structures for QuasiOptical Systems
, 1993
"... Heron, Patrick Lascelles Modeling and Simulation of Coupling Structures for QuasiOptical Systems. Under the direction of Michael B. Steer and James W. Mink Sponsored research was directed toward developing millimeter wave power sources utilizing quasioptical techniques. A system consisting of ..."
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Cited by 5 (0 self)
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Heron, Patrick Lascelles Modeling and Simulation of Coupling Structures for QuasiOptical Systems. Under the direction of Michael B. Steer and James W. Mink Sponsored research was directed toward developing millimeter wave power sources utilizing quasioptical techniques. A system consisting of an array of oscillators that radiated into a quasioptical 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 FabryPerot 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 Xband resonator was designed and fabricated, then one and twoport measurements were used to validate the theoretical calculations. A technique was determined for simulation of antennas that are not electrically ...
Dielectricfibre surface waveguides for optical frequencies
"... A dielectric fibre with a refractive index higher than its surrounding region is a form of dielectric waveguide which represents a possible medium for the guided transmission of energy at optical frequencies. The particular type of dielectricfibre waveguide discussed is one with a circular crossse ..."
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Cited by 4 (0 self)
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A dielectric fibre with a refractive index higher than its surrounding region is a form of dielectric waveguide which represents a possible medium for the guided transmission of energy at optical frequencies. The particular type of dielectricfibre waveguide discussed is one with a circular crosssection. The choice of the mode of propagation for a fibre waveguide used for communication purposes is governed by consideration of loss characteristics and information capacity. Dielectric loss, bending loss and radiation loss are discussed, and mode stability, dispersion and power handling are examined with respect to information capacity. Physicalrealisation aspects are also discussed. Experimental investigations at both optical and microwave wavelengths are included. List of principal symbols 5n = nthorder Bessel function of the first kind K,, = «thorder modified Bessel function of the second kind B = ^—, phase coefficient of the waveguide g J,', = first derivative of 5n K ^ = first derivative of Jn hj = radial wavenumber or decay coefficient €j = relative permittivity k0 = freespace propagation coefficient a = radius of the fibre y = longitudinal propagation coefficient k = Boltzman's constant T = absolute temperature, degK fic = isothermal compressibility A = wavelength n = refractive index H*,') = vthorder Hankel function of the /th type H ^ = derivation of Hv v = azimuthal propagation coefficient = V, — jv2 L = modulation period Subscript n is an integer and subscript m refers to the mth root of J,, = 0 1