James K. Breakall

A Simplified Analytical Urban Propagation Model (UPM) for Use in CJSMPT

RF propagation models such as TIREM and Hata used in spectrum management tools do not consider the impact of urban environments such as buildings and roads for the prediction of the propagation loss. Under the development of the Coalition Joint Spectrum Management Planning Tool (CJSMPT), US Army Communications Electronics Research Development and Engineering Center (CERDEC) took the initiative for quantifying the existing urban propagation models, both empirical and analytical, and developing a simplified urban propagation model for use in CJSMPT. The emphasis on this model was to have a minimal time and computational complexity and use data that represents the actual urban environment. The traditional empirical models developed from a set of measurements conducted in metropolitan cities between the base and mobile stations do not provide the expected accuracy since they do not consider the characteristics of the areas of interest. In addition, these empirical models do not address the propagation scenario from mobile to mobile stations. The analytical models determine the path loss as result of field reduction due to free space, multiple diffraction over passed building rows, and diffraction of the rooftop to a mobile station. However, these analytical models involve substantial amount of complexity due to the calculations of diffraction associated with multiple rows of buildings. To meet the needs for fast assessment of interference and deconfliction analysis in CJSMPT, a simplified analytical model was developed for addressing different propagation scenarios when the base station antenna is above, below and near the average rooftop level.

Lorentz invariance of absorption and extinction cross sections of a uniformly moving object

The energy absorption and energy extinction cross sections of an object in uniform translational motion in free space are Lorentz invariant, but the total energy scattering cross section is not. Indeed, the forward-scattering theorem holds true for co-moving observers but not for other inertial observers. If a pulsed plane wave with finite energy density is incident upon an object, the energies scattered, absorbed, and removed from the incident signal by the object are finite. The difference between the energy extinction cross section and the sum of the total energy scattering and energy absorption cross sections for a non-co-moving inertial observer can be either negative or positive, depending on the objects velocity, shape, size, and composition. Calculations for a uniformly translating, solid, homogeneous sphere show that all three cross sections go to zero as the sphere recedes directly from the source of the incident signal at speeds approaching c, whether the material is a plasmonic metal (e.g., silver) or simply a dissipative dielectric material (e.g., silicon carbide).

Time-domain electromagnetic scattering by a sphere in uniform translational motion

Scattering by a uniformly translating sphere of a pulse that modulates the amplitude of a linearly polarized plane wave was formulated using the frame-hopping method involving a laboratory inertial reference frame and the spheres comoving inertial reference frame. The incident signal was defined in the laboratory frame and transformed to the comoving frame with the Lorentz transformation, thereby altering the incident signals spectrum, direction of propagation of the carrier plane wave, and the direction of the incident electric field, depending on the spheres velocity. In the comoving frame, the incident signal was Fourier-transformed to the frequency domain, and the scattered field phasors were computed in all directions using the constitutive parameters of the material of the sphere at rest. The scattered signal in the comoving frame was obtained using the inverse Fourier transform. Finally, the scattered signal in the laboratory frame was obtained by inverting the original Lorentz transformation. The backscattered signal was found to depend strongly on the spheres velocity, when the spheres speed is an appreciable fraction of the speed of light in free space. The change in the backscattered signal compared with the backscattered signal from a stationary sphere is the greatest when the spheres velocity is either parallel or antiparallel to the direction of propagation of the incident signal. The backscattered signal is also affected by motion transverse to the incident signals direction of propagation; then, the backscattered signal depends on whether or not the motion is aligned with the direction of the incident electric field.

Modeling of radiowave propagation in tunnels

We investigated propagation of radio frequency (RF) waves in tunnels. An understanding of RF propagation in tunnels is needed to plan for optimal radio communication system performance. We considered tunnels with a square cross section and right-angle junctions. We developed an analytic model of tunnel propagation by considering multiple reflections from tunnel walls and diffraction around junction corners. A comparison of model results with measurements shows a strong correlation between model predictions and measured data. Finally, we briefly describe a software tool that helps users visualize field strength of the propagating field in tunnels.

Scattering characteristics of relativistically moving concentrically layered spheres

Abstract The energy extinction cross section of a concentrically layered sphere varies with velocity as the Doppler shift moves the spectral content of the incident signal in the spheres co-moving inertial reference frame toward or away from resonances of the sphere. Computations for hollow gold nanospheres show that the energy extinction cross section is high when the Doppler shift moves the incident signals spectral content in the co-moving frame near the wavelength of the spheres localized surface plasmon resonance. The energy extinction cross section of a three-layer sphere consisting of an olivine-silicate core surrounded by a porous and a magnetite layer, which is used to explain extinction caused by interstellar dust, also depends strongly on velocity. For this sphere, computations show that the energy extinction cross section is high when the Doppler shift moves the spectral content of the incident signal near either of olivine-silicates two localized surface phonon resonances at 9.7 μm and 18 μm.

Electromagnetic pulse scattering by a spacecraft nearing light speed

Humans will launch spacecraft that travel at an appreciable fraction of the speed of light. Spacecraft traffic will be tracked by radar. Scattering of pulsed electromagnetic fields by an object in uniform translational motion at relativistic speed may be computed using the frame-hopping technique. Pulse scattering depends strongly on the velocity, shape, orientation, and composition of the object. The peak magnitude of the backscattered signal varies by many orders of magnitude, depending on whether the object is advancing toward or receding from the source of the interrogating signal. The peak magnitude of the backscattered signal goes to zero as the object recedes from the observer at a speed very closely approaching light speed, rendering the object invisible to the observer. The energy scattered by an object in motion may increase or decrease relative to the energy scattered by the same object at rest. Both the magnitude and sign of the change depend on the velocity of the object, as well as on its shape, orientation, and composition. In some cases, the change in total scattered energy is greatest when the object is moving transversely to the propagation direction of the interrogating signal, even though the Doppler effect is strongest when the motion is parallel or antiparallel to the propagation direction.

Lossless impedance matching optimization for increasing bandwidth of antennas

In the design of RF radiators, impedance matching has been costing a significant amount of time and energy. Approaches to solve impedance matching problems mainly rely on computer-aided numerical optimizations, nowadays. An approach based on the MATLAB Global Optimization Toolbox™ is proposed in this paper. This approach combines brute-force techniques and the Real Frequency Technique, which are the two main components of modern impedance matching methods.

Broadband lossy impedance matching of antennas

In RF applications such as transmitters, amplifiers, receivers, and antennas, a task of vital importance is the design of an impedance matching network, one that can transfer the most power from the source to the load. Lossless matching networks at a single frequency have been well studied, while the broadband impedance matching problem was only defined 70 years ago.

Simulation and experimental results for a planar strip dipole over PEC and ferrite nanoparticle composite ground planes

Summary form only given. An important antenna design goal is to have a dipole-like antenna operating close to a metallic groundplane (structure or platform). Unfortunately, the characteristics such as radiation resistance and bandwidth reduce dramatically as the antenna approaches closely to the ground plane. However, if the antenna could be matched even to the low radiation resistance, the gain increases as the antenna gets closer to the ground plane assuming low antenna ohmic losses. For low-loss ferrite nanoparticle composite backed ground planes, completely opposite behavior occurs in that the radiation resistance and bandwidth increase as the dipole moves closer. In the practical world an antenna should include a matching circuit to prevent serious mismatch loss to circumvent lower realized gain that would result for the unmatched case. In this paper the geometry of a low-loss ferrite nanoparticle composite backed ground plane is optimized for a planar strip dipole. The radiation resistance, gain, VSWR (Voltage Standing Wave Ratio), and bandwidth are investigated for this magnetodielectric based antenna. Results are given for simulations involving the antenna in free space and at various heights over a PEC and over a low-loss ferrite nanoparticle composite medium. It is found that the radiation resistance and bandwidth are similar for the dipole in free space and at a height of .25λ over a PEC ground plane. As the dipole is lowered closer to the ground plane, the radiation resistance and bandwidth both reduce and the gain improves. Bandwidth is defined between the VSWR = 2.0 upper and lower frequencies with the antenna matched to the radiation resistance at the center frequency. The same planar strip dipole was modeled with simulation software over a finite size PEC ground plane inserted with a thin layer of specially formulated isotropic magnetic nanoparticle composite with low-loss characteristics. Experimental measurements were also obtained in an anechoic chamber and agreed with simulation results. Impedance, VSWR, gain, and bandwidth results will be presented for both the simulation modeling and the experimental measurements. It was found that all of the performance characteristics were greatly improved by utilizing the magnetic nanoparticle composite. This innovative and breakthrough ferrite nanocomposites backed antenna design will allow antennas to be very conformal to metallic groundplanes (vehicles and airborne platforms).