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The input impedance and radiation pattern of the inset-fed rectangular microstrip patch antenna are investigated. It is concluded that a shifted cosine-squared function describes well the variation of the resonant input resistance with the feed location (point of contact between the microstrip feed line and the notch) for a given patch and substrate geometry. The parameters of the shifted cosine-squared function depend on the notch width for a given patch and substrate geometry. The cross-polarization level is seen to increase as either the notch width or depth increases. However, for a fixed input resistance level, the notch depth decreases as the width increases, so that the cross-polarization level is not very sensitive to the notch width for a fixed input resistance. Index Terms--Inset-feed, microstrip antenna, rectangular patch.

A new Global Positioning System (GPS) mierostrip patch antenna designed for dual-band (L 1/L 2) operation is introduced. The antenna design is based on the reduced-surface-wave (RSW) concept and, as a result, is much less susceptible to lowangle multipath interference effects than some of the more commonly-used high-precision GPS antennas. In this paper, the radiation characteristics of this new design will be compared to a dualband choke-ring and a dual-band pinwheel antenna. In addition to having the advantages typically associated with microstrip patch antennas, this planar dual-band antenna lacks the design complications associated with the frequently-used stacked-patch method for realizing dual-band microstrip antenna performance. Thus, the simplicity of the design, together with the reduced horizon and backside radiation levels and excellent circular polarization characteristics indicate that this new antenna design is a promising candidate for dual-band, high-precision applications. Index Terms--Choke ring antennas, dual-band antennas, Global Positioning System (GPS), microstrip antennas, multipath interference.

Increasing the number of antennas for wireless communications, while concealing them within their environment, is an area of great importance as demand for wireless devices increases. One method to achieve this goal is to use the existing conducting objects in an environment as antennas. This requires altering the natural current distribution on conducting objects such that optimal radiation properties can be obtained. In this paper, a composite dielectric bead element is introduced for this purpose on electrically large wire structures. The operation of the bead element is described using transmission line theory, and a wire model of the element is given. Using the wire model, the loading for several electrically large wire structures is designed such that they resonate and radiate similarly to a half-wavelength dipole. Index Terms--Current control, cylindrical antennas, dielectric loaded antennas, linear antennas, loaded antennas, monopole antennas, wire antennas.

The far-field radiation patterns of a two-dimensional (2-D) periodic slot leaky-wave antenna (LWA) are studied. The antenna consists of a two-dimensional periodic array of slots in a conducting plane that is printed on top of a grounded dielectric slab. The antenna is excited by a simple source such as a dipole inside the slab. Reciprocity along with the spectral-domain method is used to calculate the far-field pattern, and the radiation characteristics of the structure are investigated. A comparison between the present periodic slot LWA and a 2-D periodic patch LWA discussed in Part I is given to show the advantages of the slot antenna for certain applications. The slot LWA can achieve high directivity patterns, and a circularly-polarized version of the antenna can achieve good circular-polarization at broadside. Index Terms--Circular polarization, leaky-wave antenna (LWA), slots.

General formulas for a two-dimensional (2-D) leaky-wave antenna (LWA) are obtained, which are applicable to any general class of 2-D leaky-wave antenna that consists of a partially reflecting surface that is mounted on top of a grounded substrate, and excited by a simple source. Closed-form expressions are obtained for the radiated fields, the field peak values in the E- and H-planes, the beamwidths in the E- and H-planes, and the pattern bandwidth. The formulas are obtained from a simple transverse equivalent network model of the structure. An accurate formula for the substrate thickness necessary to give a beam at any desired angle is also obtained. Index Terms--CAD formulas, leaky-wave antenna (LWA), planar antennas.

The far-field radiation characteristics of a two-dimensional (2-D) periodic leaky-wave antenna (LWA) constructed from a periodic array of metal patches on a grounded dielectric substrate is investigated. A simple dipole source is used as the excitation. Reciprocity together with a periodic spectral-domain method of moments is used to calculate the far-field pattern. Design rules for the scan angle, the substrate dielectric constant, and the periodicity are provided. Finally, a comparison of the 2-D periodic LWA and a dielectric-layer LWA is given to show the similar performance of the two antennas. Index Terms--Leaky wave, leaky-wave antenna (LWA), patches.

Four different models for the probe inductance of a circular probe in an infinite parallel plate waveguide are studied. These models include a uniform-current model, a cosine-current model, a gap-voltage source model, and a coaxial-frill model. These different models treat the vertical variation of the fields within the substrate and the field of the coaxial feed with varying degrees of rigor. Numerical high frequency structure simulator data are also compared with the results of these models in order to draw reliable conclusions about the accuracy of these models as a function of the substrate thickness. A simple computer-aided design formula for the probe inductance of a coaxial feed probe for a rectangular microstrip patch antenna is also introduced. Index Terms--Microstrip antenna, parallel-plate waveguide, probe inductance.

Scan impedances of finite reduced surface wave (RSW) arrays are studied. Center element scan impedances of linear arrays and two-dimensional (2-D) square lattice arrays are calculated and compared with those of conventional microstrip arrays. Results show that compared with conventional microstrip arrays, broadside scan impedance of RSW arrays has less variation and converges much faster when the array size increases. Scan performance of the linear and 2-D square lattice RSW arrays are also studied. Results show that the RSW array can avoid the scan blindness (when the array spacing is greater than 0.5[[lambda].sub.0]) and the scan impedance has much less variation than that of conventional microstrip array with the same array spacing. However, due to the size limitation of RSW elements, the grating lobes cannot be avoided. Hence, the scan region is limited to about 20[degrees] (with 0.75[[lambda].sub.0] array spacing). Compared with conventional microstrip arrays with 0.5[[lambda].sub.0] array spacing, the results show no favor to RSW arrays. Index Terms--Mutual coupling, reduced-surface-wave (RSW) antenna, scan blindness, scan impedance.

By using a specific normalization, it is shown that the T[M.sub.o] radiation field from a leaky mode that is excited by a source on any printed-circuit structure can be represented in a unified manner. The general properties of the normalized leaky-mode radiation field are examined in detail for a variety of phase and attenuation constants, as well as distances from the source, and for different types of source excitations. The normalized leaky-mode radiation field is compared to similarly normalized geometrical-optics and far-field radiation expressions to provide further insight into the nature of the radiation fields in the near- and far-field regions. The results provide a general view of leaky-mode radiation properties independent of the type of planar transmission line or background structure. Index Terms--Crosstalk, leaky-mode excitation, leaky waves, microstrip, printed circuits, radiation, stripline.

The T[M.sub.o] parallel-plate mode field that is radiated from the currents induced on a covered microstrip transmission line by a finite-gap voltage source is studied. The behavior of the total radiation field (the field radiated by the total strip current) is investigated, along with the field radiated by the constituent current components that make up the total current, namely the bound-mode (BM) and continuous-spectrum currents. The continuous-spectrum current is further resolved into the sum of a physical leaky-mode current and a residual-wave current, and the fields radiated by each of these separate components are examined. It is determined that leaky-mode fields can contribute to crosstalk and other interference effects near the source and within an angular leakage region, while the radiation field from the BM current is the predominant mechanism for these effects further away from the gap source, outside the leakage region. The field radiated from the residual-wave current can be quite strong in the 'spectral-gap region,' which is the frequency region where the leaky mode is nonphysical, and therefore the leaky mode does not contribute directly to the spectrum of current on the strip in the decomposition used here. Index Terms--Crosstalk, leaky waves, microstrip, microwave integrated circuits, printed circuits, radiation.

This paper presents a sensitivity study of electroencephalography-based source localization due to errors in the head-tissue conductivities and to errors in modeling the conductivity variation inside the brain and scalp. The study is conducted using a two-dimensional (2-D) finite element model obtained from a magnetic resonance imaging (MRI) scan of a head cross section. The effect of uncertainty in the following tissues is studied: white matter, gray matter, cerebrospinal fluid (CSF), skull, and fat. The distribution of source location errors, assuming a single-dipole source model, is examined in detail for different dipole locations over the entire brain region. We also present a detailed analysis of the effect of conductivity on source localization for a four-layer cylinder model and a four-layer sphere model. These two simple models provide insight into how the effect of conductivity on boundary potential translates into source location errors, and also how errors in a 2-D model compare to errors in a three-dimensional model. Results presented in this paper dearly point to the following conclusion: unless the conductivities of the head tissues and the distribution of these tissues throughout the head are modeled accurately, the goal of achieving localization accuracy to within a few millimeters is unattainable. Index Terms - Bioelectric phenomena, dipole localization, electroencephalography, finite element method (FEM), imaging, inhomogeneity, inverse problems, source localization.

Modeling wire structures with a high degree of curvature generally requires a large number of piecewise linear segments to accurately represent rapid geometrical variations. In order to reduce the number of segments required to model curved wire structures, a method of moments formulation using curved wire segments is presented. Specifically, piecewise quadratic wire segments are used to discretize the wire geometry. This algorithm is used to analyze a small wire loop antenna and a multiple-arm Archimedian spiral antenna. For each example, a comparison is made between results obtained using this quadratic segment algorithm and a linear segment algorithm. These examples demonstrate that the memory required is significantly reduced and a reduction in the solution time is achieved when quadratic segments are used.

The impedance of a rectangular patch antenna fed by an inset microstrip transmission line was measured for various feed positions. The dependence found was then compared to theoretical predictions both for this geometry and for the similar case of an inset coaxial probe feed. Index Terms--Impedance, inset feed, microstrip antennas, resonant frequency.

An investigation of the mutual coupling between reduced surface-wave microstrip antennas is presented and compared with that for conventional microstrip antennas. Numerical results are presented from a theoretical analysis of the mutual coupling along with confirming experimental results. It is shown that for electrically thin substrates, the space-wave coupling, not the surface-wave coupling, is predominant for typical element spacing, for both the conventional and reduced surface-wave antennas. In addition, the mutual coupling behavior is examined using an asymptotic analysis, which demonstrates how the coupling falls off much faster with patch separation for reduced surface wave antennas compared to conventional microstrip patch antennas. Index Terms--Antenna array mutual coupling, microstrip antennas, printed antennas, surface waves.

This paper studies the time-domain propagation and dispersion of a pulse propagating on a microstrip line with a metallic top cover. A gap voltage source is used to model a practical excitation on the line. High-frequency distortion effects are observed that cannot be accounted for by conventional transmission-line theory, since they are due to the simultaneous excitation of the bound mode and a strong leaky mode. The bound-mode and leaky-mode components of the pulse are identified and separately studied to aid in the physical interpretation of the pulse distortion. The excitation of a dominant leaky mode gives rise to an interesting pulse-splitting phenomenon, due to the different velocities of the bound mode and the leaky mode. The influence of dielectric and conductor losses on the pulse shape is also studied. [ABSTRACT FROM AUTHOR]

The input impedance and radiation pattern of the inset-fed rectangular microstrip patch antenna are investigated. It is concluded that a shifted cosine-squared function describes well the variation of the resonant input resistance with the feed location (point of contact between the microstrip feed line and the notch) for a given patch and substrate geometry. The parameters of the shifted cosine-squared function depend on the notch width for a given patch and substrate geometry. The cross-polarization level is seen to increase as either the notch width or depth increases. However, for a fixed input resistance level, the notch depth decreases as the width increases, so that the cross-polarization level is not very sensitive to the notch width for a fixed input resistance. [ABSTRACT FROM AUTHOR]

General formulas for a two-dimensional (2-D) leaky-wave antenna (LWA) are obtained, which are applicable to any general class of 2-D leaky-wave antenna that consists of a partially reflecting surface that is mounted on top of a grounded substrate, and excited by a simple source. Closed-form expressions are obtained for the radiated fields, the field peak values in the E- and H-planes, the beam widths in the E- and H-planes, and the pattern bandwidth. The formulas are obtained from a simple transverse equivalent network model of the structure. An accurate formula for the substrate thickness necessary to give a beam at any desired angle is also obtained. [ABSTRACT FROM AUTHOR]

The far-field radiation patterns of a two-dimensional (2-D) periodic slot leaky-wave antenna (LWA) are studied. The antenna consists of a two-dimensional periodic array of slots in a conducting plane that is printed on top of a grounded dielectric slab. The antenna is excited by a simple source such as a dipole inside the slab. Reciprocity along with the spectral-domain method is used to calculate the far-field pattern, and the radiation characteristics of the structure are investigated. A comparison between the present periodic slot LWA and a 2-D periodic patch LWA discussed in Part I is given to show the advantages of the slot antenna for certain applications. The slot LWA can achieve high directivity patterns, and a circularly-polarized version of the antenna can achieve good circular-polarization at broadside. [ABSTRACT FROM AUTHOR]

The far-field radiation characteristics of a two-dimensional (2-D) periodic leaky-wave antenna (LWA) constructed from a periodic array of metal patches on a grounded dielectric substrate is investigated. A simple dipole source is used as the excitation. Reciprocity together with a periodic spectral-domain method of moments is used to calculate the far-field pattern. Design rules for the scan angle, the substrate dielectric constant, and the periodicity are provided. Finally, a comparison of the 2-D periodic LWA and a dielectric-layer LWA is given to show the similar performance of the two antennas. [ABSTRACT FROM AUTHOR]

Four different models for the probe inductance of a circular probe in an infinite parallel plate waveguide are studied. These models include a uniform-current model, a cosine-current model, a gap-voltage source model, and a coaxial-frill model. These different models treat the vertical variation of the fields within the substrate and the field of the coaxial feed with varying degrees of rigor. Numerical high frequency structure simulator data are also compared with the results of these models in order to draw reliable conclusions about the accuracy of these models as a function of the substrate thickness. A simple computer-aided design formula for the probe inductance of a coaxial feed probe for a rectangular microstrip patch antenna is also introduced. [ABSTRACT FROM AUTHOR]

A closed-form expression is derived for the integration over a triangle of the normal component of electric flux from a dipole in a homogeneous space, weighted by a linear basis function. This integral arises in the finite element solution of the three-dimensional Poisson equation with a dipole source when solving for the "subtracted potential," i.e., the total potential minus the potential of the dipole in an infinite homogeneous medium. This closed-form integral evaluation allows for an efficient finite element solution for the subtracted potential that is more accurate than can be achieved using a direct finite element solution for the total potential, since the subtracted potential is a smoother function with no singularity. The formulation begins by first deriving a formula for the electric flux through a triangle due to a dipole source in a homogeneous medium (no basis function weighting). This formulation is based on an identity that is derived, which equates the electric flux from a dipole source through an arbitrary surface to a contour integral of the electric field of a point (monopole) source along the boundary of the surface. This identity results in a simple closed-form expression for the electric flux of a dipole through a triangular surface. As an extension of this result, a closed-form expression is then derived for the more complicated case where the dipolar flux density through the triangular surface is weighted by a linear basis function. Compared to numerical integration, the closed-form expression is more computationally efficient and main tains accuracy regardless of how close the dipole gets to the surface. [ABSTRACT FROM AUTHOR]

Observes leaky dominant modes at high frequencies on microstrip lines with isotropic substrate resulting in a mechanism for power loss in the circuits. Analysis of the numerical and experimental results; Measurements results using HP8510-B network analyzer; Role of the mode and comparison to conventional type.