On the Wiener-Hopf analysis of thick solid antenna with nonzerofeed gap width

Hurd's Wiener-Hopf-type analysis for the admittance of a long, thin, tubular antenna is extended to the case of an electrically thick solid antenna. Expressions for the input admittance and the current distribution along a solid dipole antenna without restriction on the thickness are presented. It is found that as with thin antennas, using one term of the final solution asymptotic series also produces accurate results for thick long antennas. It is found that two series terms have to be used when the antenna is short     

Analysis of a wire antenna in the presence of a body of revolution

The problem of an arbitrarily oriented thin-wire antenna located near a body of revolution is analyzed. The usual integrodifferential equation for a thin wire in unbounded space is generalized to account for scattering from the nearby body. The presence of the body is accounted for by a numerical dyadic Green's function. The modified wire equation is solved by standard numerical techniques to obtain the current distribution on the wire. The effects of various bodies on input admittance are compared with results for an isolated antenna. Measured and theoretical input admittance data for a monopole near several different bodies of revolution are found to be in good agreement.     

Frequency characterization of a thin linear antenna using diakopticantenna theory

A frequency-dependent analytical expression for the input impedance of a thin wire antenna is obtained using diakoptic theory. The linear antenna is diakopted into electrically short segments, where each is treated as a component with two terminals (except for end pieces, which have only one terminal). An impedance matrix is found which characterizes coupling between all segments. By expanding the free-space Green's function in a power series in wavenumber k, each entry in the resultant impedance matrix is obtained as an explicit function of frequency. The input admittance is found as a ratio of two polynomials in wavenumber k. A more systematic approach for the solution of the input admittance is achieved by expanding both the unknown current vector and the Green's function in power series in k. Equating coefficients of like powers in k leads to a numerically efficient algorithm which is used to determine the input admittance as a function of frequency. Numerical results compare well with the input impedance obtained from a conventional integral equation solution     

An experimental and theoretical study of the monopole embedded in a cylinder of anisotropic dielectric

The characteristics of a monopole antenna embedded in an anisotropic cylinder of semi-infinite length were studied. The anisotropic medium was created artificially by thin layers of lossless material whose dielectric constant alternated between two values, 15.0 and 1.06. A theoretical and experimental analysis was carried out for the axially anisotropic (uniaxial) orientation of the dielectric medium with curves shown for input admittance and current distribution. An experimental investigation was also carried out for the radially anisotropic orientation with measurements made for the input admittance, axial charge distribution, and the angular and axial current distributions.     

The input impedance of a monopole antenna mounted on a cubical conducting box

An experimental investigation has been performed to determine the input admittance characteristics of a monopole antenna mounted on a conducting cubical box over a ground plane. Input admittances of monopoles from 2 to 6 cm long mounted on a 10 cm box were considered in the investigation so that effects of changes in the electrical size of the box could be evaluated. The monopoles were placed at various points to determine the functional dependence of input admittance on the position of the monopole antenna. A numerical analysis of the radiating structure was performed using the method of moments to compare the experimental data with the computed input admittance. This comparison and the observed empirical behavior of the input admittance were then utilized to predict the effects of the conducting box on the overall admittance of the radiator.     

Modeling strategies of the input admittance of RC interconnects for VLSI CAD tools

In this paper, models of input admittance of RC interconnects are discussed in depth to understand and evaluate their loading effects on driving CMOS gates. From a detailed analysis of input admittance pole-zero location, arguments are derived to prove that their input admittance can be accurately approximated to that of a low-order equivalent RC circuit, in contrast to the case of timing analysis of RC wires. More specifically, 1st- or 2nd-order equivalent circuits are derived analytically via the moment matching approach, in contrast to previous analyses that rely on purely numerical approaches. Moreover, simple analytical rules to extend results to arbitrarily complex networks are derived, as opposed to the usual approach that requires numerical estimation of moments. Being fully analytical, the proposed approach permits one to develop models that are extremely simple (i.e. computationally efficient), as well as to gain an insight into the properties of input admittance of RC interconnects.The proposed equivalent circuits are evaluated and validated in situations that occur in real CAD design flows, where RC wire loading effects are estimated by CAD tools to perform the timing/power analysis of the buffer driving the wire. The analysis is validated through extensive simulations on a 65 nm CMOS technology. Well-defined criteria are also derived to select the appropriate model of RC wire input admittance for accurate timing/power estimations in VLSI CAD tools.     

Measurement techniques for antennas in dissipative media

Methods used to simulate dissipative media environments for antennas are reported and special techniques developed to determine the electrical properties of antennas in such media are discussed. Tank systems for simulating infinite homogeneous isotropic media characterized by ratios ofalpha/betain the range0 < alpha/beta < 1.0are described along with the apparatus for determining the constitutive parameterssigmaandepsilonof the media. A new device for measuring antenna input admittance is presented which permits a simple measurement of admittance over a broad frequency range where conventional methods are cumbersome in field use. Apparatus for measuring antenna current and charge distributions is described together with a discussion of the associated probing errors. Measured admittances and current and charge distributions are compared with current theories for thin wire linear and loop antennas in the dissipative media and are found to be in good agreement.     

A generalized expansion for radiated and scattered fields

At a given frequency every perfectly conducting obstacle has associated with it a particular set of surface currents and corresponding radiated fields which are characteristic of the obstacle shape and independent of any specific excitation. These characteristic modes form a useful basis set in which to expand fields radiated or scattered at a great distance from the obstacle. Once these modes are known for a given obstacle, the scattering of plane waves incident from arbitrary source directions into arbitrary receiver directions may be evaluated concisely. To support the theory, a method is described for determining characteristic mode currents on thin wires of general shape and is applied to several shapes to generate certain backscattering and input admittance data. Wherever possible comparison is made with existing data.     

A theoretical study of the input impedance of a circular microstrip disk antenna

A theoretical study is presented of the input impedance of a circular microstrip disk antenna excited by a coaxial line. The theory is based on Green's function technique applied to the disk cavity with the boundary admittance at the edge. Both the feed pin size and the boundary admittance are shown to be important in deriving the analytical expression for the input impedance. The boundary admittance is obtained by considering the radiated power and the electric and magnetic stored energies in the fringe capacitance. The analytical expression for the input impedance includes the feed location, the feed pin size, the disk size and thickness, and the dielectric constant of the material, and is useful for optimizing various parameters. The calculations are compared with experimental data showing a good agreement.     

A telegrapher equation for electric - telemetering in drill strings

A reliable method of transmitting downhole information to the surface while drilling is essential to improve drilling applications. We have designed a numerical algorithm for simulation of electric-signal transmission through the drill string, based on the telegrapher equation (a circuit model). The drill string is then represented by a transmission line with varying geometrical and electromagnetic properties versus depth, depending on the characteristics of the drill string/formation system. These properties are implicitly modeled by the series impedance and the shunt admittance of the transmission line. The telegrapher equation is solved in the high-frequency range by using a direct method     

The Input Admittance of Thin Prolate Spheroidal Dipole Antennas with Finite Gap Widths

The input admittance of a thin prolate spheroidal dipole antenna of major and minor axes a, b and fed by a gap of finite width 2d operating at the wavelength λ (k=2π/λ) is expressed as a very slowly convergent sum of symmetric prolate spheroidal angle and radial modal functions whose computation in this paper is facilitated by a novel method for evaluating radial functions of the second kind for small and large order with high accuracy. Then, by using Infeld's (1947) method of replacing a sum by an integral, the slowly convergent part of the admittance is evaluated. Three different types of distributions for the gap electric field are considered, and numerical results for the admittance are given as a function of the spheroidal dipole's length (0⩽2a⩽λ) with its thickness (2b⩾2×10^-5 λ), as well as the gap ratio d/b, as parameters     

The input admittance of a TEM excited annular slot antenna

The admittance problem solution of a TEM excited annular slot antenna embedded in an infinite perfectly conducting ground plane is accomplished in the rigorous Maxwell equation-boundary value sense. The net result is a complete closed form solution for the admittance which includes the effects of all beyond-cutoff higher order TM modes. Infinite integrals related to the TEM admittance and to perturbations produced by the presence of higher order TM modes are solved in an approximate manner. The TEM admittance solution obtained is shown to compare favorably with admittance values accurately determined by numerical integration. The presence of beyond-cutoff higher order TM modes is shown to produce a minor effect to the annular slot admittance. The form of the admittance solution reported upon herein is such that the results may be readily applied in estimating the input admittance of physical annular slot antennas without recourse to the usual infinite integral reduction problem.     

A high input impedance buffer amplifier using bipolar transistors

The input impedance of conventional emitter follower circuits is limited due to the finite value of the passive emitter resistance, shunting effect of biasing resistors and that of intrinsic collector to base feedback admittance and also to the fall in current amplification factor at low operating currents. Further, the input admittance is frequency dependent because the device parameters involved therein are themselves frequency dependent. However, the shunt positive feedback incorporated in such circuits minimizes the shunting effect of the biasing network and also that of the intrinsic feedback admittance. The simulation of negative capacitance across the input terminals nullifies the effect of the presence of the otherwise positive capacity. This technique extends the bandwidth over which the input impedance remains constant. A typical buffer amplifier circuit employing five conventional epitaxial planar bipolar silicon transistors has been described in the present communication. The input impedance of which is found to be constant over a frequency range of 10 HZ to 2 KHz and its magnitude is about 25MΩ.     

Admittance of rectangular waveguide radiating from a conductingcylinder

Theory and experiment are compared for the admittance presented to a rectangular waveguide which terminates at an arbitrary angle in the surface of a conducting cylinder. Two methods are described for calculating the admittance: a single-mode approximation from the modal solution and an alternative asymptotic solution. Using these methods, the effect of aperture orientation on admittance, and the results obtained are compared with the experiment. The single-mode approximation is in good agreement with experimental results for the case when the input waveguide supports the TE₁₀ mode only. The accuracy of the approximate formula for waveguide admittance was also verified. The admittance is shown to be weakly dependent on aperture orientation for moderately large cylinders     

Electromagnetic scattering from three-dimensional cavities via aconnection scheme

The electromagnetic scattering from arbitrary three-dimensional cavities is presented. To alleviate computational constraints for three-dimensional problems, a connection scheme is developed based on microwave network theory. This scheme allows the cavity to be divided into sections and each section to be analyzed independently of the rest of the cavity. Each section of the cavity is represented by a generalized admittance matrix which if formulated via a boundary-integral equation approach. Using the concept of input and load admittance, the aperture admittance matrix of the cavity can be derived by cascading the admittance matrices of individual sections. Once the cavity aperture admittance matrix is obtained, the aperture electric field and the backscattered field are found by the standard generalized network formulation. Numerical results are compared against modal solutions of regularly shaped cavities with good agreement. This connection scheme leads to a reduction in computational resources, especially for cavities with one dimension much larger than the other two     

CADMIC---Computer-Aided Design of Microwave Integrated Circuits

A computer program for the analysis and design of distributed lumped circuits, including microwave integrated circuits, is discussed. It is capable of frequency-domain analysis, optimization of transducer power gain, reflection coefficient, and/or noise figure. Also, the program can compute the return difference with respect to any admittance parameter so that the stability of the circuit can be determined by the Nyquist criterion. The program handles complex impedances, resistors, capacitors, inductors, transmission lines, independent current sources and grounded voltage sources, voltage-controlled current sources, and multiport elements, such as transistors and circulators, described by their scattering or admittance parameters. It contains a free-format input. The implementation is based on the indefinite admittance matrix, sparse matrices, adjoint networks, the Fletcher-Powell or Fletcher minimization algorithm, and Bode's feedback theory.     

The input admittance of the rectangular cavity-backed slot antenna

The input admittance of the rectangular cavity-backed slot antenna is investigated. The slot is assumed narrow so that the voltage distribution in its aperture is sinusoidal. Equations which represent the input admittance of this slot, backed by a rectangular cavity in which a single propagating wave is assumed to exist, are given. Calculations based on these representations are compared to available measured data. As the depth of the cavity increased the resonant frequency decreased and the bandwidth became narrower. Input admittance curves as a function of electrical slot length are also presented for several size cavities.     

Input admittance of a multilayer insulated monopole antenna

An efficient numerical technique based on the modal-expansion method in conjunction with a recursive algorithm is developed for a multilayer insulated monopole antenna fed by a coaxial transmission line. The modal-expansion analysis is facilitated by introducing a perfectly matched boundary (PMB) at a variable height over the ground plane of the monopole. The current distribution and input admittance are computed by finding the expansion coefficients of the electromagnetic field expressions. Numerical results for the input admittance of a dielectric-coated monopole antenna and an air-insulated monopole are compared with experimental ones available in the literature. Good agreement is achieved. Calculated results for the effects of various parameters on the input admittance of an air-insulated monopole antenna are presented and discussed     

Mutual admittance for axial rectangular slots in a large conducting cylinder

An asymptotic expression is derived for the mutual admittance between axial rectangular slots on a large conducting cylinder. The isolation between slots determined from this mutual admittance approximation is compared with that obtained using the admittance from direct numerical integration and with experimental results for a cylinder in free space and in the presence of a simulated thin plasma sheath.     

Direct analysis of folded dipole by method of moments

The integral equation for the current on a folded dipole is reduced to a matrix equation by the Galerkin method. The resulting current distribution allows the input impedance `step-up? to be deduced, and also the variation in input admittance with frequency to be examined.