Field Radiation Pattern Research Articles

Electromagnetic fields in circular bends of slab waveguides

AbstractA method for rigorous analysis of transmission in and radiation from a uniformly bent finite‐length section of a slab wave length is proposed. The eigenmodes with continuous eigenvalues, which are similar to the radiation modes of the straight waveguide, are defined first for expressing fields in circular bends of slab waveguides, and a kind of orthogonality relation for these eigenmodes is derived. The spectral integral of these eigenmodes can give a rigorous expression of fields in circularly bent sections, which is proved by using the radiation condition and the Fourier transformation technique. The theory is applied to the analysis of transient phenomena of fields in the uniformly bent section connected to the straight section. Numerical examples of transition of field distributions and radiation patterns are presented and the results are discussed in detail.

Performance of short-backfire antenna with different excitation sources

The exact representation of the short back-fire antenna (SBA) which consists of the main reflector surrounded by a rim, and the subreflector is modelled using the surface integral equations. The numerical solution of these equations is used to calculate the far field radiation patterns, from which the directive gain is calculated by an integration of the radiation patterns. The optimum dimensions of SBA are obtained for two different types of the feed in structure a half wave dipole and a coaxial circular waveguide. The feed is located between the two reflectors. The geometrical dimensions are optimized to maximize the directive gain and the aperture efficiency. For the first excitation type a directive gain of 16.39 dB is obtained with an aperture efficiency of 91.17%. The second type is a new one and yields a directive gain of 18.035 dB with an aperture efficiency of 92.45%.

Characterisation of single-mode channel waveguides from far field measurements

A method for the experimental characterisation of single mode channel waveguides using their far field radiation pattern is proposed. It is shown that if the substrate and cover refractive indices are known (which is true in most cases) then the core refractive index and the core dimensions, and hence the aspect ratio can be predicted by the far field patterns of the fundamental modes. The present method should find application in the characterisation of elliptical core fibers and in predicting the carrier induced index changes in diode-lasers.

Experimental Study of the Controllable Microwave Troughguide Applicator

The design and evaluation of a new class of focussed electromagnetic hyperthermia applicators to increase penetration depth and improve control over the radiated field pattern is presented. Unlike currently available RF and microwave applicators, this new troughguide applicator provides a continuous aperture distribution with built-in deposited power monitoring.

Sound radiation from ducts: Theory and experiment

The paper deals with a method of prediction of noise radiated from finite length ducts with arbitrary shape. The computation of the internal and external acoustic field is based upon a new variational formulation by integral equations. Numerical results of far and near field radiation patterns are compared with experimental data for various higher order mode source conditions.

HYBRID MODE HORN ANTENNAS

ABSTRACT Hybrid mode horns are of considerable practical importance, especially as feeds for lens and reflector antennas. In this tutorial review the boundary conditions necessary to support hybrid modes in round waveguide are derived. Expressions for the field components in HE1n and EH1n modes are given and from these the transverse field over the open mouth of the guide is found. The Fourier transform of this field is then used to calculate far field radiation patterns. Solutions to the characteristic equation for hybrid modes are indicated and the dispersion characteristics for balanced modes are presented graphically. Finally, a brief discussion of dielectric-lined waveguide is given and asymptotic solutions are developed to show that nearly balanced HE11 and EH11 modes can exist over a limited frequency range when the dielectric is lossless, but over an unlimited range when the dielectric is highly lossy.

Radiation Fields of a Two Element Microstrip Array Antenna in Plasma

In an earlier paper, authors have investigated the radiation properties of a linearly polarized microstrip antenna in an ionized medium. The same work is extended for a two-element microstrip array antenna. Expressions for the far-zone electromagnetic and the plasma mode radiation field patterns for the array antenna have been developed and computed. It is observed that the EM-mode field patterns are modified to a great extent whereas the P-mode field patterns are similar to a single-element antenna. Results are also computed for the free space field patterns of the array.

Radiation Field Results from the Speed Triax Diode, a Large Area, High Dose Rate, Short Pulse 1 MV Bremsstrahlung Source

A flash X-ray source with a high dose rate and fast risetime, but which has a low concurrent total dose, is described. Monte Carlo code predictions of dose are compared with measurements of both radiation field patterns and cross-correlation of dose in thermoluminescent detectors (TLDs) and PIN diodes. Reasonable agreement between predictions and measurements is observed for low-Z materials. Large discrepancies exist, however, for dose enhancement effects in Si from a thin Au layer.

Radiation field of underwater organ pipes.

An ensemble of monopoles can approximately describe the radiation field of underwater organ pipes in low frequencies. Two extreme monopoles represent the mouth and the end opening respectively. Each of middle ones represents a pipe segment of halfwavelength. Phase difference and strength ratio between a middle monopole and a extreme one are theoretically considered. Experiment on the radiation field pattern of first mode confirms theory on it based on the above monopole approximation. Radiation field largely epends on pipe material because its distensibility governs the radiative strength of pipe wall.

Propagation and radiation characteristics of the disc‐on‐rod antenna

The disc‐on‐rod antenna is analyzed as a traveling wave antenna. The propogation characteristics along the rod are predicted by modal matching, including the effect of space harmonics. The analysis is confirmed by an open resonant cavity experiment. A parametric study shows that the ratio of the inner to the outer radius is the most important factor in controlling the phase velocity of waves along the disc on rod. The far field radiation patterns are predicted by Fourier transforming the aperture fields. This enables the variation with frequency of the copolar beamwidth and the peak cross‐polar power to be studied.

Computer Programs for the Calculation of the Horizontal Far Field Radiation Pattern and Directivity of Full Wave Dipole Panel Antennas

Two computer programs have been developped for the calculation of the horizontal far field radiation pattern and the directivity of full wave dipole panel antenna arrays for the VHF TV Broadcasting. The programs are written in Basic and were run with the aid of a HP-86 personal computer.

Finite Element-Integral Acoustic Simulation of JT15D Turbofan Engine

An iterative finite element-integral technique is used to predict the sound field radiated from the JT15D turbofan inlet. The sound field is divided into two regions: the sound field within and near the inlet which is computed using the finite element method, and the radiation field beyond the inlet which is calculated using an integral solution technique. The velocity potential formulation of the acoustic wave equation was employed in the program. For some single mode JT15D data, the theory and experiment are in good agreement for the far field radiation pattern as well as suppressor attenuation. Also, the computer program is used to simulate flight effects that cannot be performed on a ground static test stand.

Acoustic radiation from a semi-infinite annular duct in a uniform subsonic mean flow

By using a Wiener-Hopf approach, an analytical description is derived of the scattered field of a harmonic sound wave coming out of an open ended annular duct (a semi-infinite cylinder inside of which, coaxially, is a doubly infinite hub), submerged in a subsonic, coaxial, uniform mean flow. The possibility of vortex shedding from the pipe exit edge is included. Explicit expressions are given for the acoustic power inside the pipe, in the acoustic far field and, in the presence of vortex shedding, in the hydrodynamic far field, and of the power absorbed by the vortex sheet. The formulae are evaluated numerically with the aid of asymptotic expansions, and a method in which complex contour deformation is used, which is more convenient than those usually employed for this type of diffraction problem. The equality of power appeared to be an important check on the calculations. A numerical survey is made of the behaviour of the acoustic power loss, due to vortex shedding from the trailing edge, at frequencies near cut-off, as a function of Mach number, mode number of the incident wave, and hub radius. The power loss appears to increase with increasing Mach number, increasing hub radius and with decreasing frequency. Only in the case of the plane wave (where k→0) does the ratio of radiated and transmitted power become zero; for the other modes (at their cut-off frequencies) this ratio tends to a finite value. Somewhat surprising is that, in comparison with the jet, the power loss in a uniform flow is much higher. As a typical example for higher frequencies, the far field radiation pattern of a k=50, m=4 wave is considered as a function of the Kutta condition and hub radius.

Propagation and radiation of sound in a finite length duct

An analysis has been carried out to investigate sound transmission in an unflanged circular duct of finite length. A new formulation for calculating the generalized radiation impedance of the opening of a finite length duct with a spinning source inside is presented. The effect of interference between the duct apertures at its two ends is identified in the calculations of radiation impedance, reflection coefficient, and the far field radiation pattern. The results show that the degree of interference between the two ends reduces for high frequency waves and/or for long ducts. Further, the interference effects on the far field for spinning sound are more serious than those for non-spinning sound.

Analysis of longitudinal discontinuities in dielectric slab waveguides

The interaction of waves propagating in dielectric slab waveguides with longitudinal discontinuities is treated analytically. An integral-equation approach is employed to formulate the corresponding boundary-value problem. Transverse electric (TE) and transverse magnetic (TM) waves are considered in parallel. A Fourier-series-type expansion is utilized to expand the induced field inside the discontinuity region. The unknown coefficients of this expansion are determined by solving an integral equation. Scattered wave amplitudes in the forward and back-ward directions are computed by applying a steepest-descent integration technique. Radiation-field patterns are also obtained for the region outside the slab waveguide. Numerical results are presented for several cases. Resonance scattering, mode mixing, and several other interesting physical phenomena are examined.

Scattering of Guided Modes Caused by an Arbitrarily Shaped Broken End in a Dielectric Slab Waveguide

Electromagnetic scattering of guided modes in a dielectric slab waveguide caused by an arbitrarily shaped broken end is analyzed theoretically by using the integral equation method. By solving the integral equations iteratively, the tangential components of the electric and magnetic fields on the broken end surface are determined, from which the reflected mode power, the radiation wave power and field patterns, and the total scattered power are obtained. Numerical results are presented for the plane-perpendicular, plane-tilted, and arc-shaped end surfaces. Both TE and TM modes are assumed as an incident wave.

Radiation properties of a vacuum‐insulated infinite flat slotted plate antenna in a cold isotropic homogeneous plasma

The properties of an infinite flat plate antenna in a cold isotropic homogeneous plasma are investigated for the case in which the antenna is excited by means of a delta function voltage source across the infinitely long and narrow slit. Special attention was paid to the influence of an insulating vacuum layer between the antenna and the plasma. The far field radiation pattern and the power transport into the plasma and along the plasma‐vacuum boundary are analyzed.

Finite element formulations for acoustical radiation

Finite and infinite element techniques are applied to linear acoustical problems involving infinite anechoic boundaries. Theory is presented for a simple one dimensional model based on Webster's horn equation. Results are then presented both for the one dimensional model and for two axisymmetric test cases. Comparisons with exact solutions indicate that both the infinite element and wave envelope schemes are effective in correctly predicting the near field. The wave envelope scheme is also shown to be capable of resolving the far field radiation pattern.

Near field radiation pattern of tapered monomode optical waveguides

The Near Field radiation pattern of a tapered monomode planar waveguide is investigated for the first time. A theoretical technique is developed and the results obtained are shown to agree sufficiently well with experiments performed on tapered ion-exchanged glass guides to permit using this technique to predict taper performance.

The Use of Ultrasonic Spectroscopy to Characterize Calcified Lesions

A quantitative basis is developed for the medical application of ultrasonic spectroscopy, particularly in the characterization of calcified lesions associated with atherosclerotic conditions. A theory of the field radiation patterns of disk and ring sources is presented which can be used to predict minima in the reflection spectra of a target as a function of frequency and angle relative to the acoustic axis. The theory is then tested experimentally for objects of known geometry by the use of a time delay spectroscopy system using a swept frequency technique, and results are obtained which demonstrate the usefulness of the technique. Finally, the theory is verified in the determination of lesion diameter and orientation from spectra received from calcified lesions on in vitro arterial specimens as a function of angle.