Dielectric Loading Research Articles

Dielectric-supported helix in a metal shell

Abstract The equivalent circuit analysis for a helix in free space has been extended to include the effects of the surrounding dielectric and the metal shield, and an expression for the dielectric loading factor derived. The result agrees with that of field analysis, and is more accurate than is obtainable by a previous method of combining the equivalent circuit parameters for simpler helix configurations. The present method, unlike a held analysis, does not involve any lengthy algebraic manipulation to work out a determinantal dispersion relation

Resonance, phase front, and polarization-independence constraints of inhomogeneous fabry-perot interferometers

The major objective of this paper is to demonstrate the feasibility of imposing local resonance conditions while simultaneously controlling phase front properties upon transmission through slowly-varying Fabry-Perot type interferometers. The interaction of arbitrarily distorted incident phase fronts with double and triple-screened resonators is formulated, and appropriate design procedures are outlined. Special attention is paid to the significant effects of dielectric loading on the effective frequency band and to the cross polarization problem which arises, unavoidably, in conjunction with two-dimensional phase front distortions. The suggested design procedures are demonstrated via concrete numerical examples which are subsequently analyzed throughout a finite (20%) bandwidth.

Comments on "Ridged Waveguides with Inhomogeneous Dielectric Slab Loading" [Letters

In the above paper/sup1/, Magerl derives dispersion equations for TE/sub m0/ modes of ridged waveguide with inhomogeneous dielectric-slab loading. The existence of TE modes was evidently assumed a priori (a seemingly natural assumption); unfortunately, true TE modes do not exist in this waveguide (with a singuIar exception to be noted).

Some effects of dielectric loading on periodic slot arrays

The applications of arrays of rectangular slots have been severely limited since their resonant frequency (where unity transmission occurs) and bandwidth change with incident angle. By utilizing a modal analysis solution which includes the effects of dielectric slabs on both sides of the array, we show that these dielectric effects can, with proper design, reduce or eliminate the unwanted changes in resonant frequency and bandwidth. The presence of the dielectric slabs also cause other changes in the transmission curves. Two of these changes are the occurrence of the Wood's anomaly (blind angle) null at a lower frequency, and additional narrow resonances in the transmission curves. These phenomena are explained by considering the behavior of the Floquet modal impedances in the presence of the dielectric layer.

Radiation Characteristics of a Rectangular Aperture Centrally Loaded with a Dielectric Slab in theH-Plane

A rectangular radiating aperture with an H-plane dielectric slab in the centre is considered in this paper. The radiation pattern associated with the dominant LSM 11 mode is examined theoretically and experimentally and the if-plane pattern shaping is studied in detail. Such dielectric loading results in reduced E-plane sidelobe levels and may be utilized to equalize the patterns in the two principal planes.

Bandwidth Optimization by Dielectric Loading

The known theory of dielectrically loaded rectangular waveguides is combined with appropriate optimization procedures to yield optimal bandwidth design. The minimal acceptable power handling capacity and/or the maximal allowed losses are used as contraints. Alternatively, power handling capacity or losses may be considered as the desired optimization targets. The numerical determination of the relevant cutoff frequencies is carried out by the efficient mode-matching technique as well as the more generally applicable moment solution. Alternative search algorithms are used and compared. Results of the optimization process are given a simple physical interpretation.

Microwave Oven Mode Tuning by Slab Dielectric Loads

Cold-test measurements have been made of mode tuning in a microwave oven cavity containing a slab water load of variable height. Two distinct types of mode behavior are observed: 1) a mode which is tuned generally upward in frequency, proceeding in sawtooth stew and 2) a mode whose resonant frequency is nearly constant, except for slight downward perturbations at regular intervals. Two theoretical treatments are presented to understand and verify the observed mode behavior. A plane wave analysis is found to illustrate most of the qualitative aspects of mode tuning, such as its stairstep behavior and the phenomenon of mode linking by loss. A more accurate, quantitative description of mode behavior is obtained by generalizing dispersion relationships which have been developed in the past for the analysis of rectangular waveguides with dielectric slabs. Agreement between theory and measurement is good in general except for light loads in case 2 above.

Radiation from dielectric sphere loaded horns

The measured radiation pattern of a dielectric sphere fed from a conical horn is given. An appropriate matching device is shown to be a circular dielectric rod in the horn. Improvements in gain and circularity of the beam obtained by dielectric loading are demonstrated.

Radiation Characteristics of a Dielectric Sphere Loaded Surface-Wave Horn Antenna

The analytical and experimental investigations into the radiation characteristics of a high-gain antenna system are made. The antenna system consists of an H-plane sectoral horn with a layer of dielectric coating at the bottom E-plate (the top plate is removed) as a surface-wave source and a dielectric sphere placed off-set in front of the horn aperture. The radiation characteristics are derived by treating the antenna system as a microwave lens illuminated by an aperture source. There is good overall agreement between theoretical and experimental results of radiation pattern and gain measurements especially for dielectric spheres of diameters less than two wave lengths. It is observed that the on-axis gain of the surface-wave horn antenna is increased due to dielectric sphere loading. The system also possesses reduced 3-dB beamwidth. The proposed antenna system can be used either as a highly directive variable beamwidth feed for parabolic reflectors or as a convenient and effective high-gain source of radiation of UHF and microwave frequencies.

Analysis of rectangular waveguide partially loaded with lossy dielectric

An analysis is presented for rectangular waveguides with partial dielectric loading in the H-plane. Accurate results are given for attenuation and phase constant for lossy dielectric, using both exact and perturbation approaches. Particular attention is paid to the abnormal situation where attenuation can be greater for partial loading than for complete loading by the same lossy material. This abnormality was reported by Bui and Gagne but discounted by them as being mathematically spurious. By contrast, in this paper an exact theory has been used and the abnormality is shown to be genuine, and due to the hybrid mode redistribution of fields.

Analysis of rectangular waveguide partially loaded with lossy dielectric

An analysis is presented for rectangular waveguides with partial dielectric loading in the H-plane. Accurate results are given for attenuation and phase constant for lossy dielectric, using both exact and perturbation approaches. Particular attention is paid to the abnormal situation where attenuation can be greater for partial loading than for complete loading by the same lossy material. This abnormality was reported by Bui and Gagne but discounted by them as being mathematically spurious. By contrast, in this paper an exact theory has been used and the abnormality is shown to be genuine, and due to the hybrid mode redistribution of fields.

Mutual coupling in a linear array of rectangular waveguides

Asymptotic decay of the mutual coupling coefficient (C) aS a function of interelement distance (S) is measured in a linear array of rectangular waveguides with and without dielectric loadings. It is found that for dielectric plug loading, a plug thickness of half the guide wavelength in the dielectric (λge) gives the strongest mutual coupling between the elements of the array. This plug thickness matches an isolated guide opening in a ground plane. For no dielectric loading and for plugs, the decay law is C ∞ Sp, p being some constant.

Scattering by a dielectric-loaded trough in a conducting plane

A low-frequency solution to the diffraction problem of an E-polarized plane wave incident on a dielectric-loaded trough in a conducting plane is obtained. The dielectric loading consists of a circular cylinder which fits the semicircular trough in the conducting plane. The method used is a powerful low-frequency technique which has been succesfully applied to other problems of cylindrical geometry.

Properties of dielectrically loaded antennas

An analysis is made of the effect of dielectric loading on electric dipole antennas. Theoretical and experimental evidence is reviewed and an overview of properties in several distinct regimes obtained. The possible use of dielectrically loaded antennas for (a) broadband and (b) narrowband applications is assessed.

Numerical solution for nonreciprocal inhomogeneous waveguide interface

Mode matching is used to analyse the interface between a reciprocal homogeneous waveguide and a nonreciprocal inhomogeneous waveguide. The configuration used for the nonreciprocal structure is that of the twin-slab ferrite-loaded waveguide. The investigation is restricted to symmetrical E-plane loading, and to lossless structures in which only one mode may propagate. Based on the analysis, the interface and the nonreciprocal waveguide are described by relatively simple equivalent transmission circuits. In these circuits, unique equivalent transmission-line characteristic admittances are defined for the nonreciprocal waveguide. Results show that although the phase coefficients in the two directions of propagation can be very different, the equivalent characteristic admittances are nearly the same. Measurements on a practical version of the twin-slab configuration yield similar results. It is also noted that the energy stored, which is associated with the inhomogeneous interface, does not depend solely on the type of modes excited, in contrast to the case of (reciprocal) dielectric loading.

Radiation from a homogeneous sphere mounted on a waveguide aperture

The results of an experimental and theoretical study of the effects of placing a dielectric sphere over the aperture of a circular waveguide are presented. A dielectric sphere excited by a Huygens' source is used us the theoretical model to interpret the experimental results. Calculations based on this model show good overall agreement with experimental patterns and directivity measurements. It is concluded that dielectric loaded antennas such as the dielectric sphere excited by a waveguide can produce directivities in excess of that obtained by a uniformly illuminated aperture of the same cross section, particularly for dielectric objects with dimensions of two wavelengths or less. Measurements of the coupling between these antennas show that they, in general, are not as closely coupled as plain apertures without dielectric object loading.

Application of a unimoment technique to a biconical antenna with inhomogeneous dielectric loading

Except for the most trivial cases, antenna radiation problems involving inhomogeneous media escape analytical solution. For these problems, it is necessary to seek computer solutions. To this end, we have investigated Mei's [1] unimoment technique as it applies to a biconical antenna immersed in an inhomogeneons medium. The technique is used in conjunction with finite difference methods to analyze some dielectric loading schemes with the goal of improving performance of the biconical antenna. The technique is shown to be sufficiently general to allow analysis of any rotationally symmetric antenna inside an inhomogeneous medium by using more flexible finite element methods. Results of experimental investigations bear out the validity of the technique.

Power Generation and Efficiency in GaAs Traveling-Wave Amplifiers (Short Papers)

The effect of the dielectric loading in a bidimensional analysis that follows. GaAs traveling-wave amplifier (TWA) is investigated, with respect to the EM power generated by the structure and the efficiency of the dc to RF conversion. The validity of some usual approximations and assumptions is studied and a parameter, i.e., the power gain X efficiency product, is proposed as a useful tool for comparing the possible performances of TWA's.

Diffraction by a conducting wedge loaded with radial dielectric slabs

The paper reports a theoretical analysis of the diffraction of an E-polarized line source by A conducting wedge loaded with radial wedge-shaped dielectric slabs with a common virtual apex. Since the angular eigenfunction expansion method is not suitable for this problem, the radial eigenfunction method is employed with a small cylindrical cap introduced at the apex and is found to be more rapidly convergent than the angular method in the absence of dielectric loading. It is shown that the eigenvalues are complex while the resulting series solution for the electric field is found to converge in the shadow region only. The results are specialized to study the effect of an air gap between a single dielectric layer and the illuminated face of the wedge, It is shown that the electric field at the forward shadow line decreases with air and dielectric angular thicknesses while the field in the shadow region remains practically unchanged relative to the field at the forward shadow line.

The effect of dielectric surface loading on the stability of epitaxial coplanar Gunn diodes

The existence of current instabilities in epitaxial coplanar Gunn diodes was observed as a function of the nd product for air and oxide surface loading. Theoretical considerations indicate that the GaAs substrate and a surface depletion layer may substantially affect the stability of coplanar devices.