Design consideration for modeless integrated circuit substratesusing planar periodic patches

In recent years, there has been significant interest in complete surface-wave elimination (meaning in all possible directions) through the use of periodic elements incorporated into integrated circuit structures. However, to date there is no comprehensive theory for the design of the surface-wave bandgap, and it also appears that leaky modes with complex propagation constants that may exist on the planar periodic structures have not been properly taken into account. As shown here, fast periodic leaky modes may exist within a surface-wave bandgap zone. These leaky modes may result in more energy loss and crosstalk than the surface-wave modes and should be taken into account in circuit design. This paper presents theory and experimental validation for guided surface-wave and leaky modes on a printed circuit structure consisting of planar periodic metal patches over a grounded substrate. The existence of surface-wave bandgaps and leaky modes is attributed to either element resonances or the weakly bounded dielectric slab modes. It is also found that fast periodic leaky modes may exist within a surface-wave bandgap zone. Design procedures for achieving a complete surface-wave bandgap without leaky-modes are outlined and examples are given     

The theory of surface-wave and space-wave leaky-mode excitation onmicrostrip lines

This paper discusses the excitation and physical validity of both surface-wave and space-wave leaky modes on microstrip lines. This is done by analyzing the discrete modal spectrum excited by a realistic source on or near an infinite microstrip line. A semi-analytical three-dimensional (3-D) Green's function is used for this purpose, which provides the current excited on the conducting strip due to the source. The 3-D Green's function is in the form of a spectral integration (inverse Fourier transform) in the longitudinal wavenumber plane. The poles of the integrand directly determine the excitation amplitudes of the modes on the structure that are launched by the source. The integrand also has different types of branch points, and the location of the poles on the various Riemann sheets is used to determine the physical significance of the leaky modes. Although the theory presented here is illustrated for a microstrip line, the conclusions apply in general to open printed-circuit structures     

Launching of the HE11 surface-wave mode on a dielectric rod

The fields excited by a point electric dipole situated on, but oriented perpendicularly to, the axis of an infinitely long dielectric rod are examined. A technique, which involves expressing the fields and the source in a Fourier integral in the z direction and a Fourier series in the ? direction in a cylindrical co-ordinate system (p, ? z), is adopted for the analysis. Only the dominant HE11 dipole modes are found to be excited. Some preliminary numerical results for the dispersion characteristics and the surface-wave power are presented.     

Surface waves on a grounded dielectric slab covered by a periodically slotted conducting plane

The surface-wave modes in a dielectric slab covered by a periodically slotted conducting plane are investigated. Two methods-sampling and variational-are used to obtain the surface-wave modes. The dispersion curves obtained by the two methods agree very well. The experimental and the theoretical results are in good agreement, except close to the stopband.     

A note on the mode characteristics of a ferrite slab

Properties of guided-wave modes of a ferrite slab propagating in the direction transverse to the bias field are reexamined. Analytic results for the frequencies where magnetostatic and dynamic modes exist simultaneously are found. The method of eliminating the dynamic modes in the magnetostatic-wave operation is described. The formulas for the distinction of oscillatory and surface-wave modes are also derived     

High-gain meanderless slot arrays on electrically thick substratesat millimeter-wave frequencies

Introduces new techniques and architectures for the implementation of linear slot arrays on electrically thick dielectric substrates at millimeter-wave frequencies. The slot arrays are fed by a coplanar waveguide series line and lead to high gain by utilizing the phase cancellation technique to reduce coupling to the dominant surface-wave mode. Unlike traditional designs, no meander lines are used in the proposed structures, easing their fabrication by eliminating the need for air bridges and leading to patterns with low cross-polarization and high gain. In addition, the option of including a backing ground reflector to render the patterns unidirectional is explored and implemented. In this latter case, it is shown that simultaneous reduction of the dominant surface-wave and TEM modes through phase cancellation can be achieved. The design of the proposed arrays is based on an intuitive transmission-line model, which enables the implementation of arrays with a gradual current taper and, thus, maximum gain. This study is verified experimentally around a nominal frequency of 27.8 GHz     

Surface Waves on Radially Inhomogeneous Cylinders

A characteristic equation and a cutoff equation are derived for higher order surface-wave modes on lossless isotropic cylinders with arbitrary radial permittivity variation. The derivation, based on the use of the fundamental matrix of a set of differential equations, reduces analytical work and results in expressions well suited for digital computer evaluation of surface-wave eigenvalues and mode spectra. The theory is applied in an investigation of HE/sub 21/ and EH/sub21/ mode propagation for a particular set of models for the radially varying permittivity. Typical results showing eigenvalue variation, dispersion characteristics and radial field variation, including experimental verification of dispersion characteristics, are shown. The method of analysis can be extended to anisotropic cylinders with permittivity a function of both radius and frequency.     

On the Physical Meaning of the Spectral Decomposition

In the analysis of open planar structures, it is widely accepted that the spectral decomposition of the fields excited by a given source into its continuous and discrete spectrum components has an apparent physical meaning. The continuous spectrum is associated with radiation and/or reactive effects whereas the discrete spectrum corresponds to the bound fields guided by the structure. Although this interpretation is usually correct, the present work will show that it is not general. In particular it will be shown that a lossy grounded dielectric waveguide near the cutoff frequencies of its higher-order surface-wave modes is a simple and interesting counterexample in which the continuous and the discrete spectrum fail to bear their intended physical meaning. A careful analysis of the modal cutoff mechanism provides numerical results that fully support the above assertion.      

High-frequency leaky-mode excitation on a microstrip line

The excitation of leaky modes (LMs) and the continuous spectrum (CS) on a microstrip line at high frequencies from a delta-gap source is studied. The delta-gap source models a practical source or discontinuity on the line. It is shown that the current excited from the source exhibits spurious effects at high frequencies due to the excitation of the CS (radiation spectrum), which may or may not be dominated by a physical LM, depending on the frequency range and the substrate permittivity. In some cases, the spurious effects are due to a physical LM, while in other cases the effects are due to the excitation of one or more "residual-wave" (RW) currents, which have not been previously studied for open microstrip lines. There are two types of RW currents: a free-space type and a surface-wave type. Depending on the frequency and the structural parameters, either of these may be the more dominant. At certain frequencies, weakly attenuated high-order LMs may also be excited, in which case spurious effects are observed out to large distances from the source     

Higher-Order Cylindrical Surface-Wave Modes

A general theory of the propagation of higher-order modes on cylindrical surface-wave structures is examined and applied to the dielectric-clad rod. A theory is developed in which the boundary conditions at the guide are specified by an impedance dyadic. The characteristic equation for the structure is then obtained in terms of the elements of the dyadic. The equation is solved and yields a set of conditions which are satisfied by the values of the dyadic elements at the cutoff points for each of the higher-order modes. A mode without a cutoff frequency is shown to exist on the structure used. The relationship between the guide wavelength and frequency has been verified experimentally.     

Two-dimensional surface-wave diffraction from an arbitrary source in an anisotropic medium

It is shown that, if a parabolic function approximates closely to the relevant wavenumber surface, the surface-wave diffraction pattern radiated from any source is related, by a simple scale factor, to that launched by the same source into an isotropic medium. The argument, based on resolution of the source into an orthogonal Gaussian?Hermite mode set, may find application both in integrated optics and in the design of acoustic-surface-wave matched filters.     

Full-Wave Analysis of Microstrip Open-End and Gap Discontinuities

A solution is presented for the characteristics of microstrip open-end and gap discontinuities on an infinite dielectric substrate. The exact Green's function of the grounded dielectric slab is used in a moment method procedure, so surface waves as well as space-wave radiation are included. The electric currents on the line are expanded in terms of longitudinal subsectional piecewise sinusoidal modes near the discontinuity, with entire domain traveling-wave modes used to represent incident, reflected, and, for the gap, transmitted waves away from the discontinuity. Results are given for the end admittance of an open-ended line, and the end conductance is compared with measurements. Results are also given for the reflection coefficient magnitude and surface-wave power generation of an open-ended line on substrates with various dielectric constants. Loss to surface and space waves is calculated for a representative gap discontinuity.     

Magnetostatic Surface-Wave Propagation in Ferrite Thin Films with Arbitrary Variations of the Magnetization Through the Film Thickness

A variational formulation for the magnetostatic problem in an anisotropic and inhomogeneous region bounded by perfect conductors is described. The method is applied to the special case of magnetostatic surface-wave (MSSW) modes propagating in a ferrite thin film with arbitrary variations of the saturation magnetization through the film thickness. Methods for calculating dispersion relations, delay characteristics, and magnetostatic potential functions are discussed. The functional that is minimized is interpreted in terms of contributions to the mode energy. Also, concepts pertaining to homogeneous films such as mode bandwidth and dimensional scaling effects are extended to the general inhomogeneous case. Calculations for a two-layer film with a gradual transition region and an ion-implanted film are presented as numerical examples.     

The Elliptical Surface Wave Transmission Line

Electromagnetic wave propagation on an elliptical cross-sectional surface-wave transmission line is investigated theoretically. Characteristic equations for odd and even hybrid modes are derived and solved numerically. Expressions are obtained for power flow, energy storage and power loss using a perturbation method. Numerical results on propagation characteristics of three lower order modes are presented. The /sub 0/HE/sub 11/ mode is shown to have low attenuation particulary at high eccentricities. The propagation characteristics of lines of high eccentricities are found to be slowly varying functions of dimensions.     

Surface-wave radiation loss from curved dielectric slabs and fibers

A newly developed systematic procedure to calculate the real and imaginary parts of the change in propagation constant of a surface-wave mode on a curved open waveguide of general cross section is used here to determine these quantifies for the TE modes of an asymmetric slab waveguide and for all the modes of an optical fiber. Comparison of these results with the existing literature points up the care which must be taken in making approximations in this problem, since errors of significant factors in the radiation loss have been made in previous work.     

Improvements to a surface-wave antenna measurement range with troublesome site effects

A surface-wave antenna measurement range used for ship antenna modelling work has been improved by the development of a novel source antenna. The antenna, a large `half-truncated? corner reflector, has reduced unwanted range reflections to allow phase measurements to be made to an accuracy of approximately ±2°. Also, the screening effect of the reflector allows an adjacent range on the same reflecting ground plane to be operated simultaneously without noticeable effect on the surface-wave range performance.     

EM-wave propagation through semi-elliptic cylindrical dielectricwaveguide on a perfectly conductive planar substrate

This is a theoretical study of modes in a semielliptic cylindrical dielectric waveguide on a perfectly conductive planar substrate. Interest is mainly in high eccentricity, electrically large, hence multimode, structures. The theory applies to light propagation through surface-wave transmission lines or microwave ducting by shore-bounded evaporation ducts. The rigorous formulation of fields in terms of radial and azimuthal Mathieu eigenfunctions is followed by accurate computations of the longitudinal phase constant, the fractional power trapped within the waveguide and the group velocity. The effects of size, ellipticity and refractive index step on mode features are investigated. As information, previously unavailable, about high-order modes is reported, an interesting classification of modes readily unfolds     

Influence of surface metallisation on magnetoelastic surface wave

The surface-wave coupling which obtains between an elastic bulk shear wave and two magnetostatic modes (one of which is a bulk wave and the other a surface wave) is discussed in the context of a metallised semi-infinite ferrite geometry.     

Short-wave radiation generation by strip electron beams in the surface-wave excitation mode

The quasi-optical theory of short-wave Cherenkov oscillators, in operation of which surface waves are excited by relativistic electron beams moving above periodically corrugated structures, is constructed. π-mode oscillations characterized by the generation rate close to the Bragg frequency, as well as backward-wave tube modes in which generation rate is shifted downward from the Bragg frequency, are analyzed. It is demonstrated that surface-wave excitation can be employed to generate submillimeter radiation with multimegawatt power levels.