Surface Waves on Symmetrical Three-Layer Sandwiches (Correspondence)

The theory of surface waves on plane dielectric slabs has been presented by Plummer and Hansen. Additional numerical results are shown in Figs. 1 and 2 for the lowest order TM and TE modes that can exist on a grounded dielectric slab. The slab has thickness d, and a relative dielectric constant of 4. It is separated by an air gap of thickness a from the ground plane. c/v represents the ratio of the velocity of light in free space and the phase velocity of the surface wave. By image theory, these modes (TM/sub 0/ and TE/sub 1/) can also exist on a symmetrical, three-layer, air-core sandwich to which the given numerical data also apply.     

Dual-frequency circularly polarised annular-ring microstrip antenna

The design of the circular polarisation (CP) for an annular-ring antenna operated at its TM/sub 11/ and TM/sub 12/ modes is presented. The CP radiations of the proposed design are achieved by placing an L-shaped strip connected to two orthogonal sides of the inner boundary of the annular patch. The dual-frequency CP operations are excited by a single probe-feed, and no additional 90/spl deg/ phase shifter and impedance-transformer circuit are required. A prototype of the proposed design was implemented and measured. Measured results show that broadside radiation patterns with good CP characteristics are obtained at the two operating resonant modes. Agreement between measured and numerical results is satisfactory.     

Rigorous Analysis of the Scattering of Surface Waves in an Abruptly Ended Slab Dielectric Waveguide

The reflection and the scattering properties of even TE and TM surface waves incident in an abruptly ended dielectric slab waveguide are analyzed. The discontinuity is regarded as a junction between two open waveguides namely the dielectric slab waveguide and the free space waveguide. The boundary conditions acting together with the orthogonality provide singular coupled integral equations on the discrete and the continuous wave amplitudes at the discontinuity. These singular coupled intergral equations with Cauchy kernels and infinite limits of integration are solved by iteration via the Neuman series. Numerical results are presented for the reflectivity of the even TE/sub 0/ and TM/sub 0/ fundamental modes, together with their mode conversion on even TE/sub 2/ and TM/sub 2/ in a slab where two guided modes can propagate. Reflectivity and mode conversion of higher order excitations are also investigated     

Transmission Characteristics of Spherical TE and TM Modes in Conical Waveguides (Short Papers)

The transmission properties of spherical TE and TM modes in a perfectly conducting conical waveguide are treated in detail. To start with, an analytically simple and highly accurate digital-computer based iterative algorithm has been employed to evaluate the eigenvalues associated with the spherical TE and TM modes within the guide irrespective of the flare angle (2alpha/sub 0/) of the conical waveguide (theta < 2alpha/sub 0/ < 360/spl deg/). Subsequently, explicit expressions for the attenuation constant, phase constant, phase velocity, and wave impedance are obtained for the spherical modes transmitted within the guide. Accurate eigenvalues obtained numerically are used to study the variation of attenuation constant, phase constant, phase velocity, and wave impedance as a function of the radial distance from the apex with alpha/sub 0/ as a parameter. Measured data on the phase constant of a conical waveguide for the TE/sub 11/ mode have been compared with the analytical results obtained by calculation and an excellent agreement between the two justifies the validity of the analysis presented. Finally, a study of the phase coherence between the dominant spherical TE and TM modes within the guide is presented which may be fruitfully employed in the design of dual-mode conical waveguides.     

Mode Analytical Study of Cylindrical Cavity Power Combiners

A mode analytical treatment of cylindrical cavity power combiners is presented to discuss power-combining capability and the method for attaining stable desired mode operation. Both the conventional coaxial-probe output type and the window output type are treated, based on a circuit model which can support TM/sub 010/, TM/sub 020/, and TM/sub m10/ modes (1<=m<=N, N being the number of active devices employed). It is shown that adoption of the window output largely facilitates undesired mode suppression and also enables power combining in some azimuthal modes.     

On the Mode and Square Correspondence Between Circular Multimode Tapered Waveguides

In an axially straight multimode circular waveguide taper excited with a pure TE/sup /spl circle// /sub 11/ dominant mode, the first and only converted mode at and near cutoff is the TM/sup/spl circle// /sub 11/ mode. It is shown that in an axially straight multimode square waveguide taper excited with a pure TE/sup/spl square// /sub 10/ dominant mode, the TM/sup/spl square// /sub 12/ mode corresponding to the TM/sup/spl circle// /sub 11/ mode in circular case is not the only first converted mode at and near cutoff. The overall behavior or coupling mechanism of waveguides is similar whether the waveguide is rectangular, square, circular, or elliptical: i.e., the overall coupling coefficient at cutoff of a converted mode or modes approaches an ininfinity of the order 0/sup -1/4/.     

TM/sub 0n0/ - and TM/sub m10/ - Mode Oversized Cylindrical Cavity Power Combiners

TM/sub m10/ -mode power combining is treated in addition to conventional TM/sub 0n0/-mode combining in a multiple-device oversized cylindrical cavity having a window output structure. Mode analysis gives the condition for stable power-combining operation in the desired mode. By experiments both on TM/sub 0n0/ -mode combining (n = 2, 3, and 4) and on TM/sub m10/ -mode combining (m = 2 and 8), it is shown that almost perfect power combining in the TM/sub 210/ mode can be achieved as in the TM/sub 020/ mode and that the power combining efficiency decreases gradually with increasing n or m. A possible advantage of TM/sub m10/ -mode combining in an oversized cavity is suggested based on the experimental result that power combining in the TM/sub 810/ mode gives higher efficiency than in the TM/sub 040/ mode.     

Propagation Losses of Guided Modes in an Optical Graded-Index Slab Waveguide with Metal Cladding

Analytical results for propagation Iosses of guided modes in a graded-index slab waveguide (GISW) with metal cladding are presented. When the permittivity in the guiding layer decreases linearly away from the metal surface, the attenuation constant alpha/sub G/ of well-guided modes, TE and TM, is approximately proportional to only the ratio (Delta epsilon/sub i/ / epsilon/sub 0/) / d/sub i/, where Delta epsilon/sub i/ is the increment in the permittivity at the metal surface in the direction of the polarization of optical waves, d/sub i/i is the diffusion depth in this direction, and epsilon/sub 0/ is the permittivity of free space.     

Scattering at Circular-to-Rectangular Waveguide Junctions

A formally exact solution is given for the problem of scattering at a circular-to-rectangular waveguide junction and at a thick diaphragm, with a centered circular aperture, in a rectangular waveguide. The method uses normal TE and TM mode expansions of the waveguide fields and traditional mode matching of the transverse electric and magnetic fields at the junction boundary. Exact closed-form expressions are obtained for the electric field mode-matching coefficients which couple the TE(TM) modes in the rectangular guide to the TE(TM) and TM(TE) modes in the circular guide. Numerical results are presented for the case of TE/sub 10/ mode propagation in the larger rectangular guide with all other modes cutoff. Convergent numerical results for the equivalent shunt susceptances of such junctions are obtained when about 12 modes (eight TE and four TM) are retained in the circular waveguide or in the circular aperture of the diaphragm. The results are graphically compared with formulas and curves due to the quasi-static theory of Bethe and the variational theory given in the Waveguide Handbook [2].     

Excitation and Scattering of Modes on a Dielectric or Optical Fiber

A technique similar to that of Kirchhoff is used to obtain an analytic expression for mode Iaunching on a semi-infinite rod. The approximation is quasi-optical and only valid for small angles of incidence /spl theta/. When /spl theta/ = 0 only HE/sub 1M/ modes are excited; however, for /spl theta/<<1 many modes can be launched. The effect on HE/sub 11/ mode propagation of small imperfections in a dielectric waveguide is analyzed. At the frequency of interest for optical communication (cutoff for the TM/sub 01/ mode) the radiated power is 160 times larger than that scattered into the HE/sub 11/ mode.     

Modal analysis for a bounded-wave EMP Simulator - part II: radiation leakage and mode suppression

Radiation leakage from a high-power bounded-wave electromagnetic pulse simulator can cause severe electromagnetic interference (EMI) with surrounding equipment. In Part I, we analyzed the electromagnetic mode structure inside a simulator. In Part II, we examine the relative contribution of these modes to radiation leakage. We have calculated the temporal cross correlation between the electromagnetic modes inside the simulator and the temporal waveform of the forward-radiated far field. The TM1 and TM2 modes show strong cross correlation over a range of switching times. For the TEM mode, on the other hand, this holds true only for larger values of the switching time. Hence, for a given mode amplitude, higher order TM modes tend to produce more leakage than the TEM mode. However, since TEM is far stronger than TM throughout the simulator, it may still contribute more in absolute terms. Increasing the angle between simulator plates excites more higher order modes and increases their strength, thereby enhancing leakage. Pulse compression with respect to time increases the relative strength of higher order modes. Placing a spatial mode filter inside the simulator significantly reduces TM/sub 1/ without modifying the desired TEM mode. However, TM/sub 2/ remains largely unchanged. The reduction in TM/sub 1/ depends sensitively upon the parameters of the filter. These observations illustrate a new method of understanding and improving simulator design from the point of view of EMI.     

Dual mode and stacked concentric ring patch antenna arrays

A dual mode concentric ring patch antenna is discussed which is suitable for vehicles operating with mobile satellite communication systems. It is operated at two modes, the TM/sub 21/ and TM/sub 41/ modes, which possess conical radiated beams. Switching between these modes provides omnidirectional azimuth coverage with elevation beam steering.<>     

Phase matching in magneto-optic YIG films by waveguide temperature control

Demonstrates the tuning of linear birefringence in magneto-optic planar thin-film waveguides by temperature adjustment. Using this method, phase matching between coupled TE/sub 0/ and TM/sub 0/ modes, a necessary condition for the integrated optical isolator based on mode conversion, has been obtained at lambda =1.52 mu m in bilayer gadolinium gallium-substituted YIG films. The waveguide temperature was 85 degrees C. Moreover, the phase-matching temperature can be modified by a slight variation of gadolinium and gallium substitutions as shown by a phase matching observed in a waveguide at room temperature.<>     

Bandwidth-enhancing ultralow-profile compact patch antenna

A novel method to extend the operation bandwidth and reduce the size of the ultralow-profile patch antenna is presented in this paper. The designed results indicate that two orthogonal modes of TM/sub 10/ and TM/sub 01/ can be excited simultaneously in the antenna, resonate at two close frequencies, and also are matched well. Thus, a bandwidth-enhancing characteristic is achieved. The size reduction is obtained due to utilizing the slot-loading technique. Because most patch currents of the two modes flow in the same direction, the similar radiation characteristics is observed at two resonance frequencies. The significantly high cross polarization makes the proposed antenna applicable for the wireless communication in multipath environment.     

Mode Conversion in Tapered Waveguides At and Near Cutoff

The coupling coefficient between the TE/sub 11/ mode and the TM/sub 11/ mode in tapered circular waveguides is derived, and at cutoff frequency it tends to approach an infinity of the order of 0/sup -1/4/. It is surprising to discover that the corresponding coupling coefficient between the TE/sub 10/ mode and the TM/sub 12/ mode in tapered rectangular waveguides approaches instead a zero of the order of 0/sup 1/4/ at cutoff frequency. Accordingly, for the modes concerned, the choice of using circular or square waveguides as tapers for transition at and near cutoff frequency is significant in reducing mode conversion level. At and near cutoff frequency a "synthesized" square taper is better in that it is shorter than a "synthesized" circular taper for the same mode conversion levels. On the other hand, for frequencies far away from cutoff the choice is insignificant. Design procedures for "synthesized" waveguide tapers at and near cutoff are presented, and the results of measurements are in agreement with the theoretical calculations.     

Complex Gyrator Circuits of Planar Circulators Using Higher Order Modes in a Disk Resonator

Tire use of resonators or waveguides utilizing higher order modes is often an attractive solution to the design of millimeter microwave networks. This paper investigates the complex gyrator circuit of a planar junction circulator employing higher order solntions in a disk resonator. The first such solution displays many of the features of weakly magnetized junctions using the dominant mode in a disk resonator, but its loaded Q-factor is incompatible with the realization of quarter-wave coupled devices. Although the second one exhibits more useful equivalent circuits, it requires a relatively large magnetization, which is not altogether practical at millimeter frequencies. A circulator configuration that has a frequency response akin to that of a quarter-wave coupled one is one where the in-phase eigennetwork is degenerate with those of the demagnetized counter-rotating eigennetworks. The degeneracy between the in-phase limit, TM/sub 2, 0, -2/ and the second-order counter-rotating limit, TM/sub 1, 1, -2/ modes, in an oversized irregular hexagonal resonator, is used in this paper to construct such a device.     

Application of Dual TM Modesto Triple- and Quadruple-Mode Filters

The cylindrical cavity dual orthogonal transverse magnetic (TM) mode is introduced as a basic building block for the realization of microwave multiple-coupled-cavity bandpass filters. This concept is shown to offer significant advantages in the design of triple-mode filters and permits the design of the new quadruple-mode filter. Experimental verification is provided by the realization of a triple-mode, six-pole elliptic function bandpass filter with dual TM/sub 110/ and single TE/sub 211/ (transverse electric) modes and a quadruple-mode, eight-pole bandpass filter with dual TM/sub 110/ and dual TE/sub 112/ mode cavities. All units exhibit good agreement between theory and experiment.     

Artificially integrated synthetic rectangular waveguide

A synthetic rectangular waveguide (SRW), which consists of two electrical sidewalls and two parallel periodical structures placed at the top and bottom surfaces of the waveguide, is presented. The SRW is made by multilayered integrated circuit processes, which typically have large ratios of SRW lateral dimensions to substrate thickness. Two theoretical methods, finite-element method and deembedding of composite structure consisting of SRW and mode converters, are applied to investigate the propagation characteristics of the SRW. Application of the dispersion characteristics of the two-dimensional periodical structures coupled with appropriate mode converter designs leads to results in SRW designs supporting TE/sub 10/, TM/sub 00/, and TM/sub 10/ modes. Measurements and the two theoretical approaches indicate that the slow-wave factor is 4.9 and Q-factor is 260 at 6.85 GHz for the TE/sub 10/ mode propagation with a cutoff frequency of 4.10 GHz (0.348 factor of cutoff frequency of conventional rectangular waveguide using the same material and dimensions). The theoretical data show the TM/sub 00/ mode to have a slow-wave factor of 1.8, Q-factor of 187.6 at 11.4 GHz, and cutoff frequency of 10.2 GHz. The TM/sub 10/ mode has a slow-wave factor of 1.98, Q-factor of 187.6 at 12.5 GHz, and cutoff frequency of 10.4 GHz.     

Dielectric Loaded Elliptical Waveguides

Wave propagation in a metallic elliptic waveguide loaded with a dielectric rod or a dielectric lining is investigated theoretically. The mode spectrum for both slow and fast hybrid modes is obtained by numerical solution of the characteristic equations. Correspondence is established between the modes of the loaded and unloaded elliptical waveguides. Typical field plots for /sub e/HE/sub 01/ and /sub 0/EH/sub 01/ modes are presented. Power flow, power loss, and attenuation are obtained using a perturbation method.     

Loss Increases in Multimode Rectangular Infrared Waveguides Due to Helical Deformations

The coupling coefficients for all TE/sub pq/ and TM/sub pq/ modes of multimode rectangular waveguides, caused by elementary rotations about the three axes of symmetry, are calculated in the microwave approximation. The modes b coupled to a common mode a by these independent rotations form three nonoverlapping families. Furthermore if a deformation consisting of no more than two of these rotations is considered, none of the modes b are coupled to each other by that deformation. These properties lead, in the case of mild deformations, to the formulation of a multimode coupling theory which shows that the loss increase due to such deformations can then be viewed as the result of multiple two-mode coupling. Explicit formulas are derived for the loss increase of TE/sub p0/ due to mild circular bending. Qualitative features of twists and helical deformations are also brought out.