X-band TM/sub 01/-TE/sub 11/ mode converter with short length for high power

A mode converter for X-band located between a generator and an antenna to convert TM/sub 01/ to TE/sub 11/ mode with high efficiency for a high power transmitting system is presented. The proposed mode converter has extended radius and excessive curvature with symmetric structure in order to convert between two modes efficiently with short length. The measured and simulated results of the return loss, mode patterns and efficiency of the proposed mode converter with 200 mm length are provided.     

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.     

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.     

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.<>     

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.     

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.     

Circular polarised microstrip patch antennas for broadband and dual-band operation

A novel design of microstrip patch antennas for circular polarisation (CP) is proposed. As an example, two CP patch antennas are investigated: a broadband CP patch antenna and a dual-band CP patch antenna. The proposed structure can be achieved by embedding circular holes in the microstrip circular resonator. By changing the size and position of loaded holes, two orthogonal modes are simultaneously excited with equal amplitude and /spl plusmn/90/spl deg/ out of phase. Without any 90/spl deg/ phase-shifter, the proposed CP patch antennas are excited by single feed.     

Frequency-adjustable circularly polarised dielectric resonator antenna with slotted ground plane

Circularly polarised (CP) dielectric resonator antennas (DRAs) with a slotted ground plane are proposed. The proposed CP design is achieved by embedding two pairs of unequal slots in the finite ground plane of the feed substrate, which results in the excitation of two near-degenerate orthogonal modes and leads to CP radiation. For the proposed design, a large CP bandwidth, determined from 3 dB axial ratio, as high as 2.7% is also obtained. The resonant frequency can be tuned by changing the slot length. This proposed design is applicable to DR antennas where post-manufacturing trimming is required. Details of the proposed designs and experimental results of the constructed prototypes are presented.     

An analytical approach for the inverse scattering solution of radially inhomogeneous spherical bodies using higher order TE and TM illuminations

A novel method for the reconstruction of inhomogeneous permittivity profiles of spherical dielectric objects illuminated by higher order TE/sub mn/ and TM/sub mn/ spherical modes is presented. The overall technique is based on the derivation of Riccati-similar nonlinear differential equations in a spherical coordinate system for both TE and TM illuminations as a part of the direct problem formulation. These differential equations are then inverted using a quasi-linear approach to obtain a closed-form expression of the radially varying permittivity profile of spherical objects in terms of a spherical Fourier-Bessel transform of the measured spectral domain reflection coefficient data. To validate the proposed method, several examples with different mode illuminations and with different noise levels are considered for reconstructions. A good agreement between the actual and the reconstructed permittivity profiles even under high noisy conditions shows that our method is not much sensitive to the presence of noise in the reflection coefficient data.     

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.     

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].     

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/.     

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.     

Solution of the Finite Length Septum Problem with Application to Periodic Mode Suppressors

A square waveguide with periodic septums is considered with a view towards determining the parameters of a structure which suppresses three of four possible propagating modes. The analysis is presented in two parts, the first of which is concerned with the isolated septum. Using available techniques, semi-infinite scattering matrices are determined for the semi-infinite septum for arbitrary TE/sub N0/, TE/sub N1/, and TM/sub N1/ incident modes. These are used to derive Fredholm matrix equations which yield the field everywhere near the finite length septum. The leading terms of the inverted equations are the far-field transmission and reflection coefficients. The solutions are evaluated for several frequencies, and fifth degree polynomials are fitted for the computation of S/sub 11/ and S/sub 12/. The analysis for the TE/sub 10/ mode is applicable to an arbitrary height waveguide and may be used without modification for the "finite length" septum in conventional waveguide. The second part is concerned with the periodic waveguide and assumes that the septums are far apart. A contour chart is introduced to visualize the performance of the periodic structure. The chart is especially useful when more than one propagating mode is involved and simplifies the design problem so that the parameters of practical structures may be obtained with little effort.     

Modal analysis for a bounded-wave EMP Simulator - part I: effect of test object

We have analyzed the electromagnetic-mode structure inside a bounded-wave electromagnetic pulse (EMP) simulator. This has been done by the application of the singular value decomposition method to time-domain data generated by self-consistent, three-dimensional finite-difference time-domain simulations. This combination of two powerful techniques yields a wealth of information about the internal mode structure which cannot be otherwise obtained. To our knowledge, this is the first time such a comprehensive study has been done. In the absence of a test object, the transverse electromagnetic (TEM) mode is dominant throughout the simulator length. TM/sub 1/ dominates over other transverse electromagnetic (TM) modes over most of the length. Close to the termination, the TEM mode weakens marginally, while higher order TM modes become stronger. The enhancement of TM/sub 2/, and the weakening of TEM near the termination, have been explained in physical terms. Placement of a perfectly conducting test object in the parallel-plate section increases the strength of higher order TM modes, at the cost of TEM. Hence, the object is subjected to electromagnetic fields that deviate significantly from the desired TEM form. A physical interpretation has been provided for this phenomenon. The enhancement of electromagnetic fields near the top and bottom faces of the object are explained in terms of the Poynting flux distribution.     

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.     

Investigation of "Twist" Mode Propagation in Indium Antimonide at 70 GHz

An experimental and theoretical investigation of the propagation of axially symmetric ("twist") modes in an axially magnetized sample of indium antimonide is described. Measurements of the TE/spl deg//sub 01/-mode reflection coefficient are shown to agree well with computer calculations based upon a convergent multimode analysis. Observed maxima and minima are seen to correspond to dimensional resonances and antiresonances of the two lowest order twist modes. These results are qualitatively explained in terms of twist mode standing waves. Under certain conditions of magnetic field and sample thickness, energy conversion from the TE/spl deg//sub 01/ mode to the TM/spl deg//sub 01/ mode occurs. This conversion has a maximum calculated efficiency of 95 percent under the conditions of the present experiment.     

A Simple Numerical Method for Studying the Propagation Characteristics of Single-Mode Graded-Index Planar Optical Waveguides

A simple numerical method based on the Runge-Kutta method is presented to compute the propagation constant, the modal field, and the cutoff wavelength corresponding to the fundamental TE/sub 0/ and TM/sub 0/ modes of a planar optical waveguide with an arbitrary refractive index profile. The method is much simpler and requires less computational effort than the earlier reported numerical methods. We have also used the technique for an estimation of the effect of the /spl nabla/epsilon term in TM modes.     

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.