Dual-frequency electric-magnetic-electric microstrip leaky-mode antenna of a single fan beam

This paper presents a dual-frequency electric-magnetic-electric (EME) microstrip exhibiting two leaky-wave regions of similar radiation characteristics like the microstrip EH/sub 1/ mode. The EME microstrip incorporates a photonic bandgap (PBG) structure, which is a two-dimensional array consisting of unit cell made of coupled coils connected by a via. The PBG structure employed in the EME prototype conducts at dc and shows the first stopband between 8.8-12.4 GHz, thus rendering the so-called magnetic surface. The EME microstrip is essentially made by substituting the PBG cells for the metal strip of a conventional microstrip. The finite-element method (FEM) analyses of the PBG structure show that the first and second modes are TM-like and TEM-like, respectively. The latter is leaky between 12.4-12.9 GHz and is found to be responsible for the second leaky region of the EME microstrip. The dispersion characteristics of the EME microstrip are obtained by two theoretical methods, namely, the matrix-pencil method and the FEM. Both show excellent agreement in the two leaky regions. Furthermore, the measured far-field radiation patterns of the two leaky regions also validate the dispersion curves. The first leaky region is of EH/sub 1/ type and between 5.05-5.45 GHz. The second leaky region radiates a frequency-scanning fan beam between 11.95-13.0 GHz, similar to those of the EH/sub 1/ mode. Detailed modal current analyses show even and odd symmetry along longitudinal and transverse plane of EME microstrip, respectively, further confirming the two leaky regions behave like the well-known EH/sub 1/ leaky mode. The proposed EME microstrip enriches the modal characteristics of the conventional, uniform microstrip and is thus a manifestation of application of PBG structure for new guiding device.     

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.     

Hybrid-Frequency Cutoffs in Gyrotropic Waveguides (Short Papers)

The behavior of the Brillouin diagram /spl omega/ versus /spl beta//sub z/ is analyzed for axially magnetized gyrotropic waveguides in the vicinity of the hybrid frequencies /spl omega//sub k/ and /spl omega//sub i/. Starting from the exact dispersion relation for the modes in the waveguides under consideration it is shown that 1) the dispersion curves terminate at discrete cutoff points located along the /spl omega/ = spl omega//sub k/, /spl omega//sub i/ line and 2) the group velocity at these points is zero. These results modify the behavior of the dispersion curves existing in the literature.     

Radio Communication in Tunnels

The attenuation constant of radio waves in tunnels was obtained experimentally and theoretically. According to this study, the tunnel is a transmission channel of high-pass type. It is found that the higher the frequency, the smaller the attenuation constant. The experimental values of attenuation constants are similar to the theoretical values of the the TE/sub 01/ and EH/sub 11/ and modes when the tunnel is regarded as a circular waveguide with the same cross-sectional area as the tunnel. Radio communication using the tunnel was proven to be fully possible in spite of the standing wave effects due to the interference of the propagation modes.     

Influence of the fiber index profile on vectorial fiber modes and application to tapered fiber devices

The correspondence between the scalar modes LP and the nearly degenerate true vectorial modes in circular two-layer fibers is well established. For example, LP/sub 21/ corresponds to a combination of EH/sub 11/ and HE/sub 31/, while LP/sub 02/ is composed only of HE/sub 12/. For the multilayer fibers, inversion of the correspondences for certain modes can occur. We illustrate this inversion for a three-layer fiber. We propose a method permitting to distinguish the hybrid modes HE/sub /spl nu//spl mu// and EH/sub /spl nu//spl mu// in such fibers and we show the possibility of major taper-induced power coupling between these modes in SMF-28 fiber.     

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.     

Dispersion characteristics of cylindrical metal-clad opticalwaveguides

A study of the dispersion characteristics of cylindrical metal-clad optical waveguides indicates that: (1) the propagation of electromagnetic energy in metal-clad optical waveguides differs in principal from that of dielectric step-index waveguides and ideal metallic waveguides; (2) hybrid modes exist in this structure, and the cutoff frequency of the HE₁₁ mode does not equal zero; (3) TM and HE(EH) modes have attenuation higher at least by an order of magnitude than that of TE modes; and (4) the surface plasma wave can propagate in this structure. Thus, the lowest order mode is TE₀₁      

Computer Analysis of E-Plane Resonance Isolators

E-plane ferrite resonance isolators are commonly used in most medium-power waveguide systems, allowing to effectively decouple successive stages. The study of propagation in this type of structure leads to a set of transcendental equations, for which exact theoretical results have not been available so far. The design of these devices has been done experimentally, which is time consuming and does not allow for achievement of optimal performance due to the large number of parameters involved. The present study considers the TE/sub m0/, modes in an isolator structure. A matrix formalism is used to derive the dispersion relation, which is then solved with the help of a computer program. Experimental results for a simple structure show good agreement with the computed values. The influence of ferrite parameters on the isolation and forward losses is presented. Higher order modes in the structure and the methods to avoid them are discussed. Finally, the field distribution in the device is determined, showing a large concentration of the fields within the loading material.     

Higher-Order Modes in Dielectrically Loaded Rectangular Waveguides

The problem of propagation in a waveguide containing E-plane slabs of dielectric was considered previously by several authors. However, their treatment was limited to the TE/sub mo/ modes. A more general and complete derivation of the dispersion equations for all the modes existing in these structures is presented here. It is shown, on the basis of theoretical and experimental results, that the frequency bandwidth is much smaller than the values previously obtained, considering only the TE/sub mo/ modes, for many cases of practical interest     

Dispersion characteristics of ring line through the conformal mapping approach

Dispersion characteristics of EH/sub 11/ and EH/sub 21/ modes in open ring lines are theoretically calculated using conformal mapping applied to a three dimensional problem. The validity of the solution is tested by comparison with experimental data.<>     

Wavelength dispersion of effective refractive indices of Rb:KTiOPO/sub 4/ optical waveguides

Multimode planar optical waveguides in z-cut KTiOPO/sub 4/ (KTP) substrates have been fabricated using Rb/sup +/:K/sup +/ ion-exchange process. Variations in the refractive index profile and the surface index change with wavelength in these waveguides are approximated by a simple relation. The dispersion characteristics of the effective refractive indices for different guided modes before and after annealing are calculated based on this approximation and the WKB method. Furthermore, the wavelength dispersion can also be expressed using a sellmeier-like equation, and there is an excellent agreement between the calculated values and the measured data.     

Single-conductor strip leaky-wave antenna

This paper presents a leaky-wave antenna with only a single-conductor strip on a substrate without a practical ground plane. The full-wave integral equation method is used to investigate the EH/sub 01/ leaky mode of this single-conductor strip structure. When this single-conductor strip is on a thin substrate with a low dielectric constant, a broad-band radiation regime can exist for the EH/sub 01/ leaky mode. The balanced microstrip lines and the inverted balanced microstrip lines are used to excite this EH/sub 01/ leaky mode. This work presents both the numerically simulated and measured data. The measured bandwidth of a voltage standing-wave ratio /spl les/2 is from 6.55- 13.75 GHz (2.34:1). In this case, the normalized phase constant is very close to 1 and this results in a fixed main-beam radiation pattern in the end-fire direction. This leaky-wave antenna with only a single rectangle stripline of length 110 mm can achieve the same broad-band performance as a tapered microstrip leaky wave antenna with a length 310 mm, as previously reported by the authors.     

Electromagnetic Properties of Shielded Ring Lines and Attenuation of the Fundamental Dipolar Mode

This paper presents a theoretical analysis of the eletromagnetic properties of the shielded ring line and provides expressions for field components, stored energy, and power flow. The dispersion relation obtained by equating electric and magnetic stored energies is discussed. The shielded ring line is shown to have a fundamental dipolar hybrid mode. The attenuation of this mode is evaluated. Measurements have corroborated the theoretical values.     

Calculating the Characteristic Impedance of Finlines by Transverse Resonance Method

The characteristic impedance of finlines with up to three slots is calculated by a rigorous hybrid-mode analysis which includes the finite metallization thickness and finite depth of the mounting grooves. The transverse resonance principle utilized reduces considerably the order of the involved matrix eigenvalue problem. The propagation constants for the fundamental HE/sub 1/ mode (and EH/sub 0/ mode at related structures), as well as for the higher order modes (up to HE/sub 7/), and the characteristic impedances for the fundamental modes are computed as a function of frequency for the bilateral and unilateral finline, as well as for the unilateral finline with two coupled slots, and an additional slot on the opposite side of the substrate surface. The finite metallization thickness and mounting groove depth considered show significant influence on the behavior of the characteristic impedance.     

具有混合形状空气孔的OAM传输光纤设计研究

本文提出了一种新型轨道角动量模(OAM)传输的光子晶体光纤(PCF)结构,该光纤由最中心空气孔、高折射率环形层和外包层构成,其中外包层由一圈椭圆形空气孔和多圈呈周期排列的扇形空气孔共同组成,无需通过额外的掺杂,就可以使中心空气孔和外包层空气孔之间形成一个用来传输OAM光束的等效高折射率环形区。通过对该PCF的传输特性进行仿真分析,发现在1.55μm处,各模式的限制损耗维持在10^-6 dB/m-10^-10 dB/m,在C波段的色散值均维持在310 ps/(nm×km)以下,HE2,1模在1.55μm-1.6μm波段内的色散变化为3.1 ps/(nm×km)。在1.55μm处最大的Δnneff能够达到4.83×10^-3,大的有效折射率差可有效地抑制了模式间的简并,避免HE模和EH模耦合成LP模。验证了该光纤具有大带宽、小而平坦色散、大有效折射率差、低限制损耗和低非线性系数等优良性能。在1.25μm-2.0μm波段内共可以支持34个OAM模式的有效传输,每个模态都可作为独立的信道传递信息,适合用于大量数据的传输,大幅提高了光通信的系统容量和频谱效率。     

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.     

Helix Leaky Waveguide

The propagation characteristics of leaky waves in a helix waveguide covered with a slitted cylinder are presented by a method of transverse network representation. The main interest is in helix waveguides with small pitch angles, characterized by a hybrid mode consisting of TE/sub 01/, and a small amount of TM/sub 01/ modes. The leaky wave discussed in this paper may then be regarded as a perturbation of the TM/sub 01/ wave by the slitted cylinder outside the helix. The radiation, metal, and dielectric losses are calculated numerically at a frequency of 50 GHz. The relation between the radiation loss and aperture angle of slit is very different from that of an ordinary leaky waveguide composed of a slitted cylinder without helix, especially when the distance between the helix and shield cylinder is about a quarter of the radial wavelength. The metal and dielectric losses are the same order as radiation loss, however the dielectric loss decreases as the power factor /spl epsiv/"/ /spl epsiv/' increases. The measured total attenuation constant averages about 5 dB/km, almost twice the theoretical value.     

Analysis of the Hybrid Modes for an Eccentrically Cladded Fiber

This paper examines the hybrid-cladding modes of an eccentrically cladded three-layer dielectric fiber. The solutions are specialized to small eccentricities, and exact closed-form expressions for the normalized deviations of the cutoff wavenumbers from those of the concentric case are determined. Numerical results for various types of hybrid-cladding modes of the fiber are given. For certain values of the parameters, it is possible to enhance the operating bandwidth of the basic hybrid mode HE/sub 11/ over the conventional concentric fiber because its cutoff frequency can be shown to remain zero.     

On the design of RF spiral inductors on silicon

This review of design principles for implementation of a spiral inductor in a silicon integrated circuit fabrication process summarizes prior art in this field. In addition, a fast and physics-based inductor model is exploited to put the results contributed by many different groups in various technologies and achieved over the past eight years into perspective. Inductors are compared not only by their maximum quality factors (Q/sub max/), but also by taking the frequency at Q/sub max/, the inductance value (L), the self-resonance frequency (f/sub SR/), and the coil area into account. It is further explained that the spiral coil structure on a lossy silicon substrate can operate in three different modes, depending at first order on the silicon doping concentration. Ranging from high to low substrate resistivity, inductor-mode, resonator-mode, and eddy-current regimes are defined by characteristic changes of Q/sub max/, L, and f/sub SR/. The advantages and disadvantages of patterned or blanket resistive ground shields between the inductor coil and substrate and the effect of a substrate contact on the inductor are also addressed in this paper. Exploring optimum inductor designs under various constraints leverages the speed of the model. Finally, in view of the continuously increasing operating frequencies in advancing to new generations of RF systems, the range of feasible inductance values for given quality factors are predicted on the basis of optimum technological features.