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This work explores the production and characterization of pedestal-type active waveguides based on PbO-Ge[O.sub.2] (PGO) thin films codoped with [Tm.sup.3+]/[Yb.sup.3+] rare earth ions. Silicon wafers containing around 1.7 µm of Si[O.sub.2] thickness were used as substrate, and the pedestal structure was obtained by conventional photolithography and plasma etching in a reactive ion etching reactor. Plasma etching procedures were made in steps to reduce roughness at the laterals and sidewalls of waveguides. Around 0.5 µm of [Tm.sup.3+]/[Yb.sup.3+] codoped PGO thin film was obtained by radio frequency magnetron sputtering deposition after etching procedures. Results of scanning electron microscopy confirmed the waveguide pedestal profile. Optical propagation losses around 4, 5, and 20 dB/cm were observed at 1050, 633, and 543 nm, respectively, for waveguide width in the 30-100 µm range. Near field profiles at these wavelengths and also at 980 nm are also reported and confirmed the multimode coupling behavior. The present results corroborate the possibility of using [Tm.sup.3+]/[Yb.sup.3+] codoped PGO thin films as active waveguides for photonic applications. PACS Nos.: 78.66.Jg, 42.82.Et, 81.15.Cd. Nous etudions ici la production et la caracterisation de guides d'onde actifs sur socle, bases sur des films minces de PbO-Ge[O.sub.2] (PGO) co-dopes aux ions de terres rares [Tm.sup.3+]/[Yb.sup.3+]. Des plaques de silicium avec une couche de Si[O.sub.2] de 1.7 µm sont utilisees comme substrats et le socle est obtenu par photolithographie conventionnelle et par gravure dans un reacteur de type reactive ion etching. Les procedures de gravure au plasma se font par etapes, afin de reduire la rugosite de surface des murs du guide d'onde. Suivant les procedures de gravure, le co-dopage autour de 0.5 µm du film de PGO par [Tm.sup.3+]/[Yb.sup.3+], est depose par pulverisation dans un magnetron a radio frequence. Le microscope electronique a balayage confirme le profile de guide d'onde sur socle. Nous observons des pertes de 4,5 et 20 dB/cm a 1050, 633 et 543 nm respectivement, pour un guide d'onde d'une largeur de 30 a 100 µm. Nous rapportons des profiles de champ proche a ces longueurs d'onde et confirmons le couplage multimode. Nos resultats corroborent la possibilite d'utiliser des films minces de PGO co-dopes avec [Tm.sup.3+]/[Yb.sup.3+] comme guides d'onde actifs en photonique. [Traduit par la Redaction], 1. Introduction Pedestal-type waveguides show promising applications in integrated optics and photonics because their characteristics are favorable for high confinement of optical field and fabrication of laser microcavities [1-3]. They [...]

A metal-clad waveguide (MCWG) sensor comprised of a nanoporous waveguiding layer on a metal cladding layer is advantageous in sensing of biomolecules because of a high surface area of nanopores and a sharp dip in the reflection spectrum due to characteristics of the MCWG mode. Here, a porous anodic alumina (PAA)/aluminum (Al) film was fabricated on a glass substrate as a MCWG sensor with the Kretschmann geometry, and the sensor response was examined for both colorless bovine serum 'albumin (BSA) and colored metal complexes by measurements of reflection spectra and Fresnel calculations. The BSA adsorption on the PAA layer induced a parallel redshift of the waveguide coupling dip in the reflection spectrum. The experimental results were well simulated by the five-phase Fresnel calculations which indicated that the redshift of the dip was linearly dependent on the adsorbed amount of BSA. When the response of a MCWG sensor with a PAA layer was compared with that of a MCWG sensor with a nonporous alumina layer, the former showed larger redshift than the latter, due to a large adsorbed amount of BSA in the PAA layer with high surface area. For the adsorption of colored Ru[[[Bphen.sub.3]].sup.2+] and Fe[[[Phen.sub.3]].sup.2+], the effect of both the real and imaginary parts of the complex refractive index on the sensor response was examined. As a result, a redshift of the waveguide coupling dip was observed for both metal complexes irrespective of the wavelength region examined; tiffs could be ascribed to the changes in the real part of the refractive index due to the adsorption of metal complexes on the PAA layer. Meanwhile, an increase in the reflectivity was observed when the coupling wavelength was close to that of the absorption 'bands of the metal complexes; this could be ascribed to the changes in the imaginary part of the refractive index of the PAA layer. Using the sensor response caused by the changes in the imaginary part, absorption spectral profiles of metal complexes could be reproduced. 10.1021/ac100654b

We fabricate single-mode polymer waveguide structures exhibiting polarization-independent ultra-low loss of 0.04 and 0.05 dB/cm at the 1310 and 1550 nm bands, respectively, with a [delta]n of 1.6%. A porous structure that arises during the fabrication process is studied by considering its implications in the propagation loss based on the Rayleigh--Mie scattering loss mechanism. We demonstrate that the porous structure is to be reduced to the nanoscale (i.e., < 10 nm) to realize waveguide structures with ultra-low propagation losses based on fabrications and measurements of morphologies with various degrees of porosity. Further, the bending loss and its respective polarization-dependent propagation loss behavior are analyzed to realize compact devices with ultra-low-loss and polarization-independent features, where a 4 mm bending radius is found to be adequate for such a performance over the 1550 nm band. [c] 2010 Optical Society of America OCIS codes: 130.0130, 130.5460.

Metallic nanoscale structures are capable of supporting surface plasmon polaritons (SPPs), propagating collective electron oscillations with tight spatial confinement at the metal surface. SPPs represent one of the most promising structures to beat the diffraction limit imposed by conventional dielectric optics. Ag nanowires have drawn increasing research attention due to 2D sub-100 nm mode confinement and lower losses as compared with fabricated metal structures. However, rational and versatile integration of Ag nanowires with other active and passive optical components, as well as Ag nanowire based optical routing networks, has yet to be achieved. Here, we demonstrate that SPPs can be excited simply by contacting a silver nanowire with a Sn[O.sub.2] nanoribbon that serves both as an unpolarized light source and a dielectric waveguide. The efficient coupling makes it possible to measure the propagation-distance-dependent waveguide spectra and frequency-dependent propagation length on a single Ag nanowire. Furthermore, we have demonstrated prototypical photonic-plasmonic routing devices, which are essential for incorporating low-loss Ag nanowire waveguides as practical components into high-capacity photonic circuits. waveguides | subwavelength | Ag nanowires | Sn[O.sub.2] nanoribbons | propagation length doi/10.1073/pnas.0902064106

A new method is described based on inverse scattering theory for designing the refractive index profile of single-mode planar waveguides in order to obtain a desired TE-mode profile. The method can be directly implemented for designing multi mode planar waveguides and it can be used for analyzing TM-modes in waveguides with a relative small change in the refractive index.

In this paper, a study of the coupling between a rectangular waveguide and circular waveguide is presented, aimed at developing a design procedure for a rectangular to circular waveguide directional coupler. Since radio-astronomical receivers often exploit circular horns, a coupler sharing the same waveguide type is at a premium, and furthermore, it reduces the feeding network complexity in dual polarization applications. A novel approach for obtaining traveling wave modal amplitude coefficients is presented, suitable for modes of any order. This approach is used to analyze the behavior of a single hole coupler between a rectangular and circular waveguide. From this starting point, a four holes directional coupler with good performance is designed in the 22-GHz band. Measurements and full-wave numerical simulations show excellent agreement with the proposed theory. Index Terms--Directional couplers, polarization, waveguide couplers, waveguide theory.

Uniplanar 180[degrees] hybrids are basic building blocks in uniplanar technology. In this paper, a new rigorous analysis of a uniplanar 180[degrees] magic-T hybrid based on an air-bridged coplanar cross is performed. The analysis proposed is multimodal since it takes into account the coplanar even and odd fundamental modes simultaneously. From this analysis, a complete circuit model for the hybrid is extracted, and the conditions for ideal performance are derived. This new multimodal model is necessary for the design of the hybrid, and allows a quantitative analysis of its performance, notably bandwidth, isolation, and return loss under any actual loading condition. It has been used to design and implement a 180[degrees] hybrid on alumina with a working frequency of 15 GHz. A very good agreement between simulation and measurement is obtained. The experimental results prove a frequency-independent phase-shift behavior with a measured phase error less than [+ or -] 2[degrees]. Index Terms--Coplanar waveguide (CPW) cross, magic T, multimodal models, 180[degrees] hybrid, uniplanar circuit.

This paper proposes miniaturized bandpass filters with double-folded substrate integrated waveguide (SIW) resonators using multilayer low-temperature co-fired ceramic (LTCC) technology. Formed by inserting a metal plate with two orthogonal slots into the cavity, the double-folded SIW resonator is used for the circuit size reduction with its footprint about a quarter of the conventional [TE.sub.101] mode. With LTCC technology, there is more flexibility to organize the cavities of filters because of the 3-D arrangement. The vertically stacked cavities are coupled by 'L'- or 'U'-shaped slots, and if arranged horizontally, by an inductive window on the common sidewall or a suspended stripline between the cavities. Through experimental measurements and simulations at both the Ka- V-bands, it has been demonstrated that the proposed filter has compact sizes and good frequency responses. The area of the fully stacked Chebyshev filter has 88% size reduction in comparison with a three-pole planar waveguide filter, while the vertically stacked quasi-elliptic filter has 74% size reduction in comparison with a four-pole planar waveguide filter. Index Terms--Bandpass filter, cavity, coupling coefficient, folded waveguide resonator, low-temperature co-fired ceramic (LTCC), miniaturized filter.

A parallel plate waveguide antenna is presented with microstrip patches as radiating elements. Rectangular patches are also placed inside the waveguide as coupling field structures from the waveguide to the radiating elements. The connections from the coupling to the radiating patches are made by means of vias. The field propagated along the parallel plate waveguide corresponds to a high order TE mode, creating virtual smaller rectangular waveguides in the parallel plate structure. An antenna prototype has been manufactured and measured. A 60% efficiency and 27 dBi antenna gain were obtained; with a 6.5% reflection bandwidth. Nevertheless, the resonant behavior becomes evident in the radiation pattern measurements. Index Terms--Microstrip coupling horizontal lines, parallel plate waveguide, patch antenna, virtual waveguide.

Multimode signal transmission concept is employed in this paper to increase the channel capacity of a substrate integrated waveguide (SIW) interconnect. In order to generate two uncoupled channels without adding an additional physical link, [TE.sub.10] and [TE.sub.20] modes of an SIW interconnect are harnessed as signal carriers. To excite these two orthogonal modes simultaneously, a multimode double launcher is proposed and characterized. It is shown that the performance of the launcher is limited by the coupling between the two mode launchers (transitions). Therefore, a method for improving port isolation is suggested, which results in increasing the channel bandwidths. A balun structure based on an SIW is presented and included in the multimode waveguide in order to efficiently excite the [TE.sub.20] mode. Ultimately, the multimode waveguide with the optimized transitions is used in a parallel data transmission system demonstrating excellent transmission quality for the data rate of a 1-Gb/s/channel. Index Terms--Balun, higher order mode, multimode transmission, parallel signaling, substrate integrated waveguide (SIW), waveguide transitions.

An analytical method to estimate the scattering of RF power into multiple modes inside a nonuniform waveguide using perturbation techniques is presented. This method is quite general, much faster than numerical methods, and may be applied to a wide variety of nonuniform waveguides. We have used this method to design and analyze a three-section mode transformer that converts a [TE.sub.01] circular waveguide mode to a [TE.sub.20] rectangular waveguide mode. This mode converter is specially suitable for use in ultra-high-power applications. Due to the complexity of the problem, we have used the symbolic solver Mathematica to produce most of our analytical results. The results match within reasonable accuracy with High Frequency Structure Simulator field solver simulations. We also present the application of this mode converter to variety of ultra-high-power microwave components and experimentally show the performance of these devices. Index Terms--Accelerator RF systems, coupled mode analysis, electrodynamics, electromagnetic analysis, electromagnetic fields, high-power RF, microwave devices, microwave power transmission, waveguides.

A new design method of dual-band filters with laminated waveguide (or substrate integrated waveguide) is proposed by taking advantage of the existence of multiple cavity modes. The major design concept is adequately choosing geometric shape of laminated waveguide resonators to control the frequency bands, and positions of open slots and feeding probes to realize the desired coupling coefficients and external quality factors at both bands simultaneously. Two design examples with third-order and quasi-elliptic filter responses are given and verified by experiments. By using the low-temperature co-fired ceramic technology, the laminated waveguide resonators are vertically stacked, and the filter size can be miniaturized. Index Terms--Coupling coefficient, dual-band filter, external quality factor, laminated waveguide, low-temperature co-fired ceramic (LTCC) technology, substrate integrated waveguide (SIW).

This paper presents transition from coplanar waveguide (CPW) to rectangular waveguide for W-band (75-110 GHz) operations. The waveguide consists of a cosine-shaped fin extending from the upper waveguide wall onto the CPW signal electrode. The design features direct integration of the waveguide with opto-electronic devices on lithium niobate (LiNb[O.sub.3]) for the applications of millimeter wave to optical signal processing. Simulations and measurements show that the model works very well over the entire W-band. Measurements of fabricated devices have yielded return loss of more than 10 dB and insertion loss of about 2.8 dB over the operating bandwidth. Index Terms--Coplanar waveguide (CPW), lithium niobate (LiNb[O.sub.3]), millimeter wave, rectangular waveguide, transition.

We describe a novel type of MEMS optical switch based on moving waveguide which has merits inherited from both MEMS and integrated optics technologies. It provides an expandable 2 x 2 switching capability, a first in this category of switches. The switch is built by assembling independently optimized latching silicon actuator and soft polymer waveguides. The actuator is based on two new structures: a microhinge, dubbed the fork hinge, and a latching structure using a precompressed microspring. The mechanical switching speed was measured below 0.5 ms. The complex polymer waveguide structure was thoroughly characterized to obtain all the components of the optical loss. This analysis allowed us to estimate robustly the insertion loss of the assembled optical switch below 3 dB and to identify the possibilities to improve this figure. [2008-0142] Index Terms--Microelectromechanical systems (MEMS), optical switch, waveguide.

A novel design of a dual-band dual-sense circularly-polarized CPW-fed slot antenna with two spiral slots loaded is presented. The two loaded spiral slots in the ground plane can result in different senses of circular polarization. The dual-band operation is achieved by using the T-shape strip. The ratio of two frequencies is 1.375. The antenna is designed, fabricated, and measured. It is shown that the proposed antenna has good circular polarization characteristic. The measured 10 dB return loss impedance bandwidths are 8.7% for the lower band (RHCP) and 23% for the upper band (LHCP). The measured 3 dB axial-ratio bandwidths are 8.4% and 19.24%, with respect to 1.6 GHz (RHCP) and 2.2 GHz (LHCP), respectively. Index Terms--Circular polarization, coplanar waveguide (CPW)-fed, dual band, slot antenna.

A 24-beams slot array antenna, which achieves 360-degrees coverage over azimuth direction, based on substrate integrated waveguide (SIW) technology is designed, fabricated and measured for supporting the concept of triangle cell, beam diversity and multiple input multiple output (MIMO) wireless communications. Constructed by six 4-beams single layer SIW antennas which integrate the 4 x 8 modified Butler matrix with a low side lobe level (SLL) amplitude distribution, measured SLLs are reduced as low as -14.5 dB for all beams in E-plane. The size of the SIW single layer multibeam antenna is 385 mm x 110 mm including feeding network. The usable bandwidth of the proposed antenna is 3.75% at 16 GHz. Index Terms--Beam-forming, Butler matrix, substrate integrated waveguide (SIW).

A printed semi-elliptic monopole slot antenna for use in ultrawideband (UWB) communication systems is presented. The antenna features a coplanar waveguide signal strip terminated with a semi-elliptic stub and a modified ground plane to achieve wide bandwidth from 2.85-20 GHz. An exhaustive study of the radiation characteristics of this antenna in the frequency and time domains are presented. Design equations are derived and experimentally validated. Transient analysis indicates linear phase response and minimum dispersion to the transmitted pulse. The proposed radiator is omnidirectional with appreciable gain throughout the band. Index Terms--Coplanar waveguide (CPW) antennas, monopole, planar antenna, slot antenna, ultrawideband (UWB).

We report the fabrication and optical properties of planar and channel wavegnides on z-cut near-stoichiometric LiNb[O.sub.3] crystal formed by 6.0MeV [O.sup.3+] implantation at a dose of 5 x [10.sup.14] ions/[cm.sup.2]. The properties of the planar wavegnide are characterized by use of prism coupling and the reflectivity calculation method. It is found that the effective refractive indices of the transverse magnetic modes increase but the transverse electric ones decrease when an appropriate heat annealing treatment is performed. We also find that only transverse magnetic polarized light could be guided in this waveguide effectively, although the dark mode could be detected in both the transverse electric and the transverse magnetic directions. OCIS codes: 230.7380, 240.5440.

This work proposes the combined use of split ring resonators (SRR) in a middle slab position with side slab ones to create two different passbands (stopbands) below (above) the cutoff frequency in a rectangular waveguide. The same effect can be achieved by using only SRR loadings on the side walls with different sizes of the elements on each side. Furthermore, by combining both techniques, three bands can be obtained. By adjusting the SRR sizes and with the dielectric materials, the passbands (stopbands) can be targeted at the desired frequencies. Both types of muitiband structures could find application in multifunction array antennas comprising interlaced arrays of open-ended waveguides. The work is supported by experimental results. Index Terms--Passband, split ring resonators (SRR), stopband, waveguide.

In this communication, several coplanar waveguide topologies to the hemispherical DRA are presented. It is seen that the inductive and the circular-loop CPW feed configurations offer the flexibility to excite the fundamental [TE.sub.111] resonant mode of the hemispherical DRA close to the source free resonant frequency, due to the presence of metallization in the coupling region. Dual-band behavior is observed with the capacitive feed due to the DRA and slot resonant modes, which are displaced with respect to the unperturbed modes due to the uninterrupted slot. The radiation characteristics of the antenna are also explained. Index Terms--Capacitive, coplanar waveguide (CPW), circular-loop, dielectric resonator, inductive.

In this paper, a novel modified dielectric frequency selective surface (MDFSS) is proposed and analyzed under 3-D plane wave incidence. Unlike classic DFSS, this MDFSS can easily be developed. The electromagnetic analysis is carried out using the multimode equivalent network (MEN) approach. A new development of electromagnetic fields in non homogeneous dielectric regions is proposed in order to correctly define the Z matrix of these blocks. Results are shown for an MDFSS which ensures total reflection with a larger bandwidth than the classic DFSS. Bandwidth can be enlarged and modified by doubling the MDFSS. Similarly, two MDFSS can be combined to ensure total reflection for elliptically polarized wave incidence. Index Terms--Dielectric waveguide grating, frequency-selective surfaces, three-dimensional (3-D) incidence, Z-matrix definition.

Transverse slot array antennas fed by a half-mode substrate integrated waveguide (HMSIW) are proposed and developed in this paper. The design concept of these new radiating structures is based on the study of the field distribution and phase constant along the HMSIW as well as on the resonant characteristics of a single slot etched on its top conducting wall. Two types of HMSIW-fed slot array antennas, operating, respectively, in X-band and Ka-band, are designed following a procedure similar to the design of slot array antennas fed by a dielectric-filled rectangular waveguide. Compared with slot array antennas fed by a conventional rectangular waveguide, such proposed HMSIW-fed slot array antennas possess the advantages of low profile, compact size, low cost, and easy integration with other microwave and millimeter wave planar circuits. It is worth noting that the width of HMSIW slot array antennas is reduced by nearly half compared to that of slot array antennas fed by a substrate integrated waveguide. Index Terms--Half-mode substrate integrated waveguide (HMSIW), transverse slot array antenna.

An integrated horn antenna is presented for 60-GHz WPAN applications. Compared with other types of antenna for 60-GHz WPAN applications, an integrated horn antenna features wide bandwidth and high gain. This integrated H-plane horn is elevated on the top of the substrate using CMOS-compatible microfabrication steps. Antenna efficiency is greatly improved after eliminating dielectric loss. This antenna is excited using an integrated vertical current probe connected with a coplanar-waveguide (CPW) by surface micromachining technologies. The lower part of the horn is constructed by rows of metallized pillars. The upper part and the top wall are built by stacking two layers of micromachined silicon wafers. The horn bottom is formed by metalizing the substrate's top surface. A prototype antenna is designed, fabricated, and characterized. Simulation and measurement results have shown wide input matching bandwidth and radiation bandwidth. The measured radiation pattern agrees well with the simulated one, demonstrating a gain as high as 14.6 dBi. Index Terms--Coplanar waveguide, integrated horn, micromachining, millimeter wave, V-band.

In this paper, a fast and robust optimization scheme is presented and applied to the optimal design of planar photonic crystals. It is based on a parallel hybrid (stochastic-deterministic) algorithm coupled to a semi-analytic solution of 'full Maxwell' equations by multiple scattering technique. The numerical results of the optimal design of different waveguide bends are presented. Index Terms--Hybrid algorithms, multiple scattering technique (MST), photonic crystals.

A thermal oxidation fabrication technique is employed to form low-loss high-index-contrast silicon shallow-ridge waveguides in silicon-on-insulator (SOI) with maximally tight vertical confinement. Drop-port responses from weakly coupled ring resonators demonstrate propagation losses below 0.36 dB/cm for TE modes. This technique is also combined with 'magic width' designs mitigating severe lateral radiation leakage for TM modes to achieve propagation loss values of 0.94 dB/cm. We discuss the fabrication process utilized to form these low-loss waveguides and implications for sensor devices in particular. OCIS codes: 130.0130, 130.3120, 130.3130, 130.2790, 130.5990.

We present a theoretical analysis of coherent microwave photonic filters (MPFs), which employ intensity modulation and direct detection. Expressions for the frequency dependent power gain are derived. The noise and distortion performance of MPFs is also analyzed. Two example filter implementations are given which provide a 100-MHz passband centered at 40 GHz. Index Terms--Microwave photonic filter (MPF), microwave photonics, nonlinear distortion, optical waveguide filter.

A waveguide based noninvasive procedure to measure the complex permittivity of epoxy resins and catalysts normally employed in the composite industry is presented. The proposed method combines an analytical approach with a numerical optimization technique, and is based on the injection of the liquid under test beforehand into a cuvette (disposable container) with rectangular cross section. The cuvette filled with the liquid specimen is positioned at the center of a WR-340 rectangular waveguide for measuring the scattering coefficient data in the S-band. The approximate value of the complex permittivity of the specimen is reconstructed from the measured scattering coefficient data using the newly proposed analytical closed-form relations. These analytical expressions are based on derivation of the transcendental equation for the multilayered partially filled waveguide structure using the transverse resonance method. In order to determine quite accurate values of dielectric parameters of the liquid specimen, the experimental setup is simulated with the help of a 3-D full-wave electromagnetic field simulator and accordingly theoretical values of the scattering coefficients are computed. The complex permittivity of the liquid specimen in this case is determined using an optimization algorithm, which minimizes the error between the theoretical and measured values of scattering coefficients. To avoid the local minima problem commonly encountered with optimization routines and to increase the convergence rate, the complex permittivity of the specimen reconstructed using the analytical approach is used as the initial guess. The applicability of the overall procedure is determined by measuring a number of liquid specimens used in the composite industry. Index Terms--Complex relative permittivity, dielectric materials, electromagnetic heating, microwave measurements, partially filled rectangular waveguides, waveguide discontinuities.

This paper presents a new wire-bond free technique for suppressing slot-line mode excitation in coplanar waveguides (CPWs) bends. The suppression of slot-line mode is obtained by applying a slow wave structure to the shorter slot of the right-angle bend. The structure is modified into a circular-shaped bend where the slow wave compensation is then used to equalize the electrical length of the inner and outer slots. The insertion loss of the modified CPW bend with slow wave structure is evaluated on a silicon substrate and is similar to straight CPW lines with return loss ([S.sub.11]) values below -20 dB over a 50-GHz bandwidth. Index Terms--Coplanar waveguides (CPWs), slow wave structures, waveguide discontinuities.

A new microwave imaging technique is proposed for reconstruction of 2-D complex permittivity profiles in dielectric samples located in a waveguide system. The spatial distributions of the dielectric constant and the loss factor are approximated by continuous functions whose functional parameters are determined using a neural network technique backed by full-wave finite-difference time-domain analysis. The profiles are reconstructed from measurements of reflection and transmission characteristics obtained with the tested sample at different locations. Operational capabilities of the technique are illustrated through a series of computational experiments for rectangular and cylindrical samples at two (original and 90[degrees]-rotated) positions. The results demonstrate excellent agreement between the reconstructed and actual profiles approximated by linear, quadratic, and Gaussian functions: the average relative errors do not exceed 0.4%, 2.2%, and 4.8%, respectively. Finally, the assumption of functional approximation, uniqueness of the reconstruction, and prospects of practical use of the technique are thoroughly discussed. Index Terms--Artificial neural network (ANN), finite-difference time-domain (FDTD) simulation, microwave imaging, model functions, permittivity profile, S-parameters, waveguide.

A new grouping strategy for the analysis of two-port arbitrarily shaped H-plane devices in rectangular waveguides is presented. The new grouping strategy accelerates a previous method based on the method of moments and the Green's function of an infinite line source placed inside two parallel plates. The computational cost of analyzing several H-plane filters of different geometries is reduced by about 50%, while maximum accuracy is maintained, as a result of using the new grouping strategy. Index Terms--Cavity resonator filters, Green's function, method of moments (MoM), rectangular waveguides, scattering.

An innovative method for fast analysis of geometrical variations in electromagnetic wave problems is proposed. The method is based on a perturbative approach applied to the solution of the linear integro-differential operator of the electromagnetic problem in presence of small domain modifications. This approach has been embedded in a classical finite-element framework to achieve a very fast technique for field evaluation in synthesis or tolerance investigation of microwave passive devices. The proposed technique can handle geometrical variations without the need of re-meshing the domain and without any deformation of the original mesh of the problem. Index Terms--Computer-aided design (CAD), finite-element methods (FEMs), sensitivity analysis, waveguide filters.

Substrate integrated waveguides (SIWsl are presented and demonstrated in a flexible printed circuit board (flex PCB) for application in the 77-81 GHz range. The vertical walls of the SIWs presented in this paper consist of multiple electrodeposited metallic wires. The diameters of these wires and the spacing between them are on the order of hundreds of nanometers. Hence, the walls can be seen as continuous metallic walls, and the leakage losses through them become negligible. In turn, the SIWs presented in this paper can operate at higher frequencies compared with previously presented structures that are realized with PCB fabrication processes. The attenuation of the SIWs is comparable to that of microstrip lines on the same sample. The SIWs are successfully demonstrated in a SIW-based slot antenna. The antenna gain along the z-axis (normal-to-plane) was found to be around 2.8 dBi at 78 GHz which is in agreement with the simulated values. [2008-0047] Index Terms--Flexible printed circuit boards (flex PCB), millimeter-wave (mm-W) antennas, millimeter waves, polyimide foils, substrate integrated waveguides (SIWs).

An original and flexible pyramidal antenna for satellite or terrestrial application services is presented. The ground plane of the antenna is perforated and loaded with a cutoff open-ended waveguide: this original configuration leads to a good tradeoff between rear radiation and impedance matching. Trap-loads are used to achieve multiband operation while frequency agility may be simply obtained by loading the radiating element by radio-frequency switches. The antenna radiates linearly or circularly polarized electromagnetic fields with quasi-hemispheric radiation patterns at multiple operating frequencies. Several prototypes have been simulated, manufactured, and finally measured. A specific application is given in this paper for a triband GPS/Galileo/MicroSat Telemetry antenna to combine positioning and telemetry applications. The experimental results confirm the good performances observed with the electromagnetic simulations. Index Terms--Cutoff waveguide loading, GPS/Galileo/MicroSAT telemetry services, multiband antenna, pyramidal structure, trap-loads.

A Ka-band compact single layer substrate integrated waveguide monopulse slot array antenna for the application of monopulse tracking system is designed, fabricated and measured. The feeding network as well as the monopulse comparator and the subarrays is integrated on the same dielectric with the size of 140 mm x 130 mm. The bandwidth ([S.sub.11] < - 10 dB) of the antenna is 7.39 % with an operating frequency range of 30.80 GHz-33.14 GHz. The maximum gain at 31.5 GHz is 18.74 dB and the maximum null depth is -46.3 dB. The sum- and difference patterns of three planes: H-plane, E-plane and diagonal plane are measured and presented. Index Terms--Difference pattern, monopulse antenna, null depth, substrate integrated waveguide, sum pattern.

Novel ultrawideband (UWB) antennas with multiresonant split-ring loops and with coplanar waveguide (CPW) feed are presented in this communication. Dual concentric microstrip split-ring loops with different geometrical ground planes have been analyzed and compared. UWB antennas are designed, of which the dimension of each split-ring loop varies proportionally to the arithmetic progression sequence. The dimensions of the rectangular ground planes and the split-ring loops are tuned for achieving a very wide bandwidth. A tapered transmission line is adopted to improve the return loss performance in the required band. Measurement results show that the proposed UWB antennas have a wide bandwidth from 2 to 20 GHz, and the measured return losses are less than--10 dB in this band combined with relative stable radiation characteristics. Index Terms--Coplanar waveguide (CPW), split-ring loops (SRLs), ultrawideband (UWB) antenna.

The concept and results of investigation of a waveguide slot antenna with reconfigurable aperture is presented. Solutions are based on the utilized semiconductor material, which allows one to design the electronically reconfigurable antennas. The key element of the reconfigurable antenna is a surface PIN (SPIN) diode whose conductivity changes proportionally to the plasma density. SPIN structures can be activated selectively and cause, in turn, the generation of the desired shapes of radiation pattern. It allows one to extend the function possibilities of waveguide slot antennas compared with the conventional one. Index Terms--Reconfigurable antennas, semiconductors devices, slot arrays, traveling wave arrays.

The propagation characteristics of twisted hollow waveguides are considered, and various analysis methods are proposed. It is shown that a twisted hollow waveguide can support waves that travel at a speed slower than the speed of light c. These modes are of particular interest, as slow wave structures have many potential applications in accelerators and electron traveling wave tubes. Since there is no exact closed form solution for the electromagnetic fields within a twisted waveguide or cavity, several previously proposed approximate methods are examined. It is found that the existing perturbation theory methods yield adequate results for slowly twisted structures; however, our efforts here are geared toward analyzing rapidly twisted structures using newly developed finite-difference methods. To validate the results of the theory and simulations, rapidly twisted cavity prototypes have been designed, fabricated, and measured. These measurement results are compared to simulated results, and very good agreement has been demonstrated. Index Terms--Finite difference frequency domain (FDFD), finite difference time domain (FDTD), guided waves, slow wave structures.