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A new efficient technique for computing the Green's functions inside rectangular waveguides is presented. After a summary of the classical approaches and their difficulties, a new strategy is proposed, based on the decomposition of the main spectral series into simpler terms. Although the resulting series present better convergence rate, several acceleration techniques are combined to further improve the efficiency. Several results are presented to demonstrate the improvements in convergence rates obtained using the new decomposition. Index Terms--Acceleration techniques, dyadic Green's functions, Ewald methods, integral equations, rectangular waveguide.

In this paper, we propose an alternative configuration for the design of bandpass inductive filters using transversal topologies. The structure is based on the use of a dielectric post asymmetrically placed on a cavity resonator. The input and output windows will couple energy to the [TE.sub.102]- and [TE.sub.103]-mode resonators at the same time, therefore obtaining the transversal topology. The proposed configuration is very compact, and allows to implement transmission zeros for maximum selectivity in an easy way. Results are validated with Ansoft's finite-element High Frequency Structure Simulator tool, and with an integral-equation technique to demonstrate the validity of the proposed structure. Index Terms--Dielectric posts, doublet topology, inductive filters, transmission zeros, transversal filters, waveguide filters.

In this paper, we propose to use the surface integral-equation technique for the analysis of arbitrarily shaped H-plane obstacles in rectangular waveguides, which can contain both metallic and/or dielectric objects. The Green's functions are formulated using both spectral and spatial images series, whose convergence behavior has been improved through several acceleration techniques. Proceeding in this way, the convergence of the series is not attached to the employment of any particular basis or test function, thus consequently increasing the flexibility of the implemented technique. In order to test the accuracy and numerical efficiency of the proposed method, results for practical microwave circuits have been successfully compared with other numerical approaches. Index Terms--Dielectric resonators, Green's functions, integral equations (IEs), waveguide components, waveguide discontinuities.

Experimental results are presented to show how a planar circuit, printed on a laterally shielded dielectric waveguide, can induce and control the radiation from a leaky-mode. By studying the leaky-mode complex propagation constant, a desired radiation pattern can be synthesized, controlling the main radiation characteristics (pointing direction, beamwidth, sidelobes level) for a given frequency, This technique leads to very flexible and original leaky-wave antenna designs. The experiments show to be in very good agreement with the leaky-mode theory. Index Terms--Hybrid waveguide printed circuit technology, leaky-wave antennas, sidelobes level control, tapering antennas.

In this paper, a neural-network-based method for the analysis of practical multilayered shielded microwave circuits is presented. Using this idea, a radial basis function neural network (RBFNN) is trained to approximate the space-domain multilayered media boxed Green's functions used in the integral-equation (IE) method. Once the RBFNN has been trained, the outputs of the neural network (NN) replace the exact Green's functions, during the numerical solution of the IE. The computation of the RBFNN output values is very fast in comparison with the numerical methods used to calculate the exact Green's functions. This paper describes two novel strategies for efficiently training the RBFNN. In the first strategy, the input space of the RBFNN is divided into several spatial and frequency regions. The spatial subdivision is extended for the first time to both observation and source regions. In addition, the subdivision of the observation points regions is applied in a novel manner to the whole cross section of the metallic box. The second strategy combines the above region subdivision with an adaptive selection of the neurons variances in each region. The accuracy and the computational gain achieved with the NN method proposed makes possible the implementation of computer-aided-design tools that can be used for the analysis and design of integrated shielded microwave circuits (e.g., monolithic microwave integrated circuit devices) on a real-time basis. Index Terms--Computer-aided design (CAD), multilayered circuits, multilayered Green's functions, neural networks (NNs), printed circuits, radial basis function neural network (RBFNN), shielded microwave circuits.

In this paper, a spatial images technique is used to efficiently calculate the mixed potential Green's functions associated to magnetic sources when they are placed inside a circular cylindrical cavity. The technique places magnetic dipole images and charges outside the cylindrical region. Their strength and orientation are then calculated by imposing the appropriate boundary conditions for the fields at discrete points of the metallic wall. In this paper, the basic technique is combined with spatial domain multilayered Green's functions formulated with Sommerfeld integrals. This allows the analysis of practical multilayered circuits shielded in circular cavities. Convergence results are shown to demonstrate the usefulness of the technique. Two practical microwave circuits are also analyzed to show the validity of the formulation. Index Terms--Boxed circuits, cavities, circular waveguides, Green's functions, integral equations (IEs), printed circuits, shielded circuits.

In this paper, the orthogonality relations between complex modes are investigated to demonstrate the coupling effect that exists along a transverse direction (z-axis) between T[E.sup.z] and T[M.sup.z] hybrid modes when power storage, loss, or leakage occur in the longitudinal direction (y-axis) of a transmission line. As an example, the parallel-plate waveguide modes are used to study a laterally shielded top-open microstrip line. The study of leaky waves is a very interesting application of the novel orthogonality relations derived in this paper. This study is carried out using the correct and incorrect orthogonality formulations, showing that physically valid results are obtained only when the orthogonality relations derived in this paper are properly introduced in the formulation. A physical explanation of this novel coupling effect between T[E.sup.z] and T[M.sup.z] hybrid modes with respect to the y-direction is given in terms of inhomogeneous plane waves. Comparisons with previous results for a laterally shielded slot-line antenna are presented to confirm the accuracy and usefulness of this novel proposed method. Index Terms--Coupled-mode analysis, electromagnetic coupling, leaky waves, planar waveguides.

This paper presents an efficient technique for evaluating Green's functions associated to layered media, when formulated as Sommerfeld integrals in the space domain. The key step in the formulation is that Sommerfeld integrals are computed choosing a suitable integration path which is closed through the imaginary axis of the complex spectral plane. It is shown that with this original choice of the integration contour, the numerical effort usually involved in the evaluation of Sommerfeld integrals can be greatly reduced, specially when large source-observer distances are involved. One asset of this technique is that it can be easily incorporated into integral equation based CAD packages for the efficient analysis of complex printed microwave circuit and antennas. In addition, the theoretical developments needed to set up the numerical algorithm throw a new light on the asymptotic behavior of the layered media Green's functions for large source-observer distances. Index Terms--Asymptotic behavior, integral equation, multilayered Green's functions, printed antennas, printed circuits.

In this paper, we propose a novel approach for the analysis of shielded microstrip circuits, composed of a number of thin metallic areas with arbitrary shapes and finite conductivity, embedded in a multilayered lossy medium. The analysis is based on the solution of an integral equation (IE) obtained by enforcing the proper boundary condition to the electric field on the metallic areas. The IE is solved by using the method of moments with entire domain basis functions, which are numerically determined by the boundary integral-resonant-mode expansion (BI-RME) method. The use of the BI-RME method allows for the efficient calculation of the basis functions independently on the shape of the domain, thus permitting the analysis of a wide class of circuits. Two examples demonstrate the accuracy, rapidity, and flexibility of the proposed method. Index Terms--Entire domain basis functions, integral equations, microstrip filters, MMICs, moment method.

In this paper we present novel, rigorous, multimode equivalent network representations for a variety of zero-thickness capacitive windows and obstacles in a parallel plate waveguide. A key feature of these representations is that the coupling between all of the modes excited is described by a matrix whose elements do not depend on frequency or absolute dimensions. The value of the results presented is that the networks developed can be used to analyze rigorously a large variety of single and coupled planar transmission line structures.

This brief presents a novel frequency reconfigurable microstrip non-reciprocal bandpass filter based on time-modulated microstrip $\lambda _{g}/2$ resonators. The modulation is achieved by loading both ends of the $\lambda _{g}/2$ transmission line resonators with time-modulated capacitors. The modulation voltage source is connected at the center of the resonator, where there is a natural voltage null, and a single inductor is used to further enhance the biasing isolation. The wideband nature of this isolation scheme enables the tuning of the devices over a wide frequency range. With more than 30-dB RF to modulation isolation, the proposed resonator structure also enables low insertion loss by eliminating RF signal leakage to the modulation ports. A 3-pole bandpass filter example is simulated and measured, showing a minimal insertion loss of 3.9dB, a 20-dB isolation bandwidth of 42MHz at 1.0GHz, and frequency tuning range of 885–1031MHz. [ABSTRACT FROM AUTHOR]

In this paper, we describe a very accurate and computationally efficient computer-aided design (CAD) tool for the analysis and design of a wide class of boxed microwave circuits composed of arbitrary rectangular elements printed on dielectric layers. The theoretical derivations are based on an integral equation formulation, and call for the evaluation of the boxed multilayer Green's functions, thus leading to a tool that is valid for an arbitrary number of circuits and dielectric layers. In addition to theory, comparisons with measured results are presented, and several practical filter structures are also investigated, thus clearly demonstrating that the CAD tool developed can indeed be used very effectively for the design of a large variety of microwave circuits. Index Terms - Broadside coupled, integral equation, microwave filters, modal expansions, shielded printed circuits, transmission zeros.

This study presents a technique to rigorously derive a complete lossy equivalent circuit of narrowband direct-coupledcavity filters with arbitrary cross-section and arbitrary coupling geometries. Traditionally, only dissipation loss and stored energy because of closed unperturbed cavities have been taken into account in the design of complete filters and the contribution because of coupling structures has been neglected. An additional challenge is the non-trivial discrimination of cavities and couplings in a direct-coupled-cavity filter. With the proposed circuit, the contribution of the coupling structures to the total dissipated power and total stored energy of the filter can be derived and a clear separation between resonators and couplings is established. The technique developed uses the even and odd mode theory to successfully derive lossy equivalent circuits for inter-cavity couplings. The lossy circuit of external (input/output) couplings is also derived. A fifth degree direct-coupled-cavity filter has been designed, simulated and manufactured. Its lossy equivalent circuit has been extracted and comparisons with simulations and measurements show excellent agreement. Applications of the novel equivalent circuit in the prediction of losses in waveguide filters and in yield analyses are also illustrated. [ABSTRACT FROM AUTHOR]

In this paper, the design of a novel planar narrowband microstrip filter is presented. The structure is designed and manufactured in microstrip technology, and it is formed by set of pairs of resonators of different lengths. The length of one resonator in each pair is adjusted so that a suitable odd resonance is tuned to the center frequency of the filter. The length of the other resonator is adjusted so that the next even resonance is tuned again to the center frequency of the filter. The different path of the signal in each resonator produces a cancellation of energy at a given frequency, therefore implementing a transmission zero in the insertion-loss response of the filter. First, this paper presents a design example of a single set of resonators (basic unit cell) working at the fifth and sixth resonances. Then, two basic unit cells working at the first and second resonances are first optimized, and then they are cascaded to show how higher-order filter responses can be implemented. The measured results confirm the theoretical predictions, and validate the new structures for high-selectivity applications. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 450–455, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20499 [ABSTRACT FROM AUTHOR]

A transformer-based voltage-controlled oscillator for a W-band frequency-modulated continuous-wave (FMCW) automotive radar application is presented. The design challenges imposed by the millimeter-wave frequency operation were faced through a circuit and layout co-design approach, supported by extensive electromagnetic simulations and accurate analysis of both the start-up condition and the tank quality factor. The oscillator was implemented in a 28-nm fully depleted silicon-on-insulator (SOI) complementary metal–oxide–semiconductor (CMOS) technology. It provided a 37 GHz oscillation frequency with a variation of around 4 GHz, thus achieving a tuning range of 11%. Moreover, a 77 GHz output signal was also delivered, which was extracted as a second harmonic from the input-pair common-mode node. The circuit exhibited low phase noises, whose average performances were −97 dBc/Hz and −121 dBc/Hz at 1 MHz and 10 MHz offset frequencies, respectively. It delivered a 77-GHz output power of −10.5 dBm and dissipated 26 mW with a 1 V power supply. The silicon area occupation was 300 × 135 µm. [ABSTRACT FROM AUTHOR]

With the huge requirement of high frequency, multi-function and high reliability, the quality of microwave circuit interconnection has become an important factor that significantly affects the improvement of microwave electronic system performance. This paper has presented an identification method for flexible conductor wire interconnection (FCWI) electromechanical coupling parameters in microwave circuits with the consideration of their interaction effect. First, a parametric characterization cascade function has been proposed to design the FCWI, and consequently, a three-dimensional electromagnetic structure model of FCWI has been developed and verified. In order to identify the electromechanical coupling parameters of the flexible interconnection considering the interaction effect effectively, this paper has used the range multi-objective function to select the optimal level of the configuration parameter of the flexible interconnection that affects the signal transmission loss. Based on the variance analysis and range analysis of the experimental results, the comprehensive judgment criterion of electromechanical coupling parameters of flexible interconnection can be defined, and therefore, the calculation of electromechanical coupling degree can be derived and the electromechanical coupling property identification of flexible interconnection has been obtained. An example has been used afterwards to verify the accuracy of the proposed method. The method proposed in this paper can be a promising tool for microwave circuit comprehensive design and the optimization of its interconnection, considering both mechanical reliability and electrical performance. [ABSTRACT FROM AUTHOR]