Multimode Equivalent Network Representation Research Articles

On Multimode Equivalent Network Representation of Finite Arrays of Open-Ended Waveguides

This communication describes a multimode equivalent network (MEN) representation of a finite array of open-ended lossless waveguides on an infinite ground plane. The derivation is based on an integral equation formulated at the interface between the waveguides and the free-space region. The MEN is formulated using the concept of accessible and localized modes, and includes ports for the free-space plane waves. The MEN derived can be easily combined with the MENs of other microwave components, thus allowing for the accurate analysis and design of more complex systems composed of waveguide elements and radiating apertures. Both simulated and experimental results are presented showing a very good agreement, thereby fully validating the proposed equivalent network representation.

A new family of all-inductive dual-mode filters

In this paper, we describe a new family of dual-mode filters that is based on the use of simple inductive discontinuities in a rectangular waveguide environment. The proposed filter structure can be analyzed and optimized very efficiently using multimode equivalent network representations, thus leading to a simple and rapid development procedure. In addition to theory, the measured performance of a number of filter structures is also presented, thereby fully validating the proposed filter concept.

Multimode equivalent network representation for junctions between coaxial and circular waveguides

In this article we present two contributions to the study of coaxial waveguide structures. First, we present an efficient and accurate technique to evaluate the modes in the coaxial waveguides; second, we analyze junctions involving coaxial and circular waveguides using the multimode equivalent network representation. Numerical and experimental results are presented, showing good agreement. © 1997 John Wiley & Sons, Inc. Int J Microwave Millimeter-Wave CAE 7: 180–194, 1997.

Multimode equivalent network representation for junctions between coaxial and circular waveguides

Multimode equivalent network representation for junctions between coaxial and circular waveguides

Multimode equivalent network representation for the Y-junction of rectangular waveguides

Symmetrical Y-junctions in rectangular waveguides are commonly used components in microwave subsystems. The authors describe an alternative multimode equivalent network representation for this junction in terms of multimode admittance coupling matrices. The elements of the admittance coupling matrix are obtained as a summation of geometrical coefficients which are independent from either the frequency or the specific waveguide dimensions so that they need to be evaluated only once. The general formulations are described together with the detailed derivation for the E- and H-plane cases. Finally, comparisons between the authors' simulations and both measured and theoretical data are presented, fully validating the networks derived.

Multimode equivalent network representation for planar junctions involving elliptical waveguides

Multimode equivalent network representation for planar junctions involving elliptical waveguides

Multimode equivalent network representation for H- and E-plane uniform bends in rectangular waveguide

Uniform bends in rectangular waveguides are frequently used components in many microwave subsystems both for ground and space applications. Their accurate and efficient full-wave characterization is therefore required for the development of modern CAD tools to analyze and design complex waveguide structures. In this paper we describe new multimode network representations for both H- and E-plane uniform bends in terms of impedance and admittance multimode coupling matrices, respectively. The key element of the network is the transition from the straight waveguide to the curved waveguide. The relevant multimode equivalent network representation is obtained following a simple procedure that has already been used with success for other types of junctions involving straight waveguides. The convergency properties of the method are discussed, and comparisons between our simulations and theoretical and experimental data are presented, indicating that the approach proposed is at the same time accurate and computationally very efficient.

A new solution for TE plane-wave scattering from a symmetric double-strip grating composed of equal strips

The paper presents a new rigorous solution for the problem of TE plane-wave scattering from a periodic planar symmetric double-strip grating, i.e., the grating which has two equal strips per unit cell. The grating is placed at a dielectric interface and is assumed to be perfectly conductive and infinite in length and width. The formulation is based on a multimode equivalent network representation and the relevant integral equation defined on two separate intervals is rigorously solved by reducing to two simpler equations with known solutions. From this a new simple analytic expression is obtained for the coupling matrix elements which involves no integration. Some computations based on this new expression are carried out and the results are compared to those obtained by the Riemann-Hilbert method and also to some of the previously obtained single-strip results in the limiting case.

Multimode equivalent network representation for the scattering from multistrip gratings

A multimode equivalent network representation (MEN) is proposed for the scattering from a multistrip grating. Previously, rigorous analytical results were developed involving gratings with one or two strips in a period. In the present paper, the MEN representation is extended to planar gratings with an arbitrary number of strips or apertures per unit cell. Both TE and TM incidence are described. The extension is obtained combining the MEN formulation with the method of moments solution (MoM) of the relevant integral equation. The code thus obtained retains the key feature of the MEN representation, namely the frequency independence of the characterization, and is much more flexible than the analytical solutions previously derived. The MoM solution procedure is described in detail and several application examples are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Multimode equivalent network representation of inductive and capacitive multiple posts

Novel multimode equivalent network representations for multiple inductive and capacitive posts in rectangular waveguides are presented. The network representations art derived from a rigorous formulation that leads to frequency independent integral equations. The network representations developed are used to compute the response of several waveguide devices, and comparisons between measured and simulated performances are also included, showing very good agreement up to millimetre-wave frequencies.

Multimode network analysis of planar transmission lines

An alternative approach for the full wave analysis of single or coupled planar transmission lines is presented. Following the proposed approach, a multiple (or single) transmission line structure is viewed as series of stacked (or single) transverse discontinuities in a parallel plate waveguide. As a consequence, both top and side coupled structures can be studied. Each individual discontinuity is described in terms of a multimode equivalent network representation. The complete cross section of the planar transmission line structure is then described in terms of a transverse equivalent network and a simple transverse resonance technique is then used to obtain the dispersion behavior, the modal field of the structure, and the characteristic impedances. The multimode equivalent network representations of the individual discontinuities used in this paper have been derived elsewhere and are given in terms of impedance or admittance matrices that are essentially independent from frequency. As a result, they need to be computed only once for each given geometry thus leading to codes that are computationally very efficient.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Rigorous multimode network numerical representation of inductive step

Discontinuities such as inductive steps are very frequently used in waveguide components and several descriptions can be found for them in the technical literature. These descriptions can be broadly divided into two groups. The first group can only take into account fundamental-mode interactions and is generally very efficient from a computational point of view. Representations of the second group can account for higher-mode interactions but are in general much less efficient numerically. This paper derives a novel, rigorous, multimode equivalent network representation for arbitrary inductive step discontinuities in rectangular waveguide that is computationally very efficient. The coupling between the modal voltages and currents for all higher order modes explicitly included in the calculations is directly expressed in terms of an impedance coupling matrix that is essentially frequency independent. The expression for the generic coupling matrix element is found in terms of the numerical solution of an integral equation. The novel contribution of this paper is that it combines two powerful techniques, namely the Multimode Network Formulation of boundary-value problems and the Method of Moments for the solution of integral equations. The result is a very powerful tool that can be applied to the analysis of a wide class of discontinuities. In addition to the theoretical derivation, numerical results are also presented indicating that the theory developed is indeed very accurate and computationally efficient.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Rigorous, multimode equivalent network representation of capacitive discontinuities

Novel, rigorous, multimode equivalent network representations for a variety of zero-thickness capacitive windows and obstacles in a parallel plate waveguide are presented. 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.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Scattering from a double-strip grating: rigorous equivalent network formulation

An exact solution for the problem of transverse electric (TE) or transverse magnetic (TM) plane-wave scattering from a periodic, planar double-strip grating at a dielectric interface is described. The metal-strip grating is assumed to be perfectly conductive and infinite in length, with two different strips within a unit-cell. The formulation is based on a multimode equivalent network representation, and uses a rigorous solution for the relevant integral equation that extends the novel solution developed previously for the single-strip grating. Expressions for the elements of the multimode coupling matrices are given, together with a comparison of results for power transmitted through the grating, obtained by using the networks developed with the present method and a simple point-matching solution. Results are presented to illustrate the differences between single and double-strip gratings.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Rigorous, multimode equivalent network representation of inductive discontinuities

The theoretical derivation of the equivalent networks has been carried out by following the rigorous procedure used by M. Guglielmi and A.A. Oliner (1989) for the case of a metal strip grating at an air-dielectric interface. Following this procedure, network representations involving multimode coupling matrices are found in terms of the solution of a singular integral equation. The solution to this equation is shown to be known so that rigorous, multimode equivalent network representations for zero-thickness inductive windows and inductive obstacles in a rectangular waveguide can be derived. The network representations developed are valid for arbitrary aperture/obstacle dimensions and offset, and can accommodate a different medium on each side of the discontinuity. The analytic expressions obtained involve double integrations which are easily evaluated numerically. Numerical results are also presented indicating that the network representations developed are rapidly convergent so that they can be easily used to carry out computations involving an arbitrary number of propagating higher-order modes.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Multimode network description of a planar periodic metal-strip grating at a dielectric interface. III. Rigorous solution

For pt.II see (ibid., vol.37, no.3, p.542-52, 1989). In pt.I the solution to the scattering problem posed by a plane-wave incident at an angle on a plane, periodic, metal-strip grating at a dielectric interface was formulated in terms of novel multimode equivalent network representations. The analytical phrasing followed in pt.I led to two Fredholm integral equations of the first kind with singular kernels. Here, the authors derive a rigorous analytical solution for one of the two integral equations derived in pt.I (see ibid., vol.37, no.3, p.534-41, 1989). Closed-form, rigorous, analytical expressions for the elements involved in the equivalent network representations derived are obtained. Numerical results obtained by using these rigorous equivalent network representations are presented for TE-mode and TM-mode incidence for the case in which the same dielectric is present on both sides of the grating as well as for the case in which the two dielectric media are different. >