B.N. Das

S matrix of a broad wall coupler between dissimilar rectangular waveguides

The paper describes a method of moment analysis of a four-port junction between two dissimilar rectangular waveguides coupled through either a longitudinal slot or a transverse slot on the common broad wall. The Greens function approach has been used to obtain the scattered field inside the primary and the secondary waveguide for both cases. The coupled integro-differential equations, arising from the continuity of the tangential component of the magnetic field at both the interfaces of the slot, are transformed into matrix equation using entire domain sinusoidal basis functions in conjunction with global Galerkins technique. The results obtained using the present method have been compared with the results available in the literature. The theoretical results on the magnitude and phase of the scattering parameters have been compared with the experimental results for the case of a longitudinal slot coupler with moderate offset from the centerline. The use of global sinusoidal basis functions gives a much faster rate of convergence compared to the use of subsectional basis functions. The equivalent loading of a single slot derived in the paper can be effectively utilized to design a multiaperture coupler. >

S matrix of slot-coupled H-plane tee junction using rectangular waveguides

Complex scattering matrix parameters of a slot-coupled, waveguide tee junction are determined using a moment method of analysis with entire orthogonal basis functions and a rigorous analysis of the effect of wall thickness. The variations of the equivalent network parameter, coupling, and return loss with frequency are evaluated, and the results are compared with experimental data. The unitary property of the S matrix is verified. The dependence of coupling on slot length, slot width, and thickness is presented. >

Narrow wall axial-slot-coupled T junction between rectangular and circular waveguides

An analysis is presented of a T junction between rectangular and circular waveguides coupled through a long axial slot in the narrow wall of the rectangular waveguide. A moment method with entire orthogonal basis functions is used for deriving expressions for the elements of the scattering matrix. The effect of the wall thickness is taken into account by treating the coupling slot as a short section of a rectangular waveguide and matching the boundary conditions at the interfaces. The conditions satisfied by the scattering matrix of the junction are verified. A comparison between theoretical and experimental results on variation of coupling with frequency is presented. >

Analysis of a transition between rectangular and circular waveguides

An analysis is presented of a transition between rectangular and circular waveguides coupled by a rectangular slot in a metallic wall of finite thickness in the common transverse cross section. Expressions for VSWR (voltage standing-wave ratio) and admittance are obtained using a moment-method formulation with entire basis and testing functions. Numerical data on the variation of input VSWR with frequency are obtained, and a comparison between the theoretical and experimental results is presented. The variations in the values of minimum VSWR with change in slot dimensions are also studied. >

Analysis of dominant and higher order modes for transmission lines using parallel cylinders

The note presents a method of transforming eccentric coaxial as well as double wire line of parallel cylinders into coaxial configuration using bilinear transformation expressed in terms of mutually inverse points. Cutoff wavelength for TM and TE modes are found from the solution of the weighted Helmholtz equation. Numerical data on cutoff wavelength are presented. >

Moment method formulation of thick diaphragms in a rectangular waveguide

A method of determination of the electrical characteristics of two thick apertures in a rectangular waveguide is presented. The coupled integral equations resulting from the boundary condition of the magnetic field at the four interfaces are transformed into matrix equations using the method of moments. The numerical data on reflection and transmission coefficients are evaluated. A comparison of theoretical and experimental results is presented. >

Admittance of waveguide fed slot radiators

The authors present an accurate procedure of computation of the admittance characteristics of rectangular slots fed by rectangular waveguides. The feeding waveguide is excited with the dominant TE/sub 10/ mode. A moment method with entire domain basis functions is used for solving the electrical field in the slot. Attention is given to obtaining the appropriate dimension of the radiating slot so that the reflection coefficient due to the radiating load remains below 0.1 over a large frequency band. Computed values are compared with measured data.<<ETX>>

Analysis of cascaded sections of T junctions between rectangular and circular waveguides

An analysis of the cascaded sections of a number of slot-coupled T junctions between rectangular and circular waveguides is presented, taking into account the mutual interactions of all possible modes generated by the discontinuities as well as the effect of wall thickness. The formulation is based on solving a set of coupled integral equations resulting from the boundary conditions at the two interfaces of the waveguide sections representing the coupling slots. The integral equations are transformed into sets of matrix equations using the moment method with entire basis and testing functions. Numerical results on input VSWR (voltage standing wave ratio) and coupling are presented for the case of a cascaded section of two air-filled T junctions for different frequencies and different values of interelement spacing. >

Analysis of E-H plane tee junction using a variational formulation

A three-port equivalent network for an E-H plane tee junction is determined taking into account the effect of waveguide wall thickness and considering the contribution of the dominant mode to the imaginary part of the self-reaction. The parameters of the three-port equivalent network are determined. From a knowledge of the equivalent network parameters, the net impedance loading, reflection coefficient, and coupling are evaluated for an E-H plane tee junction. A comparison between theoretical and experimental results is also presented. >

Cutoff frequencies of transmission lines consisting of pair of cylinders

The paper presents a method of evaluation of cutoff frequencies of higher-order modes of transmission line of parallel cylinders by transforming them into a parallel plate configuration using cotangent hyperbolic transformation. Application of the method of finite difference to the weighted Helmholtz equation leads to a set of simultaneous equations. The eigenvalues related to cutoff frequencies are determined from the characteristic equation expressed in terms of matrices obtained from the simultaneous equations. Numerical data are presented.