Efficient moment method solution for a longitudinal slot in a rectangular waveguide

Numerical analysis is presented for the characteristic parameters of centered-inclined coupling slot in rectangular waveguides, taking into account the transverse distribution of the electric field across the slot aperture. Integral equations are formulated based on dyadic Green’s function theories and solved using the method of moments. Trigonometric basis functions are adopted. It is found that the method will converge with up to ten basis functions. The characteristic parameters can be easily obtained for different slot sizes. Resonant length and resonant resistance of the coupling slots are calculated. It is shown that the calculated results have very high accuracy, compared with simulated results obtained from commercial software. Therefore, it can be effectively applied in the synthesis of antenna arrays. Effects of the transverse distribution on calculating resonant parameters of the coupling slot are also analyzed. The results show that if the transverse distribution of the electric field is neglected, the calculated error tends to become larger when the slot gets wider or thinner.

In this paper, the admittance characteristics of a dielectric filled inclined slot in the narrow wall of a rectangular waveguide have been calculated. By enforcing the continuity of the tangential magnetic field through the slot aperture, an integral equation with the tangential electric field in the slot as the unknown is obtained. An entire domain method of moments (MoM) is used to solve the integral equation. Numerical results show that the slot can resonate without penetrating onto the top and bottom broad walls of the waveguide. It has also been shown that the resonant frequency (length) and the resonant conductance of the slot depend on the dielectric constant of the material filling the slot. The computed results are shown to be in good agreement with those obtained by HP‐HFSS. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 222–226, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10876

A complete analytic array design process [1] with slots fed by dielectric filled waveguide requires accurate prediction of slot characteristics. A theoretical analysis of a longitudinal slot on the wall of a rectangular waveguide was given by Vu Khac [2] and Vu Khac and Carson [3]. It is assumed that the magnetic current J has no variation along the narrow dimension of the slot. This assumption violates the edge condition and therefore reduces the accuracy of the final results. In this paper we formulate the same problem with the edge condition and analyze slots.

Waveguide coupling and radiation by means of apertures is modelled using a hybrid technique which combines the finite element method with the moment method. Unlike the conventional pulse expansion and point matching technique, it ensures the convergence of the resultant admittance matrix elements without introducing any assumptions about the field distribution on the apertures. Coupling and radiation problems formed by a conventional transverse slot in rectangular waveguide and a complex T-shaped slot in a bifurcated waveguide are examined respectively, and excellent agreement has been obtained for both cases when compared both with alternative theoretical predictions and with measurements.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Slots in rectangular waveguides are often used at elements in linear array antennas. The polarisation of the radiated energy is usually linear. Circular polarisation can be obtained with compound slots in the broad wall. Experiments have shown that circular polarisation can be obtained from certain I-shaped slots in the narrow wall.

Rectangular waveguide slot arrays are commonly used in several microwave antenna systems. The slots are most often located in the broad wall of the rectangular waveguide, arranged longitudinally parallel with the waveguide axis, because this provides good control of the excitation of each slot over a large dynamic range by adjusting the offset of the slot from the center line of the waveguide. However, longitudinal slots can only radiate electrical fields that are transversely polarized with respect to the waveguide axis. If longitudinal (or dual) polarization is required, the slots (or half of them) must be located transverse to the waveguide axis. Transverse resonant slots in the broad wall are too strongly excited for use in large arrays, so transverse narrow slots in the narrow wall are preferred. In the latter case the slots are not excited unless they are tilted or coupled to tilted parasitic elements like wires or posts inside the waveguide. The purpose of the present paper is to analyse an untilted narrow wall slot excited by two tilted wires. An improved and extended analysis in which the slot extensions into the neighboring two broad walls are included, is described. The virtual cylinder method is applied to the calculation of the external admittances of the slot using wedge dyadic Green's functions and entire-domain basis functions in order to get good convergence of the integrals of the spectral domain formulations.

An accurate computation of the admittance characteristics of longitudinal shunt slots in a rectangular waveguide is presented. A moment method with entire basis functions is used for solving the electric field in the slot. The waveguide wall thickness is accounted for by introducing higher order waveguide modes in the short waveguide connecting the inner and outer regions. Particular attention is given to the resonant length of the slot, which is a critical parameter in the design of waveguide slot array antennas. Computed resonant lengths compare very well with measured results.

With the advantage of small volume, light weight, high aperture efficiency and low side lobes, The Antenna Array of Slots in Rectangular waveguide is widely used in many microwave communication systems that requires narrow beam and shaped beam. This paper analyses the structure and design procedures of antenna array of slots in the narrow wall We first obtain the physical size of each slot by using the parameter sweep function of the Ansoft HFSS software. Then we created a complete model. Finally, we perform the simulation and compare against the design requirement There is a good agreement between simulation and design requirement.

The leaky-wave antennas in the form of closely spaced transverse slots cut in a broad wall of rectangular waveguide were investigated. The thickness of waveguide walls and interaction between slots were taken into account in numerical calculations.

Arrays of broadwall shunt slots in rectangular waveguides

A novel analysis for computing the admittance characteristics of edge slots with a salient feature in successfully considering the finite waveguide wall thickness is presented. The variational equation for the electric field in the slot region between the inner and outer waveguide walls is derived by applying the variational reaction theory and solved by the finite-element method. The division of the slot region into small elements of triangular cylinders and the basis function for each element are described in detail. In the limiting case of zero wall thickness, this finite-element analysis is reduced to a moment-method analysis using Galerkin's approach with triangular basis functions. The effects of waveguide wall thickness on the characteristics of the slot are investigated by comparing the numerical results with and without considering the wall thickness. Negligence of the wall thickness may result in a severe underestimation of the resonant length by as large as 14% for edge slots cut in typical X-band waveguides. The computed results with the finite wall thickness taken into account have been checked with the measured data published in previous literature and those obtained by a carefully devised experimental setup. Good agreement between theoretical and experimental results is obtained to demonstrate the validity of the analysis.

Technique is proposed for the calculation of radiation field from a slot in a rectangular waveguide, the slot shape being nonrectangular. The technique is based on a boundary-value problem formulation in terms of Hertz electric and magnetic potentials introduced for the interior and exterior domain of the slot and for the slot space as well.

A coaxial line flush mounted on an infinite perfectly conducting ground plane and covered by a dielectric hemisphere is investigated. Green's functions for the region above the ground plane are derived with separated homogeneous and particular solution parts so as to be compatible with numerical analysis techniques. A magnetic field integral equation is obtained in terms of the unknown annular aperture tangential electric field and is solved by the method of moments. A comparison between the present case and that of a flush-mounted coaxial line with an infinite homogeneous region above the ground plane is presented in terms of the tangential aperture electric field, the coaxial line apparent input impedance and the far radiated field.

In the work titled ‘‘Ensuring Safety of Implanted Devices Under MRI Using Reversed RF Polarization,’’ the authors propose a method based on reversed polarization, which can be used as a prescan technique for patients with implants. In their work, to visualize qualitatively the induced radiofrequency (RF) currents on a metallic lead inside the patient, they propose to reverse the RF polarization for the transmit and/or the receive procedure. They performed simulations and experiments to investigate the performance of this technique and correctly identified the dangerous coupling currents that may cause risk to the patients. They formulated the RF field that is generated by an induced current on a straight wire, and they calculated its effect on the image intensity in both the forward and the reversed polarization cases. They compared these analytical test results with the experiments and showed that the results accurately match. They claim that the coupling currents can be visualized with better sensitivity when reversed polarization is used. According to the authors, the transmit polarization reversal provides better background suppression, making it easier to distinguish signal variation in the vicinity of the lead from variations due to anatomy. With polarization reversal, they claim that better wire-signal accuracy is provided. Although using reversed polarization to visualize the coupling currents is an innovative idea and could enhance the safety of patients with implants who are undergoing MRI, with this letter we would like to note that there may be certain situations where the proposed method may not work efficiently to accurately visualize the induced currents. In these specific cases, the RF safety of the patient could still be under question.

The propagation properties of the TEW mode and their dispersion relations in a high temperature superconductor (HTS) rectangular waveguide using the Meissner boundary conditions on all four superconducting walls are presented. In addition to recovering some previously known results, we have obtained some unique and novel results: the dominant mode for HTSWG is the TE11 mode (instead of the conventional TE10 mode) and the tangential electric field and normal magnetic field for the dominant mode TE11 exist on the surfaces. The expressions for electromagnetic components, surface current, attenuation coefficient, the maximum transmitted power, dispersion and wave impedance are also presented. The attenuation is found to be much smaller than that of the conventional waveguides and the dispersion is negligible. The Meissner model presented here has been proved to be valid and powerful for analysis of superconducting waveguides. For the first time, we have shown that the Meissner boundary condition is a key elem...