Modeling of generalized coaxial probes in rectangular waveguides

Multiple 3-D discontinuities between rectangular ferrite loaded waveguides are analysed. This analysis is carried out by means of the coupled mode method, using a series expansion that is different from the classical one, combined with the modal matching method. Reasonable agreement is found between theoretical predictions and experimental results.

This letter is intended to point out a few typing mistakes in the above paper [1], which discusses computing the complex permittivity of a dielectric material embedded in a rectangular waveguide or a microstrip line, and to suggest corrections to its formulation.

Monopole antennas are widely used in communication systems because of features such as pure vertical polarization and omnidirectional radiation patterns in the horizontal plane. Conventionally, monopole antennas are fed through a ground plane by a coaxial probe. Recently, monopole antennas fed by printed transmission lines have attracted increasing attention. However, to the best of our knowledge, monopole antennas are seldom fed by a rectangular waveguide. We consider the problem of this type of feed because of our interest in designing an omnidirectional antenna at millimeter wave bands. At millimeter wave frequencies, rectangular waveguides are preferred to coaxial or microstrip lines because they exhibit very low loss, have a large power handling capacity and other waveguide components are readily available. The paper presents a design for monopole antennas fed by a rectangular waveguide. In order to achieve a good transition from a rectangular waveguide to the monopole antenna, a ridged waveguide section is introduced, and the vertical monopole is attached to the ridge through a circular aperture opened on the upper broad-wall of the rectangular waveguide, which is part of the ground plane. Two examples are provided and experimental tests of one of these antennas shows that the monopole can achieve about 24% bandwidth and 5 dBi gain.

The scattering properties of the H‐plane waveguide discontinuities such as the cross junction, T‐junction, and right‐angle bend are analyzed taking their symmetry into account. the solutions are synthesized in two new and simple expressions. These solutions are treated rigorously by the mode‐matching method in which each junction section is divided by a circular region and the electro magnetic fields are matched with the scattered waves into waveguide regions at the boundaries. By means of the accurate numerical results obtained in a wide frequency range, the scattering properties of the H‐plane junctions in a standard waveguide and an oversized waveguide are examined in detail. the latter is believed to be useful for an approximnte estimation of the scattering properties of crossing roads in underground shopping centers.

Several RF and microwave radiating devices, such as horn antennas, Fabry–Perot cavity antennas, and aperture-fed focusing devices, are excited through rectangular waveguides. The impedance matching of the overall system (from the waveguide feed to the radiating aperture) is a task of crucial importance that is often addressed by means of brute-force parameter-sweep full-wave analyses or blind optimization algorithms. In both cases, a significant amount of memory and time resources are required. For this purpose, we propose here a simple, yet effective solution, which only requires a single full-wave simulation and a semi-analytical procedure. The former is used to retrieve the antenna input impedance at the end of the waveguide port excitation. The semi-analytical procedure consists in a transmission-line equivalent circuit that models two waveguide discontinuities (namely two capacitive irises) within the waveguide section, whose position and geometric features are finely tuned to obtain a satisfactory impedance matching around the working frequency. The proposed method is shown to be effective in diverse and attractive application-oriented contexts, from the impedance matching of a Fabry–Perot cavity antenna to that of a wireless near-field link between two aperture-fed focusing devices. A remarkable agreement between full-wave simulations and numerical results is found in all cases. Thanks to its versatility, simplicity, and a rather low demand of computational resources, the proposed approach may become an essential tool for the effective design of waveguide-fed antennas.

The scattering matrix of a transition between one or two parallel rectangular waveguides and a larger rectangular waveguide which contains two metallic or dielectric cylinders is investigated by means of the orthogonal expansion method. Mathematical programming is applied in order to improve the characteristics of the branchings. Reflection at a rectangular step discontinuity can be reduced by 30 dB using metallic or dielectric obstacles. Using Teflon cylinders, coupling of a transition can be reduced by 40 dB without debasing reflection. Physical interpretations are given with the help of field patterns.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

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>

An accurate design technique of dual-mode microwave dielectric or air-filled rectangular waveguide filters is described. Dual-mode coupling is realized by a section of rectangular waveguide with square-corner-cut. The unequal couplings between dual-mode pairs of the cavities is provided by a section of evanescent mode waveguide. Rigorous analyses are applied to characterize the microwave junctions and to obtain the design parameters for the filter. The design procedure used to determine the dimensions of the waveguide junctions with a minimum of computational effort is described. The design is demonstrated by four-pole and six-pole dual-mode rectangular waveguide elliptic function filters. Excellent agreement between computer simulation and experimental results with absolutely no tuning justifies the design.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The advent of carbon loaded composite materials gave a boost to many industries. This is because of their light weight, durability and strength. As new structures utilizing carbon loaded composites are built, the need for a reliable nondestructive testing technique increases. A carbon-loaded composite testing poses a challenge to most nondestructive testing and evaluation (NDT&E) techniques. Microwave NDT&I techniques main challenge is the lossy nature of carbon, especially at high microwave frequencies. Lower frequencies penetrate deeper in carbon-loaded composites, however, to operate at lower frequencies the size of the waveguide probe increases significantly which degrades the resolution rapidly. Open-ended rectangular waveguide sensors filled with a dielectric material will be used to inspect carbon-loaded composites. The filling of the waveguide reduces the frequency of operation and keeps the small size of the waveguide (i.e. increases the penetration depth and maintains the resolution). However, varying the waveguide filling material dielectric properties will have an impact on the measurement parameters optimization process and consequently on the detection sensitivity. In this paper, the use of the waveguide filling material as an optimization parameter will be investigated. Carbon-loaded composites with disbonds will be inspected and the variation of the dielectric properties of the loading material of rectangular waveguide probes for carbon loaded composites inspection will be assessed.

The paper considers the general problem of a waveguide double junction consisting of three dissimilar waveguides coupled together via apertures. An equivalence theorem is utilized to set up an integral equation which is solved by using the method of moments. The method is attractive in that it forms the basis for a common computer code for a wide category of waveguide discontinuities. Numerical results are presented for a number of test problems which show the versatility of the method.

A new microwave photonic filter structure that can achieve a high factor, high stopband rejection, and high skirt selectivity bandpass filter response simultaneously is presented. It is based on reflecting the signal back into a single amplified optical recirculating delay line and comprises coherent summation of the multiple signals that constitute each tap and incoherent summation of the successive taps. This introduces a new class of filter operation and effectively enables the realization of a higher order bandpass filter characteristic in a very simple structure. Experimental results are presented that demonstrate a multiple-tap high- bandpass filter response that also displays high stopband rejection level and high skirt selectivity.

A rigorous field theory CAD (computer-aided design) of rectangular waveguide sidewall aperture couplers coupled by rectangular apertures of different sizes is introduced. Based on the rectangular waveguide T-junction and the double-step discontinuity key-building block modal S-matrices calculated by the mode-matching method, the design rigorously takes into account both the finite wall thickness and the higher-order mode interaction between all discontinuities. Design examples for rectangular aperture 10-dB, 8.34-dB, and 3-dB couplers in the waveguide Ku-band (12-18 GHz) demonstrate the efficiency of the design method. For computer optimization, the evolution strategy method is applied. As the initial values are derived by using the classical network theory synthesis methods, relatively fast and very reliable designs are achieved. The theory is verified by excellent agreement with measurements. >

Substrate Integrated Waveguide (SIW) is a new kind of microwave transmission structure appeared in recent years. The SIW technique makes it possible that a complete circuit including planar circuitry, transition, and rectangular waveguide are fabricated in a planar form using a standard printed circuit board (PCB). From analysis of the susceptance of symmetrical window and designing process of Chebyshev bandpass filter in rectangular waveguide, an X-band filter based on SIW is designed and fabricated in this article. The simulated results show that the bandwidth of the filter is 5%. The insertion loss is about 1.4 dB, and return loss is about 25 dB at 10 GHz. The measured insertion and return losses are about 2.9 dB and about 13 dB, respectively at mid-band frequency. The filter has a small insert loss and good frequency selective performances from 9.82GHz to 10.20GHz. It is suitable for designing millimeter-wave circuits, and can be produced with batches to be widely used in the microwave systems with the simple structure.

This paper presents the simulation, design and implementation of bandpass filters in rectangular waveguides. The filters are simulated and designed by using a numerical analysis program based on the Wave Iterative Method (WIM) called WFD (Waveguide Filter Design) simulation. This simulation program can analyze the electrical network of filters. The sample waveguide filter is designed based on a proposed structure consisting of three circuits serving as a simple bandpass filter with two inductive irises and three inductive irises in a cascade. We determined that the operating frequency was equal to approximately 4.20-4.84 GHz. The waveguide filters were then implemented using an aluminum material. The analyzed results for the inductive iris obtained with the WFD program agree well with the results of CST Microwave Studio®. Finally, the measured results of sample waveguide filters are consistent with the simulation tool.

The computer‐aided analysis and design of direct‐coupled and quarter‐wave‐coupled bandpass filters utilizing monomode rectangular waveguides with 1‐dimensional offset discontinuities are described. The equivalent networks of these discontinuities, which consist of a shunt reactance and additional transmission lines connected at both sides, have been derived from the rigorous field‐theoretical investigations of E‐plane and H‐plane displacements in rectangular waveguide. Both network elements are tabulated in terms of geometry and wavelength with fine steps to allow accurate interpolation by means of computational methods, Simple design formulae for the filter geometry as a function of the electrical specifications are given which are based upon narrow‐band approximations. The analytical relationships required for a computer simulation of the filter's wide‐band performance are summarized. The predicted frequency characteristics showed such close agreement with the experimental results obtained on two X‐band filter models that neither tuning elements in the waveguide sections nor final adjustments of the offset widths had to be provided.