Optimization-oriented design of rectangular and circular waveguide components with the use of efficient mode-matching simulators in commercial circuit CAD tools (invited article)

Efficient mode-matching waveguide building blocks are described for user-friendly utilization in common commercial circuit CAD tools. This hybrid mode-matching/circuit theory CAD approach allows the accurate, convenient, and fast design of a comprehensive class of rectangular and/or circular waveguide components, such as filters, transformers, and multiplexers by advantageously combining the accuracy of the rigorous electromatic simulators with the efficiency of mature and well-established circuit theory design instruments. Moreover, an adequate multimode combination technique between the individual elements enables the utilization of additional design parameters resulting from higher-order mode interaction effects. The efficiency of the hybrid CAD method is demonstrated at typical microwave design examples that are optimized by use of the mode-matching waveguide building blocks in powerful commercial CAD packages, such as hp-EEsof's Touchtone ^TM or Libra ^TM and OSA's Osa 90/hope^TM. Advanced high-power asymmetrical iris coupled TE₁₀₃/TE₂₀₁ filters with high edge steepness show that the presented hybrid method is also applicable to more specialized design tasks. Its accuracy is verified by measurements and by comparison with the results of the conventional mode-matching/modal scattering matrix technique. © 1997 John Wiley & Sons, Inc. Int J Microwave Millimeter-Wave CAE 7: 37–51, 1997.     

Characteristics of rectangular dielectric waveguide with sinusoidally varying width

Wave propagation along a rectangular dielectric waveguide with slowly varying width has been studied using a transformed coordinate system and an effective cross-section approach. The associated differential equation has been solved using numerical analysis and Hill's analysis. The computed results have been verified using the cascaded transmission line matrix analysis of the structure in the original coordinate system. The agreement is found to be excellent. Many properties of the modulated periodic structure, for example, the propagation constant, the phase and the group velocities, the axial dependence of the E^y₁₁ mode. and the space harmonic, have been studied. The results and the method will be useful in computer-aided design of dielectric waveguide phase shifters and filters. © 1995 John Wiley & Sons, Inc.     

Design of dual‐mode dual‐band rectangular waveguide filtering antenna

A dual‐mode dual‐band rectangular waveguide filtering antenna with fourth‐order Chebyshev response is presented. First, design equations and processes of filtering networks are presented. Then, filtering antenna is constructed through cross‐shaped slot for radiation instead of the output port of filtering networks. A pair of degenerated modes are exploited in waveguide resonator design to miniaturize the whole size and form two passbands. In addition, the bandwidth can be adjusted flexibly in proper range. A prototype at C‐band is fabricated and measured, showing two operation channels of 5 to 5.05 GHz and 5.1 to 5.15 GHz with high rejection between two bands. Good agreement is achieved between the simulations and measurements, showing excellent performance in terms of filtering, out‐of‐band rejection, and gain in bands.     

A broadband coplanar waveguide to rectangular waveguide power divider using a slot

In this article, a broadband coplanar waveguide (CPW) to rectangular waveguide power divider using the dipole slot is proposed. The power divider consists of an input CPW port and two output rectangular waveguide ports. The CPW to rectangular waveguide power divider using the dipole slot has a return loss larger than 15 dB and an insertion loss equal to 3.08–3.27 dB in the whole X‐band (8.2–12.4 GHz). Furthermore, to broaden the bandwidth, the dipole slot is replaced by the bow‐tie slot. The CPW to rectangular waveguide power divider using the bow‐tie slot yields a return loss larger than 16 dB and an insertion loss equal to 3.05–3.29 dB from 8 to 13 GHz, which exceeds the X‐band. To verify our design, power dividers that use the dipole slot or the bow‐tie slot are fabricated and measured. The measurement results of both power dividers are in good agreement with the simulation results. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

Modeling of cavity-backed coaxial line to rectangular waveguide junction

A coaxial line to a rectangular waveguide junction, backed by an iris-coupled cavity, is analyzed using a new approach based on the five-cavity moment method. The scattering matrix of the junction is obtained by combining the mode-matching method and an interpolation technique. The computed results are checked for orthogonality and unitary conditions, and are verified against experimental results. The proposed structure and the analysis method will be useful in the design of extracted pole filters, diplexers, and multiplexers. © 1998 John Wiley & Sons, Inc. Int J RF and Microwave CAE 8: 20–26, 1998.     

Miniaturized rectangular waveguide filters

Two types of miniaturized rectangular waveguide filters are presented. Miniaturization is achieved using the slow‐wave effect of electromagnetic bandgap (EBG) surfaces and the left‐handed properties of split ring resonators (SRRs). The proposed EBG waveguide bandpass filter performs passband in the frequency range, which corresponds to the waveguide with the lower recommended operating band consequently enabling significant miniaturization of the structure. The SRR‐loaded bandstop filter makes use of the effect imposed by left‐handed medium (LHM), which is created by a combination of SRRs and wireline on the dielectric slab. Both filters are designed, simulated, and tested. Experimental results of the SRR‐loaded bandstop filter are presented to demonstrate feasibility of the proposed structures. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2007.     

Ridged waveguide structures with improved fundamental mode cutoff wavelength and bandwidth characteristics

A new circular waveguide loaded with two T‐shaped septa and a new triple ridge loaded trough rectangular waveguide are proposed and theoretically analyzed using the Finite Element Method. Numerical results are presented demonstrating that these structures offer a significant increase in both fundamental mode cutoff wavelength and bandwidth when compared to various unloaded and loaded waveguides. © 2002 Wiley Periodicals, Inc. Int J RF and Microwave CAE 12: 190–197, 2002.     

Calculation of dielectric waveguide systems using finite-difference method

Application of finite-difference (FDM) and finite-element (FEM) methods for the analysis of electromagnetic fields in dielectric structures and waveguides is considered. The main approaches to solution of these problems are discussed. Some new algorithms for such problems and their applications are presented.     

Investigations on fractal frequency selective diaphragms in rectangular waveguide

In this article, self‐similarity and space‐filling properties of fractal structures are explored as frequency selective diaphragms in rectangular waveguide, which can find applications in the design of compact, lightweight, and multiband waveguide filters with better out‐of‐band rejection ratio. Some self‐affine fractal structures, based on Sierpinski gasket and plus shape fractals, are proposed, and the effect of scaling factor on the location of transmission bands is investigated. Self‐similar structures like Hilbert curve, Koch curve, and Minkowski fractals are shown to be efficient in reducing resonant frequency of the diaphragm. Numerical results are presented along with the results obtained from HFSS, which show a good agreement. A typical application of the fractal diaphragm in the design of waveguide bandstop filter has also been demonstrated. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010.     

Analysis of passive intermodulation between rough rectangular waveguide flanges using fractal method

In nature, most of the surfaces are rough and waveguide flanges are not exception. And these surfaces topography are of high importance in the response of the waveguide flanges connection system. These surfaces topography are usually described by statistical parameters. And statistical parameters depend strongly on the resolution of the roughness‐measuring instrument, and hence the values of statistical parameters are not unique for a surface. As a result, the predictions of passive intermodulation (PIM) level of microwave devices based on these statistical parameters also may not be unique to a pair of contacting surfaces. Fortunately, fractal method is independent on the resolution of the roughness‐measuring instrument. Therefore, the randomness of the rough surface is not affected by the differences in the model. Consequently, if PIM level of rectangular waveguide is predicted with fractal parameters, the predicted value will be unique. Based on this motivation, a new model is developed. In this model, the fractal method is used to characterize the surface topography of waveguide flanges. Then, the third order PIM level of a rectangular waveguide flange is predicted. The analytic results are verified by PIM test set‐up. This work is help to understand PIM phenomenon and design the low‐PIM waveguide.     

Design equations of arbitrary power split ratio waveguide T‐junctions using a curve fitting approach

Design equations have been developed for the design of an H‐plane rectangular waveguide T‐junction with an arbitrary power split. These design equations were derived using curve fitting of data produced from a large number of EM simulation runs. A design procedure has been successfully developed and resulted in scalable, practically manufacturable structures. Various types of discontinuities were judiciously placed in the junction to provide adequate degrees of freedom and concurrently achieve diverse design goals. Added discontinuities included wedges and diaphragms which have been implemented as an integral part of the prescribed structures. For demonstration, T‐junction designs at Ku‐band have been fabricated and tested, which have adequate bandwidth performance covering the US‐DBS 12.2–2.7 GHz frequency range. Both excellent match at the input port and in‐phase flat power‐split ratio over a relatively wide band at the output ports were successfully achieved—an essential requirement for high‐performance antenna feeds. The dimensional tolerance of the developed design was also thoroughly investigated using extensive sensitivity analysis, and the developed structures proved to be appropriate for low‐cost high‐volume fabrication methods such as casting. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.     

A folded dual‐mode bandpass filter with circular waveguide

In this article, a folded circular waveguide dual‐mode filter without tuning screws is designed for the fifth‐generation (5G) mobile communication system. The folded filter is composed of two stacked circular cavities operated at 3.5 GHz. Each cavity has two resonant modes, which can generate and control two transmission zeroes at specific frequencies. Through a coupling iris, the two single‐cavity filters are connected together, and can control four poles, which helps to expand the 3dB fractional bandwidth to 11.4%. The measured insertion losses are around 0.5 dB in the passband (from 3.4–3.6 GHz). The experiment results show an excellent agreement with the simulation results. Such folded filters have the advantages of very low insertion loss, compact size, high frequency selectivity, and low cost.     

Mode‐matching analysis of H‐plane ferrite‐loaded rectangular waveguide discontinuities

The full set of eigenmodes existing in a ferrite‐slab‐loaded rectangular waveguide is first obtained and then used to compute the scattering matrix of a junction between an air‐filled rectangular waveguide and an H‐plane ferrite‐slab‐loaded rectangular waveguide by using the mode‐matching method. Numerical results for the scattering parameters of the H‐plane waveguide discontinuity are compared to experimental data and those obtained by Ansoft's HFSS. Good agreement is observed. To demonstrate the usefulness of this structure, a computer‐optimized 90° nonreciprocal phase shifter is designed using an H‐plane ferrite‐slab‐loaded waveguide. With only one‐step impedance matching sections at both ends of the ferrite slab, a compact design is achieved to have 2° phase error and less than ?30 dB return loss over about 5% bandwidth. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 13: 259–268, 2003.     

In‐line stepped ridge coaxial‐to‐rectangular waveguide transition with capacitive coupling

An original in‐line coaxial‐to‐rectangular waveguide transition including stepped ridged sections is presented. This device differs from the state of the art because of the coaxial inner conductor not being in electrical contact with the ridge, leading to considerable mechanical advantages. In addition to this, capacitive coupling can extend the bandwidth even with a few matching sections when compared with the traditional counterpart presenting DC contact with the first ridge. An ultra‐compact transition is designed, manufactured, and tested in back‐to‐back configuration. From measured data, a return loss better than 20 dB on a bandwidth of 1.27 GHz (12.2%) is observed in this configuration. An average insertion loss of 0.11 dB can be derived for the standalone transition.     

A nonuniform array of slots in the broad‐walls of rectangular waveguides partially filled with dielectric slabs

This article describes a new nonuniform slot antenna array in the broad wall of rectangular waveguides partially filled with a dielectric slab. The slot elements are nonuniformly spaced to achieve a higher side lobe level while the amplitude and phase of their excitations are identical. Each slot element is fed by one dielectric‐loaded rectangular waveguide with one end shorted for structural simplicity. Experimental results for an 8‐element linear slot array operating at X‐band show that the side lobe level is 15 dB over a frequency range from 9.5 GHz to 10.5 GHz. The simulated side lobe level can reach 20 dB for a 16‐element linear array. Experimental results show that the side lobe level of a slot array can be improved using nonuniform element spacing without degrading the broadside radiation and gain. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2008.     

Single‐ridge waveguide T‐junctions for compact multilayer beam forming networks

In this work, an H‐plane and an E‐plane single‐ridge waveguide T‐junction exhibiting compact size and broadband performance are presented. Thanks to these features the proposed devices turn out to be key components for the implementation of high‐performance multilayer antenna beam‐forming networks. Effectiveness and suitability of such T‐junctions are demonstrated through the design of a broadband array antenna feeding network. The presented components operate at Ku band, nevertheless the adopted architectures are fully scalable to other frequency band of interest.     

Dual mode and miniaturized rectangular dielectric resonator antenna with a simple feeding scheme

The objective of this article is to propose a miniaturized rectangular dielectric resonator antenna (RDRA) configuration and dual mode operation using a simple feeding scheme. It demonstrates the potential advantages achieved by choosing a microstrip line feeding mechanism at the edge of the RDRA. Measurement and simulation results are both in good agreement. The fabricated antenna possesses wide impedance bandwidth (BW) of 800 MHz (5.65 to 6.48 GHz) and dimensions of RDRA are 17 × 7 × 3 mm³. Measured radiation patterns have linear polarization over the frequency range. By the proposed design, the BW is enhanced more than four times as compared to the conventional way to excite the RDRA by microstrip line. To validate the design, the comparison of published design is discussed. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:229–235, 2015.     

Propagation characteristics of an optically controlled double‐channel lossy‐dielectric waveguide

A double‐channel lossy‐dielectric waveguide, having its propagation characteristics controlled by the action of light, is analyzed here. The light is incident on a semiconductor material that constitutes the inner channel of the waveguide structure, generating a plasma. The analysis of the problem is done by using the finite difference in the frequency domain method which was found to be efficient for this analysis. The results presented here were confirmed with those obtained using the finite element method. © 2000 John Wiley & Sons, Inc. Int J RF and Microwave CAE 10: 127–131, 2000.     

Personal computer-based direct synthesis of optimum rectangular waveguide E-, H-, and EH-plane transformers

In this work a direct synthesis technique is presented for the optimum design of rectangular waveguide continuous and stepped impedance transformers. The synthesis technique is based on a generalized Fourier transform pair and it is implemented on a 486 DX2 machine. Unlike the conventional techniques, the proposed method is exact and does not rely on repeated analysis-based computer optimization that requires a large computer memory and speed. The proposed method requires less than a second to design a Chebyshev EH-plane transformer. The validity of the method has been shown by the design and analysis of several E-, H-, and EH-plane rectangular waveguide Ka-band transformers. The analysis subroutines were verified using published experimental results. © 1997 John Wiley & Sons, Inc. Int J Microwave Millimeter-Wave CAE 7 : 289–308, 1997.     

On the extension of commercial planar circuit CAD packages to the analysis of two‐port waveguide components

We introduce a simple algorithm that enables several commercial codes, based on the method of moments (MoM) and developed for the analysis of planar structures, to address the analysis of a class of two‐port waveguide components. Its key step is a numerical calibration that can be easily automated. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 13: 113–117, 2003.