Wideband and low‐loss waveguides of nonuniform cross‐section

Waveguides of nonuniform cross‐section are introduced, analyzed and then their cross‐section is optimized to reach wideband and low‐loss waveguides. The waveguide cross‐section is defined as a Fourier series whose unknown coefficients are optimized using genetic algorithm to reach a proper cross‐section for waveguide. A verified finite difference method is used in analysis stage of optimization. The results show that optimum designed nonuniform cross‐section waveguides have lower conductor attenuation constant in comparison with double ridged waveguides of the same bandwidth. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:115–121, 2015.     

Steady‐state electro‐thermal analysis and optimization of multilayer boards and substrate‐integrated waveguide filters

An efficient method is proposed to perform the steady‐state thermal analysis of multilayer boards by using the multilayer finite‐difference method to obtain and solve the thermal conductance network. The electro‐thermal analysis of substrate‐integrated waveguide (SIW) filter is further carried out, with its distributed heat source, that is, electromagnetic losses. Then, our method is applied to optimize the electro‐thermal performance of a composite configuration, including a SIW filter with a selfheating chip attached on it. A location with the minimum hotspot temperature is found. Good agreement is achieved between the results simulated with our method and the commercial finite element method (FEM) simulators. When the worst‐case error is set to 5.3%, the run time of our method is significantly reduced by 95% in comparison with the FEM simulators. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:594–604, 2014.     

Three‐dimensional split‐step‐fourier and finite difference time domain‐based rectangular waveguide filter simulators: Validation,verification, and calibration

The split‐step‐Fourier‐based three‐dimensional wave propagation prediction and finite‐difference time‐domain‐based simulators are developed to show network scattering parameters of rectangular waveguide filters with horizontal and/or vertical windows as capacitive and/or inductive irises, respectively. The three‐dimensional‐split‐step parabolic equation simulator is applied to rectangular waveguide filters, and the results are compared with finite‐difference time‐domain model through tests inside a rectangular waveguide. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:660–667, 2016.     

Effect of finite and different ground‐plane widths on quasistatic parameters of asymmetrical coplanar waveguides

Fast, accurate, and simple closed‐form expressions are presented for calculating the quasistatic TEM parameters of asymmetrical coplanar waveguides (ACPWs) with finite and different ground planes. The effect of the ground‐plane width and the asymmetry in the ground‐plane widths and in the spacings of ACPWs on the line parameters is investigated by using the formulas derived by conformal mapping techniques. Comparisons are also made between the present results and the results available in the literature for both the conventional coplanar waveguide (CPW) and the ACPW. The results in this article are in very good agreement with the results derived by the conformal mapping technique, by the variational formulation, and by the spectral‐domain method. It has been shown that the asymmetry of both ground planes and spacings leads to a significant change of the quasi‐TEM parameters with respect to cases of the finite and infinite ground planes. © 2000 John Wiley & Sons, Inc. Int J RF and Microwave CAE 10: 383–389, 2000.     

A finite‐difference time‐domain approach to waveguide discontinuities using one‐dimensional modal perfectly matched layer based on diagonally anisotropic material

In this paper, one‐dimensional modal perfectly matched layer (PML) is applied to improve the computational efficiency in waveguide discontinuity problems. The proposed PML formulation is based on an anisotropic medium. A WG‐90 rectangular waveguide with a thick asymmetric iris is analyzed via FDTD simulations with Berenger's PML and the proposed one. Numerical results show that the computational efficiency is significantly improved by the new method. © 2000 John Wiley & Sons, Inc. Int J RF and Microwave CAE 10: 264–270, 2000     

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.     

Coaxial probe‐fed open‐ended waveguide antenna based on sand casting process with filtering characteristics and all‐in‐one structure

In this article, a coaxial probe‐fed open‐ended waveguide filtering antenna with all‐in‐one structure is proposed and fabricated by adopting sand casting process. It is known that for waveguide component with complex internal space, detached parts, and post‐processing assembly are often necessary, while unavoidably resulting in error, air gap and loss. In this context, sand casting process is here utilized to fabricate the whole waveguide structure directly, thus achieving a fully integrated antenna. Besides, by controlling the external couplings from probe feed and free space, the proposed coaxial probe‐fed antenna can provide similar impedance matching to a waveguide‐fed three‐order waveguide filter. Both the frequency‐ and time‐domain reflection coefficients of filter and antenna have been compared and analysed. An antenna prototype is fabricated and measured to validate the proposed design, which provides a successful example of all‐in‐one waveguide filtering antenna.     

A simple estimate for cut‐off wave number of lowest‐order TM mode of a hollow metallic waveguide of arbitrary cross‐section

Based on two inequalities, it is presented that the cut‐off wave number of the lowest order transverse magnetic (TM) mode of a hollow metallic waveguide of arbitrary cross‐section is a function of the area, the perimeter and the inscribed circle radius. The results obtained by the derived formulas are compared with exact data reported in the literature. It shows that the proposed method is the reliable general purpose tool for computing the cut‐off wave number of the lowest order TM mode of a hollow metallic waveguide of arbitrary cross‐section. © 2000 John Wiley & Sons, Inc. Int J RF and Microwave CAE 10: 159–163, 2000.     

Use of 3D field simulators in the synthesis of waveguide capacitive iris coupled lowpass filters

This paper presents the generalized lowpass filter design method of Levy based on three‐dimensional electromagnetic analysis and discontinuity modeling using commercially available full‐wave electromagnetic simulators. It shows how to use Levy's method for very accurate theoretical design of a waveguide capacitive iris lowpass filter, using modern 3D EM field‐solvers based on the finite element method (FEM), the mode matching method (MM), and the transmission line matrix (TLM) analysis method. This is the first time that design curves and equations, based on full electromagnetic modeling, have been presented for constant thickness capacitive iris filters. We will demonstrate our approach by designing a number of waveguide capacitive iris filters. This paper also demonstrates the generality of the method. This method can be applied to many other types of waveguide lowpass and bandpass filters. © 2000 John Wiley & Sons, Inc. Int J RF and Microwave CAE 10: 190–198, 2000.     

Flexible and efficient computer‐aided design tool for advanced comb‐line rectangular waveguide filters

A very flexible and efficient computer‐aided design (CAD) tool, specifically suited for advanced comb‐line rectangular waveguide filters, is presented in this work. The developed software tool, which makes use of a full‐wave analysis technique based on the Boundary Integral—Resonant Mode Expansion method, allows loading the considered comb‐line resonators with any number of radially symmetrical partial‐height metallic posts. The implemented CAD tool also allows dealing with coupling windows of arbitrary cross‐section, thus drastically enhancing the flexibility of the CAD process. The excitation of the analyzed components, which is performed using generalized coaxial probes, has also been integrated in the implemented software tool, thus achieving a full‐wave electromagnetic characterization of the whole component. Furthermore, a novel simple procedure to efficiently connect all the obtained wide‐band matrices is proposed. To validate the accuracy and efficiency of this novel CAD tool, several new designs concerning advanced band‐pass comb‐line waveguide filters are presented. The accuracy of the developed CAD tool has been successfully validated by comparing the obtained results with numerical data provided by a commercial tool based on the finite‐element method. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:696–708, 2015.     

A plastic holographic waveguide combiner for light‐weight and highly‐transparent augmented reality glasses

There is a high demand for light‐weight, stylishly designed augmented reality (AR) glasses with natural see‐through capabilities for the wide‐spread distribution of novel wearable device to general consumers. We have successfully developed a unique production process of a holographic waveguide combiner that enables us to laminate holographic optical elements (HOEs) onto a plastic substrate with optical grade quality. The plastic substrate waveguide combiner has a number of advantages over conventional glass substrate combiners; the plastic substrate makes AR glasses lighter in weight and unbreakable. With the lamination process of HOEs, we can apply them to a various designs to satisfy general customers' wide range of preferences for the style. We also potentially made it possible for the holographic waveguide combiner to be produced in larger volumes at lower costs by using our novel roll‐to‐roll hologram recording and laminating process. In this paper, we present our approach of the plastic substrate HOE production process for AR glasses.     

Propagation characteristic analysis of ridged circular waveguide using 2D finite‐difference frequency‐domain method

The propagation characteristics of ridged circular waveguides are analyzed by using 2D finite‐difference frequency‐domain (2D FDFD). Based on the 2D FDFD method in a cylindrical coordinate system, general difference formulas for the ridged circular waveguide are deduced, and modified difference formulas are built at some special points of the ridged circular waveguides. To verify the proposed method, three ridged circular waveguide structures are investigated and the numerical results are compared with available ones obtained by other research methods. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE 15, 2005.     

Analysis of 3D ferrite‐loaded waveguide discontinuity problems

In this article, an approach is presented to compute the scattering parameters of the ferrite‐loaded waveguide discontinuity using the finite‐element method (FEM) and perfectly matched layers (PMLs). The propagation constants of a uniform ferrite‐loaded waveguide are first calculated to validate the proposed approach. Then a 2D ferrite‐loaded discontinuity problem is computed to further confirm the accuracy of the approach. Finally, several 3D discontinuity results are given to show the efficiency and generality of the approach. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 13, 341–347, 2003.     

Full‐wave analysis of H‐plane waveguide junction loaded with metallic posts

A hybrid method that combines moment method and mode matching technique is presented to study H‐Plane waveguide discontinuity loaded with metallic posts at the junction of two waveguides. By expanding Eigen modes in waveguides, applying continuity of tangential fields at the discontinuity and finally nulling the tangential electric field on the post surface, a system of algebraic equations is solved to obtain current distribution on the posts and consequently scattering parameters of the structure. Then, as an application, an in‐line dual‐mode rectangular waveguide bandpass filter is analyzed using the proposed method along with generalized scattering matrix method. The numerical results are in good agreement with existing full wave finite element method in high frequency structure simulator (HFSS) results and measurements. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE , 2011.     

Widely separated dual‐band half‐mode SIW bandpass filter

A novel half‐mode substrate integrated waveguide (HMSIW) based dual‐band bandpass filter (DBBPF) is proposed. Back to back connected two defected ground structure (DGS) resonators on the top layer of HMSIW cavity constitute the passband with two transmission zeros (TZs) at a lower frequency. The higher modes TE₃₀₁ and TE₃₀₂ of HMSIW cavity give the passband response at higher frequency using the mode shifting technique with slot perturbation. The source‐load coupling has been used to create finite frequency TZs to improve the selectivity of the second passband. Therefore, the proposed filter gives two widely separated passbands, center frequencies (CFs) at 5.83 and 18.1 GHz with an attenuation of greater than 10 dB between the passbands. The synthesized filter is fabricated using a low‐cost single layer PCB process, and the measured S‐parameters are almost mimic the EM‐simulation results.     

An unbalanced‐to‐balanced diplexer based on substrate integrated waveguide cavity

A novel unbalanced‐to‐balanced diplexer based on a dual‐mode substrate integrated waveguide (SIW) cavity is proposed and implemented. The diplexer is realized using one dual‐mode cavity and two single‐mode cavities. By properly choosing, feeding and coupling the cavity operating at the TE₁₀₂ or TE₂₀₁ mode, so as to not only provide capabilities to realize the desired unbalanced‐to‐balanced transmission within both Rx and Tx channels but also realize good differential‐mode channel‐to‐channel isolation. To the author's knowledge, we present for the first time an unbalanced‐to‐balanced type diplexer based on the application of SIW. The proposed diplexer was successfully designed, simulated, and fabricated. Good agreement can be observed between simulated and measured performances in our letter. The measured in‐band common‐mode rejection is better than 33 dB for both channels. A minimum differential‐mode isolation of about 50 dB across the Rx band and about 40 dB across the Tx band is also observed in the measurement. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:173–177, 2015.     

High‐mobility self‐aligned top‐gate oxide TFT for high‐resolution AM‐OLED

High‐mobility and highly reliable self‐aligned top‐gate oxide thin‐film transistor (TFTs) were developed using the aluminum reaction method. Al diffusion to the oxide semiconductor and homogenization of the oxygen concentration in the depth direction after annealing were confirmed by laser‐assisted atom probe tomography. The high mobility of the top‐gate TFT with amorphous indium tin zinc oxide channel was demonstrated to be 32 cm²/V s. A 9.9‐in. diagonal qHD active‐matrix organic light‐emitting diode (AM‐OLED) display was fabricated using a five‐mask backplane process to demonstrate an applicable solution for large‐sized and high‐resolution AM‐OLEDs.     

Toward sub‐micron oxide thin‐film transistors for digital holography

High‐performance 2‐μm‐channel oxide thin‐film transistors (TFT) on glass substrate for a 7‐μm‐pixel‐pitch spatial light modulator panel for digital holography applications were fabricated using a two‐step source/drain etching process. It showed a μ_FE of 45.5 cm²/Vs, SS of 0.10 V/dec, and Von of near zero voltage. Furthermore, we succeeded in the demonstration of sub‐micron TFTs, which is an indispensable route to next‐generation spatial light modulation devices with near 1‐μm pixel pitch. The issue of short‐channel transistors for display applications is also introduced. Finally, the digital holographic demonstration results based on the fabricated backplane are presented.     

Analysis and modeling of microstrip‐to‐coplanar flip chip package interconnects

In this paper, the discontinuity of a flip chip transition between a microstrip line and a coplanar waveguide is investigated and modeled using the finite‐difference time‐domain method (FDTD) to predict the overall S‐parameters of the package. Effects of the bump and via interconnects on the package performance are investigated and discussed. This includes the effects of different staggered transitions and ground connects on the package performance. A reduction of about 10 dB in the bump and via reflections can be achieved by staggering the signal (bump) and the ground connects (bump/via). A staggering distance of about twice the slot width gave minimum reflection over a wide band of frequencies. Moreover, the larger the relative distance between the ground and the center connects the less the reflection due to the discontinuity. Finally, the computed S‐parameters of the flip chip package using the FDTD solution are used to develop an equivalent circuit model for the transition discontinuity over a wide frequency band. The equivalent circuit model of the microstrip to coplanar waveguide discontinuity includes more elements and is more complex than other types of transitions. A TEE or PI circuit model has been used to approximate the general circuit model of the discontinuity. Good agreement has been obtained between the S‐parameters of the FDTD model and the equivalent circuit models over a wide frequency band. © 2001 John Wiley & Sons, Inc. Int J RF and Microwave CAE 11: 202–211, 2001.     

Signal reconstruction in the presence of finite‐rate measurements: finite‐horizon control applications

In this paper, we study finite‐length signal reconstruction over a finite‐rate noiseless channel. We allow the class of signals to belong to a bounded ellipsoid and derive a universal lower bound on a worst‐case reconstruction error. We then compute upper bounds on the error that arise from different coding schemes and under different causality assumptions. When the encoder and decoder are noncausal, we derive an upper bound that either achieves the universal lower bound or is comparable to it. When the decoder and encoder are both causal operators, we show that within a very broad class of causal coding schemes, memoryless coding prevails as optimal, imposing a hard limitation on reconstruction. Finally, we map our general reconstruction problem into two important control problems in which the plant and controller are local to each other, but are together driven by a remote reference signal that is transmitted through a finite‐rate noiseless channel. The first problem is to minimize a finite‐horizon weighted tracking error between the remote system output and a reference command. The second problem is to navigate the state of the remote system from a nonzero initial condition to as close to the origin as possible in finite‐time. Our analysis enables us to quantify the tradeoff between time horizon and performance accuracy, which is not well studied in the area of control with limited information as most works address infinite‐horizon control objectives (e.g. stability, disturbance rejection). Copyright © 2009 John Wiley & Sons, Ltd.