Implementation and optimization of GPU‐based parallel one‐step leapfrog ADI‐FDTD for far‐field scattering problems

The one‐step leapfrog alternative‐direction‐implicit finite‐difference time‐domain (ADI‐FDTD), free from the Courant‐Friedrichs‐Lewy (CFL) stability condition and sub‐step computations, is efficient when dealing with fine grid problems. However, solution of the numerous tridiagonal systems still imposes a great computational burden and makes the method hard to execute in parallel. In this paper, we proposed an efficient graphic processing unit (GPU)‐based parallel implementation of the one‐step leapfrog ADI‐FDTD for the far‐field EM scattering simulation of objects, in which we present and analyze the manners of calculation area division and thread allocation and a data layout transformation of z components is proposed to achieve better memory access mode, which is a key factor affecting GPU execution efficiency. The simulation experiment is carried out to verify the accuracy and efficiency of the GPU‐based implementation. The simulation results show that there is a good agreement between the proposed one‐step leapfrog ADI‐FDTD method and Yee's FDTD in solving the far‐field scattering problem and huge benefits in performance were encountered when the method was accelerated using GPU technology.     

Design and optimization of a tunable W‐band subharmonic cavity based Gunn diode oscillator using computer‐aided design technique

In this work, a systematic computer‐aided design technique is proposed to minimize the fabrication iteration for the design and development of W‐band subharmonic Gunn diode oscillator with wideband tunable bandwidth at W‐band. Gunn diode based single diode oscillator structure was divided into passive and active parts to facilitate the modeling of the component on appropriate simulation environment. Resonating structure and package of Gunn diode are modeled as passive circuit in high frequency structure simulator (HFSS). To satisfy the oscillator design equation, disc‐post resonating structure is tuned in HFSS and its S‐parameters are collaborated with the model of Gunn diode in advanced design system. Magnitude and phase of reflection coefficient (S11) is observed to ascertain the desired frequency of oscillation. Proper tuning of disc‐post structure is done on simulation platform, which reduces the fabrication complexity and cost as well. The measurement results validate the models designed using EM and circuit simulator. The measured maximum stable RF power without any fabrication iteration is 14.2 dBm. A tunable bandwidth of 4 GHz with power output ripple of ±1 dB is measured by using a movable backshort.     

A de‐embedding method with matrix rectification and influences of residual errors on model parameters extraction of InP HEMTs

As the cutoff frequency of InP HEMTs enters the terahertz band, high frequency measurement and modeling techniques in hundreds of gigahertz become urgent needs for further millimeter monolithic integrated circuits design. We proposed a new de‐embedding method linking device measurements and modeling based on full EM simulation data acquired from HFSS and advanced design system (ADS). The simulation results for passive dummy structures are well consistent with experiments, and the de‐embedding method is proved very effective for a resistive passive device with high distributed embedding surroundings in frequency range below 40 GHz. Based on these experimental facts, the EM simulations were extended up to 300 GHz and corresponding de‐embedding deviation was further investigated. Results show that the proposed de‐embedding method has very high accuracy in the whole frequency region with a maximum S‐parameters deviation of only 2.58%. However, further analysis proves that the small residual errors still significantly affect extracted small signal model parameters of InP HEMTs especially for transit time τ. Thus, further improvements on de‐embedding accuracy or careful considerations of more error functions in modeling process are necessary for obtaining physically meaningful model parameters.     

A comparison of three‐dimensional electromagnetic and RC parasitic extraction analysis of mm‐wave on‐chip passives in SiGe BiCMOS low‐noise amplifiers

Layout parasitics significantly impact the performance of mm‐wave microelectronic circuits. These effects may be estimated by including foundry‐qualified pcell interconnect models in schematic with or without additional RC parasitics extraction (RCPE), or by generating an EM simulation (FEM and MoM) of the layout and cosimulating with active device models. In this paper, these methods are compared at by simulating the compression (P1db), gain (S₂₁), and noise figure (NF) of a V‐band LNA in 130 nm SiGe BiCMOS and comparing the results of different simulation approaches to measurements. It is found that the FEM cosimulated results agree better with the measurements than the other methods, providing a maximum error of 0.8 dB in gain, 0.18 dB in NF, and 0.6 dB in P1dB. This is a significant improvement over the errors obtained with pcell‐based schematic (2.6 dB in gain, 0.1 dB in NF, and 2.2 dB in P1db), schematic simulation with RCPE (1.55 dB in gain, 1.15 dB in NF, and 0.8 dB in P1db), and MoM cosimulation (0.67 dB in gain, 0.72 in NF, and 0.67 in P1db). This experiment validates the preference to FEM cosimulation in mm‐wave microelectronic circuits yet would indicate that reasonably accurate first‐iteration results may be obtained through a combined pcell‐RCPE approach with significantly shorter simulation time.     

Tuning space mapping with tuning exponent of T‐matrix

Tuning space mapping (TSM) with tuning exponent parameter of T‐matrix is proposed. A section of design interest in the electromagnetic (EM) model is replaced by “n” pieces cascaded T‐matrixes, and each T‐matrix is the EM‐simulated T‐parameter of preassigned unit cell circuit (PUCC). Finally the optimal exponent parameter of T‐matrix is transferred to original design variables. The proposed TSM not only inherits the advantages of circuit tuning element‐less (CTEL) TSM in prior art but also overcome the number range limitation that the tuning parameter must be positive for tuning in CTEL TSM. The proposed method has the minimal specification error and lowest simulation time comparing with other TSM methods. Verification examples, comparisons and discussions are also implemented. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:232–239, 2016.     

GPU‐accelerated finite‐difference time‐domain method for dielectric media based on CUDA

The simulation of electromagnetic (EM) waves propagation in the dielectric media is presented using Compute Unified Device Architecture (CUDA) implementation of finite‐difference time‐domain (FDTD) method on graphic processing unit (GPU). The FDTD formulation in the dielectric media is derived in detail, and GPU‐accelerated FDTD method based on CUDA programming model is described in the flowchart. The accuracy and speedup of the presented CUDA‐implemented FDTD method are validated by the numerical simulation of the EM waves propagating into the lossless and lossy dielectric media from the free space on GPU, by comparison with the original FDTD method on CPU. The comparison of the numerical results of CUDA‐implemented FDTD method on GPU and original FDTD method on CPU demonstrates that the CUDA‐implemented FDTD method on GPU can obtain better application speedup performance with reasonable accuracy. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:512–518, 2016.     

Phase‐spacing optimization of linear microstrip antenna arrays using simulation‐based surrogate superposition models

A technique for simulation‐driven optimization of the phase excitation tapers and spacings for linear arrays of microstrip patch antennas is presented. Our technique exploits two models of the array under optimization: an analytical model which is based on the array factor, as well as an electromagnetic (EM) simulation‐based surrogate model of the entire array. The former is used to provide initial designs which meet the design requirements imposed on the radiation response. The latter is used for tuning of the array radiation response while controlling the array reflection response as well as for validation of the final design. Furthermore, the simulation‐based surrogate model allows for subsequent evaluation of the array responses in the beam scanning operation at negligible computational costs. The simulation‐based surrogate model is constructed with a superposition of simulated radiation and reflection responses of the array under design with only one radiator active at a time. Low computational cost of the surrogate model is ensured by the EM‐simulation data computed with coarse meshes. Reliability of the model is achieved by means of suitable correction carried out with respect to the high‐fidelity array model. The correction is performed iteratively in the optimization process. Performance, numerical efficiency, and accuracy of the technique is demonstrated with radiation pattern synthesis of linear arrays comprising 32 microstrip patch antennas by phase‐spacing optimization. Properties of the optimal designs in the beam scanning operation are then studied using the superposition models and compared to suitably selected reference designs. The proposed technique is versatile as it also can be applied for simulation‐based optimization of antenna arrays comprising other types of individually fed elements. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:536–547, 2015.     

Wide‐band analysis of wire antenna using MoM combined with best uniform rational approximation and surface–surface configuration

In this article, an efficient method based on the method of moments (MoM) combined with the best uniform rational approximation and surface–surface configuration is presented for the wide‐band analysis of wire antenna. Compared with the asymptotic waveform evaluation technique, the major advantage of the Maehly approximation is that it can be easily implemented into an existing MoM computer code. Compared with the wire‐surface configuration, the surface–surface configuration is easy to ensure the current continuity at the junction and maintain the required good accuracy. Numerical results including the input admittance and return loss show that the CPU time took by Maehly approximation is about 1/10 of the CPU time used by the traditional MoM. Good agreement between the presented method and the exact solution is observed. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010.     

Coupled nonlinear/electromagnetic CAD of injection‐locked self‐oscillating microstrip antennas

This article presents a systematic approach to the simulation and design of self‐oscillating integrated antennas, based on the combination of state‐of‐the‐art nonlinear and electromagnetic (EM) CAD techniques. The linear subnetwork, including the oscillator circuit and the antenna, is treated as a whole and its admittance matrix is computed at all frequencies of interest (including harmonics) by EM analysis. The oscillating subsystem is then analysed by harmonic balance (HB) for autonomous circuits. The design problem is turned into the solution of a nonlinear system, with a significant reduction in the overall number of EM analyses with respect to a conventional optimization. A simple linear model of the radiated far field in terms of the exciting voltages is generated by inexpensive post‐processing of the data generated by EM analysis. This allows the far‐field properties to be directly specified during the design step. The conditions for stable injection locking are then determined by nonlinear methods based on the numerical implementation of bifurcation theory. Finally, when the antenna is injection‐locked by a digitally modulated RF/microwave carrier, the system response in terms of radiated far‐field is efficiently computed by envelope‐oriented HB analysis. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 13, 398–414, 2003.     

Design of hexa‐band planar inverted‐F antenna using hybrid BSO‐NM algorithm for mobile phone communications

This article presents a new design of multiband planar inverted‐F antenna with slotted ground plane and S‐etched slot on the radiation patch. The proposed antenna is optimized using an efficient global hybrid optimization method combining bacterial swarm optimization and Nelder‐Mead (BSO‐NM) algorithm to cover a very important six service bands including GSM900, GPS1575, DCS1800, PCS1900, ISM2450, and 4G5000 MHz with enhanced bandwidths. The BSO‐NM algorithm in Matlab code is linked to the CST Microwave studio software to simulate the antenna. To validate the results, the antenna is analyzed using the finite difference time domain (FDTD) method. A good agreement is achieved between the results of EM simulation and that produced from the FDTD method. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

EM‐simulation‐driven design optimization of compact microwave structures using multi‐fidelity simulation models and adjoint sensitivities

Reliable design of miniaturized microwave structures requires utilization of full‐wave electromagnetic (EM) simulation models because other types of representations such as analytical or equivalent circuit models are of insufficient accuracy. This is primarily due to considerable cross‐coupling effects in tightly arranged layouts of compact circuits. Unfortunately, high computational cost of accurate EM analysis makes the dimension adjustment process challenging, particularly for traditional methods based on parameter sweeps, but also for conventional numerical optimization techniques. In this article, low‐cost simulation‐driven designs of compact structures were demonstrated using gradient search with adjoint sensitivities as well as multi‐fidelity EM simulation models. The optimization process was arranged sequentially, with the largest steps taken at the level of coarse‐discretization models. Subsequent fine tuning was realized with the models of higher fidelity. Switching between the models was realized by means of adaptively controlled termination conditions. This allowed for considerable reduction of the design cost compared with single‐level optimization. The approach was illustrated using a compact microstrip rat‐race coupler with two cases considered, that is, (i) bandwidth enhancement, and (ii) minimization of the structure size. In both cases, the optimization cost corresponded to a few high‐fidelity EM simulations of the coupler structure. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:442–448, 2016.     

Wideband model of on‐chip CMOS interconnects using space‐mapping technique

A new wideband model for on‐chip complementary metal–oxide–semiconductor (CMOS) interconnects is developed by virtue of a space‐mapping neural network (SMNN) technique. In this approach, two subneural networks are used for improving the reliability and generalization ability of the model. This approach also presents a new methodology for data generation and training of the two neural networks. Two different structures are used for the two subneural networks to address different physical effects. Instead of the S parameters, the admittances of sub‐block neural networks are used as optimization targets for training so that different physical effects can be addressed individually. This model is capable of featuring frequency‐variant characteristics of radio‐frequency interconnects in terms of frequency‐independent circuit components with two subneural networks. In comparison with results from rigorous electromagnetic (EM) simulations, this SMNN model can achieve good accuracy with an average error less than 2% up to 40 GHz. Moreover, it has much enhanced learning and generalization capabilities and as fast as equivalent circuit while preserves the accuracy of detailed EM simulations. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

Hybrid Ku‐band low‐noise amplifier for mobile DBS active phased‐array antennas

In this article we present a two‐stage Ku‐band low‐noise amplifier (LNA) using discrete pHEMT transistors on non‐PTFE substrates for low‐cost direct broadcast satellite (DBS) phased‐array systems (patent pending). The vertical input configuration of the LNA lends itself to direct integration with input port of antenna modules of the phased array, which minimizes preamplification losses. DC decoupling between LNA stages is realized using interdigital microstrip capacitors such that the implementation reduces the number of discrete microwave components and thereby not only reduces the component and assembly costs but also decreases the standard deviation of such crucial parameters of phased‐array systems as the end‐to‐end phase shift of the amplifier and the amplifier gain. Using the proposed printed decoupling capacitors, a cost reduction better than 30% of the original costs has been achieved. Additionally, we present a hybrid design procedure for the complete LNA, including its input and output connectors as well as packaging effects. This method is not based on parameter extraction, but encompasses electromagnetic (EM) field simulator results which are further combined using a high‐level circuit simulator. According to the presented measurement results, the implemented Ku‐band LNA has a noise figure better than 0.9 dB and a gain higher than 20 dB with a gain flatness of 0.3 dB over a 5% bandwidth. © 2006 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2006.     

EM‐based yield optimization exploiting trust‐region optimization and space mapping technology

Design centering is a design problem which looks for nominal values of circuit parameters that maximize the probability of satisfying the design specification (yield function). Direct yield optimization of electromagnetic (EM)‐based circuits is obstructed by the high expense of EM simulations required in the yield estimation process. Also, the absence of any gradient information represents an obstacle against the optimization process. In this article, a new approach for design centering and yield optimization of EM‐based circuits is introduced. In the proposed approach, the generalized space mapping (SM) technique is incorporated with a derivative‐free trust region optimization method (NEWUOA). Moreover, a variance reduction sampling technique is implemented in the yield estimation process. Two techniques suitable for the microwave circuit design centering process are introduced. The first technique exploits the surrogate developed using any circuit optimizer, for example, minimax optimizer, in the yield maximization process. While the second technique iteratively constructs and updates an SM surrogate during the yield optimization process. Our novel approach is illustrated by practical examples showing its efficiency. One of the examples is entirely designed within the sonnet em environment. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:474–484, 2015.     

Fast simulation‐driven antenna design using response‐feature surrogates

In this article, a computationally efficient procedure for electromagnetic (EM)‐simulation‐driven design of antennas is presented. Our methodology is based on local approximation models of the antenna response, established using a set of suitably selected characteristic features rather than the entire response (such as reflection versus frequency). The approximation model is utilized to verify the level of satisfying/violating given performance requirements, and to guide the optimization process towards a better design. By exploiting the fact that the dependence of the response features on the designable parameters of the antenna of interest is simple (close to linear or quadratic), the feature‐based optimization converges faster than conventional optimization of frequency‐based EM‐simulated responses. In order to further speed up the design, coarse‐discretization simulations are utilized to estimate the feature gradients with respect to adjustable parameters of the problem at hand. The optimization algorithm is embedded in the trust‐region framework for safeguarding convergence. The proposed technique is demonstrated using two antenna examples. In both the cases, the optimum design is obtained at the computational cost corresponding to a few high‐fidelity EM antenna simulations. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:394–402, 2015.     

Numerical deembedding technique for planar discontinuities with periodically nonuniform feed lines

A numerical short‐open calibration technique is applied to deembedding of planar discontinuities with periodically perturbed nonuniform feed lines in the full‐wave method of moments (MoM) algorithm. Different from the other deembedding techniques that are based on the assumption of uniform feed lines, this proposed technique exhibits an unparalleled capability on modeling of planar circuits with nonuniform feed lines. To demonstrate this feature, the open and gap discontinuities are modeled under periodically nonuniform feed configuration, and the effective per‐unit‐length transmission parameters of slow‐wave and electromagnetic bandgap structures are extracted from the full‐wave MoM simulation. Two periodically nonuniform microstrip‐line resonator circuits are modeled and then confirmed by EM simulators and measurement. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2008.     

A closed‐form analysis of printed wide‐slot antennas

A mixed‐potential integral equation is formulated for the wide‐slot antenna, fed by a microstrip line, and solved using the method of moments (MoM). Our MoM implementation makes use of the Ge and Esselle (G–E) closed‐form Green's functions for layered substrates. The key advantage of this new approach is that all the MoM matrix elements are evaluated using closed‐form expressions, without any numerical integration, and with minimal approximations. Hence a significant increase in computational efficiency has been achieved while maintaining the high precision of the full‐wave MoM. The numerical results obtained from the new method are compared with measured results, and good agreements are observed. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 13, 389–397, 2003.     

Improved trust‐region gradient‐search algorithm for accelerated optimization of wideband antenna input characteristics

Full‐wave electromagnetic (EM) simulation models are ubiquitous in carrying out design closure of antenna structures. Yet, EM‐based design is expensive due to a large number of analyses necessary to yield an optimized design. Computational savings can be achieved using, for example, adjoint sensitivities, surrogate‐assisted procedures, design space dimensionality reduction, or similar sophisticated means. In this article, a simple modification of a rudimentary trust‐region‐embedded gradient search with numerical derivatives is proposed for reduced‐cost optimization of input characteristics of wideband antennas. The approach exploits information and history of relative changes of the design (as compared with the trust region size) during algorithm iterations to control the updates of components of the antenna response Jacobian, specifically, to execute them only if necessary. It is demonstrated that the proposed framework may lead to over 50% savings over the reference algorithm with only minor degradation of the design quality, specifically, up to 0.3 dB (or <3%). Numerical results are supported by experimental validation of the optimized antenna designs. The presented algorithm can be utilized as a stand‐alone optimization routine or as a building block of surrogate‐assisted procedures.     

A design method for flicker‐free liquid crystal display panels based on indium‐gallium‐zinc‐oxide thin‐film transistors

This paper proposes a design method to reduce the flicker of liquid crystal display panels based on indium‐gallium‐zinc‐oxide (IGZO) thin‐film transistors (TFTs). The proposed design method employs a human factor model to convert the flicker measured at low frame frequency (F _FRAME) to a modification value of the measured flicker (MVMF ) having a frequency sensitivity of flicker, which can distinguish between no blinking and weak blinking. To investigate the causes and characteristics of flicker, the frequency component and increase factor of flicker are analyzed using the checkerboard and solid images. The increase factor in flicker is examined using IGZO TFTs with different antenna ratios (AR s) that cause the variation in threshold voltage of IGZO TFT. To verify the proposed design method, two test panels are implemented with asymmetric and symmetric AR s. The MVMF s of the 15 Hz component at a low F _FRAME of 30 Hz show that the solid image with a symmetric AR has an MVMF of ?62.9 dB, which is improved by 24.3 dB compared to that with an asymmetric AR . Therefore, the proposed method is applicable for a flicker‐free liquid crystal display panels at a low F _FRAME.     

Surrogate‐assisted EM‐driven miniaturization of wideband microwave couplers by means of co‐simulation low‐fidelity models

This article proposes a methodology for rapid design optimization of miniaturized wideband couplers. More specifically, a class of circuits is considered, in which conventional transmission lines are replaced by their abbreviated counterparts referred to as slow‐wave compact cells. Our focus is on explicit reduction of the structure size as well as on reducing the CPU cost of the design process. For the sake of computational feasibility, a surrogate‐based optimization paradigm involving a co‐simulation low‐fidelity model is used. The latter is a fundamental component of the proposed technique. The low‐fidelity model represents cascaded slow‐wave cells replacing the low‐impedance lines of the original coupler circuit. It is implemented in a circuit simulator (here, ADS) and consists of duplicated compact cell EM simulation data as well as circuit theory‐based feeding line models. Our primary optimization routine is a trust‐region‐embedded gradient search algorithm. To further reduce the design cost, the system response Jacobian is estimated at the level of the low‐fidelity model, which is sufficient due to good correlation between the low‐ and high‐fidelity models. The coupler is explicitly optimized for size reduction, whereas electrical performance parameters are controlled using a penalty function approach. The presented methodology is demonstrated through the design of a 1‐GHz wideband microstrip branch‐line coupler. Numerical results are supported by experimental validation of the fabricated coupler prototype.