Adjoint network method applied to the performance sensitivities of microwave amplifiers

This work focuses on the performance sensitivities of microwave amplifiers using the “adjoint network and adjoint variable” method, via “wave” approaches, which includes sensitivities of the transducer power gain, noise figure, and magnitudes and phases of the input and output reflection coefficients. The method can be extended to sensitivities of the other performance measure functions. The adjoint‐variable methods for design‐sensitivity analysis offer computational speed and accuracy. They can be used for efficiency‐based gradient optimization, in tolerance and yield analyses. In this work, an arbitrarily configured microwave amplifier is considered: firstly, each element in the network is modeled by the scattering matrix formulation, then the topology of the network is taken into account using the connection scattering‐matrix formulation. The wave approach is utilized in the evaluation of all the performance‐measurement functions, then sensitivity invariants are formulated using Tellegen's theorem. Performance sensitivities of the T‐ and Π‐types of distributed‐parameter amplifiers are considered as a worked example. The numerical results of T‐ and Π‐type amplifiers for the design targets of noise figure F_req = 0.46 dB ? 1,12 and V_ireq = 1, G_Treq = 12 dB ? 15.86 in the frequency range 2–11 GHz are given in comparison to each other. Furthermore, analytical methods of the “gain factorisation” and “chain sensitivity parameter” are applied to the gain and noise sensitivities as well. In addition, “numerical perturbation” is applied to calculation of all the sensitivities. © 2006 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2006.     

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.     

Extracting Coupling Matrix From Lossy Filters With Uneven‐Qs Using Differential Evolution Optimization Technique

This article presents an approach based on differential evolution (DE) for extracting coupling matrix (CM) and the uneven unloaded Qs from measured S‐parameters of a narrow band coaxial‐resonator filter with losses. Different from analytical extraction methods and traditional optimization methods, nonideal effects and uneven‐Qs are chosen as unknown parameters to be optimized. In the optimization process, the polynomials of the S‐parameters of a filter can be obtained by the Cauchy method after the unknown parameters are given. Once the rational polynomials having been obtained; the CM with an assigned topology can be extracted. The DE approach will obtain optimal parameters when the difference between the measured S‐parameters and the extracted S‐parameters is minimized, and then the CM and the unloaded Qs of each resonator can be determined using well established techniques. The approach is useful and can be used in computer‐aided turning of microwave filters. Two examples are presented to illustrate the validity of the proposed method.     

An FDTD‐based waveguide filter simulator: Calibration against analytical models

A three‐dimensional (3D) finite‐difference time‐domain (FDTD) simulator is developed for the investigation of network (S‐) parameters of rectangular cross‐section waveguide filters. The simulator is calibrated against analytical LC equivalent models. Any number of horizontal or vertical windows can be located to act as capacitive or inductive irises, respectively, and two‐port filter characteristics can be obtained automatically. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

Global sensitivity analysis of PROSAIL model parameters when simulating Moso bamboo forest canopy reflectance

PROSAIL is a combination of the leaf optical properties spectra (PROSPECT) model and the scattering by arbitrarily inclined leaves (SAIL) canopy bidirectional reflectance model. When modelling forest canopy reflectance using the PROSAIL radiative transfer model, the sensitivities of parameters can affect the modelling accuracy. Traditionally, sensitivities have been assessed using local sensitivity analysis (LSA); however, drawbacks to this approach include a lack of consideration for coupled effects between different parameters. In this study, parameter sensitivities in the PROSAIL model were calculated using two global sensitivity analysis (GSA) methods (the Extended Fourier Amplitude Sensitivity Test (EFAST) method and the Morris method), field measurements, and Landsat 5 Thematic Mapper (TM) data for a Moso bamboo forest. The results of GSA were compared with those of LSA in order to identify the key parameters impacting the Moso bamboo forest canopy reflectance, and to provide a reference for model optimization and vegetation canopy inversion improvement. The results showed that: (1) the sensitivities of six major input parameters of the PROSAIL model were generally consistent with the sorting orders of the two GSA methods, but were not in accordance with those from the LSA method, especially in the mid-infrared band; (2) coupled effects among parameters acting on reflectance simulation in visible light bands were greater than those in infrared bands; (3) the simulated canopy reflectance was evaluated using Landsat 5 TM data, and the results simulated based on LSA analysis showed higher error than those based on GSA analysis, because the LSA method ignored the influence of some parameters on canopy reflectance, e.g. leaf mesophyll structure (N), average leaf angle (ALA), leaf water content (C_w), and leaf dry matter content (C_m). However, GSA was able to fully consider the coupled effects among parameters, and thus identified the sensitive parameters impacting on reflectance more accurately.     

The dielectric properties prediction of the vegetation depending on the moisture content using the deep neural network model

In this paper, dielectric properties of citrus leaves are predicted with long short‐term memory (LSTM) which is one of the well‐known deep neural network (DNN) models and real‐time measurements for any moisture content (MC) values in the range of 4.90 to 7.05 GHz at a fixed temperature of 24°C for microwave applications, as a novelty. Firstly, S‐parameters of samples are measured with WR‐159 waveguide and Waveguide Transmission Line Method. In addition, the MCs of samples depending on their weights are calculated. Thus, the dataset depending on various MC and frequency is obtained with the measurement results to both training and testing the DNN model. Secondly, a total of 4000 datasets are obtained, 80% of which is used for training, and 20% for testing. The proposed DNN model consists of four inputs (f, MC, S₁₁, and S₂₁) and two outputs (ε′ and ε″). Finally, the dielectric parameters for the desired MC and f are displayed with the graphical user interface in real‐time. Success criteria for the prediction such as mean absolute error, root mean squared error, mean absolute percentage error, and R‐squared are calculated. The results indicated that there is good agreement between the measured and predicted ones. R‐squared are calculated as 0.962 and 0.968 for ε′ and ε″, respectively.     

Design of pseudoelliptic filters with controllable transmission zeros using high‐Q double‐layer suspended stripline resonators

This article presents a novel synthesis‐based design procedure for pseudoelliptic filters using high‐Q double‐layer suspended stripline (DSSL) resonators. The DSSL resonator consists of an air‐filled cavity and a suspended thin substrate with metallic top and bottom strips connected using metallic via hole. The resonator achieves a much higher unloaded quality factor than the single‐layer SSL resonator. Resonant characteristics and coupling properties of the innovative DSSL resonator are analyzed in detail. In addition, a systematic design procedure of the pseudoelliptic DSSL filter is presented using two examples of sixth‐order DSSL filters with two TZs at upper or lower stopband. The procedure is completed by establishing a relationship between the coupling coefficients and the physical structure dimensions based on an efficient full‐wave simulation. The established relationship allows accurately obtaining the physical dimensions of the filter from the electrical parameters calculated by the synthesis method. Furthermore, for demonstration of the proposed design procedure, two filter prototypes are synthesized, designed, fabricated, and measured. The synthesized, simulated, and measured results show an excellent agreement.     

Use of partially overlapped suspended substrate striplines for the realization of wideband microwave filters

This article presents realization of low loss, wide stop‐band suspended substrate stripline (SSS) wideband pass filters using interdigital and stepped‐impedance resonators. SSSs have been characterized using the finite‐difference method (FDM). The experimental results of the fabricated filters are compared with the theoretical results. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2006.     

CAD modeling of coplanar waveguide interdigital capacitor

A lumped‐element circuit is proposed to model a coplanar waveguide (CPW) interdigital capacitor (IDC). Closed‐form expressions suitable for CAD purposes are given for each element in the circuit. The obtained results for the series capacitance are in good agreement with those available in the literature. In addition, the scattering parameters obtained from the circuit model are compared with those obtained using the full‐wave method of moments (MoM) and good agreement is obtained. Moreover, a multilayer feed‐forward artificial neural network (ANN) is developed to model the capacitance of the CPW IDC. It is shown that the developed ANN has successfully learned the required task of evaluating the capacitance of the IDC. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2005.     

Anisotropic analysis of polarimetric scattering and case studies with UAVSAR images

This article analyses the anisotropy of polarimetric scattering changing with azimuth incidence angle using a multi-look processed synthetic aperture radar (SAR) image. First, three canonical scattering models were developed to simulate the migration tracks on the Cameron polarimetric space. The migration tracks indicate that these polarimetric parameters have anisotropic property. Second, unmanned aerial vehicle synthetic aperture radar (UAVSAR) data are used to validate the simulated results. The Cameron scattering-type parameter z and the orientation angle calculated by SAR data are consistent with the simulated results by small perturbation method (SPM) double-scattering. Finally, based on the anisotropic analysis, a new method of extracting polarimetric information is proposed. Using this method, six parameters were obtained and two additional parameters, Purity and Stability, were derived. These parameters contain specific physical meaning and are useful in the recognition of the scattering mechanism. Purity can be used to recognize the simple structure scatterers with zero orientation. Stability has the potential to describe the dynamic property of scatterers.     

Design of waveguide microwave filters by means of artificial neural networks

Cylindrical post‐based waveguide filters are a relevant component of antenna feeding networks. Their synthesis performed via automatic optimization based on full‐wave analyses can be very time consuming. In this article a novel fast‐design approach based on Levy's and Moore's algorithms and an artificial neural network (ANN) architecture is presented. © 2006 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2006.     

Synthesis of interdigital capacitors based on particle swarm optimization and artificial neural networks

This article reports on the use of the particle swarm optimization (PSO) algorithm in the synthesis of the planar interdigital capacitor (IDC). The PSO algorithm is used to optimize the geometry parameters of the IDC in order to obtain a certain capacitance value. The capacitance value of the IDC is evaluated using an artificial neural network (ANN) model with the geometry parameters of the IDC as its inputs. Several design examples are presented that illustrate the use of the PSO algorithm, and the design goal in each example is easily achieved. Full‐wave electromagnetic simulations are also performed for some of the studied IDC structures implemented using coplanar waveguide (CPW) technology. The simulation results are in good agreement with those obtained using the ANN/PSO algorithm. © 2006 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2006.     

Evaluation of different orientation angle distributions within the X-Bragg scattering model for bare soil moisture estimation

In this paper, the applicability of three different orientation angle distributions of surface facets within the extended Bragg (X-Bragg) scattering model is investigated for estimation of soil moisture over bare surfaces using both Eigen-based and model-based polarimetric synthetic aperture radar (PolSAR) decomposition techniques. The three distributions considered for investigation in the X-Bragg model are uniform, half cosine, and the Lee distributions. In order to understand the sensitivity of the model using the three orientation angle distributions, key polarimetric parameters, such as scattering entropy (H), scattering anisotropy (A), scattering mechanism (α), cross-pol power (T₃₃), linear T₁₂ coherence (|γ_{(HH+VV)(HH–VV)}|), are simulated and analysed for various widths of distributions. The analysis of the simulated polarimetric parameters show that the Lee distribution has a reduced roughness validity range compared with the uniform and half cosine distributions. DLR E-SAR L-band data from the AgriSAR’2006 campaign over the Demmin test site in Northern Germany are inverted for soil moisture over bare surfaces. The inverted soil moisture from the physics-based X-Bragg model is compared with in situ measured TDR (time domain reflectometry) soil moisture values. The inversion results using the Eigen-based decomposition reveal similar root mean square error (RMSE = 14 vol.%) and inversion rates for three distributions. The model-based decomposition inversion results obtained at various fixed widths of distributions reveal that the Lee distribution shows less RMSE of 8 vol.% and high inversion rates for moderate surface roughness (ks = 0.5) as compared with half cosine and uniform distributions.     

Neural network based dynamic modeling of flexible‐link manipulators with application to the SSRMS

This paper presents an approach for dynamic modeling of flexible‐link manipulators using artificial neural networks. A state‐space representation is considered for a neural identifier. A recurrent network configuration is obtained by a combination of feedforward network architectures with dynamical elements in the form of stable filters. To guarantee the boundedness of the states, a joint PD control is introduced in the system. The method can be considered both as an online identifier that can be used as a basis for designing neural network controllers as well as an offline learning scheme to compute deflections due to link flexibility for evaluating forward dynamics. Unlike many other methods, the proposed approach does not assume knowledge of the nonlinearities of the system nor that the nonlinear system is linear in parameters. The performance of the proposed neural identifier is evaluated by identifying the dynamics of different flexible‐link manipulators. To demonstrate the effectiveness of the algorithm, simulation results for a single‐link manipulator, a two‐link planar manipulator, and the Space Station Remote Manipulator System (SSRMS) are presented. ©2000 John Wiley & Sons, Inc.     

A Continuous-Time Model of Autoassociative Neural Memories Utilizing the Noise-Subspace Dynamics

This paper presents a continuous-time model of Autoassociative Neural Memories (ANMs) which correspond to a modified version of pseudoinverse-type ANMs. This ANM model is derived from minimizing the energy function for a modular neural network. Through the eigendecomposition of the connection matrix, we show that the dynamical properties of the ANM are qualitatively different in the two state subspaces: a pattern-subspace and a noise-subspace. The proposed ANM has a distinctive feature in the noise-subspace dynamics. The size of basins of attraction can be varied by controlling the contribution of the noise-subspace dynamics to the whole network. The first simulation confirms this attractive feature. In the second simulation, we investigate the performance robustness of the ANM for several kinds of correlated pattern sets. These simulation results confirm the usefulness of the proposed ANM.     

Rotationally symmetric FDTD for wideband performance prediction of TM01 DR filters

The generalized perfectly matched layer (GPML) coupled with rotationally symmetric (RS)‐FDTD method has been utilized to extract the S‐parameters for several probe‐coupled TM₀₁ dielectric resonator (DR) filters to directly obtain the theoretical wideband spurious performance. The computationally efficient (RS)‐FDTD method has also been used to obtain accurate filter parameters for TE₀₁ and TM₀₁ dielectric resonators loaded in cylindrical cavities. The RS‐FDTD method combined with digital filtering and the Matrix Pencil technique are used to analyze the resonant frequencies, inter‐resonator coupling, and external Q values. When perturbation theory is used with RS‐FDTD, accurate values of unloaded Q are obtained. © 2002 Wiley Periodicals, Inc. Int J RF and Microwave CAE 12: 259–271, 2002.     

Dispersive delay structure using cascaded‐coupled CRLH‐CRLH C‐sections

The demand for analog signal processing (ASP) is rising for high‐speed and high‐frequency systems. In some ASP systems, the core is dispersive delay structure (DDS). DDS creates a steady increase or decrease in group delay over frequency bandwidth. One of the popular methods for designing DDSs is the use of coupled C‐sections structure. Analysis of the coupled C‐sections was based on the analysis of N coupled‐lines network. In this paper, we employ a fast approach for analyzing N coupled‐lines network that does not need solving an eigenmodes problem. Moreover, we propose a novel DDS structure based on the coupled composite right/left‐handed (CRLH) transmission lines with interdigital capacitors and short stub inductors. The proposed DDS operates between 3 to 3.5 GHz with relatively high group delay slope (about 5.5 ns). The measurements are presented for scattering parameters and group delay to compare with simulated results.     

Design of wideband diplexer in suspended substrate stripline medium

A wideband diplexer is designed and developed in suspended substrate medium using wide‐bandpass filters of 10–14 GHz and 14–18 GHz. Tight coupling between resonators is achieved by etching the resonators on the top and bottom layers of the substrate. The diplexer is designed by combining these filters on a common transformer. Each filter is channelised to avoid waveguide modes. Suspended substrate striplines (SSSs) are characterized using the Finite‐Difference Method (FDM). The theoretical and measured results of the diplexer are presented. © 2006 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2006.     

Neural network modeling of microwave FETs based on third‐order distortion characterization

A new method for characterization of HEMT distortion parameters, which extracts the coefficents of a Taylor series expansion of I_ds(V_gs, V_ds), including all cross‐terms, is developed from low‐frequency harmonic measurements. The extracted parameters will be used either in a Volterra series model around a fixed bias point for 3^rd‐order characterization of small‐signal I_ds nonlinearity, or in a large‐signal model of I_ds characteristic, where its partial derivatives are locally characterized up to the 3^rd order in the whole bias region, using a novel neural‐network representation. The two models are verified by one‐tone and two‐tone intermodulation distortion (IMD) tests on a PHEMT device. © 2006 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2006.