Pawel Barmuta

Compact Behavioral Models of Nonlinear Active Devices Using Response Surface Methodology

This paper presents the response surface methodology in modeling of nonlinear microwave devices. First, different combinations of sampling techniques and types of radial basis functions are evaluated in simulations of the drain current of a 0.15- μm GaAs HEMT transistor described by the Chalmers model. It allows to determine the best settings of the response surface methodology for the modeling of active microwave devices. It is shown that the best sampling strategy is a combination of space-exploration (Voronoi), problem-exploitation (LOLA), and model-error-driven sample rankers. From the various radial basis function models, the fastest convergence is achieved with exponential functions. This knowledge is then used in behavioral modeling of a low-power amplifier AG303 measured in the load-pull setup. It is shown that the response surface methodology outperforms commonly used factorial design of experiments. Moreover, it gives accurate models within just a few tens of samples. However, attention has to be paid at the noisy regions, which might be oversampled by the sampling techniques.

Microwave heater at 20 GHz for nanoliter scale digital microfluidics

This paper proposes an optimized microwave heater at 20 GHz for nanoliter scale liquid samples in digital microfluidics. The developed measurement setup allows translating of the reflection coefficient of the heater to the temperature change of the water droplet via the temperature dependency of the liquid permittivity, thus avoiding a contact-based temperature measurement. Measurements have been carried out on pure water samples of 500 nL at power levels of 20 and 23 dBm at the probe tips. The measured data agrees very well with multiphysics simulation data. Heating performance has been characterized and high temperature gradients of 30 deg. C per second have been measured.

Hybrid Nonlinear Modeling Using Adaptive Sampling

This paper proposes a direct method for the extraction of empirical-behavioral hybrid models using adaptive sampling. The empirical base is responsible for the functionality over a wide range of variables, especially in the extrapolation range. The behavioral part corrects the errors of the empirical part in the region of particular interest, thus, it improves the accuracy in the desired region. Employment of response surface methodology and adaptive sampling allows full automation of the hybrid model extraction and assures its compactness. We used this approach to build a hybrid model composed of a robust empirical model available in CAD tools and a Radial Basis Functions interpolation model with Gaussian basis function. We extracted the hybrid model from measurements of a 0.15 μm GaAs HEMT and compared it with the pure behavioral and pure empirical models. The hybrid model yields higher accuracy while maintaining extrapolation capabilities. Additionally, the extraction time of the hybrid model is relatively low. We also show that a good accuracy level can be achieved with a small number of measurements.

Microwave characterization of ink-jet printed CPW on PET substrates

This paper describes microwave characterization of coplanar waveguide (CPW) lines formed by ink-jet printed technology on flexible polyethylene terephthalate (PET) substrates. The reel-to-reel printing process uses inkjet printing as a precursor for 2μm copper plating, which allows significantly lowered resistances as compared to traditional inks. A multiline TRL calibration technique has been used to characterize the propagation constant and reflection coefficient of the CPW lines. With the aid of four sets of measurements at two identical labs, it is shown that the fabricated samples have contact repeatability, permitting redundant multiline calibrations.

Nonlinear behavioral models of HEMTs using response surface methodology

In this paper, the response surface methodology is proposed to model nonlinear microwave devices using different sampling techniques. Each of the methods represents a distinct approach: exploration-oriented (Voronoi tessellation), nonlinearity-exploitation-oriented (LOcal Linear Approximation) and model-error-minimization-oriented. This allows to build accurate and compact global behavioral models of drain voltage at different harmonics of a 0.15 μm GaAs HEMT transistor with only few hundreds of samples. After choosing the best sampling technique, two types of global models are compared: Radial Basis Function and Kriging. It is shown that the modeling convergence depends on the model type, and better results are obtained using the Kriging model.

Design of Experiments Using Centroidal Voronoi Tessellation

In this paper, the centroidal Voronoi tessellation (CVT) is proposed as a design of experiments (DoE) for the nonlinear modeling of active devices. Different method’s flavors are being described, allowing to maximize the total amount of information gathered during measurements. As a case study, the CVT designs have been tested for both simulation-based experiments of nonlinear test functions, as well as for the extraction of nonlinear transfer functions of a handset radio-frequency power amplifier. The use of CVT allowed to achieve lower interpolation error, and contrary to the most popular design in microwaves, i.e., factorial DoE, the proposed tessellation can handle any arbitrary number of samples.

Efficient behavioral model extraction of nonlinear active devices using adaptive sampling with compact nonlinearity measure

Description of nonlinear active devices is very complex, and depends on many input variables. Therefore, extraction of behavioral models based on traditional Designs of Experiments, such as factorial or Latin hypercube, may be unacceptably expensive in terms of sample evaluation time. In order to limit the total number of samples required to obtain accurate behavioral models, an adaptive sampling strategy may be used. It is based on surrogate models that are extracted for each sampling iteration. As nonlinear description consists also of many output variables, a common synthetic quantity is proposed to limit the surrogate modeling cost. It is defined as a total change of all the output quantities. The approach was evaluated in measurements of a 0.15 μm pHEMT model. The modeling accuracy is improved, while significant modeling-cost reduction can be observed.

Design and analysis of a verification device for the nonlinear vector network analyzer

We propose a verification device to validate the calibration of a nonlinear vector measurement instruments such as Nonlinear Vector Network Analyzer (NVNA). The verification device is a two-port device that has two operating modes, namely linear and nonlinear. The designed circuits response is almost insensitive to small harmonic mismatches of the instrument ports (|Γ| <; 0.1). Since neither an amplifier nor a circulator is used, the traceability procedure of the device to Electro-Optical Sampling (EOS) is less complicated compared to earlier prototypes.

0.05–3 GHz VNA characterization of soil dielectric properties based on the multiline TRL calibration

We present a methodology for characterization of soil relative dielectric permittivity in the frequency range 0.05–3 GHz. Soil samples are placed in a measurement cell constructed out of a EIA coaxial transmission line, and then measured with a calibrated vector-network-analyzer. From these measurements the relative dielectric permittivity is obtained by use of a modified Boughriet algorithm. In order to calibrate the vector-network-analyzer directly at the EIA coaxial-transmission-line measurement planes, we use the multiline through-reflect-line method. This method, while providing superior vector-network-analyzer calibration accuracy, is also easy to implement since it uses only transmission lines with known lengths and a single unknown highly-reflective termination. The implemented calibration method was compared to a simplified approach that uses the standard SOLT calibration in Type-N reference planes, and then accounts for the Type-N/EIA adapters by removing their electrical delay. Experimental results for teflon and soil samples with different moisture content and salinity confirmed the validity of our approach.

Monostatic continuous-wave radar integrating a tunable wideband leakage canceler for indoor tagless localization

Continuous-wave (CW) radars have been recently investigated in healthcare aiming at contactless health monitoring. However, a major problem in monostatic CW architectures is represented by the unwanted leakage produced by poor isolation between transmitter and receiver, which can drastically decrease the receivers sensitivity reducing therefore the radar dynamic range. Although this situation can be easily controlled in case of narrowband CW radar by an appropriate passive microwave design, it becomes much more complicated in case of stepped-frequency CW and frequency-modulated CW architectures that present an ultra-wideband nature. In this paper, a monostatic CW radar integrating a tunable wideband leakage canceler aiming at indoor tagless localization is presented and discussed. The use of the feedforward canceler allows a strong reduction of the unwanted leakage over the whole radar bandwidth. Experimental results demonstrate the feasibility of this approach, showing an outstanding improvement of the radar dynamic range.