On-Wafer Calibration Algorithm for Partially Leaky Multiport Vector Network Analyzers

A new solution for multiport vector network analyzer calibration is presented in this paper. The error model is divided in two separate leaky halves, each of them with crosstalk terms, but without the leakage between the two sides. This error model is particularly useful for on-wafer measurements, when multisignal probes are employed and the crosstalk among probe fingers may dramatically affect the measurement accuracy.We will show that, with a simple choice of calibration standards, the new procedure takes the same time of a classical two-port line-reflect-match or thru-reflect-line calibration. The proposed algorithm is verified with measurements and simulations in both coaxial and on-wafer environments

Microwave Measurements Part I: Linear Measurements

An Overview of the most relevant issues concerning RF and microwave linear measurements is presented. Vector Network Analyzer foremost used instrumentation for this kind of measures is describe

Conformal Mapping Design Tools for Coaxial Couplers with Complex Cross Section

Numerical conformal mapping is exploited as a simple, accurate, and efficient tool for the analysis and design of coaxial waveguides and couplers of complex cross section. An implementation based on the Schwarz-Christoffel Toolbox, a public-domain MATLAB package, is applied to slotted coaxial cables and to symmetrical coaxial couplers, with circular or polygonal inner conductors and external shields. The effect of metallic diaphragms of arbitrary thickness, partially separating the inner conductors, is also easily taken into account. The proposed technique is validated against the results of the finite-element method, showing excellent agreement at a fraction of the computational cost, and is also extended to the case of nonsymmetrical couplers, providing the designer with important additional degrees of freedom

Recent Advances in Real-Time Load-Pull Systems

In this paper, some of the latest advances in real-time load-pull technologies will be described. A recently introduced ultralow-loss directional coupler, which has been designed and realized by the authors, provides a number of advantages when used in load-pull test sets. This device has been called the load-pull head. The new ultralow-loss load-pull head can transform any passive precalibrated load-pull system into an easily calibrated and accurate real-time load-pull test set, without losing highreflection- coefficient capabilities. Moreover, if used to realize an active loop, the load-pull head reduces the risks of oscillations and the amount of the loop amplifier output power. As an example application, measurements with a passive real-time load-pull setup of a 30-W laterally diffused MOS (LDMOS) transistor are presented. Furthermore, some advice to bypass the remaining unavoidable losses due to probes and cables is given.We will show, with measurements and with very simple calculations, that the combined use of load-pull heads, a passive tuner, and an active loop not only boosts the available ΓL but also decreases the loop amplifier output power, with a sensible reduction in the overall cost of the syste

Millimeter-wave load-pull techniques

In this talk, the challenges in the realization of on-wafer large-signal measurement systems in W-band will be summarized and a recent implementation of a W-band on-wafer load-pull system will be presented. The availability of W-band large signal set-ups opens several possibilities, ranging from technology assessment and large-signal device modeling at sub-THz frequencies, to W-band MMIC design and characterization. Direct and accurate load-pull measurements at W-band are thus crucial in the development of sub-THz integrated circuits. The main issue at these frequencies is the realization of highly reflective loads at the on-wafer reference planes. In-situ tuners can solve this problem, but they need to be integrated with the device under test and this is not always possible. Passive mechanical tuners could be a solution, but the losses between tuner and probe tip need to be compensated in some way, otherwise the reachable reflection coefficients will present severe magnitude limitations. An active load clearly overcomes this limit and in addition, with an active load, measurement directional couplers can be placed in real-time configuration and achieve higher accuracy than purely passive systems. Active loads can be implemented in open- or closed-loop configuration. The realized system is the first load-pull system to implement a 94 GHz load by means of an active loop exploiting frequency conversion techniques. This has advantages in cost and load stability. The system is based on a HP8510 vector network analyzer. Its performances in terms of reachable load, load stability, speed and residual uncertainty will be shown and compared to a 40 GHz load-pull system based on a PNA-X. Finally, the first measurements performed on high performance InP double heterojunction bipolar transistors (DHBTs) and GaN high electron mobility transistors (HEMTs) will be presented

An approach to harmonic load- and source-pull measurements for high-efficiency PA design

High-efficiency power-amplifier design requires numerous efforts to investigate both input and output harmonic terminations effects. A simplified theoretical approach to clarify the relevance of such terminations is presented here, and design criteria to improve efficiency for high-frequency applications are briefly discussed. An advanced active load/source-pull test-bench has been used to validate theoretical harmonic tuning techniques, characterizing an active device. The adopted optimization strategy is presented, together with measured results obtained with a medium-power 1-mm MESFET at 1 GHz. Input second harmonic impedances effects are stressed, showing a drain efficiency spread between 37%-49% for a fixed input power level, corresponding to 1-dB compression. Finally, as predicted by the presented theory, after input second harmonic tuning, further improvements are obtained, increasing fundamental output load resistive part, demonstrating an additional drain efficiency enhancement, which reaches a level of 55% at 1-dB compression

Synthetic TDR Measurements for TEM and GTEM Cell Characterization

This paper describes the main features of the timedomain reflectometry (TDR) measurement technique and, in particular, the TDR analysis performed using a proper operating mode of the vector network analyzer (VNA), which is called synthetic TDR. Furthermore, some results of reflection measurement, which aim to characterize the impedance behavior of transverse electromagnetic (TEM) and gigahertz TEM cells by means of a commercial VNA in time-domain mode, are presented

Microwave Measurements. Part II - Nonlinear Measurements

This paper addresses the problems in microwave non-linear measurements. It discusses techniques to synthesize loads, the most used non-linear measurement techniques, and harmonic load-pulling. An experimental setup for characterizing power amplifiers must be able to measure the complex spectrum of the waves at the amplifier ports as a function of frequency, input power, and source and load termination at the fundamental and harmonic frequencies. The vector network analyzer (VNA) is the core instrument used in the non-linear characterization scenario. The basic idea is to keep the operations of VNA/mixers linear, diverting to them only a small portion of the signal present at the device under test (DUT) ports, therefore keeping unaltered the VNA capabilities already exhibited for small signal measurements

A new class of nonuniform, broadband, nonsymmetrical rectangular coaxial-to-microstrip directional couplers for high power applications

An innovative class of coaxial-to-microstrip broad-band high power directional couplers is studied. The new devices overcome the drawbacks of both stripline and coaxial couplers and allow simple and low cost mechanical construction. In this letter, we present the design, realization and characterization of a set of broad-band (900 MHz to 5.5 GHz) low coupling ( 30 dB, 40 dB) directional couplers with directivity of more than 10 dB over the whole band, demonstrating good agreement between predicted and obtained performances

Accuracy Improvement of Real-Time Load-Pull Measurements

This paper describes a new procedure aimed to improve the effectiveness of real-time load-pull calibration. Loadpull measurement accuracy is strongly affected by calibration residual uncertainty. The novel methodology reduces this uncertainty contribution by means of error terms optimization. The proposed method has been tested with simulations and applied to actual measurement data. Considerable improvements have been achieve