This is an author-created, un-copyedited version of the article C. D. Martino, Z. Hu, L. Galatro, G. Sarris and M. Spirito, "Power level control of mm- wave test benches for accurate small and large-signal DUT measurements," 2016 88th ARFTG Microwave Measurement Conference (ARFTG), Austin, TX, USA, 2016, pp. 1-4. IEEE is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The definitive publisher-authenticated version is available online at http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=7839723 Power Level Control of mm-Wave Test Benches for Accurate Small and Large-signal DUT Measurements C. De Martino, Z. Hu, L. Galatro, G. Sarris and M. Spirito Electronics Research Laboratory, Delft University of Technology Mekelweg 4, 2628CD Delft, Netherlands Abstract — In this contribution we describe the accuracy improvement achievable using a vector corrected, power calibrated test-bench when measuring mm-wave non-linear devices. The absence of automatic level control in commercially available network analyzer frequency extenders can result in AM distortion of the transfer characteristic. Moreover, when large- signal mm-wave test-benches are employed (i.e., using multipliers and power meters) the lack of vector correction causes transfer characteristic errors. The usage of power levelled mm-wave VNA test-benches allows to properly measure the true small-signal s-parameter response as well as accurately correct for the impedance mismatch present, providing increased correlation between small and large-signal test-benches response. The accuracy limitation of classical approaches and the improvement achieved by the levelled mm-wave VNA test-bench are validated on a 140GHz power amplifier. Index Terms — Power control, Power calibration, S- parameters measurements, mm-wave, sub-mm-wave. I. INTRODUCTION The increasing interests in millimeter-wave (mm-wave) systems for commercial applications, such as automotive and high data rate communication (falling under the umbrella of 5G), is pushing for higher quality mm-wave measurements and device models. Improving the model predictive capabilities is the path to minimize the redesign attempts, thus making the developing phase of a product commercially feasible. The mm-wave frequency range is characterized by the extensive use of frequency multiplication stages to generate signals. The testing and instrumentation field also makes use of frequency multiplication in the up- and down-converting extension modules of state-of-the-art VNAs. The frequency multiplier chains used in commercial VNA test-set extenders provide a strongly non-linear power relation between the input and output, nevertheless, as it was shown in [1] accurate power control at the mm-wave port is feasible up to the sub- mm-wave frequency range. Despite this, several contributions in the field still suffer from error arising from a non-accurate power level control during scattering parameter measurements, see Fig. 1 a), and errors arising from the simple scalar corrections of large-signal power-meter based setups, see Fig. 1 b). In this paper we analyze how these errors can be traced to the absence of amplitude power level control of mm-wave VNA extenders, and we describe how the use of full vector correction, using VNA based large-signal setups, allows to achieve an high correlation between the small-signal and large-signal test-benches response. a) b) Fig. 1: a), Small-signal model-hardware correlation of the PA from [2], b) measured (circles) and simulated (solid lines) S-parameters of the three-stage 150 GHz amplifier, measured with VNA and large- signal setup, from [3]. The paper is organized as follows, first an analysis of the AM distortion in the transfer characteristics of non-linear device excited by non-levelled drive signal is described, together with the limitation of commonly employed scalar mm-wave large-signal setups. Then, the proposed VNA based power controlled small-signal and large-signal test bench of [1] is briefly described. Finally, a 140GHz power amplifier characterization is used as a test vehicle to reproduce some of the shortcomings that can be encountered in mm-wave test- benches and highlight the high correlation between small- signal and large-signal setups when full vector correction is employed. II. MM-WAVES TEST-BENCHES SHORTCOMINGS A. Small-signal The small-signal characterization of power amplifiers, aims to look at input matching, reverse isolation and the small- signal gain. The latter is often evaluated simply looking at the S 21 at a sufficient back-off level, i.e., the linear region of Fig. 2. When the amplifier is composed by several stages, which is often the case at mm-wave frequencies due to the limited gain per stage, the compression mechanism of the gain curve can