2154 IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT, VOL. 60, NO. 6, JUNE 2011 A Synthetic Vector Network Analyzing Measurement System Magnus Isaksson, Member, IEEE, and Efrain Zenteno, Member, IEEE Abstract—In this paper, a synthetic vector network analyzing measurement system is presented. The system is based on a hardware setup, including a signal generator and a vector signal analyzer, with the vector network analyzing functionality imple- mented in the software. The measurements of the proposed sys- tem demonstrated comparable performance in terms of accuracy and speed compared with a modern traditional vector network analyzer, but it is more flexible due to its inherent software im- plementation. The proposed system’s ability to measure nonlinear phenomena is addressed and discussed, and some preliminary results are given. Index Terms—Nonlinear, S-parameters, synthetic instrument (SI), vector network analyzer (VNA), virtual instrument (VI). I. I NTRODUCTION A DVANCES of software platforms that increase their capa- bilities and reduce cost have led instrument designers to develop new kinds of instruments, namely, the so-called virtual instruments or synthetic instruments (SIs), with applications in industrial and educational fields with promising results [1]. The reason behind the success of this type of instruments is that it presents good features regarding flexibility, modularity, hardware independence, generality, and cost [2]. Considering the requirements in many research laboratories and in industrial production test workstations, it has become necessary to create instruments with new capabilities that are able to change to the current test requirements [3]; that is what SIs can offer. Any SI can be logically divided into layers, where tasks and functions can be defined at each layer, enhancing the modularity, generality, and flexibility and allowing interchange- ability of hardware. The fact that SIs are basically software Manuscript received March 25, 2010; revised September 8, 2010; accepted November 6, 2010. Date of publication March 7, 2011; date of current version May 11, 2011. This work was supported in part by Ericsson AB, by Freescale Semiconductor Nordic AB, by Infineon Technologies Nordic AB, by Knowl- edge Foundation, by NOTE AB, by Rohde & Schwarz AB, and by Syntronic AB. The Associate Editor coordinating the review process for this paper was Dr. Sergey Kharkovsky. M. Isaksson is with the Center of Radio Frequency Measurement Technol- ogy, ATM/Electronics, Mathematics, and Natural Sciences, the University of Gävle, SE 80176 Gävle, Sweden (e-mail min@hig.se). E. Zenteno was with the Department of Telecommunications Engineer- ing, Universidad Católica San Pablo, PE 51-054 Arequipa, Peru. He is currently with the Center of Radio Frequency Measurement Technology, ATM/Electronics, Mathematics, and Natural Sciences, the University of Gävle, SE 80176 Gävle, Sweden, and also with the Signal Processing Lab, Royal In- stitute of Technology, SE-100 44 Stockholm, Sweden (e-mail efnzeo@hig.se). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TIM.2011.2113132 Fig. 1. Traditional VNA structure. makes software-defined measurements (SDM) [4] an adequate terminology in this case. For instruments in the radio frequency (RF) band, measuring the linear as well as nonlinear response, varying the excitation signal, and having flexibility and modularity in pre- and post- processing digital techniques in order to deliver measurements with accuracy and speed are some of the desirable features in the measurement system. Fig. 1 shows the structure of typical vector network analyzer (VNA) architecture. A major disadvantage of this structure is the inability to measure excitation signals other than continuous wave (CW) signals due to a narrow band receiver, which is also depicted in Fig. 1. This prevents the use of other excitation signals with a higher bandwidth, which has become a necessity of modern device characterization and testing [5]. This paper presents an SI, with the ability to perform vector measurements, which will be addressed as SDM VNA for the rest of this paper. One of the differences of the proposed approach is the presence of only one receiver and the usage of modulated signals in the source; this will relax the requirements of synchronization and distortion in the receiver compared to any VNA architecture, as the one presented in Fig. 1. That is due to the fact that phase relationship is kept now in the low- pass equivalent signal, which is measured through a receiver with improvements on IQ impairments, and not in the RF carrier, where traditional VNA measures. The linear distortion introduced in the receiver will cancel off in ratio computation as in S-parameter measurement. 0018-9456/$26.00 © 2011 IEEE