Multiport Technology: New Perspectives and Applications

Hindawi Publishing Corporation Journal of Electrical and Computer Engineering Volume 2014, Article ID 194649, 4 pages http://dx.doi.org/10.1155/2014/194649 Editorial Multiport Technology: New Perspectives and Applications Serioja Ovidiu Tatu,1 Adriana Serban,2 Alexander Koelpin,3 and Mohamed Helaoui4 1 Institut National de la Recherche Scientifique-Energie, Matériaux et Télécommunications, 800 rue de la Gauchetière Ouest, Montréal, Québec, Canada 2 Department of Science and Technology, Linköping University, Bredgatan 34, SE-601, 74 Norrkoping, Sweden 3 Institute for Electronics Engineering, University of Erlangen-Nuremberg, Cauerstr. 9, 91058 Erlangen, Germany 4 Intelligent RF Radio Technology Laboratory (iRadio Lab), Department of Electrical and Computer Engineering, Schulich School of Engineering, University of Calgary, Calgary, AB, 91058 Erlangen, Canada T2N 1N4 Correspondence should be addressed to Serioja Ovidiu Tatu; Received 13 April 2014; Accepted 13 April 2014; Published 7 July 2014 Copyright © 2014 Serioja Ovidiu Tatu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 1. Introduction The multiport circuit theory was initially developed in the 1970s by scientists for accurate automatized measurements of the complex reflection coefficients, in microwave network analysis [1–3]. These multiport pioneers highlighted its usefulness in microwave low-cost circuit characterizations (Sparameters). Since 1994, the multiport techniques were further developed for microwave and millimeter-wave radios [4–6]. Until today, several multiport architectures for specific applications, such as communication transceivers [7–17], radar sensing [18–23], direction of arrival estimation [24–26], or phase noise measurements [27], have been developed and implemented. Basically, the multiport is a passive circuit composed of several couplers interconnected by transmission lines and phase shifters. Its specific architecture and design are strongly related to the target application and the operating frequency. The multiport acts as an interferometer; its output signals are linear combinations of phase shifted input signals. By using the appropriate circuit design and appropriate devices connected to the output ports, this circuit can provide specific parameters, such as reflection coefficient, distance or modal measurements, phase and frequency analysis, quadrature down-conversion, or direct modulation of microwave/millimeter-wave frequencies. As originally designed for automated measurements of the complex reflection coefficient, the multiport has a local oscillator input, a measurement port, and four outputs [3]. One of the outputs is used as a reference power level and powers measured at the other ones are function of the complex coefficient of the device under test connected to the measurement port. There are three different reflection coefficient values named 𝑞𝑖 points, which minimize the power at the corresponding 𝑖 output. The ideal architecture requests that 𝑞𝑖 points are to be spaced by 120∘ and located equidistant from the origin of the complex plane. The new application fields require a different architecture of the circuit and specific modules to be connected at its ports. The S-parameter matrix of the multiport circuit reveals that there are two clusters of ports, 1 to 4 and 5 and 6. Inside each cluster, all the ports are perfectly matched and isolated, one versus the others [15]. In all applications they play separate functions, such as four outputs and, respectively, two RF inputs for down-conversion or four control inputs and RF output/input for direct modulators. If the S matrix is further analyzed, then it is straightforward that if four matched loads are connected to the first group of ports (1 to 4) and two RF signals are applied to other pair of ports (5 and 6), all output signals at first group of ports are function of both input signals of the second group. This is a fundamental difference, if compared to the multiport used in reflection coefficient measurements, where one of the outputs is used as a power reference [3]. The multiport has now four 𝑞𝑖 points spaced by 90∘ multiples and located equidistant from the origin of the complex plane. The phase difference between the pair of odd 2 𝑞𝑖 points is 180∘ . The same result is obtained for the pair of even points [17]. The use of multiport technology in RF design is a good choice, especially if the operating frequency is in the high microwave or millimeter-wave range. The dimensions of the multiport circuit fabricated in miniature hybrid microwave integrated circuit (MHMIC) technology, usually around 1.5𝜆 𝑔 × 1.5𝜆 𝑔 , where 𝜆 𝑔 represents the guided wavelength, become small enough to be integrated on the same substrate with antennas [20]. Even if the multiport is further miniaturized, the antenna or array antenna size will determinate the final dimensions of a front end. The multiport circuit can be also used in the front-end design to operate at the frequencies where active components are not yet available in the market. In order to operate as demodulator or modulator, it requires only the use of power detectors or switches [28–32]. Therefore, research activities can be validated by front-end prototyping measurements, years before standard technologies become available. This special issue highlights, through several examples and multiple references, some of the modern applications of the multiport technology and significant advances in fabrication procedures, in the recent years. 2. Special Issue Papers This special issue dedicated to multiport technology hosts several papers covering last advances in six-port receivers, demodulators, radar sensing, and ultrawide band (UWB) phase noise measurements. An interesting question in multiport technology is how many ports should be used to fulfill a given system specification. In their paper entitled “Performance of 2–3.6 GHz five-port/three-phase demodulators with baseband analog 𝐼/𝑄 regeneration circuit in direct-conversion receivers,” K. Abdou et al. compare the performance of a five-port (FPD), a three-phase (TPD), and a quadrature demodulator. First, the authors describe the basic principles of FPD and TPD. Unlike the FPD, that uses detectors for the down-conversion, the TPD multiplies the radio frequency (RF) and the local oscillator signal with the help of mixers. A baseband circuit for the analog 𝐼/𝑄 regeneration is designed to reduce the number of analog-to-digital converters from three to two and allows suppression of DC offset and second order intermodulation distortion (IMD2). Finally, the implementation of all architectures is demonstrated; furthermore, detailed measurement results are presented. These results indicate that TPD outperforms FPD in terms of residual DC offset, IMD2 (...truncated)