Efficient Characterization of Millimeter-Wave Asymmetric Coupled Microstrip Structures Using the Quasi-Symmetric Approach A. Khodja, 1 M. C. E. Yagoub, 2 R. Touhami, 1 H. Baudrand 3 1 Instrumentation Laboratory, Faculty of Electronics and Informatics, U.S.T.H.B University, B.P 32, El Alia, Bab-Ezzouar,16111, Algiers, Algeria 2 EECS, University of Ottawa, 800 King Edward, Ottawa, ON K1N 6N5, Canada 3 ENSEEIHT, 2 rue Charles Camichel 31071, Toulouse Cedex 7, France Received 30 January 2012; accepted 2 August 2012 ABSTRACT: To sustain the ever-increasing use of coupled-line structures in RF/microwave systems, efficient design tools should be developed. In this article, an original approach com- bining accuracy and speediness is proposed to shorten time-to-market design cycles when such structures are involved. By introducing the quasi-symmetric approach, CPU-time required to analyze asymmetric coupled-lines can be significantly reduced, leading to faster models without sacrificing the overall design accuracy. To achieve this aim, a rigorous formu- lation was developed and, for the first time, trial functions of C- and p-modes were obtained from the quasi-symmetric case and applied to the asymmetric case. The proposed approach, easily implementable in commercial simulators, was demonstrated through comparisons with published data. V C 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE 23:527–538, 2013. Keywords: impedance operators; dispersion; quasi-symmetric model; trial functions I. INTRODUCTION Nowadays, ever-increasing complexity of modern commu- nication systems is becoming an ongoing challenge for professional designers. In fact, due to extensive use of sta- tistical analysis and yield optimization taking into account industrial process variations and manufacturing tolerances, the demand for more powerful computer-aided design (CAD) tools is driving the industry to long, massive and costly design processes to achieve feasible and reliable prototypes. Therefore, to minimize time-to-market and stay ahead of the competition, simple but efficient tools are often preferred in early design stages to help making cost-effective decisions on the future of such prototypes. This aspect is particularly crucial in modern RF/micro- wave integrated circuits where devices like coupled-line struc- tures are more and more exploited in fundamental functions like filtering, coupling, or detection, to name a few [1–5]. In fact, compared to symmetric structures, asymmetric ones are very attractive since they can improve circuit performance [6] while offering more design flexibility through inherent imped- ance transforming capability leading to easier matching to external element connections [7]. To successfully address the aforementioned challeng- ing issues without sacrificing to accuracy, an original quasi-symmetric modeling approach is proposed. Based on the electromagnetism operator formalism, this full- wave modal domain integral technique efficiently com- bines speediness and accuracy by maintaining a maximum error <2% within the most commonly used design param- eter ranges [8–11]. Note that characteristic impedances are not considered in this work. In fact, although they are very useful to designers, they are not uniquely defined in planar circuits and thus, different full-wave approaches could lead to different values [12]. Therefore, the focus in the present work was made on phase constants rather than characteristic impedances to demonstrate the efficiency of the proposed technique as well as its limits due to shield- ing and metal strip width differences. Easily implementable in commercial simulators and successfully applied to planar lines on iso/anisotropic truncated substrates [13, 14], this technique consists to This article was published online on 22 October 2012. An error was subsequently identified. This notice is included in the online and print versions to indicate that both have been corrected 29 October 2012. Correspondence to: A. Khodja, e-mail: hkhodja@yahoo.fr. V C 2012 Wiley Periodicals, Inc. DOI 10.1002/mmce.20686 Published online 22 October 2012 in Wiley Online Library (wileyonlinelibrary.com). 527