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ABSEACTThe IMST has recently built up a library with recently more than 18 coplanar elements for CAD applications (2), (3). The theory of the parametric models is based on a quasi static 3D Finite Difference formulation (1). Naghed also introduced in (1) the model of a coplanar interdigital capacitor and presented the verification of this element up to 25GHz. Beyond 40GHz and for long fingers these simulation results diverge from measured data. This paper will report on the enhanced coplanar IDC model and 2 new types of coplanar capacitorsa serial and a parallel MIM capacitor, where line effects are taken into account. The equivalent circuit elements are determined in units per length. The simulated results will be compared with measured data from test circuits on a GaAs wafer up to 67GHz. Parts of these activities are supported by the European Community within the ESPRIT CLASSIC project. IITRQDUCTIONOne goal of the research activities within the IMST is the development of a comprehensive library with all coplanar structures, which are necessary for (M)MIC design. This library consists of one ports like open and short, a coplanar transmission line, discontinuities like bend, tee and cross (with different kinds of airbridges) as well as lumped elements and coupled lines. The focus of (2) lies on the evaluation of the line and discontinuity models. The coplanar spiral inductor and its application in (M)MIC is presented in (4). This paper will complete the investigations of the coplanar catalogue: an improvement of the IDC model of (1) and the development of a serial and parallel MIM capacitor. Within the ESPRIT Classic project a GaAs wafer has been fabricated at the Daimler Benz foundry in Ulm. The design and evaluation of the test circuits is the task of the authors within Classic. These test structures are simple coplanar circuits, especially developed for the verification of the models. On the wafer are structures for measuring the IDC and MIM models, too. The results have been utilised for the verification of the new models and will be presented within this paper. Up to now capacitor models in CAD programs show poor results at high frequencies. Some models have been extracted from experiments (5). Another possibility is the full wave analysis, presented in (6), which is not suitable for the circuit design with optimisation. The capacitor models presented in this paper have a parametric interface and are integrated and tested into a CAD tool. COPLANAR 1NTERDIGITAL CAPACITOR MAG(S1 1) [dB] _ 0 0MAG(S 12) [dB] 0 -20' -0,5~~~~~~~-15 -,

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