CST – Computer Simulation Technology

Selected Applications of Tunable Materials for Microwave Components

Matthias Maasch, Technische Universität Darmstadt For different tunable microwave components which apply tunable materials simulations using CST Microwave Studio and measurements are presented. Simulation results for a coaxial transmission line for material characterization are shown for 1 GHz to 50 GHz. The dielectric of the coaxial transmission line is partially filled with liquid crystal (LC) to extract its complex permittivity. Extraction errors caused by leakage of the EM fields to the LC filling channels are determined. Furthermore, temperature effects in an interdigital capacitor (IDC) as shown in fig. 1 on bariumstrontium-itanate substrate are investigated. Due to dielectric and metallic losses an increase of the component temperature is expected. By using thermal analysis critical regions can be identifed and the temperature increase of the IDC can be quantified. Finally, a hollow waveguide loaded with an array of tunable split ring resonators (SRR) is presented (fig. 2). By loading the gaps of the SRRs with varactor diodes, a transmission band below the waveguide cutoff frequency is obtained which can be shifted between 0.9 GHz and 2.2 GHz. The tuning is demonstrated by simulation and measurement.

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