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Projekt Druckansicht

Elektronisch steuerbare Dual-mode Flüssigkristall-basierte substrat-integrierte Wellenleiter-Bandpassfilter für das W-Band

Fachliche Zuordnung Elektronische Halbleiter, Bauelemente und Schaltungen, Integrierte Systeme, Sensorik, Theoretische Elektrotechnik
Förderung Förderung von 2018 bis 2023
Projektkennung Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 414102181
 
Erstellungsjahr 2022

Zusammenfassung der Projektergebnisse

The aim of this DFG project was the realization of tunable compact mmW filters, combining microwave liquid crystal (LC) technology with substrate integrated waveguide (SIW). Originally, the investigations were to take place in the W-band at 100 GHz, but on the advice of the reviewers, the Ka-band was chosen for the investigations. In addition, however, liquid crystal characterization was to be performed at 100 GHz. For the LC characterization, an automated measurement setup was implemented that allows liquid crystals to be characterized via temperature and for parallel and orthogonal alignment to the RF field. Material properties are then extracted from the measurement results using full-wave simulations. Since characterization at 100 GHz proved too challenging, characterization in the V-band was performed at 60 GHz. The LC compound GT7-29001 from Merck KGaA used in this project was characterized here from 15°C to 40°C and compared with the manufacturer's specifications at 19 GHz. The presented automated measurement setup and the measurement results formed the basis for setting up a temperature-dependent high-frequency characterization of various LC components, including those for dielectric mirror line phase shifters in the frequency range from 75 GHz to 110 GHz. The realization of electrically-controllable SIW LC filters is only possible by integrating control electrodes inside the resonators. For this, a multilayer structure is needed to both mill the LC cavity into the substrate and integrate the electrodes. However, it turned out that this is not possible with standard PCB processes, since the prepreg used to bond the PCBs together would flow into the LC cavity during manufacturing. For this reason, an alternative manufacturing process was investigated in cooperation with Rohde & Schwarz, initially using a SIW LC phase shifter in the Ka-band. The layer structure consists of two PCBs: the LC cavity is milled into one PCB and the electrodes are realized in the other. These are then soldered together, sealing the LC cavity. The LC can be introduced into the cavity through two filling holes. In order to significantly improve the performance of the filters compared to all-electric control by means of a complex electrode arrangement and to reduce the technical effort, i.e. the number of electrodes per resonator, a hybrid biasing concept for liquid crystal filters was developed, used and tested, in which the LC molecules can be continuously controlled in their orientation by the simultaneous application of a magnetic and electric field. This reduces the required maximum control voltage and increases the control efficiency to nearly 100%. Two filters were designed and fabricated, a second-order filter consisting of a single LC dual-mode resonator, and a fourth-order filter consisting of two LC dual-mode resonators coupled together. The second-order filter was designed for a relative bandwidth of 1.5% and achieved a center frequency tunability of 7.4% in simulation, with insertion losses varying from 2.12 dB to 2.38 dB. The fourth-order filter was designed with a relative bandwidth of 2.4% and achieved a center frequency tunability of 5.4% with insertion losses ranging from 4.80 dB to 5.00 dB. The filters were fabricated, soldered, and filled with LC along with a designed TRL calibration kit. However, performance measurements were not possible due to manufacturing tolerances during fabrication at Rohde & Schwarz. X-ray images of the soldered filters showed that the PCBs were not soldered together at the points where the input and output couplings were located, because the galvanically applied tin layer was not applied evenly. As a result, no filter characteristic was discernible in the measurements. Beyond the scope of the project, efforts will continue to be made to remanufacture the filters in agreement with Rohde & Schwarz. The results will be published at a later date.

Projektbezogene Publikationen (Auswahl)

 
 

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