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Thick film screen-printing technology is employed to introduce planar dielectric antennas. The micron-size-thick film is made from high-permittivity dielectric paste, which is printed on a low-loss low-permittivity microwave substrate to operate as a magnetic wall boundary. A simplified theoretical model is developed to analyze the antenna structure. The accuracy of this model is evaluated by the results of a commercial three-dimensional (3-D) electromagnetic field solver. The model works well with less than 5% deviation from time-consuming simulations, providing the permittivity contrast between the film and substrate is kept high (e.g., > 30). The impact of dielectric loss of the film in antenna performance is significantly less than that of the substrate, allowing medium-loss films (e.g., \boldsymbol\varepsilon^\prime\prime = 3) results in highly efficient antennas with over 95% radiation efficiency. A prototype was made using screen printing and experimentally characterized at Ku-band. The experimental results confirm the theoretical achievements. The measured -10\;\textdB impedance bandwidth of the printable planar dielectric antenna having dimensions of 0.2 \boldsymbol\lambda0 \times 0.2 \boldsymbol\lambda0 is over 10% with a measured gain ranging from 4.5 to 5.5 dBi. Broadside radiation patterns with cross polarization levels of lower than - 20\;\textdB are achieved. This process is compatible with low-temperature cofired ceramic (LTCC) technology where similar idea can be applied to other passive microwave components. [ABSTRACT FROM PUBLISHER]

Planar microwave components are very desirable for many applications and are mainly realized by metallic structures. In this work, a planar dielectric waveguide is proposed. A high-permittivity micrometer-size thick film is patterned on a low-loss microwave substrate and is considered as a nearly perfect magnetic wall to realize the waveguide structure. The permittivity contrast between the film and substrate is kept high (e.g., >\30) in order to minimize the leakage power, and consequently, the insertion loss. The waveguide structure is theoretically analyzed using an approximation method and the results are confirmed by a simulation-based numerical method. The impact of dielectric loss of the film in waveguide performance is much less than that of the substrate, allowing waveguides with films having a medium or high loss (e.g., \varepsilon^\prime\prime = 3) result in a low insertion loss (e.g., up to 0.04 dB/mm at 40 GHz). Several prototypes are fabricated by screen-printing of barium–strontium–titanate (BST) pastes and characterized at 40 GHz. Using the extremely lossy BST film (\tan \delta = 0.2, \varepsilon^\prime\prime = 70), the insertion loss of the waveguide is measured to be 0.18 dB/mm. Based on the current technologies, the printable planar dielectric waveguide can achieve 0.08 dB/mm in insertion loss. Further improvements are expected in the future as the materials and fabrication technologies progress. [ABSTRACT FROM PUBLISHER]

The electrocaloric effect as a function of Ca concentration is studied in 0.4Na1/2Bi1/2TiO3–(0.4–x)SrTiO3–0.2PbTiO3–xCaTiO3. Weak influence of Ca at low concentrations corresponds to the previously established concentration dependence of phase transition temperature and polarization, whereas the decrease of electrocaloric effect at phase transition at higher concentrations of Ca can be explained by assuming increasing concentration of polar nanoregions. The role of thermal depoling in the case of electric-field-induced phase transition is shown. [ABSTRACT FROM AUTHOR]