Design and Fabrication of a Satellite Communication Dielectric Resonator Antenna with Novel Low Loss and Temperature-Stabilized (Sm_1–xCa_x) (Nb_1–xMo_x)O₄ (x = 0.15–0.7) Microwave Ceramics

Abstract

Phase transition−structure−dielectric properties in microwave band correlations were determined for the (Sm 1−x Ca x ) (Nb 1−x Mo x )O 4 (SNCMo@x) system. X-ray and Raman analyses along with selected-area electron diffraction indicated that SNCMo@x (0.15 ≤ x < 0.375) ceramics crystallize in the I2/a space group (monoclinic fergusonite), whereas the I4 1 /a space group (tetragonal scheelite) best describes SNCMo@x (0.375 ≤ x ≤ 0.7), suggesting that the increased ionic radius of the A-site effectively contributed to the ferroelastic phase transition and ensures the stability of the scheelite phase. The SNCMo@x ceramic materials exhibit composition-dependent permittivity (ε r ) with a distribution between 12.0 and 17.7. The distortion and deformation of the [BO] polyhedra should be responsible for the shift from negative to positive temperature coefficient of resonant frequency (TCF) and the irregular behavior of the quality factor (Q × f). An optimum microwave dielectric performance was achieved for SNCMo@0.18 (ε r ∼ 17.1, Q × f ∼ 52, 800 GHz at ∼8.80 GHz, and TCF ∼ −1.4 ppm/°C). This work demonstrates the important role of simultaneous substitution of A/ B cations on [BO] polyhedral distortion and deformation in RENbO 4 materials and its significant effect on the microwave dielectric properties. Also, the SNCMo@0.18 ceramic has been designed as a cylindrical dielectric resonator antenna with a high simulated radiation efficiency (97.1%) and gain (5.96 dBi) at the center frequency (7.75 GHz), indicating its promising application in X-band satellite communication (7.62−7.89 GHz) because of its adjustable permittivity, low loss, and good temperature stability.

Tunable Microwave Dielectric Properties in Rare-Earth Niobates via a High-Entropy Configuration Strategy To Induce Ferroelastic Phase Transition

“…When the x value increased to 0.3, a pronounced peak split was observed at 330 cm −1 B g (ν 2 ), indicating the phase transition of LnNbO 4 from fergusonite to scheelite. 15 As the x value further increases to 0.35, new Raman modes emerged, including B g (ν 2 ) at 265 cm −1 , B g (ν 3 ) at 800 cm −1 , and A g (ν 1 ) at 880 cm −1 . By comparing with the Raman spectroscopy of LaVO 4 , these additional Raman peaks were attributed to specific vibrational modes of [VO 4 ].…”

Synergistic modification of properties in Ba[(Zn0.8Mg0.2)1/3Nb2/3]O3 ceramics through ordered domain engineering

“…Most researches before focus on the relationship between tilted structure and restoring force 18,21–23 . As previously reported for the tilted perovskite structure, the increased thermal energy is supposed to be absorbed as the tilting recovers and it may contribute less to the restoring force on the ionic polarization.…”

“…Most researches before focus on the relationship between tilted structure and restoring force. 18,[21][22][23] As previously reported for the tilted perovskite structure, the increased thermal energy is supposed to be absorbed as the tilting recovers and it may contribute less to the restoring force on the ionic polarization. In the un-tilted structure, the cation ordering arrangement causes a distortion of Nb 5+ , and subsequently results in three long Nb-O1 bonds and three short Nb-O2 bonds (see Table 2).…”

Novel microwave dielectric ceramics based on CaO–MoO3–La2O3 pseudo‐ternary phase diagram and the design of patch antenna

“…Due to the proximity of the intrinsic frequencies of phonons (ranging from 10 11 to 10 12 Hz) in ceramic crystals to the far‐infrared frequency range, it is convenient to consider that the intrinsic dielectric loss of ceramic samples is predominantly caused by non‐harmonic vibrations of phonons when tested in the far‐infrared frequency range. By measuring the infrared reflectance (IR) spectra of ceramic samples and employing classical dispersion theory and a three‐parameter model, the contribution of lattice vibrations to the dielectric constant and intrinsic dielectric loss of the ceramics can be determined through extrapolation using the Reffit software 31,32 $$$$\begin{equation}{\varepsilon ^*}{\mathrm{(}}\omega {\mathrm{)\; = \;}}{\varepsilon _\infty }{\mathrm{\; + \;}}\mathop \sum \limits_{{\mathrm{j\; = \;1}}}^{\mathrm{n}} \frac{{\omega _{{\mathrm{pi}}}^{\mathrm{2}}}}{{\omega _{{\mathrm{oj}}}^{\mathrm{2}} - {\omega ^{\mathrm{2}}}{\mathrm{\; + \;}}j\omega {\gamma _{\mathrm{j}}}}}\end{equation}$$$$ $$$$\begin{equation}R{\mathrm{\; = \;}}{\left| {\frac{{{\mathrm{1}} - \sqrt {{\varepsilon ^*}\left( \omega \right)} }}{{{\mathrm{1\; + \;}}\sqrt {{\varepsilon ^*}\left( \omega \right)} }}} \right|^{\mathrm{2}}}\end{equation}$$$$ …”

“…By measuring the infrared reflectance (IR) spectra of ceramic samples and employing classical dispersion theory and a three-parameter model, the contribution of lattice vibrations to the dielectric constant and intrinsic dielectric loss of the ceramics can be determined through extrapolation using the Reffit software. 31,32…”