Microwave dielectric properties, vibrational spectrum, and antenna design of a novel melilite‐type Ba 2 CoSi 2 O 7 ceramic

ABSTRACT Low‐ε r (the low dielectric constant) microwave dielectric ceramics play an important role in sub‐6 GHz band communication by virtue of their small signal delay. In this paper, Ba 2 CoSi 2 O 7 ceramics were synthesized by the solid‐phase reaction method, and X‐ray diffraction (XRD) confirms that they belong to a new melilite structure, with C 2/ c (No.15) space group, and the ceramics have good microwave dielectric properties with an ε r ∼ 7.37, a Q × f ( Q = 1/dielectric loss, f = resonant frequency) ∼ 26,320 GHz and a TCF (the temperature coefficient of resonant frequency) ∼ −55 ppm/°C after being sintered at 1150°C, and the theoretical dielectric constants derived from the Clausius–Mosotti as well as the porosity equation, respectively, are also used to further demonstrate the low‐ε r properties. Based on the group theory, the one‐dimensional integrable representations of Γ acoustic (the phonon modes) and Γ optical (optical modes) of Ba 2 CoSi 2 O 7 are obtained, and the internal vibrational modes of Ba 2 CoSi 2 O 7 are deconstructed and the main modes of influence of the electronic polarization are analyzed in conjunction with the results of the validly fitted peaks of the 17 Raman and 25 IR tests. A microstrip Yagi antenna is also designed based on the ceramic properties, which can achieve a gain of 9.65 dBi at the center tuning frequency of 5.47 GHz, with a S 11 (return loss) close to −60 dBi. Based on the above results, the Ba 2 CoSi 2 O 7 ceramic is a low‐ε r microwave dielectric ceramic with significant potential for communication application.