We describe the design and measured performance of a 5 mm x 5 mm x 1.37 mm antenna duplexer for the U.S. PCS band (Tx: 1850-1910 MHz, Rx: 1930-1990 MHz) for cellular handsets based on FBAR (Film Bulk Acoustic Resonator) technology. The FBARs are fabricated in a silicon-based IC process technology and are hermetically sealed in a wafer-level packaging process. Two dice, Tx and Rx, are attached to a 4-level printed circuit board, ballbonded, and encapsulated in plastic to form the final product. Guaranteed worst-case Tx insertion loss is 3.5 dB, worst-case Rx insertion loss is 4.0 dB. Minimum rejection is 50/40 dB in the Tx/Rx bands, guaranteed isolation is >52/42 dB.

Crystal structure exerts dominant influence on the microwave dielectric performance enabling satisfying the demands for 5G communication system. In this study, the Ti‐doped Li3Mg2Nb1‐xTixO6‐x/2 (x = 0.0‐0.1) ceramics were prepared by the solid‐state reaction procedure. Crystal structure refinement and microstructure analysis indicate pure phase with orthorhombic structure and homogeneous microstructure with grain size (~14 μm). The relative permittivity was affected by the relative density, cell volume, and polarizability. The Q × f value was dominated by the Nb‐O bond energy and grain size. The τf value was correlated with the NbO6 octahedral distortion and Nb‐O bond valence. Particularly, the composition (x = 0.04) exhibited remarkable microwave dielectric performance: εr = 15.88, Q × f = 131 000 GHz and τf = −26.8 ppm/°C, providing a promising candidate for millimeter‐wave applications.

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