The solid-state sintering route was employed for the production of (1-x)Bi 2 (Li 0 .5 Ta 1.5 )O 7 -xTiO 2 (x = 0, 0.02, 0.04, 0.06, 0.08) ceramics. The phase, microstructure and microwave dielectric properties of each ceramic composition were determined via X-ray diffraction, scanning electron microscopy and Haki Colmon resonator technique, respectively. The dielectric constant, tan δ and AC conductivity were also determined for the composition of x = 0.04. The TiO 2 addition developed new phases of Bi 3 Ti 4 O 12 and Bi 3 TaTiO 9 for x = 0.04 along with Bi 2 (Li 0 . 5 Ta 1.5 )O 7 phase which disappeared for x = 0.08. The τ f of Bi 2 (Li 0 . 5 Ta 1.5 )O 7 was tuned through zero by TiO 2 addition and good microwave dielectric properties ε r ~67.2, Q u f õ 13,767 GHz and τ f ~ −1.45 ppm/ ° C can be obtained for the composition of x = 0.04 sintered at 1050 °C for 2 h. This ceramic composition is a suitable candidate for 5G cellular base station resonator application.
With the rapid development of 5G technology, the types and numbers of 5G base stations are becoming increasingly large. The precision electronic devices in base stations are at risk of electromagnetic interference and infrared detection. Therefore, it is of great significance to design lightweight and high-strength protective materials with electromagnetic dissipation and infrared stealth performance. In this paper, a rigid polymethacrylimide (PMI) composite foam is fabricated by in-situ copolymerization and free-foaming process. Stable polymerization of PMI and uniform dispersion of CNT are steady controlled. The appropriate pore size and density effectively enhance mechanical properties of PMI/CNT composite foam (PCF). More importantly, the hierarchical impedance matching can be constructed by systematically assembling PCF and silver coating (Ag), endowing it with a low-reflection electromagnetic dissipation performance. Thickness of the composite material can be effectively reduced. In addition, thermal insulation of PCF and low infrared-emissivity of Ag coating bring an excellent infrared stealth performance for PCF/Ag. Such excellent comprehensive performance makes it desirable to be applied as protection material for 5G base stations.
Array antenna is of great significance in realizing the Sub-6 GHz fifth-generation (5G) mobile communication systems, however, its utilization in the base station systems implementation is limited due to high power consumption. In this paper, a high radiation efficiency 4 × 4 cylindrical dielectric resonator antenna (CDRA) array fabricated using the temperature stable 0.8Zn 2 SiO 4 -0.2TiO 2 composite ceramic is proposed. TiO 2 -doped Zn 2 SiO 4 composite ceramics are synthesized by the conventional solid-state method. Notably, 0.8Zn 2 SiO 4 -0.2TiO 2 composite ceramic sintered at 1250 °C demonstrates excellent microwave dielectric properties with dielectric constant (ε r ≈ 8.24), high-quality factor ( Q × f ≈ 35 000@8.08GHz), and the temperature coefficient of resonant frequency ( TCF ≈ +4.6 ppm °C −1 ). Moreover, the composite ceramic CDRA array is designed by exciting fundamental HE 11δ mode using the aperture coupling microstrip feeding network. The fabricated composite ceramic based 4 × 4 CDRA array has enhanced measured radiation efficiency of up to 87%, high gain of 17.85 dBi and is a promising candidate for utilization in Sub-6 GHz 5G Base Station communications systems.
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