Design of a Sub-6 GHz Dielectric Resonator Antenna with Novel Temperature-Stabilized (Sm_1–xBi_x)NbO₄ (x = 0–0.15) Microwave Dielectric Ceramics

Abstract

Microwave dielectric ceramics exhibiting a low dielectric constant (ε r ), high quality factor (Q × f), and thermal stability, specifically in an ultrawide temperature range (from −40 to +120 °C), have attracted much attention. In addition, the development of 5G communication has caused an urgent demand for electronic devices, such as dielectric resonant antennas. Hence, the feasibility of optimizing the dielectric properties of the SmNbO4 (SN) ceramics by substituting Bi3+ ions at the A site was studied. The permittivity principally hinges on the contribution of Sm/Bi–O to phonon absorption in the microwave range, while the reduced sintering temperature results in a smaller grain size and slightly lower Q × f value. The expanded and distorted crystal cell indicates that Bi3+ doping effectively regulates the temperature coefficient of resonant frequency (TCF) by adjusting the strains (causing the distorted monoclinic structure) of monoclinic fergusonite besides correlating with the permittivity. Moreover, a larger A-site radius facilitates the acquisition of near-zero TCF values. Notably, the (Sm0.875Bi0.125)­NbO4 (SB0.125N) ceramic with ε r ≈ 21.9, Q × f ≈ 38 300 GHz (at ∼8.0 GHz), and two different near-zero TCF values of −9.0 (from −40 to +60 °C) and −6.6 ppm/°C (from +60 to +120 °C), respectively, were obtained in the microwave band. A simultaneous increase in the phase transition temperature (T c) and coefficients of thermal expansion (CTEs) by A-site substitution provides the possibility for promising thermal barrier coating (TBC) materials. Then, a cylindrical dielectric resonator antenna (CDRA) with a resonance at 4.86 GHz and bandwidth of 870 MHz was fabricated by the SB0.125N specimen. The exceptional performance shows that the SB0.125N material is a possible candidate for the sub-6 GHz antenna owing to the advantages of low loss and stable temperature.

Design and Fabrication of a C-Band Dielectric Resonator Antenna with Novel Temperature-Stable Ce(Nb1–xVx)NbO4 (x = 0–0.4) Microwave Ceramics

“…The relevant parameters in eqs 4 and 5 were described in a previous work. 8 All IR reflection spectra of CNVx ceramics in Figure 8a fit well using eqs 4 and 5. As x increases, some vibrational modes (Nb/V−O) below 400 cm −1 are merged as T F−S is approached, whereas the band at ∼506.3 cm −1 progressively disappears.…”

“…The domains arise as a result of the second-order ferroelastic phase transition from the scheelite (4/ m ) to fergusonite (2/ m ) structure. Alternate domains are described by different orientations (I and II) in the monoclinic fergusonite phase, ,,− as illustrated in the adjacent [010] m selected area electron diffraction (SAED) pattern (Figure b). Each alternate domain has a 94.8° rotation, equivalent to the monoclinic β angle.…”

“…C-band (4–8 GHz) antennas are used in satellite communications, point-to-point wireless, search and track radars, and fire control and imaging radars. Modern wireless technology presents new demands and challenges for antennas, necessitating high data transmission rates, high reliability, and quality of transmission link to facilitate the development and improvement of multiple-input–multiple-output (MIMO) systems. − Dielectric resonator antennas (DRAs) are distinguished by their inherent advantages of low profile, low loss, high radiation efficiency, low metal loss, and omnidirectional response. − Microwave dielectric ceramics modulate antenna performance through optimization of three selective parameters: permittivity (ε r ), quality factor ( Qf ), and temperature coefficient of resonant frequency (TCF), which regulate the size and transmission speed, transmission loss, and frequency selectivity and operating temperature stability, respectively. − …”

“…Rare earth niobate (RENbO 4 , RE = La to Lu and Y) show promise for various applications as a result of their unique crystal chemistry. − RENbO 4 compounds undergo a ferroelastic phase transition (monoclinic fergusonite type → tetragonal scheelite type, T F–S ), accompanied by a distortion from [NbO 6 ] to [NbO 4 ] polyhedral coordination. The distortion is not only controlled by the RE ion radius (Bi 3+ also substitutes on the A site) but also affected by the B-site ion radius of pentavalent substituents, such as V, Sb, and Ta, in a manner analogous to BiVO 4 ,− (Figure ). Most importantly, the structural distortion of the Nb-polyhedra associated with T F–S is instrumental in controlling the dielectric properties of RENbO 4 compounds .…”

(Hf0.25Zr0.25Sn0.25Ti0.25)O2 high‐entropy ceramics and their microwave dielectric characteristics

“…As the key materials for microwave resonators, filters, antennas, and oscillators, microwave dielectric ceramics have received the increasing attention 1–5 . In these applications, a suitable dielectric constant ε r , a high Q value (low dielectric loss) combined with a near‐zero temperature coefficient of resonant frequency τ f are generally required.…”