Microwave dielectric ceramics exhibiting a low dielectric constant (εr), 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 εr ≈ 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 (Tc) 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 of a Sub-6 GHz Dielectric Resonator Antenna with Novel Temperature-Stabilized (Sm1-xBix)NbO4 (x = 0-0.15) Microwave Dielectric Ceramics.

This paper presents a wideband and high-gain rectangular microstrip array antenna with a new frequency-selective surface (FSS) designed as a reflector for the sub-6 5G applications. The proposed antenna is designed to meet the US Federal Communications Commission (FCC) standard for 5G in the mid-band (3.5–5 GHz) applications. The designed antenna configuration consists of 1 × 4 rectangular microstrip array antenna with an FSS reflector to produce a semi-stable high radiation gain. The modeled FSS delivered a wide stopband transmission coefficient from 3.3 to 5.6 GHz and promised a linearly declining phase over the mid-band frequencies. An equivalent circuit (EC) model is additionally performed to verify the transmission coefficient of the proposed FSS structure for wideband signal propagation. A low-cost FR-4 substrate material was used to fabricate the antenna prototype. The proposed wideband array antenna with an FSS reflector attained a bandwidth of 2.3 GHz within the operating frequency range of 3.5–5.8 GHz, with a fractional bandwidth of 51.12%. A high gain of 12.4 dBi was obtained at 4.1 GHz with an improvement of 4.4 dBi compared to the antenna alone. The gain variation was only 1.0 dBi during the entire mid-band. The total dimension of the fabricated antenna prototype is 10.32 λo × 4.25 λo ×1.295 λo at a resonance frequency of 4.5 GHz. These results make the presented antenna appropriate for 5G sub-6 GHz applications.

https://www.mdpi.com/2072-666X/13/8/1215/pdf?version=1660123163

A Wideband High-Gain Microstrip Array Antenna Integrated with Frequency-Selective Surface for Sub-6 GHz 5G Applications

A planar rectangular slot antenna with dual-band operation and realized higher peak gain is proposed, designed, and fabricated for sub-6 GHz 5G applications. The antenna possesses a rectangular radiating slot with the inverted stub on its upper edge excited simultaneously by a micro-strip feed line having a double folded T-shaped structure. The fabricated design is of compact size with the radiating portion of 0.3 λ0 × 0.17 λ0 (λ0 represents free-space wavelength) and profile of 0.009 λ0. The measured results show the operating frequency bands of 3.29–3.63 GHz and 4.3–5.2 GHz, with a peak gain of around 7.17 dBi. The higher frequency band is generated by the feed patch and the slot whereas lower resonant frequency band is generated by the stub loaded on the slot. The measured results are in a good agreement with the simulated results. The proposed design is suitable for the International Telecommunications Union sub 6 GHz applications.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S1759078720001269

A compact double-band planar printed slot antenna for sub-6 GHz 5G wireless applications

In this paper, single-layer ultra-Wide Band (UWB) microstrip patch antennas loaded with asymmetrical U-shaped slot in both microwave and millimeter wave applications are presented These novel antennas cover a fractional bandwidth around 40% in both microwave and millimeter applications The applications cover the C-band (4–8) GHz, V-band (40–75) GHz, and W-band (75–110) GHz In addition to that, it is the sole article that cover the bands (515–5825) GHz and (8025–84) GHZ for WiMaX and ITU band applications, respectively Moreover, it covers three bands for Automotive radar applications within (71–76) GHz, (81–86) GHz, and (92–95) GHz, in addition to further 5G/mm-wave applications at 60 GHz Each antenna is coaxial fed and implemented on a Roger 5880 substrate with relative dielectric constant of 22, thickness of $1575~mm$ and loss tangent of 00009 They operate over the frequency band (55–95) GHz for microwave band and (55–95) GHz for mm-wave band To achieve either a notch in other bands or develop a multi-band structure, the conventional ground is replaced by two different structures The first ground is an array of patches and the other is a mushroom ground The first ground results in a notch within the band (73–79) GHz while the second one achieves a multi-band within (55–68) GHz and (81–95) GHz Both antennas are simulated and verified using Finite Difference Time-Domain analysis (FDTD); CST Microwave Studio and Finite Element Method (FEM); Ansoft HFSS For microwave band, the antenna is fabricated and measured for verification Concerning the mm-wave version, three different types of ground planes are presented; traditional, periodic structure of patches and mushroom The structure with periodic patches conducts the same band as the traditional ground plane does This is a prestep for the design of the notches The mushroom ground is carried out for multi-band applications The average gain of the antennas is 7 dBThe measured two dimensional cuts of the radiation pattern, radiation efficiency, and reflection coefficient of the microwave version are presented and are in good agreement with the simulated results while for the mm-wave antenna the same parameters are simulated with two different methods and are in good agreement

/pdf/design-and-implementation-of-uwb-slot-loaded-printed-antenna-54qcwoof1c.pdf

Design and Implementation of UWB Slot-Loaded Printed Antenna for Microwave and Millimeter Wave Applications

A compact hybrid-mode antenna is proposed for sub-6 GHz communication. The proposed antenna is composed of a slotted rectangular patch, a feeding dipole, and a balun. Three modes are sequentially excited in a shared patch to achieve a compact size. A prototype antenna with a major size of 0.48 λ0 × 0.31 λ0 × 0.16 λ0 (λ0 is the wavelength in the free space at the center of the operating frequency band) is fabricated and measured. The measured results demonstrate an impedance bandwidth of 56.87% from 2.97 GHz to 5.33 GHz and an average gain of approximately 8.00 dBi with 1 dB variation in the operating frequency band of 3.0–5.0 GHz. The proposed antenna can be an element for microbase stations in sub-6 GHz communication.

/pdf/a-compact-slotted-patch-hybrid-mode-antenna-for-sub-6-ghz-4ym5xhq383.pdf

A Compact Slotted Patch Hybrid-Mode Antenna for Sub-6 GHz Communication

A low-profile antenna with a high gain and broad bandwidth is proposed for Sub-6GHz communication in this paper. A narrow-band patch mode and a narrow-band dipole mode are shared in one radiator and simultaneously excited to broaden the bandwidth. A compact prototype with a projection size of 0.90 λ0 × 0.78 λ0 and a profile of 0.13 λ0 (λ0 is the wavelength in the free space at the center of the operating frequency) is fabricated and measured. The measurement demonstrates an impedance bandwidth of 67.50%, covering the frequency range from 2.75 GHz to 5.45 GHz and an average gain of 8.4 dBi in the operating band of 3.0–5.0 GHz.

A Patch/Dipole Hybrid-Mode Antenna for Sub-6GHz Communication.

A shared aperture enabled hybrid-mode antenna in a compact structure is proposed for Sub-6GHz communication in this paper. The proposed antenna is composed of a slotted rectangular patch to enhance the impedance bandwidth, a feeding dipole to excite the patch, and a ground plane to obtain unidirectional radiation. Three modes are sequentially excited in the operating band. The slot mode dominates the low frequency band, the patch mode determines the middle frequency band, and the dipole mode governs the high frequency band. The size of the proposed antenna is $0.46\lambda_{0}\times 0.32\lambda_{0}\times 0.13\lambda_{0}$ ( $\lambda_{0}$ is the wavelength in the free space at the center of operating frequency). The simulated results demonstrate a wide impedance bandwidth of 55.35% (2.94 GHz to 5.19 GHz) and a stable gain around 8.96 dBi in the band of 3 GHz to 5 GHz. The proposed compact antenna is applicable for micro base station in Sub-6G communication system.

A Compact Shared-Aperture Hybrid-Mode Antenna for Sub-6G Communication

A dual-band base station antenna is introduced in this paper. The proposed antenna is composed of baluns, bowtie patches, and a split ring. The two pairs of bowtie patches excited by the two orthogonal balun structures can achieve dual polarization. The split ring is used to yield two additional resonances to broaden the impedance bandwidth. In this way, a compact dual-band base station antenna is obtained with the size of 0.41 λc × 0.41 λc × 0.13 λc (λc is the wavelength in the free space at the lowest operating frequency band) and the average gain of 8.2 dBi. Moreover, the operating frequency bands of the proposed antenna cover 2515–2675 MHz, 3400–3600 MHz, and 4800–5000 MHz, which can function as an element for macro- or microcells in sub-6 GHz communications.

/pdf/a-dual-band-base-station-antenna-with-a-split-ring-for-sub-6-34qi6kalip.pdf

A Dual-Band Base Station Antenna with a Split Ring for Sub-6 GHz Communication

The utility model discloses a miniature multi-frequency antenna and a terminal. The miniature multi-frequency antenna comprises two branch feed monopoles, a floor, a substrate and a reconfigurable switch. Wherein the feed monopole is printed on the front surface of the substrate, the floor is printed on the back surface of the substrate, the floor is provided with a defected ground structure, thefeed monopole comprises a feed unit, an upper branch unit and a lower branch unit, the feed unit is provided with a feed point, and the lower branch of the feed monopole is provided with a reconfigurable switch; according to the utility model, a defected ground structure on the floor is utilized to generate a frequency band required by 3G; frequency bands required by 4G and 5G are generated by tworadiation branches of the feed monopole, and an upper frequency band required by 5G is generated by reconstruction of a lower branch, so that one antenna can cover the frequency bands required by 3G,4G and 5G at the same time, and the occupied area of the antenna in the terminal is reduced; therefore, the influence among a plurality of antennas is avoided, and the channel capacity is improved.

Small multi-frequency antenna and terminal

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