In this paper, an end-fire antenna for 28 GHz broadband communications is proposed with its multiple-input-multiple-output (MIMO) configuration for pattern diversity applications in 5G communication systems and the Internet of Things (IoT). The antenna comprises a simple geometrical structure inspired by a conventional planar helical antenna without utilizing any vias. The presented antenna is printed on both sides of a very thin high-frequency substrate (Rogers RO4003, ${\epsilon }_{\mathrm{r}} =$ 3.38) with a thickness of 0.203 mm. Moreover, its MIMO configuration is characterized by reasonable gain, high isolation, good envelope correlation coefficient, broad bandwidth, and high diversity gain. To verify the performance of the proposed antenna, it was fabricated and verified by experimental measurements. Notably, the antenna offers a wide −10 dB measured impedance ranging from 26.25 GHz to 30.14 GHz, covering the frequency band allocated for 5G communication systems with a measured peak gain of 5.83 dB. Furthermore, a performance comparison with the state-of-the-art mm-wave end-fire antennas in terms of operational bandwidth, electrical size, and various MIMO performance parameters shows the worth of the proposed work.

This paper presents a compact frequency reconfigurable antenna for flexible devices and conformal surfaces. The antenna consists of a simple easy to fabricate structure consisting of a stub loaded circular radiator, designed on commercially available RT5880 flexible substrate (εr = 2.2) with a thickness of 0.254 mm. The combination of stub loading and slot etching techniques are utilized to achieve the advantages of compactness, frequency reconfigurability, wide impedance bandwidth, and stable radiation pattern with structural conformability. The frequency reconfigurability is achieved by employing two p-i-n diodes. Simulated and experimental results showed that the antenna operates in various important commercial bands, such as S-band (2 GHz– 4 GHz), Wi-Max (3.5 GHz and 5.8 GHz), Wi-Fi (3.6 GHz, 5 GHz, and 5.9 GHz), 5G sub-6-GHz (3.5 GHz and 4.4 GHz – 5 GHz), and ITU-band (7.725 GHz – 8.5 GHz) with the additional advantages of structural conformability. Furthermore, the performance comparison of the proposed flexible antenna with the state-of-the-art flexible antennas in terms of compactness, frequency reconfigurability, and number of operating bands demonstrates the novelty of the proposed antenna and its potential application in heterogeneous applications.

This paper presents a compact and simple reconfigurable antenna with wide-band, dual-band, and single-band operating modes. Initially, a co-planar waveguide-fed triangular monopole antenna is obtained with a wide operational frequency band ranging from 4.0 GHz to 7.8 GHz. Then, two additional stubs are connected to the triangular monopole through two p-i-n diodes. By electrically switching these p-i-n diodes ON and OFF, different operating frequency bands can be attained. When turning ON only one diode, the antenna offers dual-band operations of 3.3–4.2 GHz and 5.8–7.2 GHz. Meanwhile, the antenna with single-band operation from 3.3 GHz to 4.2 GHz can be realized when both of the p-i-n diodes are switched to ON states. The proposed compact size antenna with dimensions of 0.27λ₀ × 0.16λ₀ × 0.017λ₀ at the lower operating frequency (3.3 GHz) can be used for several wireless applications such as worldwide interoperability for microwave access (WiMAX), wireless access in the vehicular environment (WAVE), and wireless local area network (WLAN). A comparative analysis with state-of-the-art works exhibits that the presented design possesses advantages of compact size and multiple operating modes.

Metamaterials exhibit properties in terms of subwavelength operation or phase manipulation, among others, that can be used in a variety of applications in 5G communication systems. The future and current 5G devices demand high efficiency, high data rate, computational capabilities, cost-effectiveness, compact size, and low power consumption. This variation and advancement are possible when the antenna design is revised to operate over wideband, high gain, and multiband and has characteristics of compact size, reconfiguration, absorption, and simple ease of fabrication. The materials loaded with antennas or, in the same cases, without antennas, offer the aforementioned characteristics to bring advancement in order to facilitate users. A number of works on designing metasurfaces capable of improving bandwidth, gain efficiency, and reducing the size and cost of antennas are available in the literature for this purpose. Not only are these applications possible, but the intelligent metasurfaces are also designed to obtain reconfiguration in terms of frequency and polarization. The number of absorbers loaded with metamaterials is also designed to improve the absorption percentage used for radar applications. Thus, in this paper, the general overview of different types of metamaterials and their role in performance enhancement and application in 5G and 6G communication systems is discussed.

A dual-band, compact, high-gain, simple geometry, wideband antenna for 5G millimeter-wave applications at 28 and 38 GHz is proposed in this paper. Initially, an antenna operating over dual bands of 28 and 38 GHz was designed. Later, a four-port Multiple Input Multiple Output (MIMO) antenna was developed for the same dual-band applications for high data rates, low latency, and improved capacity for 5G communication devices. To bring down mutual coupling between antenna elements, a parasitic element of simple geometry was loaded between the MIMO elements. After the insertion of the parasitic element, the isolation of the antenna improved by 25 dB. The suggested creation was designed using a Rogers/Duroid RT-5870 laminate with a thickness of 0.79 mm. The single element proposed has an overall small size of 13 mm × 15 mm, while the MIMO configuration of the proposed work has a miniaturized size of 28 mm × 28 mm. The parasitic element-loaded MIMO antenna offers a high gain of 9.5 and 11.5 dB at resonance frequencies of 28 GHz and 38 GHz, respectively. Various MIMO parameters were also examined, and the results generated by the EM tool CST Studio Suite^® and hardware prototype are presented. The parasitic element-loaded MIMO antenna offers an Envelop Correlation Coefficient (ECC) < 0.001 and Channel Capacity Loss (CCL) < 0.01 bps/Hz, which are quite good values. Moreover, a comparison with existing work in the literature is given to show the superiority of the MIMO antenna. The suggested MIMO antenna provides good results and is regarded as a solid candidate for future 5G applications according to the comparison with the state of the art, results, and discussion.