Rajesh Kumar Dhandapani

A miniaturized ten-element MIMO antenna array for sub-6 GHz 5G mobile devices is introduced in this work. The structure covers a broad band from 3.2 GHz to 6.2 GHz, which provides isolation of more than 19 dB, extremely low ECC < 0.01, and high efficiency between 78% and 85%. The antennas are located on the edge of a 150 mm x 80 mm FR4 substrate, which can be approximated to 1.6 λ × 0.85λ at f₀ = 3.5 GHz, and each antenna size is 0.11 λ × 0.03λ, which has been optimized to provide wide-band coverage by using proper current distribution on the slots. Under different operating positions, e.g., single-hand, two-hand conditions, and under various obstacles such as batteries, LCDs, the antennas maintain their high efficiency and peak channel capacity, i.e., 46-50.25 bps/Hz, which confirms the ability to meet the high data rate requirements of 5G. In addition, due to its small size and excellent performance, the new antenna array could also be used in different wearable devices, ultrathin laptops, and other IoT terminals requiring high-performance MIMO antennas in sub-6 GHz 5G and beyond.

This paper presents the design and experimental validation of a compact triple-band two-port MIMO antenna based on a star-shaped slot-loaded circular radiator for multi-frequency wireless applications. The proposed antenna operates over three distinct frequency bands of 3.1–4.2 GHz, 6.3–8.4 GHz, and 10.1–12.3 GHz, with overall dimensions of 87.5 mm × 35 mm × 1.6 mm (approximately 1.0 λ × 0.4 λ × 0.0187 λ at 3.5 GHz). A key feature of the design is the use of a segmented ground-plane architecture , which effectively confines surface currents and suppresses mutual coupling, enabling high isolation despite a compact edge-to-edge radiator spacing of only 17 mm (≈0.2 λ at 3.5 GHz). As a result, the antenna achieves isolation better than 20 dB in the first band, above 18 dB in the second band, and greater than 11 dB in the third band without employing bulky or complex decoupling structures. Circular polarization is realized in the upper band (10.1–12.3 GHz) through controlled perturbation of higher-order modes using symmetrically placed star-shaped slots, with the axial ratio maintained below 3 dB. The antenna provides a peak gain of up to 8 dBi, with gains ranging from 2 to 8 dBi across the operating spectrum. A fabricated prototype was measured, and the results show good agreement with simulations. The MIMO performance metrics demonstrate excellent diversity characteristics, with ECC < 0.01 , DG ≈ 9.9–10 dB , CCL < 0.4 bits/s/Hz , and TARC < −10 dB across the operating bands, confirming the antenna’s suitability for compact triple-band MIMO systems supporting sub-6 GHz 5G, emerging upper-midband, and X-band wireless applications.

A compact dual‐port antenna is proposed for Dedicated Short‐Range Communications (DSRC) operating in the 5.85–5.925 GHz frequency band. The antenna employs a symmetric slot‐loaded cross‐shaped patch configuration with closely spaced central feed points to intrinsically suppress mutual coupling and control surface current distribution. Without using any external decoupling networks, parasitic elements, or complex feeding structures, the proposed antenna achieves high port isolation exceeding 25 dB, reaching approximately 35 dB at the centre frequency of 5.88 GHz. The antenna exhibits an ultra‐compact electrical size of 0.43 λ × 0.43 λ × 0.012 λ on a Rogers RT/Duroid 5880 substrate, making it well suited for space‐constrained DSRC on‐board unit integration. In addition to compactness and high isolation, the antenna demonstrates highly directional radiation characteristics with a measured front‐to‐back ratio of approximately 17.6 dB, which is explicitly quantified and experimentally validated. These attributes—an electrical footprint of 0.43 λ × 0.43 λ × 0.012 λ , measured isolation of approximately 35 dB at 5.88 GHz, a gain of 6.4 dBi, and a front‐to‐back ratio of 17.6 dB collectively make the proposed antenna a practical and self‐contained solution for DSRC on‐board unit deployment in vehicular and point‐to‐point communication platforms.

This study explores a novel approach to mitigate the challenge of a small ground plane inducing substantial back lobes in high front-to-back ratio (FBR) microstrip patch antennas. Introducing a combined technique employing rectangular strip and connecting strip methods, this research aims to counteract backward radiation by generating supplementary magnetic currents through an inductive effect. The hybrid method effectively reduces the backward radiation from the original patch. The proposed single antenna element occupies a notably smaller area (approximately 0.029 λ × 0.036 λ, where λ denotes the cutoff wavelength at 5.9 GHz), making it particularly suitable for wearable applications. Additionally, an equivalent circuit model illustrates the coordinated action, offering comprehensive insights into the physical mechanisms. The achieved FBR surpasses directivity by up to 6.03 dB, leading to a diminished specific absorption rate (SAR) when worn while maintaining minimal impact on radiation efficiency due to human presence, a crucial quality for wearable devices.

This work introduces a compact and novel MIMO antenna system with close spacing and exceptional isolation, tailored for broadband usage across frequencies from 3.7 to 11 GHz. The antenna configuration consists of two octagonal radiators, each individually powered by a 50 Ω microstrip line. The use of a modified ground structure ensures a wideband frequency range. A key novelty of this design is the incorporation of a strategically placed stub (25.6875 × 0.5 mm²) between the radiating sections, which significantly enhances inter-port isolation, achieving over 15 dB despite the minimal 3 mm port separation—an improvement over conventional MIMO antennas. This design enables high isolation without increasing antenna size, making it highly efficient for compact wireless systems. Performance evaluation, including fabrication and testing, demonstrates a strong alignment between simulation and experimental data. Metrics such as envelope correlation coefficient (ECC), diversity gain (DG), and channel capacity loss (CCL) were analyzed to assess MIMO efficiency. The proposed antenna is ideal for broadband wireless systems with a peak gain of 6.5 dBi and excellent resonance, offering superior isolation and compactness compared to existing designs.

This paper presents the design and analysis of a circularly polarized coplanar waveguide (CPW) antenna specifically tailored for X-band applications. The antenna, with compact dimensions of 27 mm × 28 mm, is fabricated on a flexible 0.1 mm thick polyimide substrate. It operates effectively within the frequency range of 10.5 GHz to 12 GHz. To enhance performance metrics such as gain and radiation characteristics, two complementary split-ring resonators (CSRRs) are integrated into the radiating patch. Comprehensive simulations were conducted, followed by the fabrication and experimental testing of the antenna. The results indicate a high degree of agreement between the simulated and measured performance parameters. The antenna achieves a gain of up to 6 dBi, with an axial ratio maintained below 3 dB across the operating frequency band, signifying excellent circular polarization characteristics. These findings underscore the potential of the proposed CPW antenna design as a highly efficient solution for X-band applications, offering notable improvements in gain and axial ratio performance. This work contributes to the development of advanced antenna technologies suitable for modern communication systems operating in the X-band spectrum.

A dual-band circularly polarized antenna has been designed for millimeter-wave applications, operating over the frequency ranges of 27 GHz to 28.45 GHz and 34.3 GHz to 35.8 GHz. The proposed coplanar waveguide (CPW) antenna features a central feed line serving as the main signal conductor, with circular structures arrayed around it acting as radiating elements. These elements are strategically designed for optimal performance at millimeter-wave frequencies. The antenna, with physical dimensions of 8 mm × 7 mm × 0.757 mm, corresponds to approximately 0.72λ × 0.63λ × 0.068λ at 27 GHz, where λ represents the free-space wavelength. Fabricated on a Rogers RT/duroid 5880 substrate, the antenna’s practical measurements exhibit good agreement with simulated results. The antenna achieves an overall gain of up to 6 dBi across the operating bandwidth, maintaining an axial ratio of less than 3 dB. These results confirm the antenna’s efficacy, making it a superior choice for millimeter-wave 5 G applications.

This research presents a novel four-port metamaterial-backed Multiple Input Multiple Output (MIMO) antenna system designed for X-band applications. Each modified circular-shaped antenna element is meticulously printed on a 1.6 mm thick FR4 substrate, resonating within the 9.2 to 9.9 GHz frequency range, encompassing a significant portion of the X-band spectrum. To enhance overall gain, a tilted square-shaped 4 × 4-unit cell is strategically printed on the ground plane of the substrate. The proposed MIMO antenna achieves a maximum gain of up to 8 dBi across the operating spectrum, coupled with an impressive radiation efficiency of up to 80%. Fabrication of the designed antenna is performed, and comprehensive parameter measurements validate its performance, exhibiting a close correlation with simulated results. Essential MIMO parameters such as ECC (10 dB), CCL (<0.3), and diversity gain are calculated to affirm the antenna’s proficiency further. The results show that the proposed antenna could be a suitable contender for X-band applications.