A printed monopole antenna for millimeter-wave applications in the 5G frequency region is described in this research. As a result, the proposed antenna resonates in three frequency bands that are designated for 5G communication systems, including 28 GHz, 38 GHz, and 60 GHz (V band). For the sake of compactness, the coplanar waveguide (CPW) method is used. The overall size of the proposed tri-band antenna is 4 mm × 3 mm × 0.25 mm. Using a watch strap and human tissue, such as skin, the proposed antenna gives steady results. At 28 GHz, 38 GHz, and 60 GHz, the antenna’s gain is found to be 5.29 dB, 7.47 dB, and 9 dB, respectively. The overall simulated radiation efficiency is found to be 85% over the watch strap. Wearable devices are a great fit for the proposed tri-band antenna. The antenna prototype was built and tested in order to verify its performance. It can be observed that the simulated and measured results are in close contact. According to our comparative research, the proposed antenna is a good choice for smart 5G devices because of its small size and simple structure, as well as its high gain and radiation efficiency.

Wearable antennas are essential for human body applications, requiring thorough analysis of radiation properties and current distribution. This study employs Characteristic Mode Analysis (CMA) to identify distinct modes, radiation characteristics, and polarization behavior, while utilizing a superstrate, shorting pins, and 45° slots to achieve miniaturization. A key contribution of this work is the use of CMA to strategically design a circularly polarized (CP) antenna, where polarization is achieved through carefully introduced slots. CMA reveals how these slots excite specific modes and provides control over their phase difference using modal significance and characteristic angles—enabling a targeted, mode-based approach to CP design. The proposed antenna features a circular patch with 45-degree slots, an Al2O3 superstrate ( ${\varepsilon }_{r} = 9.8$ ), and a $50~\Omega $ -coaxial probe feed. The fabricated model has electrical dimensions of $0.32\lambda \times 0.32\lambda $ at 2.45 GHz. Tested in both vacuum and under human proximity, the antenna demonstrates impedance bandwidths of 4.16% and 4.2%, and axial ratio bandwidths of 4.0% and 4.02%. Specific absorption rates for 1g and 10g of human tissue are 0.231 W/kg and 0.35 W/kg, and for a complete human arm model, the SAR values are 0.274 W/kg (1g) and 0.396 W/kg (10g)—all well below regulatory limits. A link budget analysis shows reliable communication over a range of 100 meters. The antenna exhibits an omnidirectional radiation pattern and operates within the 2.45 GHz ISM band. This work provides a compact, miniaturized solution for wearable CP antennas, overcoming challenges in flexibility, gain, and SAR compliance while ensuring effective communication and patient tracking.

This paper addresses the growing need for multifunctioning microwave components by proposing a miniaturized reconfigurable stopband filter. The compact size is the outcome of the novel metamaterial split-ring resonator used for realizing this filter. Six PIN diodes are used to achieve real-time frequency and mode reconfigurability. This filter is designed to reject three important frequencies in wireless communication systems: 1.9, 2.4, and 3.6 GHz. Moreover, depending on the use, it is possible to reject one, two, or all the three frequencies, which resulted in seven different cases with three possible modes: single, dual, or triple stopbands. A prototype was manufactured for this filter, and strong agreement between simulation and measurement results is observed. Due to its target bands, this reconfigurable stopband filter is suitable for various cellular communication technologies from 3 G and 4 G up to 5 G and many other S-band applications.

In this work, a compact S-band bandpass filter based on a half-mode substrate integrated waveguide (HMSIW) is developed and experimentally validated, operating around a center frequency of 3.9 GHz. The proposed approach combines the inherent high-pass characteristic of the HMSIW structure with a stop-band effect introduced through Hilbert-cell-based defected ground structures (DGS). This hybrid configuration enables the realization of a wide transmission bandwidth of 1.5 GHz, corresponding to a fractional bandwidth of 37.97 %, within a compact footprint of only 48.5 × 16 mm ² . To further enhance the filter performance, transverse slots are introduced on the top metallization layer to improve impedance matching, while maintaining thetransmission efficiency. The fabricated prototype exhibits a measured insertion loss below 2.8 dB and a return loss better than 25 dB over the operating band. In addition, two well-defined transmission zeros are observed near 5.8 GHz and 7.8 GHz, where attenuation exceeds 45 dB, leading to a sharp roll-off of approximately 56 dB GHz ⁻¹ and significantly improved out-of-band rejection. By exploiting the magnetic-wall symmetry of the half-mode configuration, the proposed structure achieves nearly 50 % reduction in transverse size compared to a conventional SIW design, while preserving similar propagation characteristics. Overall, the presented filter offers a balanced compromise between miniaturization, wide bandwidth, and high selectivity, making it a strong candidate for practical S-band wireless communication systems.