Thomas Joachim Afullo

In this article, a second-order iterated Circular Minkowski fractal antenna (CMFA) tailored for ultra-wideband (UWB) applications is designed and developed. Leveraging the power of Minkowski fractal geometry, this antenna design achieves a high gain across the UWB frequency spectrum. The design utilizes a circular groove on the ground plane and an arc slot on the radiating element for improving the antenna performance. The proposed antenna is fabricated using cost-effective material, an FR-4 substrate. The antenna is simulated and optimized. The fabricated optimized antenna undergoes real-world testing. Measured results reveal an impressive 120.6% impedance bandwidth spanning from 3.37 GHz to 13.6 GHz, with resonant frequencies at 4.43 GHz, 6.07 GHz, and 9.3 GHz. Meanwhile, the simulated results indicate an impedance bandwidth of 118% ranging from 3.17 GHz to 12.44 GHz. Real-world measurements validate the anticipated UWB traits, closely aligning with the simulation data, and confirming efficient impedance matching with a VSWR of less than 2 across the 3.37 GHz to 13.6 GHz frequency range. The radiation pattern analysis demonstrates a robust bidirectional E-plane pattern and a nearly omnidirectional H-plane pattern. This research introduces a highly promising circular Minkowski fractal antenna for UWB applications, offering exceptional bandwidth and resonance characteristics. This antenna design holds excellent potential for multi-functional wireless systems and opens avenues for enhanced UWB communication and sensing capabilities in diverse applications.

A novel I-shaped metamaterial (ISMeTM) using split-ring resonator (SRR) for multi-band wireless communication is presented in this paper. The proposed ISMeTM unit cell structure is designed using the three-square split-ring resonators (SSRRs) and I-shaped copper strip at the center. The size of the proposed ISMeTM is 10 × 10 × 1.6 mm³ while utilizing the FR-4 dielectric substrate material. The analysis of various array arrangements, variation in the ring gap, variation in strip length, and the variation in strip width is performed to achieve the optimum results for multi-band operation. The effective permittivity, permeability, and refractive index of the unit cell have been analyzed. The design and simulation of the ISMeTM unit cell and arrays are performed using the Computer Simulation Technology (CST) Studio Suite and MATLAB. The equivalent circuit of the ISMeTM is designed using the Advanced Design System (ADS) software. The split ring’s inner loop’s gap functions as a capacitor, while the metallic ring itself functions as an inductor. Electric resonance is created by the interaction between the split ring and the electric field. The interaction of magnetic fields with metallic loops during EM propagation in the structure causes the magnetic resonance. The variation in dimensions of the structure causes the variation in the inductance and capacitance, which causes the variation in resonant frequency. The proposed design is optimized after several parametric analyses. A comprehensive analysis of 1 × 2, 2 × 2, and 2 × 4 array is also investigated. The results confirm the multi-band operation of the proposed ISMeTM. The proposed ISMeTM is suitable for the multi-band C/X/Ku-band microwave applications.

Path loss is the primary factor that determines the overall coverage of networks. Designing reliable wireless communication systems requires accurate path loss prediction models. Future wireless mobile systems will rely mainly on the super-high frequency (SHF) and the millimeter-wave (mmWave) frequency bands due to the massive available bandwidths that will meet projected users’ demand, such as the needs of the fifth-generation ( $5G$ ) wireless systems and other high-speed multimedia services. However, these bands are more sensitive and exhibit a different propagation behavior compared to the frequency bands below $6~GHz$ . Hence, improving the existing models and developing new models are vital for characterizing the wireless communication channel in both indoor and outdoor environments for future SHF and mmWave services. This paper proposes an efficient improvement of the well-known close-in (CI) free space reference distance model and the floating-intercept (FI) model. Real measured data was taken for both line-of-sight (LOS) and non-line-of-sight (NLOS) communication scenarios in a typical indoor corridor environment at three selected frequencies within the SHF band, namely $14~GHz$ , $18~GHz$ , and $22~GHz$ . The research finding of this work reveals that the proposed models have better performance in terms of their accuracy of fitting real measured data collected from measurement campaigns. In addition, this work studies the impact of the angle of arrival and the antenna heights on the current and improved CI and FI models. The results show that the improved models provide better stability and sensitivity to the change of these parameters. Furthermore, the mean square error between the models and their improved versions were presented. Finally, this paper shows that shadow fading’s standard deviation can have a notable reduction in both the LOS and NLOS scenarios (especially in the NLOS), which means higher precision in predicting the path loss.

Fifth generation (5G) wireless communications will exploit the enormous chunk of bandwidth available at millimetre-wave (mmWave) frequency bands. Accordingly, an accurate and simple path loss model is critical for indoor environments where deployment is likely to occur. We conducted measurement campaigns in the 14 GHz and 22 GHz frequency bands in a typical indoor corridor environment on 5th floor of the Discipline of Electrical, Electronic and Computer Engineering building, University of KwaZulu-Natal, Howard Campus, South Africa. This paper presents details of measurement campaigns with unique transmitter-receiver combinations using a costume-designed channel sounder. The acquired measurement results provide large-scale path loss statistics in an open-plan indoor environment in line-of-sight (LOS) and non-line-of-sight (NLOS) conditions. An effective application of dual slope single-frequency directional large-scale path loss model is evaluated based on the acquired measurement data. The application of dual slope large-scale path loss model is supported by a comprehensive analysis and consideration of propagation mechanisms such as reflection and diffraction resulting in modal attenuation. Validated results show that dual slope large-scale path loss model applied in this paper outperforms close-in reference distance model that assumes the impact of propagating wave guiding effect in indoor corridors.