Sharul Kamal Abdul Rahim

A new four-element monopole MIMO antenna is proposed, featuring wide bandwidth, high isolation, high gain, and good pattern diversity with broad angular coverage across the entire C-band. By solely optimizing the offset-feeding position and patch width, three higher-order monopole resonances are effectively merged to achieve a 10-dB bandwidth covering 4–8 GHz. High isolation (> 23.3 dB) and low ECC (< 0.0017) are realized across the passband through the combination of rotationally symmetrical placement and shorting stubs. The stubs have minimal effect on the monopole resonances, and they can serve individually for isolation enhancement. The antenna also demonstrates good pattern diversity by producing four tilted omnidirectional radiation patterns, each with a broad HPBW (> 132°) and a passband gain of 6.5–9.4 dBi across the entire C-band.

In this paper, a novel coplanar waveguide (CPW) structure featuring top-layer geometry invariant capabilities, loaded with a defected ground structure (DGS) that serves as a CPW impedance regulator, is presented. The proposed CPW transmission line (t_x line) keeps the 50 Ω impedance stable across micron-thick films of various thicknesses without requiring changes to the CPW dimensions. This CPW model obviates the need for repetitive CPW structure design over different film thicknesses for impedance tuning while simultaneously offering manufacturing standardisation. A critical limitation in conventional CPW and Grounded CPW (GCPW) is the significant dependence of impedance on substrate thickness, requiring re-optimisation of t_x line width (S) and slot gap width (W_s) for each substrate variation. Both conventional CPW and GCPW need concurrent modification of S and W_s to reach 50 Ω impedance. In contrast, the proposed CPW model can match the 50 Ω impedance by tuning only a single parameter, the DGS width, R_sw (range between 3.08 mm - 3.16 mm). At a fixed CPW geometry, this model exhibits low characteristic impedance sensitivity to substrate variations, averaging 0.003 Ω/μm, which is 23 times lower than conventional CPW and GCPW (0.07 Ω/μm). When embedded into an antenna system, it has demonstrated an excellent S11 response, with simulation and measurement results showing a close match, with only a 1.44% frequency shift and a 2.98% S11 magnitude deviation.

In this paper, sand and dust storm characteristics and attenuation prediction methods were reviewed and summarized comprehensively. The impact of humidity on the attenuation prediction process is focally discussed while highlighting the need to incorporate it in the modeling process for accurate attenuation prediction. This review is driven by the need to develop precise prediction models that account for the impact of meteorological factors, particularly humidity, on millimeter-wave attenuation during dust storms. By addressing these shortcomings, the review seeks to improve the design of resilient communication systems to support the ultra-reliable 5G and 6G networks in challenging environments. A critique of the previous studies that highlight the contributions and drawbacks is presented in the paper. This is followed by a taxonomy of models based on their prediction concepts and the timeline of developments. Furthermore, open issues and challenges for research were presented. The review study found that existing theoretical models have failed to predict measured attenuation accurately, often deviating significantly. Most of the theoretical and analytical approaches for estimating dust storm attenuation are found to neglect the critical influence of humidity. Few empirical and machine-learning models proposed recently, have demonstrated closer alignment with measurements after considering humidity and other metrological parameters.

In this paper, a wideband circular patch antenna incorporated with a rectangular slot-loaded defective ground structure (DGS) is presented, meant for n77, n78, n79, and C band applications. The circular radiation patch of the proposed antenna is fed by a coplanar waveguide (CPW) mounted on a FR4 PCB board. At the bottom side of the board, a rectangular slot loaded on the DGS is added to establish good 50 Ω impedance matching and improve the antenna impedance bandwidth. This wideband antenna excites TM11 and higher-order TM21 modes at two distinct frequencies (3.3 GHz and 6.0 GHz). This circular patch antenna exhibits wideband behaviour with a fractional bandwidth > 90%, and an average efficiency of 76%.

The field of wireless power transfer (WPT) has recently seen much innovation and improvement and, as a result, there is an ever-increasing need for high power transfer efficiency (PTE) of the WPT systems, as well as enhanced transmission distance for end users. However, some of the currently available WPT systems have a restricted PTE and transfer distance because they use an inductive coupling technique. With this method, the PTE suffers a significant drop as the distance between the transmitter and receiver coils grows. Alternately, magnetic resonance coupling (MRC) is employed as a mid-range WPT solution. For this method, metamaterials (MTMs) are used to increase efficiency by inserting them between the transmitter (Tx) and receiver (Rx) coils. MTMs are artificially manufactured materials that demonstrate unusual electromagnetic properties. These traits include evanescent wave amplification and negative refractive characteristics, both of which have the potential to be employed for the improvement of PTE. This paper offers an in-depth summary of recent research and development in MTM-based WPT systems. In this overview, we examine previously reported MTM-based WPT systems across a range of characteristics, including configuration, operating frequency, size, and PTE. A comparative of the various MTM-based WPT systems is also provided in this paper. PTEs for these systems were also presented against their normalized transfer distances. This study was conducted with the intention of providing a resource for academics studying WPT systems and their practical implementations. This analysis exposes the developments occurring in MTM-based WPT systems.

For the first time, an eight-element MIMO antenna is designed by integrating four double-loop resonators with two pairs of inverted-L isolators. By superimposing the resonance modes of the double-loop antenna, the anti-phase currents of the loops can effectively be canceled out for achieving high isolation (S12), without requiring additional decoupling elements or lumped components. The isolators have successfully generated a null point near the operating frequency for further enhancing the isolation (S32) between the double-loop antennas. As a result, the proposed antenna can achieve good isolation levels of S12 <−21.3 dB and S32 <−29.5 dB across a 10-dB bandwidth in the N78 band (3.3−3.8 GHz) and each port provides over 78% of total efficiency and ECC below 0.01 in experiments.