Farid Zubir

This paper presents the design, fabrication, and measurement of a microstrip 0° dual-channel coupler operating at 2.4/6.2 GHz. It is designed by utilizing two new resonators consisting of a hybrid of radial and meandering cells. The resonators are designed to be identical to obtain a 0-degree symmetrical coupler with balanced magnitudes and phases. The resonators are designed in a creative way to save space, with an overall size of only 0.041 λg2. An important advantage of this coupler is having an excellent filtering frequency response with high selectivity. Meanwhile, the harmonics are suppressed from DC up to 12.6 GHz with a maximum level of -14.7 dB and from DC up to 9.65 GHz with a maximum level of -20 dB. Also, it has low insertion losses and excellent return loss characteristics. At 2.4 GHz, the coupler exhibits a maximum group delay of 1 ns, with very low phase and magnitude imbalances of 0.54° and 0.083 dB, respectively. The values of S21, S31, and S11 at 2.4 GHz are -3.192 dB, -3.109 dB, and -30 dB, respectively, showing excellent insertion and return losses. Similarly, at 6.2 GHz, the coupler achieves a maximum group delay of 0.97 ns, maintaining low insertion losses and satisfactory return loss values. The compact design and working at 2.4 GHz demonstrate its suitability for integration into Internet of Things and smart city infrastructures, where reliable and efficient signal processing is crucial.

The ability of metasurfaces to manipulate electromagnetic waves has drawn much attention especially with its ability to implement multifunctional structures such as simultaneous reflection and transmission. This paper discusses the fundamental principles and key design metrics such as bandwidth performance, efficiency, polarization control, frequency, and angular stability, which describe performance capabilities and limitations of metasurfaces. A wide operational bandwidth is indeed a requisite for multiple applications; while efficiency allows for energy efficient operations and optimal throughput. Additionally, polarization control and angular stability improves the performance of the metasurface, especially for dynamic environments and next generation communication systems. However, these metasurfaces have some design limitations; for example, trade-off between bandwidth and angular stability, and independent control of reflected and transmitted waves. This paper outlines these challenges and offers avenues for further innovation toward fully realizing the potential of metasurfaces in next-generation technologies.

Partial discharge (PD) is a localized electrical phenomenon occurring within degraded insulation of high-voltage (HV) equipment, where its discharge mechanisms and radiated electromagnetic characteristics vary significantly across air, oil, and gas-insulated systems. Undetected PD can gradually damage insulation and eventually lead to equipment failure and power outages. Therefore, researchers are urged to develop reliable detection methods that are effective across different insulation media to ensure the safe operation of power systems. In this study, ultra-high frequency electromagnetic signals generated from PD activity are analyzed using an external log-periodic dipole array (LPDA) antenna. This research focuses on broadband sensing and considers the PD activity in various insulation materials, including air, oil, and gas. Moreover, lumped inductors are added to achieve a more compact antenna design without compromising the performance. The proposed LPDA antenna is fabricated on an FR-4 substrate and evaluated using a vector network analyzer. As a result, a reflection coefficient below −10 dB from 0.4 GHz to 2 GHz with a directional gain of 4–6 dBi is obtained, which satisfies the IEC 62478 standard. The results demonstrated that the proposed miniaturized LPDA antenna is effective for PD detection in different insulation environments.

This study presents a new microstrip triplexer designed to simultaneously deliver precise lowpass and bandpass filtering functionalities for closely spaced frequency channels. Engineered to operate proficiently at three distinct frequencies, which are 1.02 GHz, 1.6 GHz, and 2.35 GHz where the proposed device demonstrates exceptionally low insertion losses of 0.4 dB, 0.19 dB, and 0.11 dB, respectively, validated rigorously through the simulations and practical measurements. Leveraging meticulous mathematical modelling, the primary structure behaviour and optimal operational frequencies are effectively identified, enabling precision tuning and significant miniaturization of the design. Subsequently, advanced optimization techniques are employed to refine the dimensions and performance, achieving optimal channel separation despite the closely spaced frequency bands. A physical prototype is meticulously fabricated and subjected to comprehensive S-parameter measurement analyses using a high-accuracy 2-port Vector Network Analyzer. The measured data closely aligns with the simulation and theoretical results, underscoring the accuracy and reliability of the proposed design methodology. The remarkably compact footprint, approximately 0.02 λg², positions this triplexer ideally for integration into advanced RF systems demanding stringent size constraints, such as 5G mid-band communication platforms and wireless energy harvesting applications. Ultimately, this work showcases a novel, compact, and high-performance solution capable of addressing critical challenges in spectrum efficiency and simultaneous multi-band operations in densely populated frequency environments.

The rapid expansion of the Internet of Things (IoT) necessitates advanced communication technologies that can efficiently manage diverse frequency requirements and ensure reliable connectivity across various applications. This paper presents the design and analysis of a microstrip 4-channel diplexer with resonance frequencies of 700 MHz, 1.39 GHz, 2.366 GHz, and 2.9 GHz. Strategically designed to support low-power wide-area networks (LPWAN), smart device connectivity, and high-speed data transfer, this versatile diplexer addresses the critical demands of modern wireless communication systems in sectors such as smart cities, healthcare, and industrial automation. The innovative quad-band diplexer achieves remarkably Minimal insertion losses of 0.52 dB, 0.14 dB, 0.33 dB, and 0.15 dB across its four passbands, along with enhanced harmonic suppression for superior signal integrity and reduced interference. Its ultra-compact structure, measuring only 0.0028λ_g², allows for easy integration into space-constrained environments. The use of novel, divided microstrip coupled lines significantly enhances performance while minimizing size, indicating that this diplexer can greatly improve the efficiency and reliability of wireless communication systems, paving the way for advanced multi-band operations and meeting the demands of modern multi-service and 5G networks.

This paper presents a wideband X-band IRS based on a novel combined inward–outward Koch fractal metasurface. The proposed unit cell integrates inward and outward Koch fractal geometries to increase the effective electrical current path and support multiple resonant modes, thereby enhancing the reflection bandwidth while maintaining a compact single-layer structure. A 300 × 300 mm² IRS prototype was designed, fabricated, and experimentally validated. Simulation results demonstrate a reflection phase bandwidth of 2.40 GHz (8.95–11.35 GHz), while measurements confirm a bandwidth of 2.25 GHz (8.90–11.15 GHz), corresponding to a fractional bandwidth of 22.44%. The measured reflection magnitude and phase responses are in good agreement with the simulated results. System-level experiments conducted in a non-line-of-sight environment further demonstrate that the proposed IRS improves the received signal strength by more than 15 dB compared with the case without an IRS, confirming its capability to redirect electromagnetic waves and enhance wireless coverage effectively. The combination of wideband performance, compact single-layer construction, and experimentally verified signal enhancement demonstrates the potential of the proposed combined Koch fractal IRS for next-generation intelligent wireless communication systems.

This paper presents a novel design methodology for an outphasing Class-E power amplifier operating at 27.12 MHz, specifically addressing limitations inherent to traditional outphasing combiners that utilize distributed microstrip transmission lines for harmonic termination. At MHz frequencies, conventional microstrip techniques become impractical due to excessively large physical dimensions. To overcome this, the proposed design employs an entirely lumped-element combiner network, eliminating the need for distributed microstrip harmonic terminations. A rigorous analytical framework is derived using two-port impedance matrices, ensuring simultaneous impedance matching at both peak and back-off power conditions. Parametric studies optimize component values, resulting in enhanced efficiency and stable output power across a broad range of outphasing angles. A prototype employing GaN-based transistors demonstrates high efficiency of 73.2% at peak output power and maintains above 50% efficiency at 6 dB output back-off, validating the effectiveness and practicality of the proposed lumped-element approach. This compact and efficient configuration offers significant advantages for MHz-band RF transmitters and wireless power transfer systems.