Noorlindawaty Md Jizat

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.

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 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.

A new class of miniaturized balanced 0° microstrip filtering couplers is presented, characterized by an ultra-compact footprint of only 0.006 λg² achieved through a unique configuration of coupled thin microstrip lines integrated with solid stubs. The proposed design exhibits a built-in filtering response with balanced output magnitudes and phase (0° phase difference) across its passband, while maintaining exceptionally low group delays (0.84 ns at S₂₁ and 0.83 ns at S₃₁). Operating at 1.2 GHz, the coupler achieves outstanding performance metrics, including a return loss of 31.1 dB, an insertion loss of 3.11 dB, and a coupling factor of 2.98 dB. These metrics surpass those of prior coupler designs by concurrently achieving extreme miniaturization, low loss, and minimal group delay in a single device. Close agreement between full-wave electromagnetic simulations and measurements from a fabricated prototype validates the design’s effectiveness and underscores its suitability for wireless network and RF energy scavenging systems, where extreme compactness, low loss, and phase coherence are critical.

This paper presents the design and experimental results of a microstrip diplexer with a high performance for 5G applications. The introduced diplexer has compact size, novel structure, low losses, and wide fractional bandwidth. Notably, it exhibits a novel microstrip layout with a very compact size of 0.004 λ_g². The resonance frequencies are tuned at 1.1 GHz and 3.2 GHz for mid-band 5G applications. The presented structure has the fractional bandwidths (57.3%, 44.6%) and insertion losses (0.07 dB, 0.04 dB). Additionally, it features two flat channels with two low maximum group delays of 0.86 ns, 0.4 ns in the 1^st and 2^nd passbands, respectively. A perfect mathematical design method is applied to find the behavior of the introduced resonator, as well as the most effective physical dimensions. For improving the performance and miniaturization, an optimization method is used. To validate the design approach, the proposed diplexer is fabricated and then measured, demonstrating a close agreement between the simulation and measurement results. This highlights the effectiveness of our design approach and underscores the potential of the proposed diplexer for enabling efficient and reliable communication in the rapidly evolving field of telecommunications.

This paper presents a novel tri-band Multiple Input Multiple Output (MIMO) antenna module designed for millimeter and microwave frequency bands, employing metamaterial (MTM) technology to enhance performance. The compact antenna module measures 36 × 36 × 1.6 mm² and uses a Rogers RT-5880 substrate. Its structure includes a multi-stubbed radiating patch, a partial ground plane, and a 2 × 1 epsilon-negative MTM array positioned between antenna elements in an orthogonal layout. Operating at 3.5 GHz, 5.2 GHz, and 28 GHz, the integration of MTM significantly improves the antenna’s overall performance by influencing phase, amplitude, and electromagnetic field distribution. Bandwidth enhancements of 10.01% and 6.4% are achieved for the 3.5 GHz and 5.2 GHz microwave bands, respectively, and 4.43% for the 28 GHz millimeter-wave band. Isolation levels improved from 20 dB to 24 dB in microwave bands and from 26 dB to 32 dB in the millimeter-wave band, ensuring reduced interference. The realized gain also increased from 3.6 dBi, 4.2 dBi, and 7.4 dBi to 4.8 dBi, 5.3 dBi, and 9.3 dBi across the respective frequency bands. The proposed MIMO antenna showcases excellent diversity performance with an envelope correlation coefficient (ECC) of below 0.002/0.001/0.0003 across all bands and a diversity gain (DG) exceeding 9.98 dB. Machine learning-based performance verification analysis assessed bandwidth and efficiency, where the K-Nearest Neighbors (KNN) model achieved 97.8% accuracy. This MIMO antenna holds great potential for various Internet of Things (IoT) applications, including Vehicle-to-Network, Vehicle-to-Cloud communications, 5G cellular networks, Wi-Fi, WiMAX, and both sub-6 GHz and millimeter-wave 5G bands, reinforcing its suitability for 5G IoT sectors.

This research paper introduces a compact dual-band crossover designed for the low and mid-band 5G frequencies at 0.7 GHz and 3.5 GHz. The innovative design is achieved by cascading two dual band branch-line couplers (BLCs), which utilize T-shaped transmission lines (TLs) with folded arms and stubs to reduce their overall footprint significantly. Additionally, the integration of metamaterial (MTM) structures, incorporating interdigital capacitor (IDC) unit cells, contributes to an impressive 90% size reduction compared to conventional components. The BLC’s and crossover’s performances were rigorously evaluated using CST Microwave Studio (CST MWS) simulations. Following successful simulations, the BLC and crossover were fabricated on a Rogers Duroid/RT5880 substrate, characterized by a dielectric constant of 2.2 and a thickness of 0.787 mm. A thorough comparative analysis between the simulated and measured results, alongside similar reported works, signifies the exceptional performance of the proposed BLC and crossover. These findings confirm their suitability for sub-6 GHz 5G frequency spectrum applications.