Salah Ismaeel Yahya

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.

This paper introduces a simulation-based design study of a high-performance 2.6 GHz Doherty power amplifier (DPA) designed for 5G New Radio n7 and n38 frequency band applications. The proposed DPA incorporates a branch-line coupler, replacing conventional impedance inverter and impedance transformer networks. Furthermore, an innovative compact two-section impedance matching network is incorporated in the amplifier structure to reduce size and improve performance. This novel approach results in superior performance, particularly at high output power levels. A class-AB amplifier serves as the main stage, whereas a class-C amplifier functions as the auxiliary stage, ensuring efficient power utilization. Operating at 2.6 GHz, the proposed DPA demonstrates a drain efficiency of 45% and a maximum gain of 15 dB. In comparison with a typical DPA, the proposed design occupies 75% of the size, which shows a size reduction of 25%.

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 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.

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.

A new microstrip lowpass-bandpass diplexer with exceptional performance characteristics is designed and analyzed. It includes microstrip meandrous thin lines loaded by solid cells. The diplexer achieves 0.058 dB and 0.013 dB low insertion losses (ILs) and 26.4% wide fractional bandwidth (FBW). Operating frequencies are obtained using a perfect mathematical method, which are verified by the simulation results. Having two equations that accurately predict the operating frequencies allows us to optimize the diplexer's performance by adjusting key parameters such as line lengths and widths. This helps in achieving the desired operating frequencies with minimal trial and error. It has 0.01 λg2 very compact size and exhibits low group delays at both channels, which make it appropriate for a varied range of applications requiring high precision and efficiency. Overall, this microstrip diplexer design offers a versatile and reliable solution for demanding RF and microwave applications.

This paper presents the design and optimization of a compact 900 MHz hybrid ring coupler using lumped reactive components, aimed at achieving harmonic suppression and size reduction for Radio Frequency (RF) applications. Traditional hybrid ring couplers rely on quarter-wavelength transmission lines, resulting in large size device and limited harmonic rejection. To address these challenges, a novel coupler structure was developed that replaces long transmission lines with composite branches, significantly reducing device dimensions while enhancing performance. In the proposed coupler, instead of the six conventional 90-degree lines, six compact networks composed of microstrip lines, three inductors, and one capacitor are used. The inductors have values of L1, L1, L2, and the capacitor has a value of C. These four parameters significantly influence the coupler’s performance; thus, they were selected as inputs for the applied neural network, with the scattering parameters S11, S12, S13, S14, and frequency considered as the five output parameters. The dielectric constant (Ɛᵣ) of the substrate is 2.2, and the substrate material is RT/duroid 5880 with a thickness of 20 mils. By feeding the neural network model with these parameters as inputs, the coupler’s output response was predicted and analyzed, enabling the selection of optimal component values. Optimal responses were obtained with L1 = 10.1nH, L2 = 2.3nH and C = 2.1pF, which allows the coupler to operate effectively at 900 MHz. At this operating frequency, the values are S11 = −32.6dB, S12 = −3.05dB, S13 = −3.03dB, and S14 = −45.9dB, indicating excellent coupler performance.