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A special issue of Micromachines (ISSN 2072-666X). This special issue belongs to the section "A：Physics".

Deadline for manuscript submissions: closed (31 March 2026) | Viewed by 6870

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Dr. Alexandre Jean René Serres

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Center of Electrical Engineering and Informatics (CEEI), Universidade Federal de Campina Grande, Av. Aprigio Veloso, 882 Bodocongo, Campina Grande 58109970, PB, Brazil
Interests: bio-inspired antennas; antenna design; optimization techniques
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Special Issue Information

Dear Colleagues,

The 21st SBMO/IEEE MTT-S International Microwave and Optoelectronics Conference (IMOC 2025) will be held from November 9 to 12, 2025, in Campina Grande, Brazil. Organized biennially by the Brazilian Microwave and Optoelectronics Society (SBMO) in partnership with the IEEE Microwave Theory and Techniques Society (MTT-S), IMOC is a well-established international forum that brings together researchers, engineers, and industry professionals in the fields of microwave engineering, optoelectronics, antennas, photonics, and wireless communications.

This 21st edition of IMOC will feature keynote lectures, technical sessions, special sessions, and tutorials addressing recent advances in RF devices, metamaterials, biomedical applications, 5G/6G systems, terahertz technologies, and optical communication systems. This conference promotes collaboration between academia and industry and provides an excellent platform for networking and knowledge dissemination.

A Special Issue related to IMOC 2025 will be published in Micromachines (MDPI), aiming to provide high-quality extended versions of selected papers presented during the conference.

For more information, visit the official website:
https://www.events.sbmo.org.br/imoc2025/home.

Dr. Alexandre Jean René Serres
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 250 words) can be sent to the Editorial Office for assessment.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Micromachines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2100 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

microwave devices
optoelectronic systems
antenna design and applications

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Published Papers (7 papers)

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Research

14 pages, 4605 KB

Open AccessArticle

A K-Band Four-Channel Beamformer with Temperature Compensation Based on 65 nm CMOS Process

by Cetian Wang, Yanning Liu, Xuejie Liao, Fan Zhang, Chun Deng, Ying Liu, Wenxu Sun, He Guan and Deyun Zhou

Micromachines 2026, 17(4), 462; https://doi.org/10.3390/mi17040462 - 10 Apr 2026

Viewed by 323

Abstract

This paper presents a K-band four-channel phased array beamformer with temperature compensation in 65 nm CMOS for 5G and satellite communications. The beamformer includes a four-way power divider/combiner, four RF channels, and digital control circuits. Each RF channel comprises a receive chain, a transmit chain, and a pair of receive/transmit (TX/RX) single-pole double-throw (SPDT) switches. The receive chain consists of a low-noise amplifier (LNA), a six-bit reflective-type phase shifter (RTPS), a drive amplifier (DA), two temperature-compensation attenuators (TCAs), and a six-bit attenuator (ATT); the transmit chain integrates a power amplifier (PA), two TCAs, a six-bit RTPS, a DA, and a six-bit ATT. Measurements show the chip exhibits 0–4.5 dB gain, noise figure (NF) < 7.8 dB, root mean square (RMS) phase error < 3.5°, and RMS gain error < 0.4 dB in receive mode operating in 19–23 GHz. In transmit mode operating in 21–23 GHz, it provides 6–10 dB gain range, RMS phase error < 3.4°, RMS gain error < 0.25 dB, and output power at 1 dB compression point (OP1dB) > 6.5 dBm. In addition, the receive and transmit gain variations are within 0.8 dB and 0.4 dB, respectively, when temperature ranges from −55 °C to 85 °C. With a compact footprint of 3.5 × 4.8 mm², the beamformer consumes 110 mW (receive) and 190 mW (transmit) DC power per channel. Full article

(This article belongs to the Special Issue Recent Advancements in Microwave and Optoelectronics Devices)

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9 pages, 2896 KB

Open AccessArticle

A 6–18 GHz High-Efficiency GaN Power Amplifier Using Transistor Stacking and Reactive Matching

by Cetian Wang, Xuejie Liao, Moquan Gong, Fei Xiao, He Guan, Fan Zhang and Deyun Zhou

Micromachines 2026, 17(3), 338; https://doi.org/10.3390/mi17030338 - 10 Mar 2026

Viewed by 501

Abstract

This article presents the design and implementation of a 6–18 GHz GaN monolithic microwave integrated circuit (MMIC) power amplifier (PA). A two-stage cascaded reactive matching network structure based on transistor stacking technology is employed to achieve circuit gain, and a multi-cell combination is used in the final stage to simultaneously achieve high power and high efficiency. For demonstration, a prototype of the proposed PA with an area of 4.5 × 3.4 mm² is fabricated in a 0.1 µm GaN-on-Si high-electron-mobility transistor (HEMT) process. The measured results of the GaN PA show a small signal gain of 25–29 dB, an output power of 40.8–42.5 dBm, and a power-added efficiency (PAE) of 27–38% in the operating frequency range of 6–18 GHz. Full article

(This article belongs to the Special Issue Recent Advancements in Microwave and Optoelectronics Devices)

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25 pages, 1171 KB

Open AccessArticle

Transverse Mode Instability in High-Power Yb-Doped Double-Clad Fiber Amplifiers: A Three-Layer Optical–Thermal Analysis Based on Stimulated Thermal Rayleigh Scattering

by Elbis Santos Cardoso, Ricardo Elgul Samad and Cláudio Costa Motta

Micromachines 2026, 17(3), 326; https://doi.org/10.3390/mi17030326 - 5 Mar 2026

Viewed by 501

Abstract

Transverse mode instability (TMI) in high-power ytterbium-doped double-clad fiber lasers is widely interpreted as being a consequence of a thermo-optic nonlinear phenomenon driven by stimulated thermal Rayleigh scattering. This work presents a coupled optical–thermal model for a continuous-wave forward-pumped ( [...] Read more.

λ_{p} = 976 nm

) fiber amplifier emitting at

λ_{s} = 1064 nm

over an optimal length of 12 m. The formulation explicitly resolves the three radial regions of a double-clad fiber, avoiding single-clad approximations. Modal fields are computed using the weakly guiding approximation (WGA) in the core combined with the semi-WGA at the cladding interfaces, enabling accurate calculation of higher-order modes of penetration into the inner cladding and of the transverse eigenvalues

U_{01}

and

U_{m n}

relevant to TMI. Within this framework, the nonlinear stimulated thermal Rayleigh scattering coupling coefficient is evaluated, including gain saturation and the thermal eigenmodes of the multi-layer geometry. The results show that the inner cladding modifies both the optical and thermal mode structures, altering the optical–thermal overlap between

{LP}_{01}

and higher-order modes and changing the effective strength of STRS, directly influencing the predicted TMI threshold. The proposed formulation provides a quantitative and physically consistent tool for analyzing thermo–optic dynamics in Yb-double-clad fiber amplifiers and supports the design of next-generation high-power fiber lasers with improved modal stability. Full article

(This article belongs to the Special Issue Recent Advancements in Microwave and Optoelectronics Devices)

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14 pages, 3076 KB

Open AccessArticle

2D and 3D Interdigital Capacitors and Bias Tees Technologies on MnM Interposer for mmWave Applications

by Gabriel Griep, Robert G. Bovadilla, Leonardo G. Gomes, Luís Q. Cartagena, Gustavo P. Rehder and Ariana L. C. Serrano

Micromachines 2026, 17(2), 274; https://doi.org/10.3390/mi17020274 - 23 Feb 2026

Viewed by 542

Abstract

This paper presents two capacitors fabricated using the metallic nanowire membrane (MnM) interposer technology operating at mmWaves. Standard 2D interdigital capacitors (IDCs) are designed to operate up to 70 GHz, which presents a straightforward and non-complex fabrication. In comparison, this work also proposes an improved device that is more compact and exhibits large capacitance density, as high-performance vias enable the realization of high-depth capacitors. The fabrication process of 3D devices presents advanced maturity and innovation as it takes advantage of the porous nature of the interposer material to overcome the device complexity, and is also described in detail. Both capacitor types are modeled by a numerical lumped-element model that also considers parasitics. The 3D capacitors were successfully fabricated and characterized up to 70 GHz, displaying capacitance values between 30 fF and 160 fF and self-resonant frequencies in good agreement with mmWave applications. The quality factor of these devices, measured at 40 GHz, lies between 16 and 4, and the superficial capacitance density is between 4 pF/mm² and 8 pF/mm², showing that these devices are indeed promising for mmWave applications. These devices present considerably larger capacitance density compared to 2D traditional capacitors fabricated on the high-performance substrate, highlighting the advantage of 3D fabrication using nanowire growth. In addition, thin-film resistances are simulated and fabricated, projecting their functions as an RF-choke in a bias tee configuration using Ti thin film sputtering deposition step that is also part of the capacitors fabrication. Full article

(This article belongs to the Special Issue Recent Advancements in Microwave and Optoelectronics Devices)

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15 pages, 4576 KB

Open AccessArticle

Design of a Compact UHF Wilkinson Power Divider Using a Combined T-Shaped–CCMRC Resonator for Harmonic Suppression

by Saeed Roshani, Salah I. Yahya, Golshan Mohamadpour and Sobhan Roshani

Micromachines 2026, 17(2), 158; https://doi.org/10.3390/mi17020158 - 26 Jan 2026

Viewed by 823

Abstract

This paper proposes a compact UHF microstrip divider with wideband harmonic suppression. A combined resonator, formed by a T-shaped resonator and a pair of coupled compact microstrip resonant cells (CCMRCs), is embedded into each divider branch to replace the conventional quarter-wavelength transmission lines. The divider is designed on an FR4 substrate (ε_r = 4.4, thickness = 60 mil) for a center frequency of 570 MHz. Full-wave electromagnetic simulations indicate equal power division at 570 MHz with return loss better than 39 dB and output-port isolation higher than 47 dB. Moreover, a wide stopband from 1.5 GHz to 3.5 GHz is obtained, yielding strong attenuation for the third-to-sixth harmonics. The proposed layout occupies 19.6 mm × 21.6 mm, which is about 76% smaller than a conventional 570 MHz divider (42.7 mm × 41 mm). The proposed design is suitable for modern wireless communication systems. Full article

(This article belongs to the Special Issue Recent Advancements in Microwave and Optoelectronics Devices)

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14 pages, 4452 KB

Open AccessArticle

Ultra-Wideband Quad-Parallel Shunt-Diode Rectifier for Sub-6 GHz Wireless Power Transfer

by Sadık Zuhur

Micromachines 2025, 16(12), 1417; https://doi.org/10.3390/mi16121417 - 17 Dec 2025

Viewed by 558

Abstract

Wireless power transfer via RF/microwave rectifiers has emerged as a sustainable solution to the energy requirements of low-power devices. In this study, a novel four-parallel-shunt-diode ultra-wideband rectifier is proposed to enable wireless power transfer in the sub-6-GHz 5G bands. The proposed circuit maintains a power conversion efficiency (PCE) above 50% across the 1.6–5.1 GHz frequency range at 10 dBm input power and also achieves an efficiency above 50% at 3 GHz for input powers between 1 dBm and 16 dBm. Designed and fabricated on a low-cost FR4 substrate, the rectifier achieves a maximum power conversion efficiency of 76% at 2.9 GHz with a 10 dBm input power. Furthermore, a wideband impedance analysis is performed, taking into account the packaging parasitics of the HSMS-2860 diodes used in the study. Despite the use of a lossy substrate such as FR4, the proposed four-parallel-shunt-diode topology improves impedance stability and provides impedance matching over both a wide input-power range and a wide frequency band when compared with single- and double-diode structures reported in the literature. Full article

(This article belongs to the Special Issue Recent Advancements in Microwave and Optoelectronics Devices)

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11 pages, 4153 KB

Open AccessArticle

A Low-Cost Dual-Frequency Dual-Polarized Antenna Array with High Gain

by Jin-Dong Zhang, Min Wang and Wen Wu

Micromachines 2025, 16(10), 1183; https://doi.org/10.3390/mi16101183 - 19 Oct 2025

Viewed by 2903

Abstract

A high-gain microstrip antenna array is proposed. The dual-frequency and dual-polarization characteristics of the array allow a satellite communication system to transmit and receive signals with a single antenna. To avoid high losses in microstrip feed lines for large apertures, the array is divided into subarrays, each fed by a low-loss separate feed network. The dual-frequency dual-polarization function is realized by utilizing two orthogonal modes of a corner-fed rectangular patch in a single-layer substrate. Moreover, to minimize losses in the separate feed network, semi-ridged coaxial lines and five four-way radial power dividers are employed. The power divider, composed of a cylindrical cavity and five SMA connectors, features very low insertion loss. Finally, to validate the design concept, a prototype of the proposed 32 × 32-element array operating at 12.5 GHz and 14.25 GHz is fabricated and measured. The measured results are in good agreement with the simulated ones. The −10 dB return loss frequency bands for the two operating frequencies are 12.04 GHz–12.69 GHz and 13.82 GHz–14.66 GHz, respectively. The measured gains at the two operating bands are 34.5 dBi and 35.2 dBi, respectively. Full article

(This article belongs to the Special Issue Recent Advancements in Microwave and Optoelectronics Devices)

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