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A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Optics and Lasers".

Deadline for manuscript submissions: closed (20 August 2020) | Viewed by 50069

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Special Issue Editors

Dr. Armando Fernandez-Prieto

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Guest Editor

Microwaves group, Dpto Electrónica y Electromagnetismo, Facultad de Física, Universidad de Sevilla, Seville, Spain
Interests: printed passive microwave; components and metamaterials

Dr. Alejandro Javier Martinez-Ros

E-Mail Website
Guest Editor

Microwaves group, Dpto Física Aplicada I, Universidad de Sevilla, Seville, Spain
Interests: leaky-wave antennas; substrate integrated waveguide devices; printed passive microwave components; metamaterials

Special Issue Information

Dear Colleagues,

Passive planar circuits play a key role in many RF/microwave applications, such as wireless communications, medical instrumentation, and remote sensing. Planar technologies were born during World War II but their use did not became popular until the 1960s (at that time, planar structures were referred as to as two-dimensional flat-surface layered topologies). Since then, the use of classical planar structures, such as striplines, microstrips, and coplanar waveguides, in high-frequency applications has drastically increased, becoming indispensable elements if devices with low weight and low cost are critical. Even today, new planar technologies are still being investigated and developed as evidenced by the most recent Substrate-Integrated Waveguide (SIW) structure. This Special Issue is focused on highlighting recent contributions on microwave devices developed on planar technologies, and encourages original contributions related, but not limited to, the following topics:

two-port circuits, such as filters;
multiport circuits, such as dividers, combiners, couplers, and multiplexers;
microwave sensors; and
antennas.

Dr. Armando Fernandez-Prieto
Dr. Alejandro Javier Martinez-Ros
Guest Editors

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Keywords

microwave;
microstrip;
stripline;
coplanar waveguide;
substrate-integrated waveguide (SIW);
planar circuit;
antenna;
sensoring.

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Published Papers (13 papers)

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Editorial

Jump to: Research, Review

3 pages, 196 KiB

Open AccessEditorial

Passive Planar Microwave Devices

by Alejandro Javier Martínez-Ros and Armando Fernandez-Prieto

Appl. Sci. 2022, 12(9), 4444; https://doi.org/10.3390/app12094444 - 28 Apr 2022

Viewed by 1694

Abstract

Passive planar circuits play a key role in many RF/microwave applications, such as in wireless communications, medical instrumentation, and remote sensing [...] Full article

(This article belongs to the Special Issue Passive Planar Microwave Devices )

Research

Jump to: Editorial, Review

13 pages, 2344 KiB

Open AccessArticle

Transition from Microstrip Line to Ridge Empty Substrate Integrated Waveguide Based on the Equations of the Superellipse

by David Herraiz, Héctor Esteban, Juan A. Martínez, Angel Belenguer, Santiago Cogollos, Vicente Nova and Vicente E. Boria

Appl. Sci. 2020, 10(22), 8101; https://doi.org/10.3390/app10228101 - 16 Nov 2020

Cited by 4 | Viewed by 3488

Abstract

In recent years, multiple technologies have been proposed with the aim of combining the characteristics of traditional planar and non-planar transmission lines. The first and most popular of these technologies is the Substrate Integrated Waveguide (SIW), where rows of metallic vias are mechanized in a printed circuit board (PCB). These vias, together with the top and bottom metal layers of the PCB, form a channel for the propagation of the electromagnetic fields, similar to that of a rectangular waveguide, but through a dielectric body, which increases the losses. To reduce these losses, the empty substrate integrated waveguide (ESIW) was recently proposed. In the ESIW, the dielectric is removed from the substrate, and this results in better performance (low profile and easy manufacturing as in SIW, but lower losses and better quality factor for resonators). Recently, to increase the operational bandwidth (monomode propagation) of the ESIW, the ridge ESIW (RESIW) and a transition from RESIW to microstrip line was proposed. In this work, a new and improved wideband transition from microstrip line (MS) to RESIW, with a dielectric taper based on the equations of the superellipse, is proposed. The new wideband transition presents simulated return losses in a back-to-back transition greater than 20 dB in an 87% fractional bandwidth, while in the previous transition the fractional bandwidth was 82%. This is an increment of 5%. In addition, the transition presents simulated return losses greater than 26 dB in an 84% fractional bandwidth. For validation purposes, a back-to-back configuration of the new transition was successfully manufactured and measured. The measured return loss is better than 14 dB with an insertion loss lower than 1 dB over the whole band. Full article

(This article belongs to the Special Issue Passive Planar Microwave Devices )

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11 pages, 3558 KiB

Open AccessArticle

Computational Characterization of Microwave Planar Cutoff Probes for Non-Invasive Electron Density Measurement in Low-Temperature Plasma: Ring- and Bar-Type Cutoff Probes

by Si Jun Kim, Jang Jae Lee, Young Seok Lee, Hee Jung Yeom, Hyo Chang Lee, Jung-Hyung Kim and Shin Jae You

Appl. Sci. 2020, 10(20), 7066; https://doi.org/10.3390/app10207066 - 12 Oct 2020

Cited by 9 | Viewed by 2329

Abstract

The microwave planar cutoff probe, recently proposed by Kim et al. is designed to measure the cutoff frequency in a transmission (S₂₁) spectrum. For real-time electron density measurement in plasma processing, three different types have been demonstrated: point-type, ring-type (RCP), and bar-type (BCP) planar cutoff probes. While Yeom et al. has shown that the RCP and BCP are more suitable than the point-type probe for process monitoring, the basic characteristics of the ring- and bar-type probes have yet to be investigated. The current work includes a computational characterization of a RCP and BCP with various geometrical parameters, as well as a plasma parameter, through a commercial three-dimensional electromagnetic simulation. The parameters of interest include antenna size, antenna distance, dielectric thickness of the transmission line, and input electron density. Simulation results showed that the RCP has several resonance frequencies originating from standing-wave resonance in the S₂₁ spectrum that the BCP does not. Moreover, the S₂₁ signal level increased with antenna size and dielectric thickness but decreased with antenna distance. Among the investigated parameters, antenna distance was found to be the most important parameter to improve the accuracy of both RCP and BCP. Full article

(This article belongs to the Special Issue Passive Planar Microwave Devices )

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10 pages, 2010 KiB

Open AccessArticle

High Selectivity Slot-Coupled Bandpass Filter Using Discriminating Coupling and Source-Load Coupling

by Jie Cui, Haojie Chang and Renli Zhang

Appl. Sci. 2020, 10(19), 6807; https://doi.org/10.3390/app10196807 - 28 Sep 2020

Cited by 2 | Viewed by 2075

Abstract

A multilayer bandpass filter with high selectivity is proposed in this letter. Discriminating coupling formed by slot-coupled quarter-wavelength and half-wavelength resonators introduces a zero at 3f

_{0}

_{0}

is the center frequency) and the second harmonic is also suppressed due to the [...] Read more.

A multilayer bandpass filter with high selectivity is proposed in this letter. Discriminating coupling formed by slot-coupled quarter-wavelength and half-wavelength resonators introduces a zero at 3f

_{0}

_{0}

is the center frequency) and the second harmonic is also suppressed due to the quarter-wavelength resonators. Owing to multilayer structure, source-load coupling is introduced to improve selectivity. Then an extra coupled line path is added with the same amplitude as the discriminating coupling path while they are out of phase. Thus signal cancellation produces three extra transmission zeros, with the selectivity and suppression performance further improved. To validate the design, a prototype bandpass filter centered at 2.49 GHz with 3 dB fractional bandwidth of 8.1% is fabricated. Both simulated and measured results are in good agreement and show good performance of the proposed bandpass filter. Full article

(This article belongs to the Special Issue Passive Planar Microwave Devices )

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11 pages, 2962 KiB

Open AccessArticle

CPW-Fed Transparent Antenna for Vehicle Communications

by Jorge Iván Trujillo-Flores, Richard Torrealba-Meléndez, Jesús Manuel Muñoz-Pacheco, Marco Antonio Vásquez-Agustín, Edna Iliana Tamariz-Flores, Edgar Colín-Beltrán and Mario López-López

Appl. Sci. 2020, 10(17), 6001; https://doi.org/10.3390/app10176001 - 29 Aug 2020

Cited by 28 | Viewed by 3430

Abstract

In this paper, a fully transparent multiband antenna for vehicle communications is designed, fabricated, and analyzed. The antenna is coplanar waveguide-fed to facilitate its manufacture and increase its transmittance. An indium-tin-oxide film, a type of transparent conducting oxide, is selected as the conductive material for the radiation path and ground plane, with 8 ohms/square sheet resistance. The substrate is glass with a relative permittivity of 5.5, and the overall dimensions of the optimized design are 50 mm × 17 mm × 1.1 mm. The main antenna parameters, namely, sheet resistance, reflection coefficient, and radiation diagram, were measured and compared with simulations. The proposed antenna fulfills the frequency requirements for vehicular communications according to the IEEE 802.11p standard. Additionally, it covers the frequency bands from 1.82 to 2.5 GHz for possible LTE communications applied to vehicular networks. Full article

(This article belongs to the Special Issue Passive Planar Microwave Devices )

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10 pages, 5636 KiB

Open AccessArticle

High Refractive Index Electromagnetic Devices in Printed Technology Based on Glide-Symmetric Periodic Structures

by Philip Arnberg, Oscar Barreira Petersson, Oskar Zetterstrom, Fatemeh Ghasemifard and Oscar Quevedo-Teruel

Appl. Sci. 2020, 10(9), 3216; https://doi.org/10.3390/app10093216 - 5 May 2020

Cited by 17 | Viewed by 3274

Abstract

We demonstrate the beneficial effects of introducing glide symmetry in a two-dimensional periodic structure. Specifically, we investigate dielectric parallel plate waveguides periodically loaded with Jerusalem cross slots in three configurations: conventional, mirror- and glide-symmetric. Out of these three configurations, it is demonstrated that the glide-symmetric structure is the least dispersive and has the most isotropic response. Furthermore, the glide-symmetric structure provides the highest effective refractive index, which enables the realization of a broader range of electromagnetic devices. To illustrate the potential of this glide-symmetric unit cell, a Maxwell fish-eye lens is designed to operate at 5 GHz. The lens is manufactured in printed circuit board technology. Simulations and measurements are in good agreement and a measured peak transmission coefficient of −0.5 dB is achieved. Full article

(This article belongs to the Special Issue Passive Planar Microwave Devices )

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13 pages, 1930 KiB

Open AccessArticle

Multilayered Balanced Dual-Band Bandpass Filter Based on Magnetically Coupled Open-Loop Resonators with Intrinsic Common-Mode Rejection

by Jose L. Medran del Rio, Aintzane Lujambio, Armando Fernández-Prieto, Alejandro Javier Martinez-Ros, Jesús Martel and Francisco Medina

Appl. Sci. 2020, 10(9), 3113; https://doi.org/10.3390/app10093113 - 29 Apr 2020

Cited by 5 | Viewed by 2719

Abstract

A new dual-band balanced bandpass filter based on magnetically coupled open-loop resonators in multilayer technology is proposed in this paper. The lower differential passband, centered at the Global Positioning System (GPS) L1 frequency, 1.575 GHz, was created by means of two coupled resonators etched in the middle layer of the structure, while the upper differential passband, centered at a Wi-Fi frequency of 2.4 GHz, was generated by coupling two resonators on the top layer. Magnetic coupling was used to design both passbands, leading to an intrinsic common-mode rejection of 39 dB within the lower passband and 33 dB within the upper passband. Simulation and measurement results are provided to verify the usefulness of the proposed dual-band differential bandpass filter. Full article

(This article belongs to the Special Issue Passive Planar Microwave Devices )

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9 pages, 3782 KiB

Open AccessArticle

Ultrawideband Low-Profile and Miniaturized Spoof Plasmonic Vivaldi Antenna for Base Station

by Li Hui Dai, Chong Tan and Yong Jin Zhou

Appl. Sci. 2020, 10(7), 2429; https://doi.org/10.3390/app10072429 - 2 Apr 2020

Cited by 10 | Viewed by 3511

Abstract

Stable radiation pattern, high gain, and miniaturization are necessary for the ultra-wideband antennas in the 2G/3G/4G/5G base station applications. Here, an ultrawideband and miniaturized spoof plasmonic antipodal Vivaldi antenna (AVA) is proposed, which is composed of the AVA and the loaded periodic grooves. The designed operating frequency band is from 1.8 GHz to 6 GHz, and the average gain is 7.24 dBi. Furthermore, the measured results show that the radiation patterns of the plasmonic AVA are stable. The measured results are in good agreement with the simulation results. Full article

(This article belongs to the Special Issue Passive Planar Microwave Devices )

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12 pages, 7074 KiB

Open AccessArticle

Design and Implementation of Quad-Port MIMO Antenna with Dual-Band Elimination Characteristics for Ultra-Wideband Applications

by Pawan Kumar, Shabana Urooj and Fadwa Alrowais

Appl. Sci. 2020, 10(5), 1715; https://doi.org/10.3390/app10051715 - 2 Mar 2020

Cited by 44 | Viewed by 5852

Abstract

A planar, microstrip line-fed, quad-port, multiple-input-multiple-output (MIMO) antenna with dual-band rejection features is proposed for ultra-wideband (UWB) applications. The proposed MIMO antenna design consists of four identical octagonal-shaped radiating elements, which are placed orthogonally to each other. The dual-band rejection property (3.5 GHz and 5.5 GHz corresponding to Wi-MAX and WLAN bands) was obtained by introducing a hexagonal-shaped complementary split-ring resonator (HCSRR) in the radiators of the designed antenna. The MIMO antenna was etched on low-cost FR-4 dielectric substrate of size 58 × 58 × 0.8 mm³. Isolation higher than 18 dB and envelope correlation coefficient (ECC) lesser than 0.07 was observed for the MIMO/diversity antenna in the operating range of 3–16 GHz. The presented four-port UWB MIMO antenna configuration was fabricated, and the experimental results validate the simulation outcomes. Full article

(This article belongs to the Special Issue Passive Planar Microwave Devices )

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17 pages, 10980 KiB

Open AccessArticle

Design of a Multi-Band Microstrip Textile Patch Antenna for LTE and 5G Services with the CRO-SL Ensemble

by Carlos Camacho-Gomez, Rocio Sanchez-Montero, Diego Martínez-Villanueva, Pablo-Luís López-Espí and Sancho Salcedo-Sanz

Appl. Sci. 2020, 10(3), 1168; https://doi.org/10.3390/app10031168 - 9 Feb 2020

Cited by 22 | Viewed by 4651

Abstract

A textile multi-band antenna for LTE and 5G communication services, composed by a rectangular microstrip patch, two concentric annular slots and a U-Shaped slot, is considered in this paper. In the ground plane, three sleeved meanders have been introduced to modify the surface current distribution, leading to a bandwidth improvement. The U-Shaped slot, the dual circular slots, and the meanders shape have been optimized by means of the Coral Reefs Optimization with Substrate Layer algorithm (CRO-SL). This population-based meta-heuristic approach is a kind of ensemble algorithm for optimization (multi-method), in which different search operators are considered within the algorithm. We show that the CRO-SL is able to obtain a robust multi-band textile antenna, including LTE and 5G frequency bands. For the optimization process, the CRO-SL is guided by means of a fitness function obtained after the antenna simulation by a specific simulation software for electromagnetic analysis in the high frequency range. Full article

(This article belongs to the Special Issue Passive Planar Microwave Devices )

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13 pages, 2935 KiB

Open AccessArticle

Monitoring of Huntington’s Disease Based on Wireless Sensing Technology

by Qiyu Zhu, Lei Guan, Muhammad Bilal Khan and Xiaodong Yang

Appl. Sci. 2020, 10(3), 870; https://doi.org/10.3390/app10030870 - 27 Jan 2020

Cited by 2 | Viewed by 2890

Abstract

Huntington’s disease (HD) is a rare genetic disorder that cannot be cured by current medical techniques. With the development of the disease, the life of patients will become more and more difficult. It is necessary to timely and effectively evaluate the development of the patient’s condition based on the patient’s clinical symptoms to help doctors to formulate a reasonable and effective treatment plan, alleviate the condition, and improve the quality of life, which reflects humane care. Currently, wearable devices or video surveillance are generally used to monitor the patients, and these schemes have some disadvantages. This paper presents a new method to monitor patients with HD using wireless sensing technology. Firstly, experimental data were collected by the self-developed microwave sensing platform (MSP), and then the data were preprocessed. Finally, support vector machine (SVM) and random forest (RF) algorithms were used to train the model. The MSP system continuously monitors patients in a non-contact way, which will not bring inconvenience to patients’ lives, and will not involve privacy issues. The experimental results show that the prediction accuracy of SVM can be as high as 98.0% and that of RF can be as high as 96.7%, which proves the feasibility of the technical scheme described in this paper. Full article

(This article belongs to the Special Issue Passive Planar Microwave Devices )

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10 pages, 5669 KiB

Open AccessCommunication

Electronically Controllable Phase Shifter with Progressive Impedance Transformation at K Band

by Mohamed T. ElKhorassani, Angel Palomares-Caballero, Antonio Alex-Amor, Cleofás Segura-Gómez, Pablo Escobedo, Juan F. Valenzuela-Valdés and Pablo Padilla

Appl. Sci. 2019, 9(23), 5229; https://doi.org/10.3390/app9235229 - 1 Dec 2019

Cited by 5 | Viewed by 5135

Abstract

This communication presents the design of a two-port electronically tunable phase shifter at K band. The phase shifter consists of a 3 dB hybrid coupler loaded with reflective phase-controllable circuits. The reflective circuits are formed by varactors and non-sequential impedance transformers which increase the operational bandwidth and the provided phase shift. The final phase shifter design is formed by two loaded-coupler stages of phase shifting to guarantee a complete phase turn. An 18 GHz phase shifter design with dynamic range of 600 degrees of phase shift is depicted in this document. The prototype is manufactured and validated through measurements showing good agreement with the simulation results. Full article

(This article belongs to the Special Issue Passive Planar Microwave Devices )

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Review

Jump to: Editorial, Research

30 pages, 13085 KiB

Open AccessFeature PaperReview

Planar Microwave Resonant Sensors: A Review and Recent Developments

by Jonathan Muñoz-Enano, Paris Vélez, Marta Gil and Ferran Martín

Appl. Sci. 2020, 10(7), 2615; https://doi.org/10.3390/app10072615 - 10 Apr 2020

Cited by 94 | Viewed by 7967

Abstract

Microwave sensors based on electrically small planar resonant elements are reviewed in this paper. By virtue of the high sensitivity of such resonators to the properties of their surrounding medium, particularly the dielectric constant and the loss factor, these sensors are of special interest (although not exclusive) for dielectric characterization of solids and liquids, and for the measurement of material composition. Several sensing strategies are presented, with special emphasis on differential-mode sensors. The main advantages and limitations of such techniques are discussed, and several prototype examples are reported, mainly including sensors for measuring the dielectric properties of solids, and sensors based on microfluidics (useful for liquid characterization and liquid composition). The proposed sensors have high potential for application in real scenarios (including industrial processes and characterization of biosamples). Full article

(This article belongs to the Special Issue Passive Planar Microwave Devices )

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