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20 pages, 9686 KiB

Open AccessArticle

Simulation-Based Approach to the Matching of a Dielectric-Filled Circular Waveguide Aperture

by Songyuan Xu, Jiwon Heo, Byoung-Kwon Ahn, Chan-Soo Lee and Bierng-Chearl Ahn

Sensors 2024, 24(3), 841; https://doi.org/10.3390/s24030841 - 28 Jan 2024

Cited by 3 | Viewed by 1612

The circular waveguide aperture or open-end radiator, one of the canonical antenna elements, can be filled with a dielectric material for miniaturization. With dielectric filling, the aperture reflection increases and impedance matching is necessary. This paper presents a simple but innovative simulation-based approach [...] Read more.

The circular waveguide aperture or open-end radiator, one of the canonical antenna elements, can be filled with a dielectric material for miniaturization. With dielectric filling, the aperture reflection increases and impedance matching is necessary. This paper presents a simple but innovative simulation-based approach to the aperture matching of a dielectric-filled circular waveguide aperture. By properly loading the aperture with two- or three-section dielectric rings, the impedance matching is possible over a wide frequency range starting slightly above the TE₁₁-mode cutoff and continuing upward. The material for the aperture matching is the same as that filling the waveguide. The proposed matching structure is analyzed and optimized using a simulation tool for the dielectric constant ε_r of the filling material ranging from 1.8 to 10. For ε_r ≥ 5, the unmatched reflection coefficient ranges from −6.0 dB to −0.9 dB while the matched reflection coefficient is from −20.4 dB to −10.0 dB. The impedance matching has been achieved over more than an octave bandwidth. Full article

(This article belongs to the Special Issue Advances in Microwave Communications and Radar Technologies)

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15 pages, 4091 KiB

Open AccessArticle

A New Technique for Broadband Matching of Open-Ended Rectangular Waveguide Radiator

by Ji-Won Heo, Songyuan Xu, Erdenesukh Altanzaya, Qiongyue Zhang, Chan-Soo Lee, Bierng-Chearl Ahn, Jae-Hyeong Ahn and Seong-Gon Choi

Sensors 2023, 23(22), 9176; https://doi.org/10.3390/s23229176 - 14 Nov 2023

Cited by 1 | Viewed by 2418

Abstract

The maximum reflection at an open end of a standard rectangular waveguide is about −10 dB in its operating frequency range. It is often used without matching. For critical applications, it is desirable to further reduce the reflection coefficient. In this paper, a [...] Read more.

The maximum reflection at an open end of a standard rectangular waveguide is about −10 dB in its operating frequency range. It is often used without matching. For critical applications, it is desirable to further reduce the reflection coefficient. In this paper, a new technique is presented for the broadband impedance matching of an open-ended rectangular waveguide. The proposed technique employs three thin capacitive matching elements placed at proper intervals via a low-loss dielectric material. The capacitance of, and distance between, the matching elements are optimized for broadband impedance matching using a simulation tool. Based on the proposed technique, two design examples are presented for the matching of a WR75 waveguide radiator. A reflection coefficient of less than −16 dB and −20 dB has been achieved over a ratio bandwidth of 2.13:1 and 1.62:1, respectively. Full article

(This article belongs to the Special Issue Advances in Microwave Communications and Radar Technologies)

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23 pages, 24695 KiB

Open AccessArticle

Triangular Sierpinski Microwave Band-Stop Resonators for K-Band Filtering

by Romolo Marcelli, Giovanni Maria Sardi, Emanuela Proietti, Giovanni Capoccia, Jacopo Iannacci, Girolamo Tagliapietra and Flavio Giacomozzi

Sensors 2023, 23(19), 8125; https://doi.org/10.3390/s23198125 - 27 Sep 2023

Cited by 4 | Viewed by 1306

Abstract

Triangular resonators re-shaped with Sierpinski geometry were designed, manufactured, and tested for potential applications in the K-Band. Prototypes of band-stop filters working around 20 GHz and 26 GHz, interesting for RADAR and satellite communications, were studied in a coplanar waveguide (CPW) configuration. Single [...] Read more.

Triangular resonators re-shaped with Sierpinski geometry were designed, manufactured, and tested for potential applications in the K-Band. Prototypes of band-stop filters working around 20 GHz and 26 GHz, interesting for RADAR and satellite communications, were studied in a coplanar waveguide (CPW) configuration. Single and coupled structures were analyzed to give evidence for: (i) the tuning of the resonance frequency by increasing the internal complexity of the triangle and (ii) resonance enhancement when coupled structures are considered. The exploited devices were part of the more extended family of metamaterial-inspired structures, and they were studied for their heuristic approach to the prediction of the spectrum using experimental results supported by electromagnetic simulations. As a result, a Sierpinski resonator, not only fed into but also fully embedded into a CPW environment, had a frequency response that was not easily determined by classical theoretical approaches. Full article

(This article belongs to the Special Issue Advances in Microwave Communications and Radar Technologies)

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15 pages, 8298 KiB

Open AccessArticle

An Improved Performance Radar Sensor for K-Band Automotive Radars

by Anwer S. Abd El-Hameed, Eman G. Ouf, Ayman Elboushi, Asmaa G. Seliem and Yuta Izumi

Sensors 2023, 23(16), 7070; https://doi.org/10.3390/s23167070 - 10 Aug 2023

Cited by 8 | Viewed by 2202

Abstract

This paper presents a new radar sensor configuration of a planar grid antenna array (PGAA) for automotive ultra-wideband (UWB) radar applications. For system realisation, the MIMO concept is adopted. The proposed antenna is designed to operate over the 24 GHz frequency band. It [...] Read more.

This paper presents a new radar sensor configuration of a planar grid antenna array (PGAA) for automotive ultra-wideband (UWB) radar applications. For system realisation, the MIMO concept is adopted. The proposed antenna is designed to operate over the 24 GHz frequency band. It is based on split-ring resonator (SRR) elements to enhance the operating bandwidth and increase the antenna gain, leading to a better-performing radar system. The PGAA consists of thirty-one radiating elements, in which each element excitation is obtained using a common transmission line centre fed by a 50 Ω coaxial probe. By introducing a superstrate dielectric layer at a distance of λ

/ 2

from the top of the antenna array, the PGAA gain and impedance bandwidth are further improved. The gain is improved by 2.7 dB to reach 16.5 dBi at 24 GHz, and the impedance bandwidth is enhanced to 9.3 GHz (37.7%). The measured impedance bandwidth of the proposed antenna array ranges from 20 GHz to 29.3 GHz for a reflection coefficient (

S_{11}

) of less than −10 dB. The proposed antenna is validated for automotive applications. Full article

(This article belongs to the Special Issue Advances in Microwave Communications and Radar Technologies)

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16 pages, 5280 KiB

Open AccessArticle

Meniscus-Corrected Method for Broadband Liquid Permittivity Measurements with an Uncalibrated Vector Network Analyzer

by Michał Kalisiak, Arkadiusz Lewandowski and Wojciech Wiatr

Sensors 2023, 23(12), 5401; https://doi.org/10.3390/s23125401 - 7 Jun 2023

Viewed by 1388

Abstract

We present a novel broadband permittivity characterization method for liquids measured in a semi-open vertically oriented test cell with an uncalibrated vector network analyzer. For this goal, we utilize three scattering matrices measured at different levels of liquid in the cell. With mathematical [...] Read more.

We present a novel broadband permittivity characterization method for liquids measured in a semi-open vertically oriented test cell with an uncalibrated vector network analyzer. For this goal, we utilize three scattering matrices measured at different levels of liquid in the cell. With mathematical operations, we remove the effects of systematic measurement errors caused by both the vector network analyzer and a meniscus shaping the top of the liquid samples in such a type of test cell. To the best authors’ knowledge, this is the first of such a calibration-independent method dealing with meniscus. We verify its validity by comparing our results with the data available in the literature and with the outcomes of our previously published calibration-dependent meniscus removal method (MR) for propan-2-ol (IPA), a 50% aqueous solution of IPA and distilled water. The new method yields results comparable with the MR method, at least for IPA and the IPA solution, revealing, however some problems when testing high-loss water samples. Nevertheless, it allows one to cut down on expenditures in the system calibration engaging skilled labor and expensive standards. Full article

(This article belongs to the Special Issue Advances in Microwave Communications and Radar Technologies)

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12 pages, 3558 KiB

Open AccessCommunication

Applicability of the Meniscus-Removal Method for Q-Band Liquid Characterization in Semi-Open Waveguide Cell

by Michał Kalisiak, Wojciech Wiatr and Radosław Papis

Sensors 2023, 23(12), 5390; https://doi.org/10.3390/s23125390 - 7 Jun 2023

Cited by 1 | Viewed by 970

Abstract

We present the broadband transmission-reflection meniscus-removal method for liquid characterization in a semi-open rectangular waveguide. The algorithm utilizes 2-port scattering parameters measured with a calibrated vector network analyzer for three states of the measurement cell: empty and filled with two liquid levels. The [...] Read more.

We present the broadband transmission-reflection meniscus-removal method for liquid characterization in a semi-open rectangular waveguide. The algorithm utilizes 2-port scattering parameters measured with a calibrated vector network analyzer for three states of the measurement cell: empty and filled with two liquid levels. The method enables the mathematical de-embedding of a symmetrical sample of a liquid, not distorted with a meniscus, and provision of its permittivity and permeability, as well as its height. We validate the method for propan-2-ol (IPA), a 50% aqueous solution of IPA, and distilled water in the Q-band (33–50 GHz). We investigate typical problems for in-waveguide measurements, such as phase ambiguity. Full article

(This article belongs to the Special Issue Advances in Microwave Communications and Radar Technologies)

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13 pages, 4010 KiB

Open AccessCommunication

Microwave Frequency Doubler with Improved Stabilization of Output Power

by Piotr Kwiatkowski, Michał Knioła and Zenon Szczepaniak

Sensors 2023, 23(7), 3598; https://doi.org/10.3390/s23073598 - 30 Mar 2023

Cited by 2 | Viewed by 2171

Abstract

The passive multipliers based on semiconductor diodes, most frequently a Schottky type, should be driven by a certain value of input power, where the conversion losses are optimal. This means that the variation in the input power level causes the change in the [...] Read more.

The passive multipliers based on semiconductor diodes, most frequently a Schottky type, should be driven by a certain value of input power, where the conversion losses are optimal. This means that the variation in the input power level causes the change in the output power level. A solution to this issue is the integration of an output power amplifier, which in the state of saturation provides quasi-stabilization of the output power. Practically, this approach gives an unsatisfactory performance: weak stabilization or narrow input power range. This paper comprises a concept of an active frequency multiplier with the use of one FET transistor and a special adaptive bias circuit in order to obtain a very wide input power range when the output power is stable. The principle of the operation, design guidelines, and measurement results have been presented for an example circuit of the frequency doubler. The results show the possibility to obtain up to 10 dB input power range for a 1 dB change in output power level without the use of additional amplifiers. Full article

(This article belongs to the Special Issue Advances in Microwave Communications and Radar Technologies)

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16 pages, 5011 KiB

Open AccessArticle

Deep-Learning-Based Antenna Alignment Prediction for Mobile Indoor Communication

by Árpád László Makara, Botond Tamás Csathó, András Rácz, Tamás Borsos, László Csurgai-Horváth and Bálint Péter Horváth

Sensors 2023, 23(7), 3375; https://doi.org/10.3390/s23073375 - 23 Mar 2023

Viewed by 2269

Abstract

A significant innovation for future indoor wireless networks is the use of the mmWave frequency band. However, an important challenge comes from the restricted propagation conditions in this band, which necessitates the use of beamforming and associated beam management procedures, including, for instance, [...] Read more.

A significant innovation for future indoor wireless networks is the use of the mmWave frequency band. However, an important challenge comes from the restricted propagation conditions in this band, which necessitates the use of beamforming and associated beam management procedures, including, for instance, beam tracking or beam prediction. A possible solution to the beam management problem is to use artificial-intelligence-based procedures to learn the hidden spatial propagation patterns of the channel and to use this knowledge to predict the best beam directions. In this paper, we present a deep-neural-network-based method that has memory that can be used to predict the best reception directions for moving users. The best direction is the highest expected signal level at the next moment. The resulting method allows for a user-side antenna management system. The result was evaluated using three different metrics, thus detailing not only its predictive ability, but also its usability. Full article

(This article belongs to the Special Issue Advances in Microwave Communications and Radar Technologies)

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13 pages, 2505 KiB

Open AccessArticle

Low-Frequency Noise Characteristics of (Al, Ga)As and Ga(As, Bi) Quantum Well Structures for NIR Laser Diodes

by Simona Armalytė, Justinas Glemža, Vytautas Jonkus, Sandra Pralgauskaitė, Jonas Matukas, Simona Pūkienė, Andrea Zelioli, Evelina Dudutienė, Arnas Naujokaitis, Andrius Bičiūnas, Bronislovas Čechavičius and Renata Butkutė

Sensors 2023, 23(4), 2282; https://doi.org/10.3390/s23042282 - 17 Feb 2023

Cited by 2 | Viewed by 2232

Abstract

Fabry–Perot laser diodes based on (Al, Ga)As and Ga(As, Bi) with single or multiple parabolic or rectangular-shaped quantum wells (QWs) emitting at the 780–1100 nm spectral range were fabricated and investigated for optimization of the laser QW design and composition of QWs. The [...] Read more.

Fabry–Perot laser diodes based on (Al, Ga)As and Ga(As, Bi) with single or multiple parabolic or rectangular-shaped quantum wells (QWs) emitting at the 780–1100 nm spectral range were fabricated and investigated for optimization of the laser QW design and composition of QWs. The laser structures were grown using the molecular beam epitaxy (MBE) technique on the n-type GaAs(100) substrate. The photolithography process was performed to fabricate edge-emitting laser bars of 5 μm by 500 μm in size. The temperature-dependent power-current measurements showed that the characteristic threshold current of the fabricated LDs was in the 60–120 mA range. Light and current characteristics were almost linear up to (1.2–2.0) I_th. Low-frequency 10 Hz–20 kHz electrical and optical noise characteristics were measured in the temperature range from 70 K to 290 K and showed that the low-frequency optical and electrical noise spectra are comprised of 1/f and Lorentzian-type components. The positive cross-correlation between optical and electrical fluctuations was observed. Full article

(This article belongs to the Special Issue Advances in Microwave Communications and Radar Technologies)

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11 pages, 5709 KiB

Open AccessArticle

Design of a Ku-Band Monopulse Antenna with a Truncated Reflector and an Open-Ended Waveguide Feed

by Ayodeji Matthew Monebi, Chan-Soo Lee, Bierng-Chearl Ahn and Seong-Gon Choi

Sensors 2023, 23(1), 118; https://doi.org/10.3390/s23010118 - 23 Dec 2022

Cited by 5 | Viewed by 4753

Abstract

This paper presents a design for a monopulse reflector antenna with asymmetric beamwidths for radar applications at the Ku band. The proposed design features a rectangular waveguide monopulse feed and a truncated parabolic reflector. An array of four open-ended rectangular waveguides were employed [...] Read more.

This paper presents a design for a monopulse reflector antenna with asymmetric beamwidths for radar applications at the Ku band. The proposed design features a rectangular waveguide monopulse feed and a truncated parabolic reflector. An array of four open-ended rectangular waveguides were employed to realize a compact monopulse feed. The reflector is cut in the H plane of the feed producing a wider beam in the azimuth plane. This type of pattern is useful in applications such as projectile tracking and airport surveillance. The design parameters for optimum performances are chosen at all stages of the design. The design and analysis have been carried out using the commercial simulation tool CST Studio Suite 2022. The directivity of the sum, elevation difference and azimuth difference channels of the reflector antenna are 32.1, 28.1, and 26.4 dB at 14 GHz; 30.9, 29, and 27.3 dB at 15 GHz; 31.7, 29.6, and 27.6 dB at 16 GHz; 31.6, 29.9, and 27.8 dB at 17 GHz. Full article

(This article belongs to the Special Issue Advances in Microwave Communications and Radar Technologies)

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