Special Issue "Antennas and Propagation Aspects for Emerging Wireless Communication Technologies"

A special issue of Electronics (ISSN 2079-9292). This special issue belongs to the section "Microwave and Wireless Communications".

Deadline for manuscript submissions: closed (15 November 2020).

Special Issue Editors

Prof. Dr. Dimitra I. Kaklamani
Website
Guest Editor
Microwave and Fiber Optics Laboratory, Intelligent Communications and Broadband Networks Laboratory, School of Electrical and Computer Engineering, National Technical University of Athens, 9 Heroon Polytechneiou str, Zografou, Athens 15780, Greece
Interests: Microwave Theory and Techniques, Microwave Systems, Computational Electromagnetism, Antennas, Wireless Communications, Radio Communications, Cellular Networks, Object-Oriented Computing, Distributed Processing, Security & Privacy
Prof. Dr. Athanasios Panagopoulos
Website
Guest Editor
School of Electrical and Computer Engineering, National Technical University of Athens, 9 Heroon Polytechneiou str, Zografou, Athens 15780, Greece
Interests: wireless and satellite communication systems; radio communications; cellular networks; software defined radios and software-defined networks; optimization; channel modeling; cyber-physical systems; high-throughput radio systems
Special Issues and Collections in MDPI journals
Prof. Dr. Panagiotis Gkonis
Website
Guest Editor
Αssistant Professor, National and Kapodistrian University of Athens, Athens, Greece
Interests: 5G wireless communications; radio communications; cellular networks; MIMO systems; adaptive antennas; LTE; cross-layer design
Special Issues and Collections in MDPI journals

Special Issue Information

Dear Colleagues,

The roadmap towards the design and implementation of next-generation broadband wireless networks is inextricably connected with the provision of even higher data rates to mobile users, delivery of zero latency multimedia content and the interconnection of heterogeneous services. The aim is to provide an environment in which sensors, appliances, cars, and drones will communicate with each other via the cellular network. In order to accommodate such communications, the cellular network has to dramatically increase its capacity. Recently, the wireless communications community has introduced the concept of 5G – a new generation of mobile wireless technology that will deliver multi-gigabit-per-second data speeds, with orders of magnitude more capacity and lower latency than today’s wireless systems. Numerous challenges lie ahead in the antenna and propagation fields such as low cost, intelligent antennas, and new radio propagation modeling and prediction techniques for future wireless networks must emerge to support the new frequency bands and wireless system architectures.

In this context, promising solutions include among others mmWave beamforming, massive MIMO techniques, and distributed antenna systems that shift today’s perception of wireless access networks (cellular structures with fixed base station locations) to a user or even service-oriented approach.

The main aim of this Special Issue is to seek high-quality submissions that highlight emerging applications and address recent breakthroughs in the design and implementation of advanced antenna components and novel propagation models in order to support high data rate transmission in the context of 5G and satellite networks and also the accurate evaluation of the new architectures.

Topics of interest include, but are not limited to the following:

  • Multi-beam antenna technologies for 5G wireless communications
  • Millimeter wave (mmWave) and THz antennas for 5G wireless communications
  • Propagation model at mmWave and THz bands
  • Compact antenna arrays for massive MIMO systems
  • mmWave and large-scale MIMO channel model
  • Antennas for implantable systems and IoT applications
  • Advanced antennas and transceivers for full-duplex communication
  • Distributed antenna systems for 5G multi-user networks
  • mmWave and THz cooperative relays for coverage extension

Prof. Dr. Dimitra I. Kaklamani
Prof. Dr. Athanasios Panagopoulos
Dr. Panagiotis Gkonis
Guest Editors

Manuscript Submission Information

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 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.

Published Papers (14 papers)

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Research

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Open AccessFeature PaperArticle
Scaled Modeling and Measurement for Studying Radio Wave Propagation in Tunnels
Electronics 2021, 10(1), 53; https://doi.org/10.3390/electronics10010053 - 31 Dec 2020
Abstract
The subject of radio wave propagation in tunnels has gathered attention in recent years, mainly regarding the fading phenomena caused by internal reflections. Several methods have been suggested to describe the propagation inside a tunnel. This work is based on the ray tracing [...] Read more.
The subject of radio wave propagation in tunnels has gathered attention in recent years, mainly regarding the fading phenomena caused by internal reflections. Several methods have been suggested to describe the propagation inside a tunnel. This work is based on the ray tracing approach, which is useful for structures where the dimensions are orders of magnitude larger than the transmission wavelength. Using image theory, we utilized a multi-ray model to reveal non-dimensional parameters, enabling measurements in down-scaled experiments. We present the results of field experiments in a small concrete pedestrian tunnel with smooth walls for radio frequencies (RF) of 1, 2.4, and 10 GHz, as well as in a down-scaled model, for which millimeter waves (MMWs) were used, to demonstrate the roles of the frequency, polarization, tunnel dimensions, and dielectric properties on the wave propagation. The ray tracing method correlated well with the experimental results measured in the tunnel as well as in a scale model. Full article
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Open AccessEditor’s ChoiceArticle
High-Gain Planar Array of Reactively Loaded Antennas for Limited Scan Range Applications
Electronics 2020, 9(9), 1376; https://doi.org/10.3390/electronics9091376 - 25 Aug 2020
Abstract
This paper proposes a novel high-gain antenna element that can be used in antenna arrays that only require a limited scan range. Each high-gain antenna element uses a linear sub-array of highly-coupled open-ended waveguides. The active central element of this sub-array is directly [...] Read more.
This paper proposes a novel high-gain antenna element that can be used in antenna arrays that only require a limited scan range. Each high-gain antenna element uses a linear sub-array of highly-coupled open-ended waveguides. The active central element of this sub-array is directly fed, while the remaining passive waveguides are reactively loaded. The loads are implemented by short-circuits positioned at various distances from the radiating aperture. The short-circuit positions control the radiation pattern properties and the scattering parameters of the array. The proposed sub-array antenna element is optimized in the presence of the adjacent elements and provides a high gain and a flat-top main lobe. The horizontal distance between the sub-array centers is large in terms of wavelengths, which leads to limited scanning capabilities in the E-plane. However, along the vertical axis, the element spacing is around 0.6 wavelength at the central frequency that is beneficial to achieve a wider scan range in the H-plane. We show that the sub-array radiation pattern sufficiently filters the grating lobes which appear in the array factor along the E-plane. To demonstrate the performance of the proposed array configuration, an array operating at 28.0 GHz is designed. The designed array supports scan angles up to ±7.5° along the E-plane and ±24.2° along the H-plane Full article
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Open AccessFeature PaperArticle
Design of True Time Delay Millimeter Wave Beamformers for 5G Multibeam Phased Arrays
Electronics 2020, 9(8), 1331; https://doi.org/10.3390/electronics9081331 - 18 Aug 2020
Cited by 2
Abstract
Millimeter wave (mm-Wave) technology is likely the key enabler of 5G and early 6G wireless systems. The high throughput, high capacity, and low latency that can be achieved, when mm-Waves are utilized, makes them the most promising backhaul as well as fronthaul solutions [...] Read more.
Millimeter wave (mm-Wave) technology is likely the key enabler of 5G and early 6G wireless systems. The high throughput, high capacity, and low latency that can be achieved, when mm-Waves are utilized, makes them the most promising backhaul as well as fronthaul solutions for the communication between small cells and base stations or between base stations and the gateway. Depending on the channel properties different communication systems (e.g., beamforming and MIMO) can accordingly offer the best solution. In this work, our goal is to design millimeter wave beamformers for switched beam phased arrays as hybrid beamforming stages. Specifically, three different analog beamforming techniques for the frequency range of 27–33 GHz are presented. First, a novel compact multilayer Blass matrix is proposed. Second, a modified dummy-ports free, highly efficient Rotman lens is introduced. Finally, a three-layer true-time-delay tree topology inspired by microwave photonics is presented. Full article
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Open AccessArticle
Coplanar Stripline-Fed Wideband Yagi Dipole Antenna with Filtering-Radiating Performance
Electronics 2020, 9(8), 1258; https://doi.org/10.3390/electronics9081258 - 06 Aug 2020
Abstract
In this article, a wideband filtering-radiating Yagi dipole antenna with the coplanar stripline (CPS) excitation form is investigated, designed, and fabricated. By introducing an open-circuited half-wavelength resonator between the CPS structure and dipole, the gain selectivity has been improved and the operating bandwidth [...] Read more.
In this article, a wideband filtering-radiating Yagi dipole antenna with the coplanar stripline (CPS) excitation form is investigated, designed, and fabricated. By introducing an open-circuited half-wavelength resonator between the CPS structure and dipole, the gain selectivity has been improved and the operating bandwidth is simultaneously enhanced. Then, the intrinsic filtering-radiating performance of Yagi antenna is studied. By implementing a reflector on initial structure, it is observed that two radiation nulls appear at both lower and upper gain passband edges, respectively. Moreover, in order to improve the selectivity in the upper stopband, a pair of U-shaped resonators are employed and coupled to CPS directly. As such, the antenna design is finally completed with expected characteristics. To verify the feasibility of the proposed scheme, a filtering Yagi antenna prototype with a wide bandwidth covering from 3.64 GHz to 4.38 GHz is designed, fabricated, and measured. Both simulated and measured results are found to be in good agreement, thus demonstrating that the presented antenna has the performances of high frequency selectivity and stable in-band gain. Full article
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Open AccessArticle
A Novel High Gain Wideband MIMO Antenna for 5G Millimeter Wave Applications
Electronics 2020, 9(6), 1031; https://doi.org/10.3390/electronics9061031 - 22 Jun 2020
Cited by 5
Abstract
A compact tree shape planar quad element Multiple Input Multiple Output (MIMO) antenna bearing a wide bandwidth for 5G communication operating in the millimeter-wave spectrum is proposed. The radiating element of the proposed design contains four different arcs to achieve the wide bandwidth [...] Read more.
A compact tree shape planar quad element Multiple Input Multiple Output (MIMO) antenna bearing a wide bandwidth for 5G communication operating in the millimeter-wave spectrum is proposed. The radiating element of the proposed design contains four different arcs to achieve the wide bandwidth response. Each radiating element is backed by a 1.57 mm thicker Rogers-5880 substrate material, having a loss tangent and relative dielectric constant of 0.0009 and 2.2, respectively. The measured impedance bandwidth of the proposed quad element MIMO antenna system based on 10 dB criterion is from 23 GHz to 40 GHz with a port isolation of greater than 20 dB. The measured radiation patterns are presented at 28 GHz, 33 GHz and 38 GHz with a maximum total gain of 10.58, 8.87 and 11.45 dB, respectively. The high gain of the proposed antenna further helps to overcome the atmospheric attenuations faced by the higher frequencies. In addition, the measured total efficiency of the proposed MIMO antenna is observed above 70% for the millimeter wave frequencies. Furthermore, the MIMO key performance metrics such as Mean Effective Gain (MEG) and Envelope Correlation Coefficient (ECC) are analyzed and found to conform to the required standard of MEG < 3 dB and ECC < 0.5. A prototype of the proposed quad element MIMO antenna system is fabricated and measured. The experimental results validate the simulation design process conducted with Computer Simulation Technology (CST) software. Full article
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Open AccessFeature PaperArticle
Radio Network Planning towards 5G mmWave Standalone Small-Cell Architectures
Electronics 2020, 9(2), 339; https://doi.org/10.3390/electronics9020339 - 16 Feb 2020
Cited by 4
Abstract
The 5G radio networks have introduced major changes in terms of service requirements and bandwidth allocation compared to cellular networks to date and hence, they have made the fundamental radio planning problem even more complex. In this work, the focus is on providing [...] Read more.
The 5G radio networks have introduced major changes in terms of service requirements and bandwidth allocation compared to cellular networks to date and hence, they have made the fundamental radio planning problem even more complex. In this work, the focus is on providing a generic analysis for this problem with the help of a proper multi-objective optimization algorithm that considers the main constraints of coverage, capacity and cost for high-capacity scenarios that range from dense to ultra-dense mmWave 5G standalone small-cell network deployments. The results produced based on the above analysis demonstrate that the denser the small-cell deployment, the higher the area throughput, and that a sectored microcell configuration can double the throughput for ultra-dense networks compared to dense networks. Furthermore, dense 5G networks can actually have cell radii below 400 m and down to 120 m for the ultra-dense sectored network that also reached spectral efficiency 9.5 bps/Hz/Km2 with no MIMO or beamforming. Full article
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Open AccessArticle
4-Port MIMO Antenna with Defected Ground Structure for 5G Millimeter Wave Applications
Electronics 2020, 9(1), 71; https://doi.org/10.3390/electronics9010071 - 01 Jan 2020
Cited by 13
Abstract
We present a 4-port Multiple-Input-Multiple-Output (MIMO) antenna array operating in the mm-wave band for 5G applications. An identical two-element array excited by the feed network based on a T-junction power combiner/divider is introduced in the reported paper. The array elements are rectangular-shaped slotted [...] Read more.
We present a 4-port Multiple-Input-Multiple-Output (MIMO) antenna array operating in the mm-wave band for 5G applications. An identical two-element array excited by the feed network based on a T-junction power combiner/divider is introduced in the reported paper. The array elements are rectangular-shaped slotted patch antennas, while the ground plane is made defected with rectangular, circular, and a zigzag-shaped slotted structure to enhance the radiation characteristics of the antenna. To validate the performance, the MIMO structure is fabricated and measured. The simulated and measured results are in good coherence. The proposed structure can operate in a 25.5–29.6 GHz frequency band supporting the impending mm-wave 5G applications. Moreover, the peak gain attained for the operating frequency band is 8.3 dBi. Additionally, to obtain high isolation between antenna elements, the polarization diversity is employed between the adjacent radiators, resulting in a low Envelope Correlation Coefficient (ECC). Other MIMO performance metrics such as the Channel Capacity Loss (CCL), Mean Effective Gain (MEG), and Diversity gain (DG) of the proposed structure are analyzed, and the results indicate the suitability of the design as a potential contender for imminent mm-wave 5G MIMO applications. Full article
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Open AccessArticle
Design of a Wideband L-Shape Fed Microstrip Patch Antenna Backed by Conductor Plane for Medical Body Area Network
Electronics 2020, 9(1), 21; https://doi.org/10.3390/electronics9010021 - 24 Dec 2019
Abstract
This paper describes a compact patch antenna intended for medical body area network. The antenna is fed using a proximity coupling scheme to support the antenna that radiates in the free space and on the human body at the 2.45 GHz ISM band. [...] Read more.
This paper describes a compact patch antenna intended for medical body area network. The antenna is fed using a proximity coupling scheme to support the antenna that radiates in the free space and on the human body at the 2.45 GHz ISM band. The conductor plane is placed 2 mm or 0.0163λ00 is free space wavelength at 2.45 GHz) below the antenna to reduce backward radiation to the human body. Separation distance must be kept above 2 mm, otherwise, gain of the proposed antenna decreases when antenna is situated on the human body. The L-shape feed line is introduced to overcome impedance mismatch caused by the compact structure. The coupling gap between the proposed antenna and the length of the L-shape feed line are optimized to generate dual resonances mode for wide impedance bandwidth. Simulation results show that specific absorption rate (SAR) of the proposed antenna with L-shape feed line is lower than conventional patch antenna with direct microstrip feed line. The proposed antenna achieves impedance bandwidth of 120 MHz (4.89%) at the center frequency of 2.45 GHz. The maximum gain in the broadside direction is 6.2 dBi in simulation and 5.09 dBi in measurement for antenna in the free space. Wide impedance bandwidth and radiation patterns insensitive to the presence of human body are achieved, which meets the requirement of IoT-based wearable sensor. Full article
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Open AccessFeature PaperArticle
Full-Duplex NOMA Transmission with Single-Antenna Buffer-Aided Relays
Electronics 2019, 8(12), 1482; https://doi.org/10.3390/electronics8121482 - 04 Dec 2019
Cited by 3
Abstract
The efficient deployment of fifth generation and beyond networks relies upon the seamless combination of recently introduced transmission techniques. Furthermore, as multiple network nodes exist in dense wireless topologies, low-complexity implementation should be promoted. In this work, several wireless communication techniques are considered [...] Read more.
The efficient deployment of fifth generation and beyond networks relies upon the seamless combination of recently introduced transmission techniques. Furthermore, as multiple network nodes exist in dense wireless topologies, low-complexity implementation should be promoted. In this work, several wireless communication techniques are considered for improving the sum-rate performance of cooperative relaying non-orthogonal multiple access (NOMA) networks. For this purpose, an opportunistic relay selection algorithm is developed, employing single-antenna relays to achieve full-duplex operation by adopting the successive relaying technique. In addition, as relays are equipped with buffers, flexible half-duplex transmission can be performed when packets reside in the buffers. The proposed buffer-aided and successive single-antenna (BASSA-NOMA) algorithm is presented in detail and its operation and practical implementation aspects are thoroughly analyzed. Comparisons with other relevant algorithms illustrate significant performance gains when BASSA-NOMA is employed without incurring high implementation complexity. Full article
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Open AccessArticle
Site-Specific Propagation Loss Prediction in 4.9 GHz Band Outdoor-to-Indoor Scenario
Electronics 2019, 8(12), 1398; https://doi.org/10.3390/electronics8121398 - 23 Nov 2019
Cited by 1
Abstract
Owing to the widespread use of smartphones and various cloud services, user traffic in cellular networks is rapidly increasing. Especially, the traffic congestion is severe in urban areas, and effective service-cell planning is required in the area for efficient radio resource usage. Because [...] Read more.
Owing to the widespread use of smartphones and various cloud services, user traffic in cellular networks is rapidly increasing. Especially, the traffic congestion is severe in urban areas, and effective service-cell planning is required in the area for efficient radio resource usage. Because many users are also inside high buildings in the urban area, the knowledge of propagation loss characteristics in the outdoor-to-indoor (O2I) scenario is indispensable for the purpose. The ray-tracing simulation has been widely used for service-cell planning, but it has a problem that the propagation loss tends to be underestimated in a typical O2I scenario in which the incident radio waves penetrate indoors through building windows. In this paper, we proposed the extension method of the ray-tracing simulation to solve the problem. In the proposed method, the additional loss factors such as the Fresnel zone shielding loss and the transmission loss by the equivalent dielectric plate were calculated for respective rays to eliminate the penetration loss prediction error. To evaluate the effectiveness of the proposed method, we conducted radio propagation measurements in a high-building environment by using the developed unmanned aerial vehicle (UAV)-based measurement system. The results showed that the penetration loss of direct and reflection rays was significantly underestimated in the ray-tracing simulation and the proposed method could correct the problem. The mean prediction error was improved from 7.0 dB to −0.5 dB, and the standard deviation was also improved from 8.2 dB to 5.3 dB. The results are expected to be utilized for actual service-cell planning in the urban environment. Full article
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Open AccessFeature PaperArticle
Spectrum Occupancy Measurements and Analysis in 2.4 GHz WLAN
Electronics 2019, 8(9), 1011; https://doi.org/10.3390/electronics8091011 - 10 Sep 2019
Cited by 4
Abstract
High time resolution spectrum occupancy measurements and analysis are presented for 2.4 GHz WLAN signals. A custom-designed wideband sensing engine records the received power of signals, and its performance is presented to select the decision threshold required to define the channel state (busy/idle). [...] Read more.
High time resolution spectrum occupancy measurements and analysis are presented for 2.4 GHz WLAN signals. A custom-designed wideband sensing engine records the received power of signals, and its performance is presented to select the decision threshold required to define the channel state (busy/idle). Two sets of measurements are presented where data were collected using an omni-directional and directional antenna in an indoor environment. Statistics of the idle time windows in the 2.4 GHz WLAN are analyzed using a wider set of distributions, which require fewer parameters to compute and are more practical for implementation compared to the widely-used phase type or Gaussian mixture distributions. For the omni-directional antenna, it was found that the lognormal and gamma distributions can be used to model the behavior of the idle time windows under different network traffic loads. In addition, the measurements show that the low time resolution and angle of arrival affect the statistics of the idle time windows. Full article
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Open AccessArticle
Time Domain Performance of Reconfigurable Filter Antenna for IR-UWB, WLAN, and WiMAX Applications
Electronics 2019, 8(9), 1007; https://doi.org/10.3390/electronics8091007 - 09 Sep 2019
Cited by 1
Abstract
A novel reconfigurable filter antenna with three ports for three dependent switchable states for impulse radio-ultrawideband (IR-UWB)/wireless local area network (WLAN)/worldwide interoperability for microwave access (WiMAX) applications is presented in this paper. Three positive-intrinsic-negative diodes, controlled by direct current, are employed to realize [...] Read more.
A novel reconfigurable filter antenna with three ports for three dependent switchable states for impulse radio-ultrawideband (IR-UWB)/wireless local area network (WLAN)/worldwide interoperability for microwave access (WiMAX) applications is presented in this paper. Three positive-intrinsic-negative diodes, controlled by direct current, are employed to realize frequency reconfiguration of one ultra-wideband state and two narrowband states (2.4 GHz and 3.5 GHz). The time domain characteristic of the proposed antenna in the ultra-wideband state is studied, because of the features of the IR-UWB system. The time domain analysis shows that the reconfigurable filtering antenna in the wideband state performs similarly to the original UWB antenna. The compact size, low cost, and expanded reconfigurable filtering features make it suitable for IR-UWB systems that are integrated with WLAN/WiMAX communications. Full article
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Open AccessArticle
A Low-Cost CPW-Fed Multiband Frequency Reconfigurable Antenna for Wireless Applications
Electronics 2019, 8(8), 900; https://doi.org/10.3390/electronics8080900 - 14 Aug 2019
Cited by 11
Abstract
A novel, cedar-shaped, coplanar waveguide-fed frequency reconfigurable antenna is proposed. The presented antenna uses low-cost FR4 substrate with a thickness of 1.6 mm. Four PIN diodes are inserted on the antenna surface to variate the current distribution and alter the resonant frequencies with [...] Read more.
A novel, cedar-shaped, coplanar waveguide-fed frequency reconfigurable antenna is proposed. The presented antenna uses low-cost FR4 substrate with a thickness of 1.6 mm. Four PIN diodes are inserted on the antenna surface to variate the current distribution and alter the resonant frequencies with different combinations of switches. The proposed antenna is fabricated and measured for all states, and a good agreement is seen between measured and simulated results. This antenna resonates within the range of 2 GHz to 10 GHz, covering the major wireless applications of aviation service, wireless local area network (WLAN), worldwide interoperability for microwave access (WiMAX), long distance radio telecommunications, and X-band satellite communication. The proposed antenna works resourcefully with reasonable gain, significant bandwidth, directivity, and reflection coefficient. The proposed multiband reconfigurable antenna will pave the way for future wireless communications including WLAN, WiMAX, and possibly fifth-generation (5G) communication. Full article
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Review

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Open AccessFeature PaperReview
Different Antenna Designs for Non-Contact Vital Signs Measurement: A Review
Electronics 2019, 8(11), 1294; https://doi.org/10.3390/electronics8111294 - 06 Nov 2019
Cited by 3
Abstract
Cardiopulmonary activity measured through contactless means is a hot topic within the research community. The Doppler radar is an approach often used to acquire vital signs in real time and to further estimate their rates, in a remote way and without requiring direct [...] Read more.
Cardiopulmonary activity measured through contactless means is a hot topic within the research community. The Doppler radar is an approach often used to acquire vital signs in real time and to further estimate their rates, in a remote way and without requiring direct contact with subjects. Many solutions have been proposed in the literature, using different transceivers and operation modes. Nonetheless, all different strategies have a common goal: enhance the system efficiency, reduce the manufacturing cost, and minimize the overall size of the system. Antennas are a key component for these systems since they can influence the radar robustness directly. Therefore, antennas must be designed with care, facing several trade-offs to meet all the system requirements. In this sense, it is necessary to define the proper guidelines that need to be followed in the antenna design. In this manuscript, an extensive review on different antenna designs for non-contact vital signals measurements is presented. It is intended to point out and quantify which parameters are crucial for the optimal radar operation, for non-contact vital signs’ acquisition. Full article
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