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A dual semicircular microstrip patch antenna implemented on a biodegradable substrate is presented for operation in the [863–873] MHz and [2.4–2.5] GHz frequency bands. To cover these frequency bands, two semicircular patches are compactly integrated onto a biodegradable cork tile, commonly found as support in laminate flooring, serving as a substrate. Thereby, the antenna tile may be seamlessly embedded as a sublayer of the floor structure. A higher-order mode is generated by applying via pins in the antenna topology to produce a conical radiation pattern with a null at broadside and sectoral coverage in the vertical plane. As such, the concealed floor antenna covers all azimuth angles of arrival in smart houses. The antenna performance is fully validated, also when the tile is covered by different polyvinyl chloride sheets. Owing to the supplementary design margins, the antenna impedance bandwidth remains covered. Moreover, the radiation patterns are measured in various elevation planes. Under stand-alone conditions, a radiation efficiency and a maximum gain of 74.3 $\%$ and 5.8 dBi at 2.45 GHz and 48.1 $\%$ and 2 dBi at 868 MHz are, respectively, obtained. Its omnidirectional coverage in the horizontal plane, stable performance on the inhomogeneous and biocompatible cork substrate and for various inhomogeneous superstrates, and its low-profile integration make the proposed antenna an excellent candidate for smart floors and smart houses.

Base station conformance testing Over-the-air has recently been adopted in 5G3GPP standardization. For an integrated Active antenna system, base band algorithms, radio and antenna parts are integrated into one enclosure, without access to physical antenna ports. Therefore the entire system needs to be tested Over-the-air. This approach comes with a set of challenges and changes in the requirements definitions compared to traditional conducted testing of a single transceiver branch. Relevant Over-the-air conformance parameters for Active antenna systems are discussed here as well as challenges, possibilities and agreed solutions of the corresponding measurements. Specifically, sparse sampling and near field measurements as well as Reverberation chambers are discussed. Moreover, the role of Measurement uncertainty in the standards is described.

A novel substrate-integrated waveguide parasitic compact antenna array without feeding network is proposed for operation in the 24 GHz Industrial, Scientific, and Medical (ISM) band. Inductive windows are exploited to couple adjacent array elements, eliminating the need for a conventional elaborate feeding network, consisting of multiple stages of power dividers. As such, this coupling technique results in an extremely compact design, facilitating integration in close proximity with active devices. Moreover, the insertion loss and the parasitic radiation from the feeding network are significantly reduced, improving the overall energy efficiency. The amplitude distribution is optimized by tuning the amount of coupling between the adjacent array elements, effectively eradicating the side lobes in the radiation pattern’s H-plane and minimizing them in the E-plane. An impedance bandwidth of 315 MHz is obtained, covering the entire 24 GHz ISM band. A 3 dB beamwidth of 43° and 46° in the H-plane and E-plane, respectively, is measured, with a broadside array gain of 10.2 dBi.

Research over the last decade has shown the potential of smart wearables in lab settings. Following the current success of smart watches [1], activity trackers [2], [3], and fitness trackers [4], recent startups are breaking through with commercial products integrating smart functionality into traditional pieces of clothing. Some representative examples include the smart sock by Owlet [5], which tracks infants? heart rate and oxygen levels; connected footware by Digitsole [6]; anti-back-pain apparel by Percko [7]; smart bikinis, dresses, and swimsuits by Spinali Design [8]; and the Iilation jacket by Teiimo [9].

ATTO targets wireless networking at fiber speed: 100 Gb/s/m2 with latencies smaller than 10 μs. To provide this tremendous wireless capacity, ultrasmall floor-integrated cells are proposed. In this way, short-reach communication can be established, reducing the effect of interference and providing full frequency reuse in the wireless domain. Radio frequency (RF)-over-fiber coherent communication and a dedicated 2-D passive optical network structure support the interconnection and selection of the cells and minimize the required transceiver electronics. To evaluate the feasibility of the proposed architecture, key principles are validated at lower frequency bands. Two main building blocks are addressed in this paper: a fully passive opto-antenna to prove that a passive remote antenna head can be realized owing to the short transmission distances. Furthermore, a low-cost RF-over-fiber system is demonstrated: sigma–delta modulation drives nonlinear optical modulators, such as electroabsorption modulators and vertical-cavity surface-emitting lasers, using a digital transmitter while remaining compatible with the passive opto-antenna. Finally, two important properties of the ATTO floor are evaluated. The exposure of a human body model to RF fields by the antenna floor is evaluated. Measurements ensure a 200-fold margin with respect to the International Commission on Non-Ionizing Radiation Protection basic restriction. To guarantee that multiple devices can communicate with the ATTO floor simultaneously, the interference between cells spaced 300 mm apart was evaluated.

The accurate characterisation of textile materials to be used as a dielectric substrate in wearable systems is fundamental. However, little information can be found on the electromagnetic properties of regular textiles. Woven, knits and non-wovens are inhomogeneous, highly porous, compressible and easily influenced by the environmental hygrometric conditions, making their electromagnetic characterisation difficult. For these reasons, there is no standard method to measure the dielectric properties of textiles. This chapter presents a survey on the evolution of flexible antennas and the textile materials used to manufacture them. Besides, it gives an overview of several methods used to characterise the permittivity of textile materials. Furthermore, it presents and applies a resonator-based experimental technique to characterise textile materials. This experimental technique is based on the theory of resonant methods and consists in calculating the electromagnetic parameters of the material under test (MUT), at a single frequency, by measuring the shift in frequency and the value of Q-factor of one resonator board with a microstrip patch antenna. To validate the experimental characterisation method, four textile antennas have been designed to resonate in the 2.45 GHz ISM band. This bandwidth (BW) also supports the Wireless Local Area Network (WLAN), Bluetooth and Short Range Communication Systems (SRCS) applications. All antennas operated in the targeted frequency band and showed excellent agreement between simulated and measured parameters, supporting the validation of this method. The resonator-based experimental technique proved to be an efficient, simple, easy and fast technique for the characterisation of electromagnetic propertiesof textile materials for the development of wearable antennas and body-centric communication.

Electromagnetic characterization of materials applied in wearable components is of paramount importance for the design and production of reliable devices. Therefore, we propose a novel approach that compares simulations and measurements performed by a resonance-perturbation method. An inset-fed patch antenna operating in the vicinity of the 2.45-GHz Industrial, Scientific, and Medical frequency band enables us to quickly estimate the properties of a given substrate sample. First, the two frequency values at which the simulated return loss peak of the fixture crosses a given threshold value are modeled as polynomial functions of the material's relative permittivity and loss tangent. Then, the comparison between modeled and measured frequencies yields the electromagnetic properties of the material. The approach is validated by characterizing the high-frequency laminate on which the antenna is implemented. Next, the method is applied to several textile materials of interest. It is shown that the proposed technique is fast, precise, and nondestructive. As such, it is suitable for integration into an assembly line, where substrate samples are first quickly characterized before being used in the production of the actual antennas.

One of the many adverse effects modifying the performance of textile antennas in real operating conditions is substrate compression. Therefore, this communication presents a stochastic collocation method (SCM) that either relies on the generalized polynomial chaos (gPC) expansion or on a novel Hermite-Pade approximant. The method is introduced to rigorously quantify the effect of random variations in the height and the permittivity of the substrate on the figures of merit of a textile antenna. Next, the joint height and permittivity probability distribution of a compressible substrate are characterized by means of a new measurement setup based on a resonant-perturbation technique. Finally, the method is validated for a probe-fed GPS textile antenna. It is shown that Hermite-Pade approximants model the highly nonlinear relationship between these substrate random variables and the figures of merit of the antenna more efficiently than the gPC. Moreover, a Kolmogorov–Smirnoff test proves that the resulting distributions of the antenna’s figures of merit are as accurate as those obtained by means of a Monte-Carlo (MC) analysis, with demonstrated speedup factors up to 123.

An advanced transmit remote opto-antenna unit is proposed that accomplishes impedance matching between a photodetector and a low-profile antenna in a specified frequency bandwidth, without requiring an area-consuming matching network. This results in a highly compact design, which also avoids the losses and spurious radiation by such an electrically large matching circuit. Instead, the photodetector is almost directly connected to the antenna, which is designed as a conjugate load, such that the extracted and radiated power are optimized. The required input impedance for the antenna is obtained by adopting a half-mode air-filled suhstrate-integrated-waveguide topology, which also exhibits excellent radiation efficiency. The proposed unit omits electrical amplifiers and is, therefore, completely driven by the signal supplied by an optical fiber when deployed in an analog optical link, except for an externally supplied photodetector bias voltage. Such a highly cost-effective, power efficient and reliable unit is an important step in making innovative wireless communication systems, which deploy extremely dense attocells of 15 cm x 15 cm, technically and economically feasible. As a validation, a prototype, operating in the Unlicensed National Information Infrastructure radio bands (5.15 GHz-5.85 GHz), is constructed and its radiation properties are characterized in free-space conditions. After normalizing with respect to the optical source's slope efficiency, a maximum boresight gain of 12.0 dBi and a -3 dB gain bandwidth of 1020 MHz (18.6 %) are observed. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

A multi-band body-worn distributed exposure meter (BWDM) is designed and calibrated for diffuse fields in a reverberation chamber (RC) for personal exposure assessment in indoor environments. The BWDM uses 22 nodes distributed over the torso and measures the incident power density ( $S_{\mathrm{ inc}}$ ) on body for 11 telecommunication bands in the frequency range of 790–5513 MHz. In order to calibrate the measurement device in diffuse fields, a protocol is proposed for on-body calibration of the BWDM. This protocol is applicable to wearable personal exposure meters in general. The BWDM and the proposed calibration protocol are validated in five indoor locations and five frequency bands (the downlink bands at 800, 900, 1800, and 2100 MHz as well as Wi-Fi 2 GHz) using a tri-axial broadband antenna and a spectrum analyzer (SA). The calibration shows that the BWDM has a relatively low measurement uncertainty with a 68% confidence interval on its antenna apertures, in the range 3.4–5.5 dB. A maximum difference of 0.9 dB is obtained for the total exposure in the test areas between the measurements of the BWDM and SA, which is an excellent agreement.

A novel dual-band substrate-integrated waveguide (SIW) antenna array topology is proposed for operation in the 28 and 38 GHz frequency bands. Four miniaturized quarter-mode SIW cavities are tightly coupled, causing mode bifurcation, and yielding an antenna topology with four distinct resonance frequencies. A pair of resonances is assigned to both the 28 and 38 GHz band, achieving wideband operation in both frequency ranges. Moreover, owing to the exploited miniaturization technique, an extremely compact array topology is obtained, facilitating easy and straightforward integration. The computer-aided design process yields a four-element antenna array that entirely covers the 28 GHz band (27.5-29.5 GHz) and 38 GHz band (37.0-38.6 GHz) with a measured impedance bandwidth of 3.65 and 2.19 GHz, respectively. A measured broadside gain of 10.1 dBi, a radiation efficiency of 75.75% and a 3 dB beamwidth of 25 degrees are achieved in the 28 GHz band. Moreover, in the 38 GHz band, the measured broadside gain amounts to 10.2 dBi, a radiation efficiency of 70.65% is achieved, and the 3 dB beamwidth is 20 degrees.

This paper studies the effect of antenna polarization on measurement uncertainty of a multi-band body-worn distributed exposure meter (BWDM). The BWDM is a device for assessing electromagnetic fields in real environments accurately. The BWDM consists of 8 nodes and is calibrated on the body for simultaneous measurement of the incident power density in four frequency bands. Each node contains an antenna that can have two potential antenna polarizations.The BWDM is calibrated on four human subjects in an anechoic chamber to determine its measurement uncertainty in terms of 68% confidence interval (CI68) of the on-body antenna aperture. The results show that using a fixed polarization of the antennas on body can lead to a different CI68 up to maximum 4.9 dB when worn by another person which is still 9.6 dB lower than the measurement uncertainty of commercial exposure meters.

A wideband substrate integrated waveguide (SIW) antenna topology is proposed for operation in the 60 GHz band. It consists of two coupled quarter-mode and one halfmode SIW resonant cavities. This novel approach combines a significant bandwidth enhancement and a small footprint with compatibility to low-cost, standard PCB fabrication technology, making it excellently suited for 5G high-datarate wireless applications. Exploiting SIW technology, a high antenna-platform isolation is obtained, enabling high-density integration with active electronics without the risk of harmful coupling. An antenna that covers the entire 60 GHz IEEE 802.11ad band is designed, with a measured fractional impedance bandwidth of 11.7% (7 GHz). The measured maximum gain and radiation efficiency of the prototype amount to more than 5.1 dBi and 65%, respectively, within the entire impedance bandwidth.

For the design and production of reliable devices applied in wearable components, characterization of the electromagnetic properties of materials is of paramount importance. Therefore, we propose a novel approach, based on a resonance-perturbation method, which compares simulations and performed measurements. An inset-fed patch antenna with a resonance frequency in the vicinity of the 2.45-GHz Industrial, Scientific, and Medical band enables us to quickly estimate the characteristics of a given material sample. In a first step, the two frequencies for which the simulated return loss of the fixture crosses a defined threshold are modeled as polynomial functions of the relative permittivity and loss tangent of the material under test. Then, the electromagnetic properties of the material are obtained by comparing the modeled and measured frequencies. The electromagnetic properties of several textile materials of interest are determined with this method. It is shown that the proposed technique is fast, precise, and nondestructive. Owing to this, it is suitable for integration into an assembly line, where substrate samples are straightforwardly characterized before being used for the manufacturing of actual antennas.

For the first time, a dual band wearable personal distributed exposure meter (DPDE) is designed. The DPDE is calibrated on-body in a reverberation chamber. The meter consists of four nodes including textile antennas operating at 2443 MHz (WiFi 2 GHz) and 2595 MHz (LTE 2600 MHz). The location of the nodes are optimized based on the calibration in a reverberation chamber. The results show that the DPDE has a high antenna-body isolation and thus its performance is less affected by presence of the human body. The measurement uncertainty of the designed DPDE is maximum 4.5 dB in terms of 68% confidence interval of its response. The results are validated in a real office environment for WiFi 2 GHz. The DPDE has a detection limit of $3\ \mu W.m^{-2}$ in diffuse fields.

The accurate, reliable and cost-effective mass production of textile wireless systems remains an important challenge and a major impediment to achieve market penetration. Therefore, we propose some novel design, characterization and manufacturing procedures to make the development of such systems more compatible with mass production in traditional assembly line processes. First, we propose a novel non-destructive characterization procedure that determines the dielectric properties of the textile substrate directly within the assembly line, just before manufacturing the textile wireless node. Then, we describe an innovative manufacturing procedure that requires less manipulations and yields more accurate ultra-wideband textile antennas. Finally we introduce a holistic design framework for autonomous textile wireless nodes with communication, sensing and energy-harvesting functionality.

This study presents a circularly-polarised substrate-integrated waveguide (SIW) antenna implemented using a textile substrate and operating at 2.45 GHz, in the industrial, scientific, and medical frequency band. The antenna topology is based on a folded cavity with an annular ring as a radiating element, and it permits to obtain compact size and low sensitivity to the environment, without deteriorating the radiating performance. These characteristics, together with the choice of adopting a textile substrate, make the SIW antenna suitable for the integration in wearable systems for body-centric applications. The electromagnetic performance of the proposed antenna achieved in simulations was verified through the measurement of the device in an anechoic chamber. The circularly-polarised antenna exhibits a maximum gain of 6.5 dBi, a radiation efficiency of 73% and a very high front-to-back ratio.

A multi-band Body-Worn Distributed exposure Meter (BWDM) calibrated for simultaneous measurement of the incident power density in 11 telecommunication frequency bands, is proposed. The BDWM consists of 22 textile antennas integrated in a garment and is calibrated on six human subjects in an anechoic chamber to assess its measurement uncertainty in terms of 68% confidence interval of the on-body antenna aperture. It is shown that by using multiple antennas in each frequency band, the uncertainty of the BWDM is 22 dB improved with respect to single nodes on the front and back of the torso and variations are decreased to maximum 8.8 dB. Moreover, deploying single antennas for different body morphologies results in a variation up to 9.3 dB, which is reduced to 3.6 dB using multiple antennas for six subjects with various body mass index values. The designed BWDM, has an improved uncertainty of up to 9.6 dB in comparison to commercially available personal exposure meters calibrated on body. As an application, an average incident power density in the range of 26.7-90.8 muW.m - 2 is measured in Ghent, Belgium. The measurements show that commercial personal exposure meters underestimate the actual exposure by a factor of up to 20.6.

A miniaturized wearable antenna, entirely implemented in textile materials, is proposed that relies on a quarter-mode substrate integrated waveguide topology. The design combines compact dimensions with high body-antenna isolation, making it excellently suited for off-body communication in wearable electronics/smart textile applications. The fabricated antenna achieves stable on-body performance. A measured on-body impedance matching bandwidth of 5.1% is obtained, versus 4.8% in free space. The antenna gain equals 3.8 dBi in the on-body and 4.2 dBi for the free-space scenario. High radiation efficiency, measured to be 81% in free space, is combined with a low calculated specific absorption rate of 0.45 mW/g, averaged over 1 g of tissue, with 500 mW input power.

In the recent decade, we have witnessed a revolution in wireless communication systems. In this contribution, some novel materials and technologies for the development of dedicated antennas systems for body-centric communication and the Internet of Things are presented. In particular, the use of textile and cork materials as antenna substrates, combined with conducting electro-textiles or very thin copper-on-polyimide layers. Next, we focus on antenna topologies that yield highly stable radiation characteristics owing to their excellent body-antenna isolation. Therefore, we implement wide band cavity-backed slot antennas in substrate integrated waveguide technology. This enables the design of highly efficient active textile antenna systems where electronic circuitry and energy harvesters are deployed in very close proximity of the radiating parts of the antenna. Finally, we demonstrate how these systems may leverage multi-antenna processing techniques to increase throughput and robustness of the wireless channel.

Rising concern about the potential harmfulness of human radio-frequency exposure causes scientists to be highly interested in measuring these exposure levels. The set of measured signal levels on a map of locations is then used for epidemiological research, looking for correlation to the incidence of certain illnesses. Currently available hand-held exposimeters have the disadvantage that the measured signal levels are often significantly different from the exposure to which the human body is actually subjected. Therefore, a personal distributed exposimeter was developed and documented in this paper. Multiple on-body antennas are employed in order to measure the electromagnetic field strengths directly on the body. In this design, 11 commonly used frequency bands are measured, with front and back textile antennas for each of those bands. These 22 antennas are implemented in substrate-integrated-waveguide technology, thereby combining a compact size with a large bandwidth. The measurement system operates autonomously, through measurement, control and data-logging circuitry directly integrated onto the antennas. The textile-antenna based nodes are unobtrusively integrated into a garment, resulting in maximum comfort for the user. A measurement campaign using the system is currently underway in a number of European countries, yielding a large amount of valuable and unique data for epidemiological analyses.

For the first time, a wearable personal distributed exposimeter (WPDE) is designed and calibrated for the Long-Term Evolution (LTE) 800 and 2600 MHz downlink bands. The proposed WPDE has a 68% confidence interval of 4.8–5.6 dB for different number of antennas and polarizations. Measurements of the WPDE are compared and validated with a commercial exposimeter in a real environment.

An autonomous wearable radio-frequency identification (RFID) tag with sensing, processing, and decision-taking capability is presented for operation in the 2.45-GHz RFID band. The tag relies on a dedicated textile shorted circular patch antenna with tailored radiation pattern for operation in a smart floor/ceiling environment. By means of an holistic design strategy, the textile antenna's functionality is augmented by reusing its surface as an integration platform for sensing, computing, transceiver, and light-energy-harvesting hardware. Special attention was paid to align the tag's power consumption profile with the power generation profile of the energy harvester. Measurements under free-space conditions and in a realistic indoor scenario demonstrate excellent wearability, very high read range, enhanced functionality, and extended system autonomy.

A novel wideband substrate integrated waveguide (SIW) antenna topology, consisting of coupled half-mode and quarter-mode SIW resonant cavities, is proposed for operation in the 60 GHz band. This innovative topology combines a considerable bandwidth enhancement and a low form factor with compatibility with low-cost printed circuit board manufacturing processes, making it excellently suited for the next generation, high data rate wireless applications. Moreover, exploiting SIW technology, a high antenna-platform isolation is obtained, enabling dense integration with active electronics without harmful coupling. The computer-aided design process yields an antenna that covers the entire 57–64 GHz IEEE 802.11ad band with a measured fractional impedance bandwidth of 11.7% (7 GHz). The measured maximum gain and radiation efficiency of the prototype are larger than 5.1 dBi and 65%, respectively, within the entire impedance bandwidth.

Variability in the fabrication process and uncertainty in deployment conditions complicate the design of wearable antennas. In this contribution, we present an overview of adapted design strategies to account for such random effects. Conventionally, overspecification of the antenna requirements accommodates for unexpected variations and, as such, ensures appropriate performance in all operational conditions. Stochastic paradigms based on polynomial chaos expansions limit these design margins to the bare essential. Their application to model fabrication tolerances, substrate compression and antenna bending is demonstrated. The specific challenges are discussed for each application scenario.

A stochastic framework is presented to enhance the design of textile antennas, by addressing the impact of production uncertainties, substrate bending and compression on the performance of textile antennas. Each effect is considered separately and the probability density functions corresponding to the design parameters undergoing variations are experimentally estimated. In order to accurately quantify the statistical distribution of the antenna's figures of merit corresponding to these variations, we introduce a stochastic collocation method based on a generalized polynomial chaos technique or on Pade approximants.

Ever since the transistor replaced the vacuum tube by the end of the 1950s and, thereafter, the invention of the integrated circuits (ICs), the influence of computers on society has increased hand over fist. Whereas, in the 1990s, we used to rely on keyboard and mouse to browse our first web pages and send our first emails, most people nowadays carry around, in their pocket, a device that lets them contact anyone, anywhere in the world, or access any piece of information from a data source more vast than all of the world's libraries combined. And all of this by simply swiping a screen or by using voice commands. But what does the future have in store for us? Where will this evolution bring us in the next 5-10 years?

With the breakthrough of the Internet of Things and the steady increase of wireless applications in the daily environment, the assessment of radio frequency electromagnetic field (RF-EMF) exposure is key in determining possible health effects of exposure to certain levels of RF-EMF. This paper presents the first experimental validation of a novel personal exposimeter system based on a distributed measurement approach to achieve higher measurement quality and lower measurement variability than the commonly used single point measurement approach of existing exposimeters. An important feature of the system is the integration of inertial sensors in order to determine activity and posture during exposure measurements. The system is designed to assess exposure to frequencies within the 389 to 464, 779 to 928 and 2400 to 2483.5 MHz bands using only two transceivers per node. In this study, the 2400 to 2483.5 MHz band is validated. Every node provides antenna diversity for the different bands in order to achieve higher sensitivity at these frequencies. Two AAA batteries power each standalone node and as such determine the node hardware size of this proof of concept $(53\ {\rm mm}\times 25\ {\rm mm}\times 15\ {\rm mm})$ , making it smaller than any other commercially available exposimeter.

Wireless medical devices implanted at different locations in the human body have a wide application range. Yet, high-data-rate communication in the 2.4-GHz Industrial, Scientific, and Medical band suffers from high in-body attenuation loss. Link improvement cannot be obtained by simply increasing transmit power, as battery life is limited and in-body absorption has to remain low. To overcome these problems, a flexible on-body textile patch antenna, robustly matched directly to the human body, is designed and developed as part of a wearable repeater, enhancing communication with implanted wireless devices. This receive antenna, which can cope with different morphologies and patient movements, enables reliable high data rate and low-power communication links with an implant. A data link measurement is performed for the on-body repeater system placed on the human torso, relaying the signals to nearby medical equipment, without wired connection to the patient. The performance of the data link is experimentally assessed in different measurement scenarios. For a repeater system relying on simple analog amplification, which is low-cost, energy-efficient, and can be fully integrated into clothing, excellent results are obtained, with an average measured signal-to-noise ratio of 33 dB for tissue depths up to 85 mm.

A novel antenna-harvester co-design paradigm is presented for wireless nodes operating in an Internet of Things context. The strategy leads to compact and highly-integrated units, which are able to set up a reliable and energy-efficient wireless communication link, and to simultaneously harvest energy from up to three different sources, including thermal body energy, solar, and artificial light. The core of the unit consists of a substrate-integrated-waveguide (SIW) antenna. Its surface serves as a platform for the flexible energy-harvesting hardware, which also comprises the power management system. To demonstrate the approach, two different SIW cavity-backed slot antennas and a novel compact dual linearly polarized SIW antenna are presented. These topologies facilitate the integration of additional hardware without degrading performance. In the meantime, they enable comfortable integration into garments or unobtrusive embedding into floors or walls. Measurements on prototypes validate the integration procedure by verifying that the integrated hardware has a negligible influence on the performance of all discussed SIW antennas. Finally, measurements in four well-chosen indoor scenarios demonstrate that a hybrid energy-harvesting approach is necessary to obtain a more continuous flow and a higher amount of scavenged energy, leading to a higher system autonomy and/or reduced battery size.