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This paper discusses the design of a cross-slotted waveguide array structure to be adopted for W-band communication between 84 86 GHz. Each array waveguide element contains 16 cross-slots along the broad wall to enable circularly polarized radiation behavior with a gain reaching up to 14 dBi and a cross-polarization isolation of more than 20 dB in the elevation plane. The design of the cross-slots is implemented with bent arms in order to accommodate them at an offset position from the waveguide narrow wall. Such position ensures the radiation of a circularly polarized wave. A waveguide-based feeding network with serpentine shaped transitions is implemented to feed the eight-element cross-slotted array topology. The design of the feeding network ensures an equal power split and in-phase distribution between the eight elements with a phase deviation that does not exceed 20°. The overall cross-slotted waveguide array is prototyped as a proof of concept. The measured results show a maximum gain of 24.5 dBi for both polarization schemes. The measured half power beam width (HPBW) is 8° in the elevation plane and 12° in the azimuthal plane. The measured cross-polarization between the two circularly polarized schemes at both ports reaches a level of more than 26 dB. The comparison between the simulation and measurement results proves the validity of the proposed approach in achieving a high-gain dual circularly polarized structure for millimeter-wave communication.

This letter describes the design of a right-hand circularly polarized planar filtenna (filter + antenna) that can reconfigure its operation between two center frequencies in the Ka-band. The filtenna structure is composed of a four-element array radiator and a reconfigurable bandpass filter, occupying an area of 31 × 14 mm. The circularly polarized array elements are fed by a sequential power divider for an enhanced polarization purity. The filter is based on a ring resonator loaded with a variable open stub. The length of the stub extends through a p-i-n diode switch, resulting in a change of the loaded reactance into the ring, and consequently tuning the filter's operating center frequency from 30.3 to 29 GHz. The proposed low-loss filtenna structure exhibits a reconfigurable fractional bandwidth up to 7.74%, a peak realized gain that can reach up to 11.5 dBic, an axial ratio of less than 1 dB, and a sidelobe level that can go as low as −12 dB. The prototype filtenna is fabricated and tested, where the measured results verify the simulated data. A figure of merit is proposed to highlight the superior performance of the presented Ka-band structure in terms of the polarization, size, reconfiguration ability, and radiation characteristics as proven by the comparison with other works in the literature.

This communication proposes the reconfiguration of a coplanar-fed single arm bowtie antenna structure by relying on the integration of a digital tunable capacitor (DTC). The coplanar-fed single arm bowtie antenna is presented in two configurations. The first configuration is a 2-D topology with a modified ground plane arrangement. The second configuration employs vertical folding for the ground plane as well as the radiating arm. In addition, vertical copper inserts are embedded within the bowtie single arm to further enhance the compactness of the structure and transform it into a 3-D topology. Both antennas are initially designed to operate at 868 MHz for Internet of Things (IoT) applications, with a digitally reconfigurable frequency operation for wireless communication. The 2-D antenna structure exhibits a 77% size reduction at the IoT operational frequency of 868 MHz in comparison with a similar rectangular patch antenna operating at the same frequency. On the other hand, the 3-D antenna structure reaches 84% of size reduction at the same frequency. A figure of merit (FOM) is derived to prove the superior performance of the presented antenna structure.

In this study, a reconfigurable, two-element, multiple-input multiple-output (MIMO) printed inverted-F antenna (PIFA) is presented with an enhanced isolation ability. The MIMO antenna system is designed using three different reconfiguration techniques that are based on positive-intrinsic-negative diodes, radio frequency micro-electromechanical switches and varactors. Their impact on the performance of the PIFA and the MIMO system is evaluated in terms of radiation characteristics, gain, power dissipated, radiation efficiency, linearity, biasing requirements and MIMO performance. Isolation between the two MIMO antenna elements is enhanced by integrating a reconfigurable band-reject filter within the ground plane between the radiating elements. The band-reject filter is reconfigured simultaneously with the radiating elements, hence resulting in less coupling and better isolation. The MIMO system along its various components is fabricated for the three different reconfiguration techniques and the comparison with predicted data shows great agreement.

This article presents a new compact lightweight radio frequency (RF) energy harvesting system. The system relies on a dual-tapered transmission line-based matching network that stretches the rectification capability of an integrated Schottky diode. This topology is demonstrated on a 2.4 GHz rigid harvesting system with a resulting power conversion efficiency that reaches up to 58% over 0 dBm input RF power. Its performance is compared with a reference rectifier that relies on a typical open circuit shunt-stub matching network. The rectifier along with a miniaturized monopole antenna is then tailored for a flexible substrate with a resulting efficiency around 50% at 0 dBm input power. The rectifier exhibits an almost flat efficiency over the 2.3–2.5 GHz frequency span despite wide load variations. The system is characterized in multiple bent configurations featuring high and stable performance. It is demonstrated that for different bent states, the proposed flexible harvester does not display large variations in harvested power. Thus, the presented rectenna demonstrates the remarkable combination of compactness, flexibility, and stability. Equipped with these features, such rectifier can be plugged into a variety of sensors, even on wearable surfaces, which makes it ideal for Internet of Things (IoT) applications.

In this article, a new 3-D printed dual tapered nested antenna design is presented. The antenna is composed of two tapered helical arms that wrap around each other in opposite orientations to exhibit orthogonal circular polarization schemes. The nested tapered helices are 3-D laser printed with copper platting. The outer helical arm is tailored to resonate at 2.4 GHz, while the inner arm is designed for operation at 5.4 GHz. The overall antenna structure is then arranged as an array of elements that can dynamically alter its lattice in either linear or triangular topologies in order to achieve reconfiguration in the radiation pattern. The change in topologies is driven by programmable robots that can reshape the antenna array’s radiation pattern dynamically and on demand. The whole system is measured and tested for various arrangements where the measured results show good agreement with the simulated data.

This letter investigates the incorporation of support vector machines (SVMs) to predict the time and location of maximum Wi-Fi coverage for energy harvesting. Such incorporation of machine learning, along with radio frequency energy harvesting systems, improves the proposed rectenna efficiency especially when scavenging wireless routers and access points. Experiments showed that the proposed framework that uses SVM was able to predict the time and location of maximum Wi-Fi coverage. Such prediction constitutes the basis of a scheduling mechanism for directed harvesting of Wi-Fi signals.

This letter advocates the use of mechanical actuation to alter the electrical length of components within antenna elements proposed for implementation onto a CubeSat platform. Such electrical length alteration reconfigures the antenna's frequency operation without affecting its polarization scheme. This concept is first demonstrated on a reconfigurable quadrifilar helix that reconfigures its frequency operation between 750 MHz and 1 GHz, while maintaining a circular polarization behavior. As a second demonstration, a Yagi–Uda antenna is reconfigured by changing the electrical length of its reflector, fed elements, and two directors. Such alteration results in a frequency reconfiguration between 1.2 and 1.5 GHz, while preserving the linear polarization behavior of the antenna array. For both antenna examples, the reconfiguration is implemented through the appropriate mechanical actuators that are integrated within the CubeSat's cavity. As a proof of concept, both structures are fabricated and integrated on the outside chassis of a 6U CubeSat $(\text{10}\times \text{20}\times \text{30}\,\text{cm}^{3})$ , where measured results greatly match the simulated data.

Power splitting of the input radio frequency (RF) signal is used to improve the efficient power range of a RF rectifier. Direct current (dc) power at the output of every rectifying branch is then combined over a resistive load and thus resulting in a single dc output. The enhancement in efficient power range, over which the power conversion efficiency (PCE) remains ≥ 50%, is determined to be 2.8 dB. The article starts by a theoretical analysis that addresses the negative effects of the diode's breakdown voltage, formulates an equation that predicts the maximum output dc voltage at saturation, and introduces a method that can improve the PCE of a typical shunt-type diode rectifier at low power levels. As a result, a rectifying system is designed and tested as a proof of concept. The proposed circuit, with the enhanced power range, is designed to operate within the power span from -10 dBm up until 10 dBm. Such system is suitable for operation in RF wireless energy transfer and energy harvesting applications.

In this paper, a digitally tuned flexible antenna is proposed for integration onto devices within the Internet of Things (IoT) paradigm. The antenna design caters for the various IoT communication standards by reconfiguring its operating frequency. Accordingly, the antenna reconfiguration allows operation at 868 MHz, 915 MHz, 1.8 GHz and 2.1 GHz. The reconfiguration is achieved digitally by resorting to a digitally tunable capacitor (DTC). The DTC changes its capacitance, and hence its frequency operation, by relying on 5-bit sequence commands through a microcontroller. The proposed antenna is coplanar waveguide fed with its ground plane surrounding the radiating structure. The gain of the antenna varies between 4 dB and 6 dB for different frequencies of operation. Its radiation efficiency varies between 78% and 92%. The antenna is fabricated and tested on a flexible substrate, where the resulting reconfigurable prototype maintains its performance characteristics for different bent states.

In this paper, the effect of sequential rotation on the beam steering capabilities of a circularly polarized phased antenna array is analyzed. Two different topologies for a phased antenna array operating at Ka-band between 28 GHz and 40 GHz are studied where each structure is tailored to produce a maximum gain of almost 19 dB with an axial ratio below 0.5 dB. The individual elements of both topologies are dual fed with a differential phase shift of 90° respectively. This paper proves that the steering capability of a phased antenna array is doubled when sequential rotation is omitted from its feeding network.

A wearable, continuous electromagnetic sensing system provides 96% glucose estimation accuracy when tested on healthy individuals., Painless, needle-free, and continuous glucose monitoring sensors are needed to enhance the life quality of diabetic patients. To that extent, we propose a first-of-its-kind, highly sensitive, noninvasive continuous glycemic monitoring wearable multisensor system. The proposed sensors are validated on serum, animal tissues, and animal models of diabetes and in a clinical setting. The noninvasive measurement results during human trials reported high correlation (>0.9) between the system’s physical parameters and blood glucose levels, without any time lag. The accurate real-time responses of the sensors are attributed to their unique vasculature anatomy–inspired tunable electromagnetic topologies. These wearable apparels wirelessly sense hypo- to hyperglycemic variations with high fidelity. These components are designed to simultaneously target multiple body locations, which opens the door for the development of a closed-loop artificial pancreas.

This paper presents novel dual tapered helical antenna structures that are 3D printed and nested within each other for size reduction. Each tapered helical antenna element is designed to operate at a distinct span of frequencies. The two helical antennas are nested together and wrapped in opposite direction to each other in order to satisfy orthogonal polarization. The two helical elements are fabricated using a laser based 3-D printing process where good measured radiation behavior is obtained.

This article proposes a new rectenna system that is based on a radio frequency (RF) rectifying circuit with enhanced power handling capabilities. The rectenna consists of an antenna that receives the RF signal and a rectifying circuit that converts it into a direct current (dc) output. The rectifier's power handling capability is improved by delaying the breakdown effect of a Schottky diode, resulting in higher maximum dc output power. The power handling capability enhancement is attained by splitting the received RF signal and directing it to feed multiple rectifying branches. The dc outputs from all branches are then combined across an optimized load. This topology results in a single-input single-output rectifier. The designed rectenna is fabricated and tested. The results indicate a 1.9 times increase in input power at which breakdown occurs. The rectenna system is proposed for use in wireless energy transfer applications, where dedicated power is transmitted towards the rectifier. This rectifier can be integrated into nodes of a wireless sensor network, where the enhanced power handling capabilities contribute to enhance the breakdown characteristics.

This letter discusses an antenna system that steers its radiation pattern to personalize coverage in a wireless local area network scenario. The change in the pattern occurs either by mechanically rotating or electrically switching the feeding network toward the appropriate antenna structure. The user controls the personalized coverage using an Android-based voice recognition application on a mobile device. Each antenna structure operates at 5.28 GHz with 110 MHz bandwidth and an increased gain around 7.5 dB. The antenna's radiation insures a redistributed sector coverage of two diametrically opposite geographical zones that are 180° apart from each other. A multiple-input–multiple-output (MIMO) implementation is also proposed with a discussion on the various possible coverage zones. The various antenna concepts are measured, and the results validate the predicted data.

This article discusses the design and dual functionality of two antenna arrays that operate from 1.8 to 2.4 GHz. Each antenna array is composed of two elements and proposed for either communication or radio-frequency (RF) energy harvesting. The antenna arrays are integrated vertically on top of a solar panel. Copper-based and transparent inverted-F antennas constitute the elements of both arrays. The transparent array has the same dimensions and topology as the copperbased one. Its purpose is to verify that the integration of the copper-based inverted-F antenna arrays on top of the solar panel does not majorly impact the solar panel's efficiency. A rectifying circuit that is positioned at the output of both arrays is also designed and tested. The rectifying circuit converts the collected RF energy into dc power that can supplement the solar panel's supply during the absence of solar energy. The measured performance results of the fabricated system, which is composed of the two array antennas in addition to the rectifying circuit, show good agreement with the simulated data.

In this letter, a frequency-reconfigurable printed meandered monopole structure is presented. The antenna structure is composed of three radiating parts that are connected through two integrated PIN diodes. Such integration allows the antenna to reconfigure its operation within four frequency bands that correspond to various LTE, UMTS, and GSM channels. A graphical user interface (GUI) using Java is employed to control the states of the switches. The interface allows the control of a microcontroller to supply appropriate current to each of the two diodes. The GUI also simulates a cognitive radio environment where the activation of the corresponding PIN diodes is determined by the users’ activities. A prototype is fabricated and tested as a proof of concept where measured results agree with simulated data.

In this paper, an antenna system that is composed of eight radiating elements is presented. The eight elements consist of a set of four curved dipoles and another set of four straight dipoles, providing two diversity antenna structures. Each curved and straight dipole is designed to produce a focused gain pattern toward one dedicated quadrant. A parasitic printed reflector is introduced into the center section of the top layer of the proposed antenna to enhance the matching and the gain pattern redirection capabilities of each radiating element. In addition, the printed reflector further enhances the isolation between the various elements. The assessment of the proposed diversity antenna system is performed in a rich multipath environment for various propagation scenarios. A diversity gain between 16.5 and 19.1 dB is attained for a 1% probability level and by assuming a Rayleigh fading channel for both structures. The control of the feeding of the various elements for both diversity structures is achieved through the design and incorporation of four reconfigurable feeding networks within the antenna system. Fabrication and testing of various prototypes display very good agreement between the simulation and measured results, which validate the presented designs.

This letter presents a new planar inverted-F antenna design that is dedicated for integration within mobile devices such as phones and tablets. The proposed antenna structure is based on nested capacitive slots in order to achieve a multiband behavior. The presented antenna is also reduced in size by 60%. The antenna is then reconfigured using positive-intrinsic-negative (p-i-n) diodes that are embedded within the antenna structure. Frequency reconfiguration is achieved to ensure that all the various commercial and required bands of interest are covered. Two prototypes are fabricated and measured where good agreement is noticed between the simulated and measured data.

In this paper, the design and implementation of a quadrifilar helix antenna are presented where the four arms are 3-D printed. The antenna structure is miniaturized by resorting to a combination of two approaches. The first approach is based on loading the tips of the four helical arms with circular conductive disks. The size and location of these elements directly affect the antenna’s operating frequency. The second miniaturization approach is based on incorporating an FR-4 dielectric material into the vacant space between the four arms of the quadrifilar helix. As a result, the length of the antenna is reduced by a ratio of 43%. The quadrifilar helix antenna is also designed on top of a ground plane with an optimized conical shape and topology. The antenna is partially fabricated using 3-D printing additive technology, where measurements show great agreement with simulated results.

In this communication, a frequency and pattern reconfigurable V–shaped printed antenna is presented. The proposed structure operates at two different frequency bands. The variation in the frequency of operation is achieved by individually extending the length of each of the two antenna arms. The directional behavior of the proposed antenna structure is improved through the incorporation of a triangular parasitic element within the empty space between the two antenna arms. More specifically, the antenna is able to steer its gain pattern to either the left or right directions based on which arm of the V–shaped printed structure is fed. A prototype structure is fabricated and tested to validate the proposed approach in achieving directional behavior over two distinct frequency bands.

In this paper, a frequency reconfigurable antenna system with a directional selectivity is presented. The reconfiguration of the antenna's radiation characteristics is wirelessly controlled through a mobile phone and a microcontroller. The antenna system is a multi-element radiator composed of four monopoles on top of a hexagonal ground plane, in addition to four rectangular microstrip two-elements antenna arrays. The monopoles and the microstrip arrays are designed to contribute to the communication requirements of the complete system. The position, orientation, and topology of the various antennas are optimized to achieve the required frequency reconfigurability in addition to the variable selective directivity performance. The whole system is fabricated and integrated in a single compact unit controlled by a microcontroller, four servo motors, and a Bluetooth module. The antenna system is tested and the measured results confirm the validity of the proposed design.

In this paper, we propose a new slot antenna for non-invasive detection of the concentrations of blood constituents. The designed antenna is composed of multiple slots that are optimized to enhance its sensitivity to the bound medium. To test its performance, the antenna is loaded by a foam container filled with fetal bovine serum (FBS) solution whose glucose concentration levels are varied. Accordingly, the magnitude and phase of the antenna’s reflection coefficient (S 11 ) are monitored at multiple frequencies for various glucose levels. A good correlation between the antenna’s S 11 and reference glucose levels, which are measured with an invasive glucometer, is observed.

This paper presents an active 8-port feeding network that achieves a full range 360° phase coverage. The network is designed to only require a phase shift tuning of 180°. The performance of the proposed feeding network along its various active components can be achieved by necessitating less than 4 V of biasing voltage requirements. The feeding network is tested on an array of eight circularly polarized helical antenna elements where polarization reconfiguration in the radiated fields is achieved. The control of the phase shift between the feeding network ports allows the overall antenna array to change its polarization across the entire frequency band of interest between 1.7 GHz and 2.3 GHz.

In this paper, a broadband reject filter for dielectric constant characterization is presented. Four complementary open loop resonators (OLRs), which follow a modified log-periodic distribution, are etched beneath a tapered feed line to achieve a broadband rejection response for the proposed filter. The configuration of the embedded log-periodic resonators is designed to attain high sensitivity to lossy material over the 1.25-2.25 GHz frequency span. A prototype of the proposed filter is fabricated and tested to validate its sensitivity and performance in terms of differentiating among various dielectric constant levels for a material under test (MUT). An average sensitivity of 0. 42 dB/e r and 3. 65°/e r is achieved at f = 2. 25 GHz.