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As a noncontact target recognition technique, radio-frequency identification (RFID) technology demonstrates attractive potential in constructing human-machine interaction (HMI) systems. However, the current development of RFID technologies in HMI systems is hampered by critical challenges in manufacturing high-performance RFID readers with superior flexibility and wearing comfort. Hence, we propose a multilevel printing strategy to overcome the difficulties in manufacturing high-performance large-scale microwave systems. Compared to traditional processes, the RFID system fabricated by the hybrid additive manufacturing technique exhibits equivalent electromagnetic performance and has obvious advantages in terms of manufacturing cost and environmental friendliness. A printed reconfigurable antenna with intelligent radiation mode is seamlessly integrated with the reader circuit via a "one-step" printing technology. Additionally, through chemical doping and artificial intelligence (AI) prediction, we have developed a modified polydimethylsiloxane (PDMS) encapsulation to miniaturize the system volume and enhance reliability. Electromagnetic and mechanical measurements demonstrated that our flexible RFID platform offers superior reliability and stability during long-term daily use. The RFID platform possesses exceptional capabilities in target positioning and accurate identification, demonstrating unique potential in noncontact sensing and recognition, which are highly demanded by flexible and wearable HMI systems.
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This paper presents a low-profile reconfigurable antenna array capable of five radiation-pattern modes for vehicular communication applications. The antenna array consists of four antenna elements, each containing four square patches. Exciting one of the square patches generates a broadside radiation. A square parasitic patch is added at the rear of the excited patch, and two square parasitic patches are placed at the front. By optimizing the design of these parasitic patches, including the treatment of center slotting and addition of shorting pins, the antenna element achieves an end-fire beam with a certain tilt angle. On this basis, a reconfigurable feeding network is designed with 1:1 and 1:4 output modes. By connecting the reconfigurable feeding network to the four antenna elements and altering the on/off states of the PIN diodes in the feeding network, a reconfigurable antenna with four end-fire beams and one omnidirectional beam in its radiation pattern is realized. Measurement results demonstrate an excellent impedance bandwidth, radiation pattern, and gain performance in all modes. The four end-fire and one omnidirectional radiation characteristics make it highly suitable for vehicular communication applications.
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This paper introduces an innovative and cost-effective approach for developing a millimeter-wave (mmWave) frequency-reconfigurable dielectric resonator antenna (DRA), which has not been reported before. The antenna integrates two rectangular DRA elements, where each DRA is centrally fed via a slot. A strategically positioned PIN diode is employed to exert control over performance by modulating the ON-OFF states of the diode, thereby simplifying the design process and reducing losses. In the OFF state, the first DRA, RDRA-I, exclusively supports the TE311 resonance mode at 24.3 GHz, offering a 2.66% impedance bandwidth and achieving a maximum broadside gain of 9.2 dBi. Conversely, in the ON state, RDRA-I and RDRA-II concurrently operate in the TE513 resonance mode at 29.3 GHz, providing a 2.7% impedance bandwidth and yielding a high gain of up to 11.8 dBi. Experimental results substantiate that the proposed antenna presents an attractive solution for applications necessitating frequency-reconfigurable and high-performance mmWave antennas in 5G and Beyond 5G (B5G) communication systems.
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In this article, an ultra-wideband (UWB) antenna featuring two reconfigurable quasi-perfect stop bands at WLAN (5.25-5.75 GHz) and lower 5G (3.4-3.8 GHz) utilizing electromagnetic bandgaps (EBGs) and positive-intrinsic-negative (P-I-N) diodes is proposed. A pair of EBG structures are applied to generate sharp notch bands in the targeted frequency spectrum. Each EBG creates a traditional notch, while two regular notches are combined to make a quasi-perfect, sharp, notch band. Four P-I-N diodes are engraved into the EBG structures to enable notch band reconfigurability. By switching the operational condition of the four diodes, the UWB antenna can dynamically adjust its notching characteristics to enhance its adaptability to various communication standards and applications. The antenna can be reconfigured as a UWB (3-11.6 GHz) without any notch band, a UWB with a single sharp notch (either at WLAN or 5G), or a UWB with two quasi-perfect notch bands. Moreover, the antenna's notch bands can also be switched from a traditional notch to a quasi-perfect notch and vice versa. To confirm the validity of the simulated outcomes, the proposed reconfigurable UWB antenna is fabricated and measured. The experimental findings are aligned closely with simulation results, and the antenna offers notch band reconfigurability. The antenna shows a consistently favorable radiation pattern and gain. The dimension of the presented antenna is 20 × 27 × 1.52 mm3 (0.45 λc × 0.33 λc × 0.025 λc, where λc is the wavelength in free space).
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A singly fed reconfigurable circular loop antenna is proposed for millimeter-wave (mmWave) communication systems. This antenna's distinctive feature lies in its capacity to adjust both polarization and bandwidth characteristics, a capability made possible by the strategic integration of two PIN diodes. These diodes are engineered to function in various modes, allowing for three distinct polarization states and accommodating two distinct bandwidths. A meticulous alignment of these PIN diodes enables the utilization of a single DC bias network as a highly effective RF choke, which simplifies the design and reduces the associated losses. Additionally, a planar biasing network that consists of coplanar strip-lines (CPS) has been employed eliminating the need for lumped elements. The simple and totally planar configuration offers a choice of right-hand circularly polarized (RHCP) radiation or left-hand circularly polarized (LHCP) radiation at 28 GHz. This is accompanied by impedance matching and axial ratio (AR) bandwidths of 12.9% and 8%, respectively, over the same frequency range with a gain of 7.5 dBic. Moreover, when the PIN diodes are unbiased, the antenna offers linear polarization (LP) over two narrow bandwidths at 27 GHz and 29 GHz featuring a maximum gain of 7.2 dBic. Therefore, the proposed configuration offers three operating modes: wide-band RHCP, wide-band-LHCP, and LP over dual narrow bands. Significantly, simulated results closely align with the measured outcomes, affirming the robustness and accuracy of this design.
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This paper presents a compact multifrequency reconfigurable patch antenna in terms of design and fabrication for operating in the S and C bands of the RF spectrum, which are overwhelmed by wireless applications. Reconfiguration is achieved by using a single PIN diode on the ground plane. By varying the voltage applied to the diode, three modes can emerge, exhibiting main resonant frequencies at 2.07, 4.63, and 6.22 GHz. Resonance switching requires a voltage of less than 0.9 V. The antenna fabricated on an FR-4 substrate, with a volume of 70 × 60 × 1.5 mm3, has a radiating patch element of a rectangular ring shape. The proposed low-cost antenna is easily implemented in a typical university lab-based environment. The total bandwidth for the three modes is close to 1 GHz, while the voltage standing wave ratio (VSWR) of the fabricated version of the antenna does not exceed 1.02, and the return loss is well below -40 dB for the three primary resonant frequencies.
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In this paper, a low-cost resin-coated commercial-photo-paper substrate is used to design a printed reconfigurable multiband antenna. The two PIN diodes are used mainly to redistribute the surface current that provides reconfigurable properties to the proposed antenna. The antenna size of 40 mm × 40 mm × 0.44 mm with a partial ground, covers wireless and mobile bands ranging from 1.91 GHz to 6.75 GHz. The parametric analysis is performed to achieve optimized design parameters of the antenna. The U-shaped and C-shaped emitters are meant to function at 2.4 GHz and 5.9 GHz, respectively, while the primary emitter is designed to operate at 3.5 GHz. The proposed antenna achieved peak gain and radiation efficiency of 3.4 dBi and 90%, respectively. Simulated and measured results of the reflection coefficient, radiation pattern, gain, and efficiency show that the antenna design is in favorable agreement. Since the proposed antenna achieved wideband (1.91-6.75 GHz) using PIN diode configuration, using this technique the need for numerous electronic components to provide multiband frequency is avoided.
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In this study, a novel microfluidic frequency reconfigurable and optically transparent water antenna is designed using three-dimensional (3D) printing technology. The proposed antenna consists of three distinct parts, including a circularly shaped distilled water ground, a sea water-based circular segmented radiator, and a circularly shaped distilled water-based load, all ingeniously constructed from transparent resin material. The presented antenna is excited by a disk-loaded probe. The frequency of the antenna can be easily tuned by filling and emptying/evacuating sea water from the multisegmented radiator. The radiator consists of three segments with different radii, and each segment has a different resonant frequency. When the radiator is filled, the antenna resonates at the frequency of the segment that is filled. When all the radiator segments are filled, the antenna operates at the resonant frequency of 2.4 GHz and possesses an impedance bandwidth of 1.05 GHz (40%) in the range of 2.10-3.15 GHz. By filling different radiator segments, the frequency could be tuned from 2.4 to 2.6 GHz. In addition to the frequency-switching characteristics, the proposed antenna exhibits high simulated radiation efficiency (with a peak performance reaching 95%) and attains a maximum realized gain of 3.8 dBi at 2.9 GHz. The proposed antenna integrates water as its predominant constituent, which is easily available, thereby achieving cost-effectiveness, compactness, and transparency characteristics; it also has the potential to be utilized in future applications, involving transparent and flexible electronics.
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A pattern reconfigurable antenna, composed of eight elements, is proposed for energy harvesting applications. Pattern reconfigurable antennas are a promising technique for harvesting from different wireless sources. The radiation pattern of the proposed antenna can be steered electronically using an RF switch matrix, covering an angle range from 0 to 360 degrees with a step size of 45 degrees. The proposed antenna primarily consists of an eight-dipole configuration that shares the same excitation. Each dipole is excited using a balun comprising a quarter-wavelength grounded stub and a quarter-wavelength open-circuit stub. The proposed antenna operates in the frequency range of 4.17 to 4.5 GHz, with an impedance bandwidth of 7.6%. By switching between the different switches, the antenna can be steered with a narrower rotational angle. In addition, the antenna can work in an omnidirectional mode when all switches are in the ON state simultaneously. The results demonstrate a good agreement between the numerical and experimental findings for the reflection coefficient and radiation characteristics of the proposed reconfigurable antenna.
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Since the CubeSats have become inherently used for the Internet of space things (IoST) applications, the limited spectral band at the ultra-high frequency (UHF) and very high frequency should be efficiently utilized to be sufficient for different applications of CubeSats. Therefore, cognitive radio (CR) has been used as an enabling technology for efficient, dynamic, and flexible spectrum utilization. So, this paper proposes a low-profile antenna for cognitive radio in IoST CubeSat applications at the UHF band. The proposed antenna comprises a circularly polarized wideband (WB) semi-hexagonal slot and two narrowband (NB) frequency reconfigurable loop slots integrated into a single-layer substrate. The semi-hexagonal-shaped slot antenna is excited by two orthogonal +/-45° tapered feed lines and loaded by a capacitor in order to achieve left/right-handed circular polarization in wide bandwidth from 0.57 GHz to 0.95 GHz. In addition, two NB frequency reconfigurable slot loop-based antennas are tuned over a wide frequency band from 0.6 GHz to 1.05 GH. The antenna tuning is achieved based on a varactor diode integrated into the slot loop antenna. The two NB antennas are designed as meander loops to miniaturize the physical length and point in different directions to achieve pattern diversity. The antenna design is fabricated on FR-4 substrate, and measured results have verified the simulated results.
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A low-profile and wide-angle radiation pattern reconfigurable antenna is designed, analyzed, and fabricated for wireless sensor network (WSN) applications, which operate at a 2.5-GHz frequency. This work aims to minimize the number of switches and optimize the parasitic size and ground plane to achieve a steering angle of more than 30° using a low cost-high loss FR-4 substrate. The radiation pattern reconfigurability is achieved by introducing four parasitic elements surrounding a driven element. In this work, the single driven element is fed by a coaxial feed, while other parasitic elements are integrated with the RF switches on the FR-4 as the substrate with dimensions of 150 × 100 mm (1.67 × 2.5 λo). The RF switches of the parasitic elements are surface mounted on the substrate. By truncating and modifying the ground plane, the beam steering can be achieved at more than 30° on the xz plane. Additionally, the proposed antenna can attain an average tilt angle of more than 10° on the yz plane. The antenna is also capable of attaining other important results, such as a fractional bandwidth of 4% at 2.5 GHz and an average gain of 2.3 dBi for all configurations. By adopting the ON/OFF condition on the embedded RF switches, the beam steering can be controlled at a certain angle, thus increasing the tilting angle of the wireless sensor networks. With such a good performance, the proposed antenna has high potential to serve as a base station in WSN applications.
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Liquid crystals (LCs) technology have a well-established history of applications in visible light, particularly in the display industry. However, with the rapid growth in communication technology, LCs have become a topic of current interest for high-frequency microwave (MW) and millimeter-wave (mmWave) applications due to promising characteristics such as tunability, continuous tuning, low losses, and price compatibility. To improve the performance of future communication technology using LCs, it is not sufficient only with the perspective of radio-frequency (RF) technology. Therefore, it is imperative to understand not only the novel structural designs and optimization of MW engineering but also the perspective of materials engineering when implementing advanced RF devices with maximum performance for next-generation satellite and terrestrial communication. Herein, based on advanced nematic LCs, polymer-modified LCs, dual-frequency LCs, and photo-reactive LCs, this article summarizes and examines the modulation principles and key research directions for the design strategies of LCs for advanced smart RF devices with improved driving performance and novel functionality. Furthermore, the challenges in development of state-of-the-art smart RF devices that use LCs are discussed.
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An integrated solution providing a bi-stable antenna with reconfigurable performance and light-responsive behavior is presented in this paper for the first time. The proposed antenna includes a radiation layer with conductivity, which is integrated onto the bi-stable substrate. First, the effect of the radiation layer material and substrate layer parameters on antenna performance was studied. The experiment showed that an antenna with CNTF has a wider impedance bandwidth than one with CSP, namely 10.37% versus 3.29%, respectively. The resonance frequency increases gradually with the increase in fiber laying density and fiber linear density. Second, the influence of state change of the substrate layer on the antenna radiation pattern was studied. The measured results showed that the maximum radiation angle and gain of states I and II are at 90°, 1.21 dB and 225°, 1.53 dB, respectively. The gain non-circularities of the antenna at states I and II are 4.48 dB and 8.35 dB, respectively, which shows that the antenna has good omnidirectional radiation performance in state I. The display of the array antenna, which shows that the array antenna has good omnidirectional radiation performance in state A, with gain non-circularities of 4.20 dB, proves the feasibility of this bi-stable substrate in reconfigurable antennas. Finally, the antenna deforms from state I to state II when the illumination stimulus reaches 22 s, showing good light-responsive behavior. Moreover, the bi-stable composite antenna has the characteristics of small size, light weight, high flexibility, and excellent integration.
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Metasurfaces (MSs) have enabled the emergence of new ideas and solutions in the design of antennas and for the control of electromagnetic waves. In this work, we propose to design a directional high-gain reconfigurable planar antenna based on a phase-modulated metasurface. Reconfigurability is achieved by integrating varactor diodes into the elementary meta-atoms composing the metasurface. As a proof of concept, a metasurface prototype that operates around 5 GHz is designed and fabricated to be tested in an antenna configuration. The metasurface is flexibly controlled by different bias voltages applied to the varactor diodes, thus allowing the user to control its phase characteristics. By assigning judiciously calculated phase profiles to the metasurface illuminated by a feeding primary source, different scenarios of far-field patterns can be considered. Different phase profiles are tested, allowing us to, firstly, achieve a highly directive boresight radiation and, secondly, to steer the main radiated beam towards an off-normal direction. The whole design process is verified by numerical simulations and is validated experimentally by far-field antenna measurements. The proposed metasurface enables the design of directive flat antennas with beam-scanning characteristics without complex feeding systems and power-consuming phase shifters, and thus provides potential interests for next generation antenna hardware.
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The proposed reconfigurable radiating antenna design is based on the integration of a reconfigurable fractal antenna and electro-optic substrate material. This antenna can be adjusted to achieve either re-configurability or tunability in the desired frequency range for wireless systems. The electromagnetic characteristics of the fractal antenna are manipulated at both the level of fractal geometry, electrical length and dielectric substrate. The designed antenna features multiband responses, in which the geometry and length change create a large frequency shift and the dielectric change using polymer dispersed liquid crystal (PDLC) creates fine and/or continuous tuning. The far field and scattering properties of the antenna are analyzed using the Computer Simulation Technology (CST) Microwave Studio Suite. The proposed approach has successfully demonstrated reconfigurable switching for up to four frequency bands between 0.2 and 0.6 THz. The dielectric constant change in the PDLC substrate shows fine and continuous frequency tuning with an 8% maximum frequency shift when operating around 0.54 THz and a high directivity of 7.35 dBi at 0.54 THz and 8.43 dBi at 0.504 THz. The antenna can also realize a peak gain of 4.29 dBi at 0.504 THz in the extraordinary polarization state of PDLC. The designed antenna can be readily integrated in the current communication devices, such as satellites, smart phones, laptops, and other portable electronic devices, due to its compact geometry and IC compatible design. In satellite applications, the proposed antenna can play a significant role in terms of security. The antenna could be extremely useful for satellites that want to keep their information secret; by constantly switching their operating frequency, spy satellites can evade detection and data collection from enemy ears.
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This study presents a U-shaped dual-frequency-reconfigurable liquid-metal monopole antenna. Eutectic Gallium-Indium (EGaIn) was used as a conductive fluid and filled in the two branches of the U-shaped glass tube. A precision syringe pump was connected to one of the branches of the U-shaped tube by a silicone tube to drive EGaIn, forming a height difference between the two liquid levels. When the height of liquid metal in the two branches met the initial condition of L1 = L2 = 10 mm, and L1 increased from 10 mm to 18 mm, the two branches obtained two working bandwidths of 2.27-4.98 GHz and 2.71-8.58 GHz, respectively. The maximum peak gain was 4.00 dBi. The initial amount of EGaIn also affected the available operating bandwidth. When the liquid metal was perfused according to the initial condition: L1 = L2 = 12 mm, and L1 was adjusted within the range of 12-20 mm, the two branches had the corresponding working bandwidths of 2.18-4.32 GHz and 2.57-9.09 GHz, and the measured maximum peak gain was 3.72 dBi. The simulation and measurement data corresponded well. A series of dual-frequency-reconfigurable antennas can be obtained by changing the initial amount of EGaIn. This series of antennas may have broad application prospects in fields such as base stations and navigation.
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This paper reviews the material properties, fabrication and functionalities of liquid metal-based devices. In modern wireless communication technology, adaptability and versatility have become attractive features of any communication device. Compared with traditional conductors such as copper, the flow characteristics and lack of elastic limit of conductive fluids make them ideal alternatives for applications such as flexible circuits, soft electronic devices, wearable stretch sensors, and reconfigurable antennas. These fluid properties also allow for innovative manufacturing techniques such as 3-D printing, injecting or spraying conductive fluids on rigid/flexible substrates. Compared with traditional high-frequency switching methods, liquid metal (LM) can easily use micropumps or an electrochemically controlled capillary method to achieve reconfigurability of the device. The movement of LM over a large physical dimension enhances the reconfigurable state of the antenna, without depending on nonlinear materials or mechanisms. When LM is applied to wearable devices and sensors such as electronic skins (e-skins) and strain sensors, it consistently exhibits mechanical fatigue resistance and can maintain good electrical stability under a certain degree of stretching. When LM is used in microwave devices and paired with elastic linings such as polydimethylsiloxane (PDMS), the shape and size of the devices can be changed according to actual needs to meet the requirements of flexibility and a multistate frequency band. In this work, we discuss the material properties, fabrication and functionalities of LM.
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UHF satellite communication for Internet of Things (IoT) technology is rapidly emerging in monitoring applications as it offers the possibility of lower-costs and global coverage. At the present time, Low Power Wide Area Network (LPWAN) solutions offer low power consumption, but still suffer from white zones. In this paper, the authors propose an UHF frequency reconfigurable Antenna for hybrid connectivity LoRaWAN (at 868 MHz) and UHF satellite communication (Tx at 401 MHz and Rx at 466 MHz) with the Low Earth Orbit (LEO) Kineis constellation. The antenna is based on a meandered line structure loaded with lumped components and a PIN diode to control the antenna resonant frequencies. It resonates at 401 and 868 MHz when the PIN diode is forward-biased (ON state) and 466 MHz in reverse-biased configuration (OFF state). The antenna is designed inside the enclosure with the presence of all the parts of the connected device. The results of EM simulations and parametric studies on the values of the lumped components and the PIN diode equivalent model, which are obtained with HFSS, are presented. The antenna is prototyped and has dimensions of 78 mm × 88 mm × 1.6 mm. The paper proposes a fast and practical method to reduce time development and compensate the frequency shift between measurement and simulation.
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In a traditional antenna array direction finding system, all the antenna sensors need to work or shut down at the same time, which often leads to signal crosstalk, signal distortion, and other electromagnetic compatibility problems. In addition, the direction-finding algorithm in a traditional system needs a tremendous spectral search, which consumes considerable time. To compensate for these deficiencies, a reconfigurable antenna array direction finding system is established in this paper. This system can dynamically load part or all of the antennas through microwave switches (such as a PIN diode) and conduct a fast direction of arrival (DOA) search. First, the hardware structure of the reconfigurable antenna is constructed. Then, based on the conventional spatial domain search algorithm, an improved transform domain (TD) search algorithm is proposed. The effectiveness of the system has been proven by real experiments, and the advantage of the system has been verified by detailed simulations.
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Electromagnetic responses are generally controlled electrically or optically. However, although electrical and optical control allows fast response, they suffer from switching or tuning range limitations. This paper controls electromagnetic response by mechanical transformation. We introduce a novel kirigami-inspired structure for mechanical transformation with less strength, integrating a shape memory alloy actuator into the kirigami-inspired for mechanical transformation and hence electromagnetic control. The proposed approach was implemented for a reconfigurable antenna designed based on structural and electromagnetic analyses. The mechanical transformation was analyzed with thermal stimulus to predict the antenna geometry and electromagnetic analysis with different geometries predicted antenna performance. We numerically and experimentally verified that resonance response was thermally controlled using the kirigami-inspired antenna integrated with a shape memory alloy actuator.