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This paper demonstrates the on‐chip terahertz (THz) helical antenna based on metal self‐rolled‐up membrane (M‐SRuM) nanotechnology, which utilizes the residual stress in multilayer metal membrane deposited by electron beam (E‐beam) evaporation to provide the rolling force and to form the radiation body of the helical antenna. Precise design method is proposed based on multi‐physics modeling for mechanical and electrical analysis, and the two operating modes of on‐chip helical antenna are modeled and analyzed. The test results show that the normal mode of self‐rolled‐up THz helical antenna is able to operate at frequency as high as 0.223 THz with the corresponding impedance bandwidth of 13 GHz. [ABSTRACT FROM AUTHOR]

The article describes a novel low‐loss microwave diplexer based on compact planar filtering elements. These are composed of spiral resonators and etched directly onto the signal layer. Furthermore, their design and optimization prove to be easy, and their native high‐pass/low‐pass characteristics are perfectly suited for assembling a diplexer. To verify the claim, a diplexer is designed and fabricated. It operates at 1.9 GHz and 3.5 GHz, and it is intended for personal communications service and 5G applications. The proposed device has an active area of 15.5 mm × $\times $ 19.5 mm. It shows an insertion loss of 0.35 dB and 0.28 dB for the two channels, representing the lowest data reported in the literature for this kind of device and technology. Additionally, the −10 dB‐fractional bandwidths for the lower and upper bandwidths are 40.6% and 20.2%, respectively, and isolation is at least 25 dB for both channels. [ABSTRACT FROM AUTHOR]

A mathematical model is presented for the optimisation of an Electromagnetic Halbach Array (EHA) for wireless power transfer. The mathematical model is based on Biot‐Savart's law of magnetic field in a current‐carrying square loop. The model is validated through static electromagnetic simulations in ANSYS Maxwell and found to be accurate and effective when predicting the magnetic field within the EHA box. To verify the analytical and simulation results, an EHA was fabricated, and experimental verification was carried out. The results show that the mathematical model can be widely used in the analysis and design optimisation of EHAs of any size and with diverse parameters in the case of single‐layer square spiral planar coils. [ABSTRACT FROM AUTHOR]

In this paper, an orbital angular momentum (OAM) mode reconfigurable antenna based on a uniform circular array (UCA) is presented. The phase superposition method is presented to overcome the limitation of the number of array units on the mode order in the conventional four‐element UCA antenna, which is limited to generating first‐order OAM beams. The unit phase is introduced by a bifilar helical antenna in this method, and the unit phase is superimposed with the feed phase of the UCA to enable the generation of 3rd‐order OAM beams from the four‐element UCA. At the same time, the DC signal‐controlled feed network assigns three distinct feed phases to the UCA, which realizes the reconfigurability of the three OAM beams. To achieve mode reconfigurability, 20 p‐i‐n diodes were integrated as switches in the feed network for controlling the ON/OFF status of p‐i‐n diodes in the feed network using DC signals. Finally, simulated and measured results show that three OAM beams (lz = −1, −2, and −3) have been generated in the frequency band from 10.6 to 11.8 GHz. [ABSTRACT FROM AUTHOR]

A compact Archimedean spiral antenna with high gain for electrostatic discharge (ESD) detection is investigated. A frustum‐shaped cavity proposed in this work is formed to optimise the maximum antenna gain. Additionally, a helix arm is loaded to enhance antenna gain in lower band. The measured results demonstrate that the proposed antenna, which employs a unidirectional radiation mode, exhibits a maximum antenna gain ranging from −0.74 dBi to 9.46 dBi and a voltage standing wave ratio less than 3 across a frequency range of 0.65–5 GHz. A test system consisted of proposed antenna and a commercial ESD detection antenna is established. The verified results indicate that the proposed antenna has a performance close to the commercial antenna, so that proposed antenna with compact size is preferred to be utilised for ESD detection. [ABSTRACT FROM AUTHOR]

A novel design of a high-frequency multiband with a circular polarisation antenna based on a four-patch antenna system consolidated with an Archimedean spiral antenna for CubeSat applications. The geometry and size are compatible with the CubeSat standard structure dimensions of 10 x 10 cm². The antenna consists of a spiral antenna in the middle of four patch antennas surrounding it; the first antenna structure consists of two sets of two orthogonal identical patch antennas with a 90° phase shift to cover the band from 1.55 to 1.94 GHz at L-band, 2, 2.1, and 2.3 GHz at S-band, the second antenna is an Archimedean spiral antenna to cover all C-bands, all X-bands, all Ku-bands, all K-bands, and from 26 to 29 GHz at Ka-band. The measured results show that the reflection coefficients (S11) and (S22) achieve < -10 dB and the axial ratio achieves <3 dB, with a reference impedance of 50 Ω. The simulated and the measured results give a better agreement. [ABSTRACT FROM AUTHOR]

Microwave imaging (MI) is a noninvasive and nonionizing procedure for detection of cancerous cells in healthy body tissues using radiofrequency (RF) and microwaves. The procedure involves the use of Ultra Wide Band (UWB) antennas for sensing purposes. Therefore, this research article presents the design, development, and testing of a low‐profile UWB Archimedean spiral microstrip‐patch antenna (ASMA) for detection of skin cancer using monostatic radar‐based microwave imaging. The proposed ASMA consists of a spiral resonator with a defective ground structure and a slotted microstrip feed line with dimensions of 38 × 38 × 0.87 mm3. The proposed antenna shows an impedance bandwidth for the frequency range of 2.2–13.9 GHz, with a peak gain of 6.8 dB at 7.8 GHz. In silico analysis of the proposed ASMA for MI is carried out with Gaustav model using Computer Simulation Technology Microwave Studio. To validate the performance of the ASMA as a sensor for MI, a prototype of the same is fabricated and a four‐layered bio‐phantom of the human forearm is prepared for in vitro and in vivo testing of the proposed procedure. The validation of ASMA radiation properties is done using a Vector Network Analyser (E‐5063A) (VNA) and an anechoic chamber with the fabricated antenna at 10 mm away from the prepared bio‐phantom. The recorded S parameter data with bio‐phantom and the VNA is processed using different beamforming algorithms like Delay and Sum and Coherent Factor‐Delay Multiply and Sum (CF‐DMAS) to reconstruct the image of the scanned area. The reconstructed images are 97%–98% accurate. The proposed ASMA sensor is also safe for human exposure as it has a specific absorption rate of 0.0546 W/Kg at 5 GHz that complies with the safety guidelines of the Federal Communications Commission to minimize potential health risks associated with exposure to RF and microwave radiation. [ABSTRACT FROM AUTHOR]

A low‐profile ultra‐wideband (UWB) circularly polarized antenna is proposed in the form of a planar Archimedes spiral structure backed by an artificial magnetic conductor (AMC). To expand its bandwidth and minimize its size, the antenna is loaded with resistors and a metal ring near the end of the spiral arms. At the same time, the bidirectional beam is transformed into a unidirectional beam using the phase compensation mechanism by introducing an AMC reflector. The antenna achieves −10 dB impedance bandwidth and 3 dB AR bandwidth in 0.7 ~ 10.2 GHz (174.3%), with a height of only 0.035 wavelengths at 0.7 GHz, which shows advantages over most similar designs. Finally, the antenna is fabricated and measured to prove its effectiveness. [ABSTRACT FROM AUTHOR]

In this paper, a modified rhombic‐shaped wide‐flare two‐arm antenna is proposed for super‐wideband applications of the next generations of mobile technologies. To enhance antenna input impedance and to improve its performance, the copper arms are lithographed on a dielectric substrate with multilayers and fed through a wideband balun that is designed to feed the balanced two‐arm antenna through the conventional (unbalanced) coaxial line. The proposed antenna is fabricated for experimental validation of the simulation results. It is shown through electromagnetic simulation as well as experimental measurements that the proposed antenna is operational in the range of frequencies (2.3‐23 GHz $2.3 \mbox{-} 23\unicode{x0200A}\mathrm{GHz}$). Parametric study is performed to obtain the optimum design of the proposed antenna. The distributions of the surface current on the antenna arms at different frequencies are presented and discussed for more understanding of the antenna operation over the entire frequency band. It is shown that the antenna has a radiation efficiency of greater than 96%, percentage bandwidth of 164%, ratio bandwidth of 10, bandwidth‐to‐dimension ratio of 1360, and maximum gain that exceeds 5 dBi $5\unicode{x0200A}\text{dBi}$. [ABSTRACT FROM AUTHOR]

A compact, flexible, long‐range, and impedance transformer balun‐like integrated UHF RFID tag antenna is proposed for the detection of water bottles. To alleviate the performance of a tag antenna in close proximity to a high dielectric material such as water, the radiating element of the tag antenna uses folded, unbalanced strips made of balun‐like arms wrapped around the tag's body. As a result, a wide bandwidth with reasonably good radiation resistance is achieved. The tag's body comprises dual loops for the impedance matching to the tag chip. This leads to a long read range of 13.33 m; >5.83 m compared to other state‐of‐the‐art designs. The proposed tag antenna conforms to a small footprint by wrapping the balun‐like arms around the tag's body, which results in a compact form. The tag is fabricated, and the results reasonably agree with simulations. [ABSTRACT FROM AUTHOR]

A novel simple antenna based on substrate integrated coaxial‐like waveguide (SICW) is presented to enhance the gain and bandwidth of circularly polarized (CP) antenna with unidirectional radiation. The stepped inner metal strip is introduced in SICW, which results in a stronger radiation gain and wider axial ratio bandwidth. In addition, unlike traditional spiral antennas, the slot spiral antenna can be directly fed by a coaxial line at the inner port of the waveguide. As SICW can make the antenna directly realize unidirectional radiation, the extra reflector is not needed, and the antenna has a low profile of 0.1λ $0.1\lambda $ (λ $\lambda $ is the free space wavelength at the lowest frequency). The simulation and measurement results show that by using SICW with a stepped inner metal strip, the overlapping bandwidth of CP antenna can be increased significantly from 57.3% (2.7–4.85 GHz) to 71.6% (2.6–5.5 GHz) and the boresight gain of the antenna is improved 2 dBi over the entire frequency band. [ABSTRACT FROM AUTHOR]

A semiellipsoidal helical antenna (SEHA) is formed by scaling a hemispherical antenna in the axial direction. Effects of scaling factors on reflection coefficient (S11), axial ratio bandwidth (AR BW), and gains were analyzed thoroughly. By considering the best scaling factor, analysis is continued for strip‐based SEHA. It is observed that keeping the strip face parallel to the ground plane eliminates the concern of extra impedance matching issues and improves the overall performance over its wire‐based counterpart. For prototyping, the antenna is constructed independently on polylactic acid and acrylonitrile butadiene styrene plastic‐based supportive structures. Simulated and measured results are well agreed upon. When the height (h) in the axial direction is twice the hemispherical radius (r), the antenna provided maximum impedance and 3‐dB AR bandwidths of 144% and 77.53%, respectively, with a maximum gain of 8.83 dBi. The proposed antenna would be a good contestant in satellite communication where a broadband circularly polarized antenna is required. [ABSTRACT FROM AUTHOR]

The antenna is one of the key building blocks of many wearable electronic devices, and its functions include wireless communications, energy harvesting, and radiative wireless power transfer. In an effort to realize lightweight, autonomous, and battery‐less wearable devices, we demonstrate a reconfigurable antenna design for 5G wearable applications that requires ultra‐low driving voltages (0.4–0.6 V) and operates over a high frequency range (3.3–3.8 GHz). For smart glasses applications, previous antenna designs were 'fixed' and mounted on the eyeglass frame itself. Here, we demonstrate a reconfigurable design that could be achieved on the lens itself using an anisotropic liquid crystal (LC) material. We demonstrate how liquid crystal alignment and electric field patterns strongly influence the tuning capabilities of these antennas in the gigahertz range and present a smart, reconfigurable spiral antenna system with a liquid crystal substrate. [ABSTRACT FROM AUTHOR]

An effective, probe‐compensated, phaseless Near‐Field‐Far‐Field (NF–FF) transformation technique with planar spiral scanning is presented. The phase retrieval problem is solved by a quadratic inverse process, whose data are the voltage squared amplitudes of the NF samples acquired on two scanning surfaces. The available information on the antenna under test and on the scanning geometry are used to provide efficient representations for both the unknowns and the data, thus improving the accuracy and reliability of the technique. Furthermore, disconnected apertures are dealt with by adopting two different sets of prolate spheroidal wave functions to represent the aperture fields. Experimental results are reported to assess the effectiveness of the proposed approach. A drastic reduction (about 90%) of the required NF samples, as compared to standard λ/4 measurements (λ being the wavelength), is observed. Aggregating the measurements on the two scanning surfaces, the technique uses less samples even when compared to the case of complex, λ/2 measurements performed on a single surface. Our approach exhibits an accuracy comparable to that achieved when adopting complex measurements with non‐redundant sampling or classical, λ/2 plane‐rectangular NF–FF transformations. [ABSTRACT FROM AUTHOR]

This work describes the design and development of a dual‐band and dual‐polarized epsilon‐negative transmission line‐inspired antenna for wireless applications. In the proposed antenna, the implementation of curved meander lines results in antenna miniaturization; bandwidth enhancement is mainly due to the additional loading of complementary split‐ring resonator‐based mushroom resonator. Further, circular polarization radiation is obtained due to the additional loading of two‐arm Archimedean spiral resonators in the backside of the antenna forming a hybrid metamaterial structure. The proposed dual‐polarized antenna provides an overall electrical dimension of 0.17λ0 × 0.25λ0 × 0.026λ0 at the first resonating frequency of 2.49 GHz. The proposed antenna provides a fractional bandwidth of 7.22% (2.40–2.58 GHz) and 1.13% (2.62–2.65 GHz) for the first and second bands, respectively. Furthermore, the intended antenna provides maximum gain values of 1.28 dBi at 2.41 GHz and 1.94 dBi at 2.64 GHz for the first and second bands, respectively. As a result, the proposed antenna is well suited for ISM 2.4 GHz (2.4–2.484 GHz), WLAN/WiFi IEEE 802.11 b/g/n (2.4–2.48 GHz) and LTE 2500 (2.5–2.69 GHz) applications. [ABSTRACT FROM AUTHOR]

Hepatocellular carcinoma has been the leading cause of death in recent centuries and with the advent of newer technologies, several thermal and cryo‐ablation techniques have been introduced in the recent past. In this regard, microwave ablation has developed into a promising method for thermal ablation technique. However, due to clinical obligations, in‐vivo analysis is not feasible and ex‐vivo analysis is inaccurate due to changes in the electrical and thermal properties of the tissue. Therefore, in this study, temperature‐dependent permittivity, electrical conductivity, and thermal conductivity along with phase change effect due to temperature reaching above 100°C are incorporated using finite element method model. Further, using an intertwined normal mode helical antenna ablation probe, a change in resonant frequency (Δf) and reflection coefficient (ΔS11) from the actual value (antenna parameter in the air at 5 GHz) is modeled using second‐order polynomial curve fitting to predict the surrounding permittivity in the range of 30–70. A maximum deviation of 0.8 value in permittivity from the actual value is observed. However, to obtain a generalized methodology, XG Boost and CAT Boost algorithms are used. Further, since ablation diameter plays a crucial role in achieving optimal tumor ablation, an artificial neural network (ANN) algorithm with three different optimizers is incorporated to predict ablation diameter using five critical parameters. Such an ANN algorithm which can predict the transversal and axial ablation zone may provide optimal ablation outcomes. [ABSTRACT FROM AUTHOR]

A low‐profile spiral antenna with three stopbands (2.55 GHz band, 3.85 GHz band, and 5.45 GHz band) is developed. The stopbands are generated using three pairs of slots cut into the spiral arms. The antenna height is 0.077 wavelength at a low band edge frequency of 2 GHz. Firstly, the effects of the slot dimensions (length, width, ending angle, and position) on the stopbands are analysed, where the spiral antenna floating in free space radiates a bi‐directional beam. It is found that the stopband centre frequency is determined by the slot length, and the stopband bandwidth is determined by the slot width, ending angle, and position. Secondly, the fabrication tolerances are investigated. Thirdly, the bi‐directional beam from the floating spiral antenna is transformed into a unidirectional beam by using a low‐profile cavity. It is revealed that three stopbands are maintained. Finally, a prototype of the antenna is fabricated and measured to verify the analysed results. [ABSTRACT FROM AUTHOR]

Curl and truncated spiral antennas are studied for input impedance matching a coaxial line. Each antenna is located at quarter wavelengths above the ground plane and analyzed using the moment method. It is found that the curl antenna shows a voltage standing wave ratio (VSWR) of less than two in a 3‐dB axial ratio bandwidth of 30% using a crank feedline with an unbalanced feed. It is also found that the spiral antenna has an axial ratio bandwidth of 24%, where the VSWR remains less than two using parallel feedlines with a quasi‐balanced feed. [ABSTRACT FROM AUTHOR]

Using the moment method, two array antennas are investigated to reveal the effects of different radiation elements on the array characteristics. Each array comprises four elements sequentially rotated by 90° and excited by a coplanar C‐figured feedline above the ground plane. It is found that a loop element array has a 3 dB axial ratio bandwidth of 30%, 3.3 times as wide as that of an isolated loop without an array environment. In contrast, a spiral element array shows a 3 dB gain drop bandwidth of 62% (72% for the axial ratio bandwidth, wider than that of an isolated spiral by a factor of 3.0). Almost the same factors of 3.0 and 3.3 for the spiral and loop element arrays are then compared with those in similar studies. It is found that factors are classified into three groups by feedline types. The simulated results are verified by experimental work. [ABSTRACT FROM AUTHOR]

A compact focused metamaterial‐based applicator is investigated for hyperthermia cancer treatment in this letter. The metamaterial‐based applicator consists of a double spiral antenna (DSA), an artificial magnetic conductor (AMC) as a reflector, and a frequency selective surface (FSS) as a lens. An AMC structure (64 × 64 mm2) is placed in the back of the antenna at a 5 mm distance that converges the bidirectional field pattern of the antenna into the directional field pattern. Further, to increase penetration inside the tissue, an FSS structure (64 × 64 mm2) is placed at the top of DSA at a distance of 4 mm. The FSS directs the energy toward the tumor location and provides a uniform heating pattern. The field and temperature distribution are numerically obtained for the proposed applicator in the heterogeneous phantom (layers of skin, fat, and muscles), and the performance of the applicator is evaluated in terms of the specific absorption rate, penetration depth, and effective field size. The performance of the applicator is also analyzed for a deeply placed (at 16 mm from the skin surface) irregular‐shaped tumor. The temperature profile calculates 44°C at an input power of 2.5 W. The results show that the applicator is capable of heating sufficiently deep‐seated tumors. [ABSTRACT FROM AUTHOR]

Due to the orthogonality, multiple orbital angular momentums (OAMs) have great potential for increasing communication capacity and improving imaging resolution. In this work, a general N‐arm Archimedean spiral antenna (ASA) synthesis method is proposed for generating broadband vortex waves carrying multiple OAMs. In the proposed method, the theoretical formulas of the whole OAM modes based on the improved current band theory for N‐arm ASA and the maximum common bandwidth of each N‐adjacent OAM mode are presented. The performance of the proposed method is verified by simulated results of three‐arm ASA, as well as simulated results and measured results of four‐arm ASA. The measured results show that the four‐arm ASA generates vortex waves carrying OAM modes of l = 0, 1, 2, 3 in 0.6–3, 1.4–3.8, 2.3–4.1 and 2.6–4.5 GHz. And the maximum common bandwidth of the four generated OAM modes is 2.6–3 GHz, which satisfies the design requirement of OAM's practical application. [ABSTRACT FROM AUTHOR]

A miniaturized lumped‐element balun is proposed for the very high frequency band applications. The miniaturization is accomplished by the inductor–capacitor (L‐C) surrounded resonator, which places a vertically interdigital‐capacitor inside spiral inductor for higher integration. The L‐C surrounded resonator only takes up one element's area without increasing the number of substrate layers. The balun is built on a 10‐layer thickness low temperature co‐fired ceramic substrate and has the smallest reported size of only 0.004 × 0.003 × 0.0003λg. Moreover, the proposed balun also has a second‐order harmonic suppression of 40 dB. Furthermore, thermal boundary analysis, comparisons, and discussions are also implemented. [ABSTRACT FROM AUTHOR]

This paper introduces a new design for a wireless body area network (WBAN) antenna employed as a body central antenna. The role of this central antenna is to receive the data from the on‐body and in‐body biosensors working at 2.45 GHz and transmit it off‐body to a worldwide interoperability for microwave access (WiMax) antenna at 5.8 GHz. The central antenna is a composite structure constructed from a spiral antenna attached to the tip of a monopole. It operates in two modes, on‐body mode at 2.45 GHz to receive data from the on‐body and in‐body biosensors and off‐body mode at 5.8 GHz to transmit data to WiMax. The antenna has a compact size and lightweight with total dimensions of 12 × 12 × 8.5 mm and a 10.8% bandwidth (BW) at 2.45 GHz to communicate with in‐ and on‐body biosensors, and wider BW of 23% at 5.8 GHz to allow for high data transmission rates to the WiMax. The radiation pattern is broadside circular symmetric at the lower operating frequency and balloon‐like with high gain at the upper‐frequency band. The gain at the lower‐ and upper‐frequency bands is 4.9 and 7.1 dBi, respectively. A prototype is fabricated for the monopole/spiral body central antenna. Experimental measurements for the reflection coefficient and the radiation patterns are performed showing good agreement with the simulation results. [ABSTRACT FROM AUTHOR]

By periodically patterning the conductor surface, the so‐called spoof surface plasmon polaritons (SSPPs) in microwave band can be transmitted and SSPP mode devices with the cutoff frequency at high frequency end can be constructed. In this paper, the spiral slots are loaded in the edge and the feed port of a printed monopole antenna element and two rejection bands are achieved. The results indicate that in the intuitive physical sense, the slot‐typed band‐stop resonator in antenna structure actually works according to the SSPP mode mechanism. Furthermore, it is proposed that its structure size should be determined according to the principle that the slot resonant frequency is a bit lower than the asymptotic frequency of SSPP modes. [ABSTRACT FROM AUTHOR]

Self‐powered arbitrary wave monitoring is a hot research topic which aims to remove of the trouble associated with managing conventional power for continuous and real‐time acquisition of wave information from the marine environment. Herein, an effective approach is presented that simultaneously generates power from arbitrary motion waves and can sense and wirelessly transmit the wave information without requiring an external supply. The hybridized ellipsoidal device inspired from an elliptical trajectory of objects over shallow water waves, consists of six planar spiral coils arranged to cover the arbitrary direction of waves for power generation. Four magnetic force‐actuated triboelectric nanogenerators (TENGs) pairs along four sides as the arbitrary direction self‐powered wave motion sensors are integrated. Furthermore, all the required circuitry for signal processing and wireless transmission are integrally powered by the generated electricity to realize a self‐sustained wireless marine environment monitoring system. The generator can deliver peak power of 106 and 44.8 mW (at 3Hz) along with major and minor axis motion directions. The self‐powered sensors have excellent motion sensitivity thus the signals obtained from these sensors are utilized to acquire useful information related to the water waves which are very crucial parameters for real‐time monitoring of the marine environment. [ABSTRACT FROM AUTHOR]

Modern robotics has made great strides in the field of agricultural harvesting. In the field of rubber tapping, however, there are still significant challenges to be faced. As one of the few agricultural harvesting areas primarily manual, rubber tapping requires precise control of the knife in the forest's unstructured environment at night. This paper presents the design of a rubber cutting robot for natural rubber plantations. An upgraded spatial spiral trajectory is established by analyzing the trunk and manual rubber cutting trajectories for the operation of a six‐axis tandem robot arm. A compact binocular stereo vision system achieved the initial perception of the parameters required for the cutting trajectory. Besides, an integrated end‐effector was developed to enable further precise perception of the cutting trajectory and cutting operations. The system was tested in the field at a rubber plantation in Hainan Province. The upgraded trajectory's adaptability and the accuracy and efficiency of the starting point positioning algorithm were verified. The operational performance of the complete system was evaluated to help guide future improvements. The error of the start point locating is 1.0 ± 0.1 mm, and the execution time is 17.01 ± 3.65 s. The bark consumption—cutting depth setting of (2.0 and 5.0 mm) is more appropriate for the rubber tapping robot. Then the accuracy of chip thickness and chip width is about 1.73 ± 0.28 mm, and 5.07 ± 0.13 mm, respectively. Furthermore, the accuracy of chip weight is 1.99 ± 0.24 mm. The average operating time of the whole tapping operation is 80 ± 5 s. Future work will include improvements in system stiffness and robustness. This study demonstrates the potential of applying industrial robotics to the field of latex harvesting. Robotics may be a future development towards mechanized rubber tapping. [ABSTRACT FROM AUTHOR]

In the study, a miniaturised printed quadrifilar helix antenna (PQHA) with isoflux coverage and wide‐angle circular polarisation is presented. It is composed of a three‐stage stepped impedance spiral arm and open stubs. Each of the three‐stage spiral arms has different pitches and number of turns. For the last‐stage spiral arm, meander lines are used. The proposed PQHA features the characteristics of wide bandwidth, isoflux radiation, small size, and wide‐angle circular polarisation. Moreover, in order to feed the proposed PQHA, a miniaturised quad‐feed network is designed to provide equal amplitude signals with sequential orthogonal phases. For demonstration, a prototype is designed, fabricated, and measured. The overall size of the proposed antenna is 88 × 88 × 132 mm (0.44 λ0 × 0.44 λ0 × 0.66 λ0). The results show that isoflux radiation with a coverage of about ±60° is realised from 1.40 to 1.62 GHz (14.6%) while maintaining more than 10 dB return loss and larger than 200° 3‐dB axial ratio beamwidth. [ABSTRACT FROM AUTHOR]

Regarding the capacitive nature of input/output impedances of millimeter‐wave amplifiers, it is necessary to utilize wideband inductive elements for the design of input/output impedance matching circuits. In this paper, the design and optimization of an ultra‐wideband transmission line inductor with an inductance of less than 100 pH are introduced for using at frequencies above 50 GHz. The reason of using this inductor is its superior performance compared to that of a spiral inductor and single‐coil inductor. The inductor consists of three rectangular microstrip line segments with nonequal and variable characteristic impedances. The design is done by calculating the impedance matrix using planar circuit analysis (PCA) based on a planar waveguide model, segmentation/desegmentation methods, and an intelligent algorithm in MATLAB. With this design method, the effect of discontinuities, fringing fields at the edges of the microstrip, and the conductor as well as dielectric losses can be considered while minimizing the dispersion effect. In this study, to reduce the calculation time of the impedance matrix, the doubly infinite series are reduced to a singly infinite series by summing the inner sum for a rectangular segment whose one side is shorted and three other sides are open. [ABSTRACT FROM AUTHOR]

The rapid development of electronic skins has allowed novel multifunctional human–machine interaction interfaces, especially in motion interaction sensors. Although motion sensing is widely used in advanced flexible electronic devices through the integration of single sensing units, the number of electrodes has increased with the increase in integration by the square multiple. This paper presents a self‐powered electronic skin based on the Archimedes spiral structure design, which can detect the multi‐directional movement of the slider without external energy supply. As the rotation angle of the Archimedes spiral increases from 2π to 4π, the maximum resolvable movement direction of the device increases from 24 to 280, and the number of electrodes is kept at 4. Through the exploration of the principle of triboelectricity, the inherent electronegativity of the triboelectric materials is used as the basis for signal discrimination, which not only increases the reliability of the device, but also solves the problem of energy supply during device operation. A reduced number of electrodes and its battery‐free nature enables this electronic skin to be easily integrated into portable electronic devices, such as laptops, smart phones, healthcare devices, etc. [ABSTRACT FROM AUTHOR]

A broadband, high radiation efficiency graphene‐based reconfigurable square spiral antenna for terahertz communication is proposed. The main part of the antenna is the graphene‐based square spiral microstrip patch. The proposed antenna is built and simulated using high‐frequency structure simulator (HFSS). By applying different combinations of chemical potentials on the graphene layer, the operating frequency of the antenna can be varied from 0.1 to 2 THz. The tuning range of frequency and beam direction with same and different chemical potentials applied to the two graphene sheets are also studied. When the antenna is applied with different chemical potentials, the required bias voltages are much lower to achieve the same frequency tuning range, and the tuning range of beam direction is about 2.5 times that of same chemical potentials. The realized beam reconfiguration of the proposed antenna is over a wide range up to 74°, and the calculated maximum radiation efficiency of the proposed antenna at 1.48 THz is 85.06%. Therefore, the proposed reconfigurable antenna makes it extremely promising for terahertz communication system. [ABSTRACT FROM AUTHOR]

Orbital angular momentum (OAM) as vortex wave has potential application for dense communication. A multi‐slot antenna is proposed based on Archimedean spirals to generate/detect the OAM waves. The antenna equips three radiation slots in a disk‐manner to realize three different OAM modes simultaneously. A serial‐fed microstrip array is designed for circularly polarized (CP) radiation. The lengths of the slots and microstrip lines are chosen to radiate at 3.5 GHz with 20% fractional bandwidth. So, it can identify the receiving modes of vortex wave with this mechanism. A prominent spiral phase plane is observed for the generated OAM wave. In addition, the far‐field pattern presents a doughnut‐shape beam. The whole antenna is fabricated on a 13 cm printed circuit disk board. Both the experimental and simulation results show that the proposed antenna has valuable features to produce different vortex modes. [ABSTRACT FROM AUTHOR]

In this article, three novel slotted substrate integrated waveguide (SIW) antenna elements are demonstrated with different radiator configurations, namely, two arms Archimedean antenna, single‐arm spiral antenna (monofilar), and four concentric circular loops antenna. Additionally, their near, as well as far‐field characteristics, have been investigated. The two arms Archimedean spiral antenna has a superior radiation characteristic of 18% return loss bandwidth (RLBW), 12% boresight axial ratio bandwidth (ARBW), and five dBi directivity. Furthermore, a 1 × 10 slotted SIW travelling wave antenna array has been designed, fabricated, and measured. The performance of the proposed antenna array versus the last reported antenna was evaluated and the proposed antenna array performance is superior to that of the others. Moreover, the measurements of the proposed array have a good agreement with the simulation results in which, 35%, 13% RLBW, and ARBW, respectively, have been achieved. The directivity of the proposed antenna array is 14 dBi. [ABSTRACT FROM AUTHOR]

A compact wideband four‐arm circularly polarized (CP) spiral antenna with both sum mode (1) and difference mode (2) is presented. The antenna is composed of a modified four‐arm equiangular spiral, a four‐arm z‐directional helix, a ring‐shaped absorber, and a ground plane. By using the modified equiangular spiral and the z‐directional helix, the impedance matching of mode 1 and mode 2 is improved, and the cross‐polarization discrimination of mode 2 is also improved in the low frequency band. The z‐directional helix is also applied to achieve a compact size of the antenna and an enhanced AR bandwidth of mode 2. A prototype of the four‐arm spiral antenna is fabricated and measured with a beamformer operating at 0.5 to 2 GHz. It is shown that both sum and difference radiation patterns are generated in the whole frequency band of 0.5 to 2 GHz. The overall size is 0.486λ0.5 GHz × 0.097λ0.5 GHz (diameter × height, λ0.5 GHz is the free‐space wavelength at 0.5 GHz). [ABSTRACT FROM AUTHOR]

In this paper, three configurations of LC (inductor–capacitor) pressure sensors are developed, namely series LC pressure sensors, compact LC pressure sensors, and far‐field LC pressure sensor tags. The modified silk protein films have been chosen as substrates due to their good biocompatibility and air/water permeability, which is suitable for continuously pasting such substrates on skin. For series LC pressure sensors, conducting wire is used to connect the flexible capacitor and spiral inductor. It exhibits good cycling stability and high sensitivities, suitable for electronic skin. For compact LC pressure sensors, the spiral coil functions as inductor, antenna, and capacitor electrode simultaneously, minimizing the space cost and is suitable for array integration, while the sensitivities remain the same. By tailoring the turn of the spiral coil, the resonate frequency can be regulated continuously. An annular array of compact LC sensors with ten distinct resonate frequencies ranged from 400 to 1000 MHz is developed to remotely monitor the press of number 0–9. Finally, far‐field LC pressure sensor tags with elongated detection distances are developed in which each compact LC sensor acts as a filter. A wireless in‐shoe plantar to detect the sole pressure distribution using the far‐field LC sensor configuration is developed. [ABSTRACT FROM AUTHOR]

This paper presents a compact wideband circularly‐polarized square slot antenna (CPSSA). The antenna is a coplanar waveguide feed structure with three T‐stubs toward the slot center and one semi‐circle tuning stub was etched to the feed line and modified inverted L‐shaped strips around the corners of the ground. Moreover, two spiral slots were loaded in the ground plane for exciting currents in a different direction. A prototype of the designed antenna is fabricated and measured to confirm the simulation results. A reasonably good agreement between the measured and simulated results in terms of the reflection coefficient <−10 dB and axial ratio are achieved. The 3‐dB axial ratio bandwidth achieved by the combination is from 4.35 to 8.15 GHz (60%, measured). The designed CPSSA has a compact size of 0.57λₒ × 0.57λₒ × 0.0116λₒ at the center frequency and fabricated on the FR4 substrate. [ABSTRACT FROM AUTHOR]

An ultra‐wideband unidirectional circularly polarized planar self‐complementary and compact Archimedean square spiral antenna is proposed in this paper. Compared to the conventional center‐fed or vertically‐connected coaxial line spiral antennas, the proposed antenna has a completely planar feed structure. The traditional impedance transformer (balun) in the third dimension is moved to the planar plane based on a wideband microstrip line to coplanar stripline transition to realize a completely planar spiral antenna. This impedance transformer is integrated with the spiral antenna to achieve a planar structure and to adapt the impedance into a conventional 50 Ω coaxial cable. The performance of the proposed antenna is simulated and measured. The proposed antenna has a compact size of 90 × 90 × 1.6 mm3 on an FR4 substrate and can yield a large −10 dB impedance bandwidth ranging from 2.14 to 9.8 GHz which is equivalent to a fractional bandwidth of 102.13% with unidirectional radiation patterns. The VSWR is less than two in the operating bandwidth and the axial ratio (AR) is less than 3 dB in the frequency range of 1‐8 GHz. The simulated radiation efficiency ranges between 20% and 80%. The characteristics of the proposed antenna make it suitable for ground‐penetrating radar applications and many others. [ABSTRACT FROM AUTHOR]

This study describes a light‐weight wideband spiral antenna that radiates a unidirectional beam. To realise a light‐weight antenna, a one‐layer thick high‐impedance surface reflector (HISR) for a reference spiral antenna is replaced by a two‐layer circular HISR (TL‐CirHISR). The TL‐CirHISR is made of fan‐shaped patches printed on a dielectric substrate. It is revealed that a voltage standing wave ratio (VSWR) of <2 and an axial ratio of <3 dB are obtained across a design frequency range of 3.2–10 GHz (a fractional bandwidth of ∼103%). A weight reduction of 50%, compared to the weight of the reference spiral antenna, is achieved. A prototype spiral antenna with the TL‐CirHISR is fabricated and measured to confirm the analysed antenna characteristics, with good agreement between analysed and measured results obtained. [ABSTRACT FROM AUTHOR]

This study presents, for the first time, a novel design of ultra‐wideband (UWB), circularly polarized and highly directive log‐spiral THz photoconductive antenna. The proposed antenna is simulated in High Frequency Structure Simulator using gold as the antenna electrode material which is backed by a quartz substrate (εr = 3.78, tan δ = 0.0001) and hemispherical silicon‐based lens with a diameter of 140 μm. A comprehensive detailed parametric study of the antenna design parameters is performed in the frequency range of 1 to 6 THz for the optimal design of the developed antenna structure. The optimal antenna structure with integrated lens has UWB characteristics with −10 dB impedance bandwidth of 5 THz and 3 dB axial ratio bandwidth of around 4 THz. The observed directivity and half‐power beam width of the presented design varies in the range 5 to 12 dBi and 34° to 62°, respectively, for the frequency range of 1 to 4 THz. The wideband, high directivity as well as high‐efficiency (>50%) characteristics of the proposed design make it a favorable choice for the THz sensing and imaging applications. [ABSTRACT FROM AUTHOR]

Over the last decade, the wearable electronics has greatly improved and the wearables market is expected to increase exponentially in the next years. Ultra high frequencies (UHF) radio frequency identification (RFID) textile yarns represent one of the most relevant solutions for adding smart functionality into clothes and more generally for any object integrating a textile tag. Among the existing textile yarn solutions, the E‐Thread technology consists on electronics embedded into textile yarn using a micro‐encapsulation method. This technology is the starting point of the work presented in this article. One of the hardest constraints that the RFID yarn should overcome is the robustness against stretching. Thus, the antenna has to be tolerant to the deformation of the associated textile yarn. Unlike the half‐wave dipole antenna used in the current E‐Thread yarn, the proposed solution is based on helical dipole antenna topology because its geometry naturally makes feasible an axial stretching. This study details the manufacturing process as well as the design methodology of the antenna taking into account the RFID context as well as the constraints imposed by the manufacturing process. The impact of the antenna's physical parameters is highlighted in order to provide design guidelines. The helical dipole antenna enables until 16% of axial elongation while the dipole antenna would tear apart. [ABSTRACT FROM AUTHOR]

This paper studies a unidirectional ultra‐wideband circularly polarized (CP) spiral antenna array. The ultra‐wideband high‐gain CP operation is realized by implementing four‐element sequentially rotated spiral array antennas fed with an ultra‐wideband feeding network. Tapered multisections power dividers and broadband microstrip‐slot phase shifters are utilized to provide accurately equal power division and constant phase shifts of 90°. In order to further improve the CP operating bandwidth, foam of absorber is adopted between the radiating aperture and the feeding network substrate. The proposed CP array is designed, fabricated, and measured. Test results show that the impendence bandwidth of the proposed array covers 2.2 to 11.6 GHz (5.3:1) and 3 dB axial‐ratio bandwidth covers 2.3 to 13 GHz (5.65:1), demonstrating a stable CP array performance within an ultra‐wide working bandwidth. [ABSTRACT FROM AUTHOR]

We report the design, fabrication, and measurements of a circularly polarized 3D‐printed helical antenna operating at 5 GHz. Several commercially‐available dielectric printers and materials (eg, PLA, ABS, PC) were evaluated for the fabrication process. Metallization was performed with nickel electroless plating followed by copper electroplating. Fabrication and metallization process completed within 24 hours. Maximum gain of the antenna is measured as 13.9 dBic at broadside (RHCP). Measured efficiency of the antenna is 89.1% which shows the effectiveness of our metallization process. The results demonstrate the feasibility of rapid fabrication of lightweight and high efficient antennas using 3D printer technology. [ABSTRACT FROM AUTHOR]

Stepped frequency continuous wave (SFCW) radar is a promising noncontact method to detection of human vital signs. Antenna as a key component of radar directly related to the performance of the radar. In this letter, we present a 0.5‐1.2 GHz compact multiple cut‐corners square spiral antenna for SFCW radar system. Compared with conventional planar spiral antennas, the improved antenna possesses the advantages of miniaturization and excellent axial ratio. The gradient‐change of the cut‐corners along the radiation determines its operation range: large cut‐corner corresponds to high frequency, while small cut‐corner affects low frequency. This design successfully leads to a small geometric size of 0.282 × 0.282 × 0.133 m. We measured this improved antenna in an anechoic chamber, and the results demonstrated that the circular polarization bandwidth for axial ratio ≤3 dB approached 100%, and a right‐hand circularly polarization (RHCP) gain of 4‐8.98 dBic in end‐fire direction is achieved in its operational range. Finally, we designed the experiment, experimental results show that the proposed antenna can work well with the SFCW radar in the detection of human vital sign (respiratory signals), indicating a great potential for detected life in practice. [ABSTRACT FROM AUTHOR]

The genetic algorithm is employed to obtain optimal designs for helical antennas that, over the frequency range of operation, provide considerably smaller axial ratio, higher gain, and an appreciably wider overall bandwidth than the conventional axial mode helices with the same size. Also, for nearly equal bandwidth and peak directivity, the new design provides a 2 to1 reduction in size. For these helical antennas the pitch angle and radius, which are constant in conventional helices, vary continuously along the length; pitch angle increases while radius decreases. Genetic algorithm is used to determine variations of these parameters such that maximum directivity and minimum axial ratio are simultaneously achieved over the largest frequency range. Radiation properties of optimized helices, including far‐field pattern, axial ratio, and directivity, are examined numerically over a wide range of frequencies. Empirical design equations are provided. A 12‐turn prototype optimized helix is constructed and measured. Comparison of measured and simulated radiation patterns shows excellent agreement. [ABSTRACT FROM AUTHOR]

The design of a stretchable inverted conical helical antenna (SICHA) applicable to maritime search and rescue is proposed, and the gain and the reflection coefficient are obtained at a resonant frequency of 156 MHz. The optimized top and bottom diameters of the SICHA are 36 and 18 mm, respectively, and its height is 115 mm, which is much shorter than a quarter‐wavelength monopole. Finally, we simulate the outdoor propagation of electromagnetic waves with the SICHA; both the simulated and measured received power intensities are similarly reduced as the distance between the two antennas increases. [ABSTRACT FROM AUTHOR]

In this research letter, a new type of miniaturized ultra‐wideband planer equiangular spiral antenna is designed. This present antenna can cover an operating bandwidth of 0.8‐6 GHz. In the new design, the original antenna is effectively miniaturized by introducing three special branches to extend the electrical length in the working band. This present method expands the bandwidth of the antenna, and finally realizes miniaturization, and ultra‐wideband of the antenna. Compared with the original antenna, the antenna can reduce the size about 37.5% at low frequencies. Finally, the new antenna has good performances, which are verified by simulation and measurement results. [ABSTRACT FROM AUTHOR]

A novel method of radiating circularly polarized (CP) impulse through a dispersive spiral antenna is presented. The proposed method utilizes time‐reversal‐based pulse compression to radiate a CP impulse without any modification to the existing antenna design, providing flexibility where the antenna can be used as a normal dispersive spiral antenna when TR is not applied. Using an Archimedean spiral antenna, the proposed method is validated with numerical simulation and measurement. [ABSTRACT FROM AUTHOR]

This article presents a high‐efficiency dual‐band rectenna, for RF energy harvesting in GSM bands (900‐1800 MHz). The rectifier used is a dual‐diode rectifier topology based on a Delon voltage doubler. To ensure, the highest efficiency as possible, source‐pull simulations are used to determine the optimal diodes input impedance. The antenna is a spiral planar structure, where two slots ring resonators have been added to expand bandwidth at low frequencies without increasing its initial size. It is associated with a broadband balun to transform its impedance into the desired 50‐Ω rectifier input impedance. The antenna and balun are sized for broadband operation to cover the main wireless communication bands. Measurement results show high RF‐DC conversion efficiencies of 28% and 20% at 890 MHz and 1780 MHz, respectively, for a low RF input power of −20 dBm and with a 10 kΩ DC load. Efficiency reaches 43.5% with a dual‐tone signal at −20 dBm. [ABSTRACT FROM AUTHOR]

A novel artificial magnetic conductor (AMC) surface based on spiral strips is proposed, which consists of 9 × 9 AMC cells. Each AMC cell includes a spiral strip to increase its inductance, thus featuring a wide bandwidth of 42% for ±90° reflection phase. The AMC surface is applied to three planar dipole antennas for lowering the antenna heights, including a linearly polarised (LP) antenna, a dual‐polarised (DP) antenna, and a circularly polarised (CP) antenna. It is shown by simulation and experiment that the LP antenna achieves an impedance bandwidth of 40% (0.68–1.02 GHz) for |S11| < −15 dB and a gain of 8 dBi, the DP antenna realises an impedance bandwidth of 33% (0.69–0.96 GHz) for |S11| < −15 dB, an isolation of 30 dB, and a gain of 8 dBi, and the CP antenna has an overlapped bandwidth of 33% (0.75–1.05 GHz) for |S11| < −15 dB and axial ratio <3 dB. The heights of all the three planar antennas are lowered from 0.265–0.3λ0 to 0.083λ0. [ABSTRACT FROM AUTHOR]

This work presents the design, manufacturing, and measurement of a miniaturized circularly polarized ultrawideband Archimedean spiral antenna that operates from 0.3 GHz to 16 GHz. It acts as a radiofrequency harvester, capturing the energy spectrum in the bands of interest (FM, DTT, LTE‐800, GSM‐900, GSM‐1800, LTE‐2100, WiFi, LTE‐2600 and WiMAX). A prototype of the Archimedean spiral has been manufactured and characterized in the laboratory, and a comparison of the harvested power with respect to other also manufactured baseline 2.4 GHz patch antennas has been carried out in two different locations: inside and outside the laboratory. These results prove that hundreds of microwatts can be acquired in a normal situation, without the spiral pointing directly at a prefixed source. [ABSTRACT FROM AUTHOR]

This paper proposes a compact spiral antenna with an improved bandwidth and miniaturized radiator for 3:1 (2‐6 GHz) wideband antenna beamforming arrays. The proposed antenna is composed of an Archimedean spiral antenna (ASA) with an annular ring and additional dielectric substrates with a circular hole. The spiral and ring radiators are printed between two substrates made of FR‐4, with a dielectric constant of 4.5 and thickness of 1.524 mm. The size of the antenna is 30 mm × 30 mm × 3.048 mm (0.2λ × 0.2λ × 0.02λ at the lowest frequency). The reduction rate of size is up to 15% compared with a conventional ASA using an annular ring, and it also has low‐profile characteristics. [ABSTRACT FROM AUTHOR]