Slot Loop Antenna Research Articles

Low-Profile Antenna System for Cognitive Radio in IoST CubeSat Applications

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.

Optically Transparent Antenna for Smart Glasses

The optically transparent antenna technology has been gaining attention in consumer electronic industry owing to its potential to release the antenna volume constraints in compact mobile devices. Earlier studies have been heavily focused on the transparent antenna integration to the display for smartphone applications, for example, to improve its spatial coverage of 5G mm-wave at the forehead side. To our knowledge, the application of the transparent antenna technology to smart glasses and augmented reality glasses, especially considering the constraints from the coexistence with optical features in the lens stack-up, has remained unexplored. Thus, for the first time, we suggest a feasible existence solution between antennas and the RF lossy layers in the lens stack-up, to reduce the negative impacts on antenna performances. A slot loop antenna formed by metal-mesh based transparent antenna film and metallic glass frame has been investigated. Experimental results of such an antenna on human head phantom shows a total efficiency better than −4.5 dB in 2.4 GHz band. Even though it is demonstrated through a 2.4 GHz antenna example, the same principle can be applied to any other sub-6 GHz antenna applications, i.e., LTE, WiFi, GNSS, etc.

Wideband circularly polarized array antenna based on sequential phase feeding metasurfaces for 5G (sub-6G) applications

In this paper, a broadband circularly polarized array antenna is presented, which consists of four loop slot antennas based on metasurfaces. The antenna element is a loop slot antenna fed by a microstrip line. Cross slots are added to the loop slot to improve the antenna bandwidth, and four corner-cut square metasurfaces are loaded above it, thus generating circularly polarized radiation. The antenna adopts a sequential phase (SP) feed network to realize broadband characteristics. The antenna has been fabricated and experimented. The overall size of the antenna is 78 × 78 × 10.1 mm3 (approximately 1.22 λ0 × 1.22 λ0 × 0.15 λ0), the antenna array has a measured |S11| < −10 dB bandwidth of 3.6–6.2 GHz (53.1%) and a 3-dB axial ratio bandwidth of 3.7–4.8 GHz (28.32%). Furthermore, the antenna also has radiation with a peak gain of 5.5 dBi.

Frequency-Tunable Slot-Loop Antenna Based on KNN Ferroelectric Interdigitated Varactors

A miniature frequency-tunable slot-loop antenna (0.128 λ 0 × 0.077 λ 0) based on ferroelectric K0.5Na0.5NbO3 (KNN) interdigitated varactors is investigated at Ku-band. KNN material has been selected among the ferroelectric oxide family because of its competitive properties for microwave applications. Its high permittivity value ( ϵr a 360 at 10 GHz) and its wide frequency tunability under an external static electric field E bias make it a promising candidate for frequency-agile antennas and circuits at microwaves. The antenna prototype has been designed and elaborated on MgO substrate ( ϵr = 9.8 and tan δ a 10−4 at 10 GHz). Fabrication details including laser microetching process of the ferroelectric layer are also described. The center frequency of the slot-loop antenna can therefore be tuned monotonously from 15.22 to 15.97 GHz under E bias = 88 kV/cm, leading to a frequency tunability rate equal to 4.6%. These results demonstrate for the first time the ability of the KNN material to be used for miniature tunable antennas, in comparison with BaxSr1−xTiO3, currently considered as the most relevant material for such applications.

Textile Electromagnetic Brace for Knee Imaging.

A wearable textile brace is introduced as an electromagnetic imaging system that breaks hospital boundaries to real-time onsite scanning for knee injuries. The proposed brace consists of a 12-element textile slot loop antenna array, which is designed to match the human knee for enhanced electromagnetic wave penetration. Wool felt and conductive fabric are used to fabricate the antenna array thanks to their flexibility and proper dielectric properties. Each antenna element has a compact footprint of 42 ×24 ×3.22 mm3 and achieves unidirectional radiation, high front-to-back ratio of 14 dB, wide bandwidth of 81% at 0.7-1.7 GHz, and safe SAR levels. A modified double-stage delay, multiply, and sum (DS-DMAS) algorithm is used to process the collected signals from the antenna array based on differential left/right knee imaging. The reconstructed images numerically and experimentally on realistic phantoms demonstrate the potential of the brace system for onsite detection of different types of ligaments/tendon tears.

Omnidirectional WLAN Antenna With Common-Mode Current Suppression

An omnidirectional wireless local area network (WLAN) loop-slot antenna with common-mode current (CMC) suppression is proposed in this communication. First, based on the analysis of the equivalent model of odd-even mode, the feeding coaxial line is led out at the voltage-zero point of the loop-slot element, which suppresses the CMC over the full band. Second, through the theory of array, three loop-slot elements form an array to obtain omnidirectional radiation. Finally, the physical size is reduced by loading Stubs T in the slot. The roundness of the radiation pattern is modified by the Stubs T and the chamfering edge of the antenna. A prototype of the proposed antenna was fabricated and measured. The measured results show that the antenna achieves |S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> | <; -10 dB in bands of 2.15-2.65 and 4.85-5.92 GHz. In addition, the roundness is 0.95 dB at 2.4 GHz, 1.84 dB at 5.2 GHz, and 2.43 dB at 5.8 GHz. The antenna effectively suppresses the CMC to keep a favorable roundness over a wide band, showing its potential in WLAN communication systems.

A Wideband Dual Polarized Dual-Mode Antenna with Simple Differential Feeding

A wideband differentially fed dual-polarized dual-mode antenna is presented in this letter. Four slots are placed a square shape to construct the slot loop antenna, and the outer ground of the slot loop is bended to achieve a compact size. A simple out-of-phase power splitter with a wide bandwidth and accurate 180° phase difference is integrated with the radiator to feed the slot loop. The 1 and 2 λ modes of the slot loop antenna are excited with the differential feeding for a wide impedance bandwidth (IMBW). By loading the distributed inductors at the ends of each slot, a radiator size of 106 × 106 mm2 is obtained to cover LTE700/GSM850/GSM900 bands. Measured results show that the antenna has the IMBWs of 0.63–1.09 GHz (0.46 GHz, 53.5%) and 0.63–1.08 GHz (0.45 GHz, 52.6%) for the two input ports, isolation of more than 31.5 dB, and stable gain of around 7.15 ± 0.35 dBi for Port 1.

An efficient hybrid solar and electromagnetic harvesting system for autonomous operation of small sensors

In this study, we propose a combination of solar cells and a rectenna to realize a solar and electromagnetic energy harvesting system. The proposed harvester consists of a circular slot antenna, a rectifier circuit which is designed with a reverse-biased Schottky diode, and SHJ solar cells with a combination of AZO/TiO2 as antireflection coating and a diffraction grating morphology. Each designed component has been characterized through simulations and measurements. First, the solar cells are designed and investigated separately. Then, they are carefully placed near the slot loop antenna, which is attached to the rectifier circuit, to realize the combined harvesting system. The heterojunction solar cells with an intrinsic thin layer (SHJ) have been designed based on light trapping mechanism, which reduces the reflection of solar radiation and interfacial traps effects significantly. Solar cells’ simulations are obtained using an analytical model. The parameters of light trapping, as well as the effects of the position of the solar cells on board of the patch, are studied carefully. Simulation and experimental results validate that the combined harvesting system is a promising candidate for autonomous operation of some sensors and small devices. Indeed, the efficiency of the rectenna is enhanced greatly from 21to 74 % when combined with the solar cells.

Review Design of Slot Antenna Based on Ansoft HFSS Software

Abstract In this paper, a micro-strip fed slot antenna array for application in the 2.4GHz industrial, scientific and medical(ISM) band is implemented using the Ansoft HFSS software. Standard formulas are used to calculate different antenna parameters. The proposed antenna is designed to work at 2.4GHz frequency band. A half power beam width(HPBW) of 57°. A bandwidth of around 7.7% is attained. This may have been brought about by poor impedance matching and a high level of surface waves. A way of improving the bandwidth would have been to use proximity coupling feeding method which offers the highest bandwidth and is somewhat easy to model and has low spurious radiation. However, its fabrication would have been more difficult. A directivity of 2.01 dB is achieved. This is a fairly high though directivity increase could have been studied through use of different substrate material and thickness. Adjusting length and width of narrow slot loop antenna will influence on the resonance frequency and bandwidth. By using HFSS software, the characteristics of antenna are investigated and analyzed, including voltage standing wave ratio (VSWR), return loss and far field radiation patterns.

Dual Polarized Cylindrical Loop Slot Antenna for Omni Cell Application

Dual Polarized Cylindrical Loop Slot Antenna for Omni Cell Application

A Compact Wideband Slot-Loop Directional Antenna for Marine Communication Applications

A compact wideband high gain directional antenna is proposed in this paper for marine communications. The antenna consists of a back plane (reflector), a slot-loop antenna (driven element), and a director of rod. Based on the current distribution, the slot-loop antenna is equivalent to an array of three linear current dipoles. The dipole acts as an element of the director, which provides a high efficient director for slot-loop antenna according to theoretical analysis. Both the impedance bandwidth and the 1 dB gain bandwidth are 45% covering 1.7–2.7 GHz in this design. A gain of 11.2 to 12.2 dBi is obtained in the working band with only one set of directors. The directors have a dimension less than the antenna aperture in the H-plane, which can be seen as one director in the end-fire direction. Compared with the classic Yagi antenna with the same gain level, the newly proposed antenna is only half of the size in radiation direction, which is a breakthrough for the Yagi antenna design. This size reduction can significantly minimize the interference between ship-borne antennas. The antenna is fabricated using only metal of low cost, which is useful for the ship-to-shore/ship communicating applications and desirable for the large-scale deployment.

Wideband low‐profile CPW‐fed slot‐loop antenna using an artificial magnetic conductor

A wideband low-profile slot-loop antenna is proposed based on an artificial magnetic conductor (AMC) reflector which is applied to a slot-loop antenna to obtain directional radiation patterns. Compared with an antenna using a metal reflector, the AMC reflector can reduce the profile of the antenna and enhance operating bandwidth. The AMC consists of 4 × 6 patches with ring slots and slits. A coplanar waveguide is introduced to the proposed slot-loop antenna so that the antenna can directly attach to the AMC surface. Thus, a low profile of 0.05λL is realised (λ L is the wavelength at the lowest operating frequency). Simulation and experimental results indicate that the proposed antenna obtained a 37.9% impedance bandwidth, a 36.7% 3-dB gain bandwidth, and a 6.85 dBi peak gain.

DC ground compact wideband omnidirectional vertically polarised slot loop antenna for 4G long‐term evolution applications

A compact, wideband, omnidirectional, vertically polarised antenna without electrostatic discharge problems is proposed in this study for 4G long-term evolution applications. The proposed antenna is composed of three identical basic radiators separated by an angle of 120°. The basic radiator is based on a slot loop which is a wideband and DC ground structure. By bending the basic radiators, the antenna achieves better impedance matching and lower gain variation in the horizontal plane in a compact size. The proposed antenna reaches a fractional bandwidth of 45.5% for the voltage standing wave ratio (VSWR) <;1.5, a peak gain from 2.4 to 3.8 dBi with a gain ripple around 2 dB in the omnidirectional plane. It operates from 1700 to 2700 MHz, covering most 4G long-term evolution frequency bands. Both simulation and measurement of a prototype is done in this study to verify the antenna performance.

Nano-Fluidic Millimeter-Wave Lab-on-a-Waveguide Sensor for Liquid-Mixture Characterization

This paper reports on a miniaturized lab-on-a-waveguide liquid-mixture sensor, achieving highly accurate nanoliter liquid sample characterization, for biomedical applications. The nanofluidic-integrated millimeter-wave sensor design is based on a near-field transmission-line technique implemented by a single loop slot antenna operating at 91 GHz, fabricated into the lid of a photolaser-based subtractive manufactured WR-10 rectangular waveguide. The nanofluidic subsystem, which is mounted on the top of the antenna aperture, is fabricated by using multiple polytetrafluoroethylene layers to encapsulate and isolate the liquid sample during the experiment, hence, offering various preferable features, e.g., noninvasive and contactless measurements. Moreover, the sensor is reusable by replacing only the nanofluidic subsystem, resulting in a cost-effective sensor. The novel sensor can measure a liquid volume of as low as 210 nanoliters, while still achieving a discrimination accuracy of better than 2% of ethanol in the ethanol/deionized-water liquid mixture with a standard deviation of lower than 0.008 from at least three repeated measurements, resulting in the highest accurate ethanol and DI-water discriminator reported to date. The nanofluidic-integrated millimeter-wave sensor also offers other advantages, such as the ease of design, low fabrication and material cost, and no life-cycle limitation of the millimeter-wave subsystem.

Design of a bandwidth enhanced hybrid slot loop antenna for GSM/UWB standards

PurposeThis paper aims to presents the bandwidth enhancement of a hybrid slot–loop antenna using a modified feed structure.Design/methodology/approachThe conventional monopole feed of the hybrid slot–loop radiator is loaded with a flat microstrip patch to excite higher-order modes. The proposed antenna combines the resonant modes of the slot antenna, the loop antenna and the patch loading.FindingsThe antenna exhibits a dual-band response suitable for GSM 1800/1900 and ultrawideband (UWB) standards. The impedance bandwidth extends from 1.65 to 1.95 GHz (11.42 per cent) and 3 to 11.1 GHz (114.9 per cent). The proposed antenna has the smallest footprint with a peak gain of 5.07 dBi at 1.8 GHz and 4.97 dBi at 6 GHz. The prototype antenna is fabricated and the simulation results are validated using experimental measurements. The performance of the bandwidth-enhanced hybrid slot–loop antenna is compared with that of other slot antennas.Originality/valueThus, a hybrid slot–loop antenna with an enhanced bandwidth has been reported in this study. The conventional monopole feed of the antenna is replaced with a monopole ending with a microstrip patch load. The antenna covers the operating bands of GSM 1800/1900 and UWB. The proposed antenna has a smaller footprint compared with other wide-slot antennas reported in the literature.

Co-simulation of a complete rectenna with a circular slot loop antenna in CPW technology

This study starts with the design of a planar and compact CPW antenna fabricated on Arlon AD1000 substrate, εr=10.35. The antenna is a coplanar waveguide (CPW) fed circular slot loop antenna matched to the standard impedance 50 Ω by two stubs. The goal is to implement this antenna with a CPW RF/DC rectifier to build an optimized low power level rectenna. The rectenna design is restricted to allow easy and fast fabrication of an array with a high reproducibility. The full rectenna is simulated and achieves 10% effciency at −20 dBm.

Vertically polarized omni-directional loop slot array antenna for mobile base station

A slim vertically polarized omni-directional feed circuit integrated loop slot antenna for mobile base station is proposed in this paper. Picocell antenna requires a compact and slim structure, because its construction space is limited in urban areas. The proposed antenna consists of loop slots and patches to improve omni-directional pattern and bandwidth. In order to enhance the directivity gain, we arrange two loop slot antennas in vertical plane with microstrip line connecting the slots. The size of antenna is only 0.17λ× 1.45λ. This antenna realizes more than 15% relative bandwidth, and an omni-directional pattern in both simulation and measurement results.

AN ISM BAND CONVENTIONAL CPW RECTENNA FOR LOW POWER LEVELS

This paper presents the design and fabrication of a coplanar waveguide (CPW) rectenna using a sequential modular approach. The rectenna is printed on high permittivity, low-loss board ARLON AD1000 (r = 10.35 and tan δ = 0.0023 @ 10 GHz). The rectifier section is realized with a single reverse-biased schottky diode SMS-7630 in reverse topology for which a diode model is obtained at −20 dBm for frequencies F 0 = 2.45 GHz and 2F 0 = 4.9 GHz. The low-pass filter and the impedance matching are synthesized from passive CPW structures. Co-simulation technique is used to overcome CPW simulation limitations and to integrate the diode characteristics. The antenna consists of a circular slot loop antenna with stub matching such that its input impedance is close to 50 Ω. The goal of this work is to design a rectifier to simplify and speed up the fabrication process of a rectenna array. We reduced the number of processes to etch the rectifier on the board and minimized the number of lumped elements. At −20 dBm, simulation of the rectifier with an ideal impedance matching network shows rectification at 2.45 GHz with efficiency of 12.8%. The rectifier and rectenna show efficiency of approximately 10% at an operating frequency of 2.48 GHz.

Pattern diversity antenna with high‐temperature tolerance for body area networks

A high-temperature tolerant pattern diversity antenna is presented for body wearable applications in hostile conditions. The proposed system consists of a dielectric resonator antenna (DRA) placed at the centre of a slot loop antenna. The combination yields pattern diversity with broadside and endfire radiation patterns from slot loop and DRAs, respectively. The antenna system offers common bandwidth of 4.95% with port isolation of better than 13 dB at 2.4 GHz. The thermal characteristics of antenna have been studied for high-temperature operation and no discernible change in the radiation behaviour is noted. The antenna undergoes 2% resonant frequency shift when operated at elevated temperature. The antenna diversity has been measured for three on-body communication channels. The antenna offers 9.5 dB diversity gain in a pure non-line-of-sight channel surrounded by a rich fading environment subjected to the selection combining scheme. The antenna has dimensions of 0.4λo × 0.4λo × 0.1λo .

Ink-jet printing of dual polarized loop slot antenna fed by tri-plate line on paper based substrates

Ink-jet printing of dual polarized loop slot antenna fed by tri-plate line on paper based substrates