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Summary: This article presents a novel wearable frequency selective surface (FSS) for shielding the communication link of implantable devices with the external environment. The proposed shield blocks a dual‐band frequency operating at 404 MHz and 2.45 GHz in the medical implant communication service (MICS) and industrial, scientific, and medical (ISM) bands. The two distinct stop bands provide a high‐frequency band ratio of 6.02 in an ultra‐miniaturized physical form factor of 0.024λo × 0.024λo, with at least 76.96% miniaturization when compared to the existing art. Each of the unit cells is imprinted on a conformal 50 μm polyester substrate in a symmetrical configuration. The polyester adheres with jean to realize its compatibility with wearable applications. The designed shield system offers a low profile of only 0.00146λo. By suppressing the grating lobe, the proposed shield achieves a high angular stability of 80° and polarization insensitivity of 90° in both transverse electric (TE) and transverse magnetic (TM) modes. The FSS is fabricated and measured results validate its performance. To evaluate the physical insight, an equivalent circuit model (ECM) analysis is done. To ensure durability, the proposed shield system is tested with Amitech SDR04. [ABSTRACT FROM AUTHOR]

Summary A novel single‐layer ultra‐miniaturized multi‐band Frequency Selective Surface (FSS) with a circular vent is designed for shielding LTE and ISM bands. The top layer of the proposed FSS unit cell incorporates a circular patch along with convoluted arms. The designed FSS unit cell exhibits band‐rejection characteristics with a resonance of 800 MHz, 2.45 GHz, and 5 GHz and bandwidths of 523 MHz, 687 MHz, and 725 MHz, respectively. The periodicity of an ultra‐miniaturized FSS unit cell is 0.024λօ x 0.024λօ, encompassing a spatial vent hole of 0.01λօ, where λօ corresponds to the lowest operating frequency. Moreover, the proposed FSS unit cell remains unaltered angular stability up to 75° with less than 1% frequency deviation in TE and TM modes. Good polarization insensitivity for the designed four‐fold symmetrical FSS unit cell is achieved. Further, an Equivalent Circuit Model (ECM) analysis is developed to infer the physical insight of the proposed FSS unit cell. The FSS prototype is measured for the assertion, and the good agreement between the findings from simulation and measurement is validated. For real‐time assertion, the FSS prototype is verified using the Amitech SDR04. Thus, FSS is a promising candidate with good ventilation for shielding the LTE, Bluetooth, and Wi‐Fi application bands. [ABSTRACT FROM AUTHOR]

This paper presents a low-profile, wideband antenna that can operate in four millimeter-wave frequency bands for 5G communication. The proposed antenna has composite geometry with extended blocks from a simple rectangular patch. Here the full ground plane is used to avoid the radiation losses by back lobes and to enhance the antenna performance. The proposed radiating element covers the wideband from 23.812 GHz to 48.253 GHz enclosing operating frequencies k band (26 GHz-F1) and Ka-band (28 GHz-F2, 32 GHz-F3, and 39 GHz-F4). The gains achieved in the designed single element antenna are 5.46 dBi, 5.6 dBi, 6.48 dBi, and 5.56 dBi respectively. Whereas the total efficiencies are 95.33%, 97.23%, 97.75%, and 97.9% for the respective operating frequencies. The proposed antenna is analyzed for Multiple Input Multiple Output (MIMO) communication, providing the isolation value greater than 20 dB. The diversity gain, Envelope Correlation Coefficient, and isolation are all well within their respective limits making the proposed antenna suitable for MIMO communications. Here, to check the versatility of the antenna design different configurations such as 2 × 2, 1 × 2, and port positionings are simulated. Furthermore, the designed single element and MIMO antenna is placed on the vehicle and the far-field results are analyzed. [ABSTRACT FROM AUTHOR]

A compact body-worn circular polarized textile monopole antenna for wearable applications is reported. The proposed antenna is fabricated on a jean fabric providing flexibility, lightweight, and easy integration into human clothes. The overall size of the proposed antenna is $25\times 30\times1.4$ mm3. Circular polarization (CP) is advantageous for on-body communication as it provides features, such as multipath immunity, suppressing interferences, and enables better link connectivity between the sensor nodes. The proposed antenna achieves the CP using an asymmetric stepped L-shaped ground plane and through the incorporation of a cross-shaped stub in the radiator. The single-fed octagonal strip monopole antenna provides good impedance matching over the entire ultrawide frequency range from 3.09 to 11 GHz. Simulation results are in good correlation with the measured results. The axial ratio bandwidth <3 dB is achieved in the frequency range of 3.4–10 GHz. Gain and efficiency obtained are about 2.3-4.4 dBi and 65%–82% at the said frequency range, respectively. Structural deformation is performed to analyze the flexibility of the proposed antenna. The simulated SAR values follow the FCC limit making it most suitable for wearable applications. [ABSTRACT FROM AUTHOR]

This paper presents a reconfigurable loop-based filter performing compound reconfiguration. The designed filter is capable of functioning as a bandstop or bandpass filter by a simple approach of cascading the resonator to the transmission line connecting source and load. Shifting of operating frequencies is characterised by switching between a loop and a C-shaped resonator. To demonstrate the working of the proposed concept, a compound reconfigurable filter operating at 1.5 GHz and 1.6 GHz is developed. The filter is developed on a compact layout of size 0.27 × 0.12 λg2. The proposed prototype is fabricated and measured for real-time validation. [ABSTRACT FROM AUTHOR]

In this communication, a compact dual‐element MIMO antenna with decoupling structure has been proposed for handheld devices. The proposed decoupling structure acts as a resonator and as a decoupling structure. The proposed antenna consists of nested slots in the radiator and it supports the application such as LTE, WLAN, Wi‐Fi, and WiMAX. The total size of the antenna is 30 mm × 10 mm. The impedance bandwidth of the antenna is 300/400/700 MHz, respectively. The decoupling structure consists of a feed line printed on one side of the substrate and swastika‐shaped array on another side. The power fed to the feed line coupled to the swastika‐shaped array for achieving the operating bands at 0.9 GHz and (8‐10) GHz. Meanwhile, the decoupling array provides isolation more than 20 dB at (2.3‐2.6) GHz, (3.4‐3.8) GHz, and (5.15‐5.85) GHz. The edge to edge spacing between the antennas is 10 mm. The percentage bandwidth of the antenna is 12.2/11.1/12.7/22.2%. The MIMO performance metrics such as envelope correlation coefficient, effective diversity gain, apparent diversity gain, and mean effective gain are evaluated. The proposed antenna is fabricated and tested. The measured results correlate with the simulated results. [ABSTRACT FROM AUTHOR]

This article presents a compact reconfigurable filter performing bandwidth reconfiguration covering the entire L‐band frequency range. The reconfigurable filter is developed using a C‐shaped resonator coupled to the source and load through varactor diodes. To reverse bias the diodes symmetrically both the diodes are fed with a common bias voltage. Hence the DC bias voltage is administered evenly to the diodes resulting is equi‐proportional coupling between the resonator and the nodes. This results in reconfiguring the bandwidth of the operating frequency. The designed filter is capable of tuning 3‐dB bandwidth from 0.613 to 1.353 GHz with the center frequency as 1.5 GHz. The percentage bandwidth of the filter is varied from 44.5% to 91.76%. The insertion loss offered by the filter is very less with the minimum value of 0.42 dB. The proposed filter is simple, compact and finds it application in power agile systems operating with different transmission power levels at different time instances. [ABSTRACT FROM AUTHOR]

A low profile, a multifrequency microstrip patch antenna with pattern reconfiguration is reported in this paper. The proposed antenna provides both omnidirectional and directional radiation characteristics suitable for Wireless Body Area Network (WBAN). Pattern switching is achieved using PIN diodes. The antenna is designed to operate at multiple frequencies, viz. 0.915 GHz (Industrial Scientific & Medical band), 2.38 GHz (Medical body area network), 3.5 GHz (Wireless Interoperability for Microwave Access), and 5.8 GHz (Wireless Local Area Network/Industrial Scientific & Medical band). The percentage bandwidths obtained are 2.89, 1.68, 2.85, 2.16 at the operating frequencies 0.915, 2.38, 3.5, 5.8 GHz, respectively. The peak gain and total efficiencies obtained for OFF mode are 3.22/4.27/4.65/4.82 dBi, 82/85/87/89%, and in ON mode are 1.12/1.80/2.44/2.68 dBi, 65/67/71/74% at the said operating bands, respectively. The path loss model is evaluated by measuring the transmission link between the antennas on the human body. The LOS path ranges from 30 to 45 dB and the NLOS ranges from 50 to 80 dB ensuring it satisfactory for WBAN application. Then human body loading characteristics are also studied. The SAR analysis is performed and it is found to be less than 1.6 W/Kg. [ABSTRACT FROM AUTHOR]

A compact, low-profile button antenna for off-body communication is reported. The proposed antenna is composed of coupled circular strips, Y-shaped and L-shaped slots. This configuration covers the application bands such as 0.867 GHz (industrial, scientific, and medical bands), 2.38 GHz (medical body area network), and 5.8 GHz (wireless local area network/industrial, scientific, and medical bands). The percentage bandwidth obtained at the said operating bands is 4.37, 2.10, and 2.56, respectively. The directional radiation pattern obtained from the developed antenna ensures the low backward radiation to the body tissue, thereby, making it more suitable for WBAN applications. The simulated gain and efficiency obtained at the operating bands are 2.5/3.52/4.8 dBi and 78%/85%/89%, respectively. To validate the simulation results, the antenna is fabricated and some experimental results on the body tissue are performed. The SAR value obtained follows the Federal Communication Commission (FCC) limit. [ABSTRACT FROM AUTHOR]

This communication presents the design of a compact loop antenna with independent frequency tuning. The proposed antenna consists of a feed line fed by a $50~\Omega $ coaxial probe and four resonating arms on the adjacent sides of the feed line. The two outer resonating arms are directly coupled to the feed line and the other two inner resonating arms are coupled to the outer arms. The proposed antenna has a footprint of 25 mm $\times 10$ mm $\times0.2$ mm. The designed antenna operates at 0.9, 2.4, 3.5, and 5.5 GHz. Each of these bands is individually tuned using varactor diodes. Thus, the aggregation of these tunable bands provides wide bandwidth. The impedance bandwidth and percentage bandwidth of the antenna are 270/1000/400/700 MHz and 33%/47.6%/11%/12.7%, respectively. Furthermore, the gain and efficiency of the antenna are 1.7/1.3/2.1/2 dBi and 60%/63%/65%/69%, respectively. The prototype antenna is fabricated and tested. The measured impedance and radiation characteristics of the antenna are in good correlation with the simulation results. [ABSTRACT FROM AUTHOR]

In this paper, a portable system for noninvasive detection of fractures in human bones is presented. A planar microwave ring resonator is used as the sensor. The proposed planar microwave sensor is designed using the finite integration-based CST Microwave Studio and tested on a human bone covered by porcine tissues. Fracture induced in the bone was detected by monitoring the transmission characteristics of the sensor as it scans the affected region. The resonant frequency of the ring resonator has been observed at every scan point, and the values are plotted using iterative curvature-based interpolation, improved new edge directed interpolation, and Lanczos imaging technique. The extent of fracture is then derived from the image. The average accuracy of the detected fracture for Lanczos method of resampling was 98.86%. The specific absorption rate was below the minimum level of 1.6 W/Kg at every point of scanning. Portable noninvasive monitoring of fractures in the tibial bone will help in immobilizing the affected part at an earlier stage, thereby reducing the recovery time for patients. [ABSTRACT FROM AUTHOR]

In this manuscript, a novel uniplanar monopole antenna for Tablet computer application is proposed. Multiband resonance is obtained by introducing multiple radiating branches and meandered stubs connected to the main monopole. Further, the impedance bandwidth of the operating bands is enhanced by introducing coupled parasitic stubs in the ground plane. The antenna has impedance bandwidth of 20 MHz (0.45-0.47 GHz), 270 MHz (0.69-0.96 GHz), 2370 MHz (1.43-3.8 GHz), 1600 MHz (4.9-6.5 GHz) for LTE 450/700/2300/2500 MHz, GPS, WLAN, Bluetooth applications, WiMAX and Wi-Fi applications. The size reduction of the proposed antenna is 60% compared to existing antenna solutions for tablet devices. The percentage bandwidth of the antenna is 4.35/34.2/90.6/23.2% for the four operating bands, respectively. Furthermore, the obtained gain of the antenna is greater than 1.8 dBi with peak gain of 5.65 dBi, and the efficiency is greater than 75%. The proposed antenna is tested on the mock-up system consisting of large ground plane of dimension 200 × 150 mm. The antenna is fabricated, and the measured results are compared with simulated results. The SAR is computed and found to be less than 1.6 W/Kg. [ABSTRACT FROM AUTHOR]

Abstract: This article presents the design and testing of a novel frequency reconfigurable microwave filter. The filter structure is composed of an all stop resonator coupled with C‐ and E‐shaped parasitic resonators. PIN diodes are located at suitable positions to achieve multi‐band reconfiguration from 1.2 to 3.2 GHz making the filter suitable for multiple wireless communication systems. The frequency and bandwidth of the filter are governed by the length of the resonators and coupling between the resonators and the transmission line, respectively. A sharp rejection of −30 dB is observed between the passbands. The proposed filter offers 56% size reduction with flat group delay performance. The prototype filter is fabricated and the simulation results are validated using experimental measurements. The measurement results show good agreement with the simulation results. [ABSTRACT FROM AUTHOR]

Purpose: The design, fabrication and experimental validation of defected microstrip structure (DMS) are proposed to address the problem of near-end crosstalk (NEXT) and far-end crosstalk (FEXT) between the microstrip transmission lines in a printed circuit board. Design/methodology/approach: The proposed DMS evolved with the combination of spur line (L-shaped DMS) and U-shaped DMS topologies. This technique reduces the strength of electromagnetic coupling and suppresses crosstalk by optimizing the capacitive and inductive coupling ratio between the linked microstrip lines. The practical inductance value is much more significant in DMS than in defected ground structures (DGS), but the capacitance value remains the same. Findings: A DMS unit is etched on the aggressor microstrip line instead of the DGS circuit. Because there is no leakage via the ground plane and the circuit size is far smaller than with DGS, the enclosure issue is disregarded. DMS structures have a larger effective inductance and are resistant to electromagnetic interference. A tightly coupled transmission line structure with minimal separation between the coupled microstrip line is designed using DMS. Further research must be conducted to improve the NEXT, FEXT and spacing between the transmission lines. Originality/value: Simulation and actual measurement results show that the proposed DMS structure can effectively suppress crosstalk by analysing the S-parameters, namely, S_12, S_13 and S_14, with measured values of 1.48 dB, 20.65 dB and 21.099 dB, respectively. The data rate is measured to be 1.34 Gbps as per the eye diagram characterization. The results show that the NEXT and FEXT are reduced by approximately 20 dB in the frequency range of 1–11 GHz for mixed signals. The substantial measured results in the vector network analyser coincide with the computer simulation technology microwave studio suite simulation results. [ABSTRACT FROM AUTHOR]

The demand for vehicular antennas increases in tandem with the need for multiple features in automobiles. The development of optically transparent antenna (OTA) has made it possible to deploy antennas on delicate surfaces such as glass. Earlier studies on OTA demonstrated its viability using materials such as transparent conducting oxides (TCO) and conductive polymers. A tri-band OTA is proposed in this paper for vehicular applications. The antenna operates at 1.8 GHz, 2.4 GHz and 3.39–12 GHz bands, covering automotive/wireless applications such as GSM, Bluetooth, Wi-Fi, vehicular communication and electronic toll collection. The proposed OTA is developed on soda lime glass, and the material TCO is used for the radiator and the ground plane. The antenna prototype is tested on windshield and in an anechoic chamber, the gain and efficiency are found to be greater than 1 dBi and 80%, respectively. Furthermore, a machine learning technique for vehicle classification is proposed, which could help in electronic toll collection, automatic vehicle identifier, and parking management applications. The presented algorithm achieves 80% classification accuracy with a minimum window size. [ABSTRACT FROM AUTHOR]

In this paper, a novel planar microwave sensor for nondestructive measurement of strain during testing of printed circuit board (PCBs) is proposed. Planar microstrip patch bridged on both sides with squared split ring resonator is used to measure strain. Measurement of stress of isotropic dielectric materials in their linear elastic region that are uses as PCB substrates is also done using the proposed method. The designed microwave probe works at a frequency of 2.45 GHz. The feasibility of the use of time-domain reflectometry method to monitor strain in materials is presented here. The proposed sensor exhibits a sensitivity of about 333 ps for every 1% change in strain. Finite integration technique and real-time measurements have been done to corroborate the relation derived between the transmit time and the strain experienced by the material. The correlation between the simulated and measured strain is about 99.3%. The proposed sensor can be used for faster and accurate testing of PCB substrates without requiring complex calibrations. [ABSTRACT FROM PUBLISHER]

A novel reconfigurable 3-D frequency selective surface (FSS) exhibiting bandstop response is proposed in this paper. The unit cell of the proposed 3-D FSS is constructed from concentric threaded cylinders. The proposed novel 3-D FSS achieves reconfigurability by sliding technique. It offers frequency tuning from 1.86 to 3.10 GHz by sliding the outer cylinder over the inner cylinder. The proposed FSS offers bandstop response in the L- and S-band microwave frequencies. In addition, the proposed 3-D FSS provides polarization- and angular-independent operation. The prototype of the 3-D FSS is fabricated, and the simulation results are validated using measurements. [ABSTRACT FROM PUBLISHER]

A novel ultrahigh frequency (UHF) near-field radio-frequency identification (RFID) reader antenna based on the complementary split ring resonator (CSRR) elements is presented in this communication. The antenna consists of a power divider and two arms. The two arms are terminated with two 50- $\Omega $ terminations. First arm is forward arm, which is a microstrip transmission line. The second arm is backward arm, which is loaded with CSRR elements, instigating backward wave propagation. The oppositely directed currents are generated by this configuration to produce strong and uniform magnetic field over the antenna plane for UHF near-field RFID operations. The proposed antenna operates from 0.76 to 0.88 GHz, and a total impedance bandwidth of 120 MHz is obtained. A near-field read range of 100 mm and an interrogation area of 220 mm $\times180$ mm over the antenna plane at a height of 50 mm is reported for this antenna. [ABSTRACT FROM PUBLISHER]

A multiservice radio-frequency identification (RFID) antenna with wideband axial ratio (AR) response around 2.4 GHz is presented in this study. This antenna offers dual band operation. The prototype follows a configuration constituting a driven element (radiator) and a parasitic element. The first band offers a voltage standing wave ratio (VSWR) bandwidth (3:1) of 183 MHz (0.85–1.04 GHz). The VSWR bandwidth (3:1) for the second band is 2.77 GHz (2–4.77 GHz). It also offers a 3 dB AR bandwidth of 1.1 GHz (2.1–3.2 GHz). The 2:1 VSWR bandwidth of 0.9 GHz (2.1–3 GHz) and cross-polarisation in the second band makes this antenna suitable for 2.4 GHz RFID reader applications. The other services supported by the proposed antenna include global system for mobile communication (0.88– 0.96 GHz), long-term evolution (2.3–2.4 GHz), wireless fidelity (2.4–2.5 GHz), bluetooth low energy (2.4 GHz) and worldwide interoperability for microwave access (3.5 GHz). To extract the multiservice characteristics, it is necessary to integrate this antenna to a handheld computing platform. For assessing the performance in such a platform, the prototype is optimised and merged with a larger ground plane of size 170 mm× 130 mm and studied in the course of this study. [ABSTRACT FROM AUTHOR]

This paper proposes a method for detection of cracks in bare printed circuit board sheets before etching of interconnects and mounting dies. A microwave planar sensor probe is designed, and the impedance matching property is used for anomaly detection in flame retardant-4 sheets. The proposed technique and apparatus is first validated through finite-integration-based technique and then through measurement. The resonant frequency information thus obtained is then plotted on a 2-D gradient representation matrix. A novel Windows VB-based application software is developed to determine the dimensions of the crack in the sample through various interpolation operations and dimensioning technique on the image matrix. These are then effectively displayed in a graphical user interface. [ABSTRACT FROM AUTHOR]

ABSTRACT This letter presents planar microstrip branch-line (BL) couplers with improved phase and amplitude stability bandwidth along with significant size reduction. The prototypes are designed to operate at 433 MHz frequency band suitable for ISM 433 MHz applications. The prototypes with symmetric polygonal modification (SPM) and asymmetric polygonal modification (ASPM) offer a wide quadrature phase bandwidth of 37.8% and 35.5% respectively, over which the phase imbalance is within 90°±5°. In SPM all four transmission lines of the BL coupler have been symmetrically modified to bring in 75.99% size reduction compared to the conventional design. Further asymmetric modification has been performed to bring an additional 12.34% size reduction, compared to symmetric, and providing an overall size reduction of 78.95% compared to conventional BL coupler. The prototypes are able to offer compactness without compromising much on the matching, transmission and isolation parameters. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1369-1374, 2016 [ABSTRACT FROM AUTHOR]

In this study, a passive Vivaldi antenna design is proposed for radar cross section (RCS) reduction using object shaping method. The implementation of annular slot along with exponential curves in the radiator reduced the scattering along the surface of the radiator. This contributes reduction in structural mode RCS throughout the operational bandwidth without affecting the impedance performance of the antenna. Monostatic RCS of the antenna is discussed for two incident angles. A minimum RCS reduction of 13 dB is achieved when the incident angle is Θ = 60° and a maximum of 19 dB reduction is achieved at Θ = 75°. The proposed antenna offers symmetric radiation pattern in both azimuth and elevation planes and also maintains co-polarisation to cross-polarisation ratio of 19 dB throughout the X-band (8-12 GHz). Prototype antenna is fabricated and tested to validate the simulated results. [ABSTRACT FROM AUTHOR]

This communication presents a bandwidth-enhanced, compact, monopole antenna with modified ground plane for modern automotive ultra wide-band (UWB) applications. The proposed antenna has hybrid geometry and is constructed using half circular ring and half square ring. The ground plane of the fundamental radiator is curved and defected to improve the VSWR bandwidth. An extended ground stub is added to further enhance the bandwidth to suit the modern automotive requirements. The designed antenna covers 3.1–10.9 GHz frequency spectrum with \mathrm VSWR \leq 2. This antenna can be conveniently placed inside the shark fin housing or it can be printed along with the existing print circuit board (PCB) electronics nullifying the need for dedicated location for in-car communications. Furthermore, a simple two-port multiple input multiple output (MIMO) antenna is constructed and its diversity performance is estimated. The prototype is fabricated and tested for impedance and radiation characteristics. [ABSTRACT FROM PUBLISHER]

Purpose: The purpose of this paper is to design a suitable guard trace to reduce the electromagentic interference between two closely spaced high frequency transmission lines. A novel cross-shaped resonator combined via fence is passed down to alleviate far-end and near-end crosstalk (NEXT) in tightly coupled high-speed transmission lines. The distance between the adjacent transmission lines is increased stepwise as a function of trace width. Design/methodology/approach: A rectangular-shaped resonator via fence is connected by a guard trace has been proposed to overcome the coupling between the traces that is separated by 2 W. Similarly, by creating a cross-shaped resonator via fence connected by guard trace that reduces the spacing further by 1.5 W. Findings: A tightly coupled transmission line structure that needs separation by a designed unit cell structure. Further research needs to be conducted to improve the NEXT, far-end crosstalk (FEXT) and spacing between the transmission lines. Originality/value: This study portrays a novel method that combines the resonators via fence with a minimum spacing between the tightly coupled transmission lines which reduce the NEXT and FEXT; thereby reducing the size of the routing area. The resultant test structures are characterized at high frequencies using time domain and frequency domain analysis. The following scattering parameters such as insertion loss, NEXT and FEXT of the proposed method are measured as 1.504 dB, >30 dB and >20 dB, respectively. [ABSTRACT FROM AUTHOR]

This study brings out the design, fabrication and performance evaluation of a compact, dual band antenna on paper substrate. The two bands of operations are 2.18 to 2.50 and 5.22 to 5.72 GHz. These bands are used by the wireless sensor networks (WSNs) and radio frequency identification systems (RFID). The antenna becomes useful for the WSN nodes and RFID systems at these frequencies. The overall size of the antenna is 40 mm× 20 mm× 0.6 mm, which makes it a compact one. Antenna was tested for the effect of bending by placing it over curvilinear surfaces. The bending was done in horizontal (X) and vertical (Y) axes. These examinations will help to understand the effect of wind loading and other packaging related bending on antenna performance. The main features of this antenna are stability in performance under bent conditions, simple configuration and low cost of fabrication. A thin polyethylene layer has been used to laminate the antenna for permanence. The effect of lamination has also been explained in the course of the study. [ABSTRACT FROM AUTHOR]

The work presented is an assay done on the effects of wearable antenna when placed in proximity to the human body. Cloth fabric is used as a substrate to design a planar antenna. Measurement results of the fabricated patch at free space and close to the human body are also presented here. The S11 of the designed antenna when placed close to the body tissue is almost -30 dB and the gain is close to 4 dB. A rectangular three layered human body model is used to evaluate the extent of the effect that the human body has on the parameters that define an antenna like its gain, directivity, etc. [ABSTRACT FROM AUTHOR]

This article clarifies the usage of the diversity gain (DG) equation adopted by Alsath and Kanagasabai in their published research article. This article also explains the usage of the DG equation for antenna related problems and the related approximations over the classical equation provided by Kshetrimayum in his comment article. [ABSTRACT FROM AUTHOR]

There is a strong demand for compact and multiband antennas as wireless technologies become more integrated into automobiles. These antennas must be able to serve multiple services without compromising the size and installation space. In addition, the antenna incorporated should not affect the aesthetic appearance of the vehicle. This paper presents a compact multiple-input-multiple-output (MIMO) antenna working at 2.45 GHz (Wi-Fi/Bluetooth/RFID) and ultra-wideband (UWB) frequencies. A basic rectangular monopole with a self-complementary structure is used to design the antenna element. The size of the antenna element is 20 × 22 mm2. The proposed MIMO cube is developed with four antenna elements in cubical orientation to achieve compactness and better isolation. The overall dimension of the MIMO antenna is 35 × 22 mm2. The diversity antenna shows impedance bandwidth of 2.4–11.5 GHz and isolation of more than 20 dB. The envelope correlation coefficient (ECC) of the MIMO antenna is less than 0.2, diversity gain (DG) is greater than 9 dB, and total active reflection coefficient (TARC) and channel capacity loss (CCL) are less than −10 dB and 0.4 bits/s/Hz, respectively. The gain and efficiency are found to be greater than 1 dBi and 72%, respectively. [ABSTRACT FROM AUTHOR]

The demand for vehicular antennas increases in tandem with the need for multiple features in automobiles. The development of optically transparent antenna (OTA) has made it possible to deploy antennas on delicate surfaces such as glass. Earlier studies on OTA demonstrated its viability using materials such as transparent conducting oxides (TCO) and conductive polymers. A tri-band OTA is proposed in this paper for vehicular applications. The antenna operates at 1.8 GHz, 2.4 GHz and 3.39–12 GHz bands, covering automotive/wireless applications such as GSM, Bluetooth, Wi-Fi, vehicular communication and electronic toll collection. The proposed OTA is developed on soda lime glass, and the material TCO is used for the radiator and the ground plane. The antenna prototype is tested on windshield and in an anechoic chamber, the gain and efficiency are found to be greater than 1 dBi and 80%, respectively. Furthermore, a machine learning technique for vehicle classification is proposed, which could help in electronic toll collection, automatic vehicle identifier, and parking management applications. The presented algorithm achieves 80% classification accuracy with a minimum window size. [ABSTRACT FROM AUTHOR]

A novel compact folded antenna for 4G and 5G application in handheld devices such as mobile phones is proposed in this paper. The radiator comprises of meandered monopole, dual L-Shaped monopole, square radiator, asymmetric U-Shaped monopole, Closed Loop resonator, F-Shaped stub for providing the desired operating bands. The size reduction is achieved using folding technique. The antenna can be easily folded and integrated at the top right corner within the metal casing of the devices. Folded structure with the foot print of 50 × 6 mm2 covers multiband operation such as LTE700 / GSM850 / 900 / LTE 2300 / WLAN 2400 / LTE 2500 / Wi-MAX 3500 / Wi-Fi 5200/5800 MHz corresponds to 2G/3G/4G/5G services. To provide high data rate and throughput, MIMO concept is exploited with the folded radiators at the top left and right corners of the printed circuit board. The realized gain and radiation efficiency of the proposed antenna are 2.45/4.12/4.54/5.03/6.58 dBi and 82/85/87/89/90% respectively at the design frequencies 0.7/2.3/2.5/3.5/5.8 GHz. The SAR values of the folded antenna is computed and found to be less than 1.6 W/Kg. [ABSTRACT FROM AUTHOR]

A low profile frequency reconfigurable antenna for WBAN applications is reported. The presented antenna design utilizes switching characteristics of PIN diode to achieve frequency reconfigurability. The dimension of the proposed antenna is 0.136 λ 0 × 0.131 λ 0 × 0.001 λ 0. The modified loop-shaped resonator, U shaped stub, and Mirrored F shaped strip provides an independent resonance for three distinct frequency bands. The application bands selected are 1.575 GHz (Global Positioning System), 2.45 GHz (Industrial, Scientific and Medical bands), and 5.2 GHz (Industrial, Scientific and Medical bands/Wireless Fidelity). The percentage bandwidth obtained is 3.17/1.83/2.69% at the said operating frequencies respectively. The simulated gain and total efficiencies are 3.26/3.47/4.04 dBi and 82/85/88% respectively. The directional radiation pattern obtained is highly suitable for off-body communication. The SAR is simulated to validate its suitability for wearable applications. The performance metrics of the fabricated prototype antenna is validated using Measurements. [ABSTRACT FROM AUTHOR]

A low profile flexible linear to circular polarizer made of paper substrate is proposed in this paper. The polarizer is constructed from frequency selective surface (FSS) comprising of crossed dipole unit cell elements. The polarizer converts the linearly polarized incident electromagnetic wave to circular polarized wave at 7.0 GHz. The polarizer provides the advantage of use in conformal system, which is substantiated using bending analysis. The proposed reflective polarizer provides a 3 dB axial ratio bandwidth of 13% at the center frequency of 7.0 GHz. In addition, the proposed flexible polarizer provides stable response for angular incidences up to 30°. Prototype of the flexible FSS polarizer is fabricated and its simulation results are validated with experimental measurements. [ABSTRACT FROM AUTHOR]

This paper presents a twelve-port ultra-wideband multiple-input-multiple-output (MIMO)/diversity antenna integrated with GSM and Bluetooth bands. The twelve-port antenna is constructed by arranging four elements in the horizontal plane and eight elements in the vertical plane. The antenna element, which is created using a simple rectangular monopole, exhibits a frequency range of 3.1 to 12 GHz. The additional Bluetooth and GSM bands are achieved by introducing stubs into the ground plane. The size of the MIMO antenna is 100 × 100 mm2. The antenna offers polarization diversity, with vertical and horizontal polarization in each plane. The diversity antenna has a bandwidth of 1.7–1.9 GHz, 2.35–2.55 GHz, and 3–12 GHz, the radiation efficiency of 90%, and peak gain of 2.19 dBi. The proposed antenna offers an envelope correlation coefficient of < 0.12, apparent diversity gain of > 9.9 dB, effective diversity gain of > 8.9 dB, mean effective gain of < 1 dB, and channel capacity loss of < 0.35 bits/s/Hz. Also, the MIMO antenna is tested for housing effects in order to determine its suitability for automotive applications. [ABSTRACT FROM AUTHOR]

The design of a silicone rubber-based wristband wearable antenna exploiting pattern diversity is presented in this paper. The wristband diversity antenna consists of four identical antenna elements with an inter-element spacing of 0.68λ0, where λ0 is the lower cut-off wavelength. A modified trapezoidal-shaped radiator with a rectangular ground structure is used to achieve ultra-wide bandwidth. The proposed multiple-input-multiple-output (MIMO)/diversity antenna covers a frequency range of 2.75–12 GHz. The antenna element offers a radiation efficiency of 89.3% and a gain of 3.41 dBi. The size of the wristband diversity antenna is 1.1λ0 × 18.4λ0 × 0.18λ0. The diversity performance characteristics of the prototype antenna are examined, with the envelope correlation coefficient (ECC) < 0.18, apparent diversity gain (ADG) > 9.5, effective diversity gain (EDG) > 9.5, mean effective gain (MEG) < 1 dB, total active reflection coefficient (TARC) < − 10 dB, and channel capacity loss (CCL) < 0.1 bits/s/Hz over the entire operating band. The specific absorption rate (SAR) of the proposed wristband antenna is analyzed to determine its radiation exposure on the human body, and the results show that the values are less than 0.02 W/kg. [ABSTRACT FROM AUTHOR]

A novel single layer miniaturized frequency selective surface made of circular unit cell elements is presented in this article. The frequency selective surface (FSS) unit cell measures 0.055λ0 × 0.055λ0, where λ0 corresponds to its free space wavelength. The proposed FSS offers band stop characteristics with bandwidth of 137.5 MHz centered at 1.39 GHz. The symmetrical structure of the unit cell elements provides polarization independency. The miniaturized unit cell elements help achieving angular independency for both TE and TM mode of polarization. The miniaturized design provides excellent angular independency with negligible frequency shift for varying incident angles. A prototype of the FSS is fabricated and its simulation results are validated using measurements. [ABSTRACT FROM AUTHOR]

This communication presents the design, fabrication, and testing of a tunable band-notched UWB filtering antenna. The proposed filtering antenna comprises a semiellipsoid radiator and a microstrip transmission line to cover the UWB communication bandwidth from 3.1 to 10.6 GHz. It also comprises two J-shaped open-ended stubs and an asymmetric T-shaped open-ended stub to create notch bands at 3.5 GHz (WiMAX), 5.2 GHz, and 5.8 GHz (WLAN) in the UWB spectrum. The center frequencies of the notch band are tuned continuously using varactors with percentage tuning of 7.5%, 5.38%, and 3.54%. The prototype is fabricated and experimentally validated. [ABSTRACT FROM AUTHOR]

In this paper, a compact, single-section, Ultra-wideband (UWB) coupled-line coupler designed using concentric loop in the signal plane and defect in the ground plane is presented. Bandwidth enhancement is achieved with low coupling at the X-band satellite downlink range to improve the signal strength for defence applications. Return loss greater than 15 dB and isolation greater than 20 dB is achieved over the entire UWB band. The prototype is fabricated and tested to validate the simulation results. Further to detect the quality of the output signal, signal integrity analysis is performed and metrics such as error vector magnitude (EVM), magnitude and phase error, eye pattern, constellation plots and signal to noise ratio are presented for the proposed UWB coupled-line coupler. [ABSTRACT FROM AUTHOR]

A reconfigurable frequency-selective surface (RFSS) for electromagnetic shielding applications is presented in this letter. The unit cell of the proposed RFSS contains a pair of shorted square loops separated by a uniform distance. Wideband RFSS with the frequency tuning ratio of 1:2.34 achieved by varying the horizontal spacing is proposed. The RFSS covers the frequencies 3.5, 5, and 5.8 GHz shielding the WiMAX, WLAN, and ISM/WiMAX bands, respectively. The prototype of the proposed RFSS is fabricated and loaded on to the mechanical tuning setup. The tuning setup has a box frame with rotating shafts attached to the bevel gears to control the horizontal spacing. The use of collapsible linkage mechanism ensures uniform spacing during reconfigurable operation. The simulated results are validated with measurements. The proposed FSS offers wideband frequency tuning for electromagnetic shielding applications. [ABSTRACT FROM AUTHOR]

In this paper, an analog multiband phase shifter using slotline configuration is proposed. To implement the design, a pair of modified Split Ring Resonator (SRR) is employed. The periodic property of SRR provides multiband characteristics, whether the coupling slot gives the phase variations over the bands. The operation is well explained with an equivalent circuit model and its characteristics have been studied both in simulation and measurement. The prototype operates in 1.77–2.16, 3.5–3.97, 5.08–5.33, 6.43–6.93, and 8.01–8.59 GHz frequency bands which can be utilized for GSM, GPS, WLAN, C-band, and X-band applications, respectively. [ABSTRACT FROM AUTHOR]

An optically transparent circularly polarized (CP) radio frequency identification (RFID) antenna is presented in this paper. The RFID antenna consists of a coplanar‐fed waveguide inverted L‐shaped monopole with a dual feeding structure. The CP wave with a bidirectional radiation pattern is obtained by feeding the radiator at both ends. The transparency of the antenna is obtained by using fluorine tin oxide (FTO) coated soda‐lime glass substrate. The proposed antenna operates at a Universal RFID frequency (800–1100 MHz) with circular polarization. The antenna has an impedance bandwidth of 300 MHz and an overlapped 3‐dB axial ratio (AR) bandwidth of 110 MHz (860–970 MHz, 12% centered at 915 MHz). It has a peak realized gain of 1.4 dBic. The antenna with the size of 100 × 100 mm2 is designed for ultrahigh‐frequency RFID reader applications. [ABSTRACT FROM AUTHOR]

A low profile dual-band frequency selective surface (FSS) for shielding the GSM applications is presented in this paper. The proposed FSS contains the unit cell made of modified double square loop elements with paper as its substrate. The overall thickness of the proposed FSS measures only 0.55 mm. The FSS offers band stop response at 930 and 1720 MHz with 18 dB shielding effectiveness for a bandwidth of 100 and 173 MHz, respectively, thus shielding the GSM signals. Additionally, the modified double square loop element-based FSS is symmetrical providing the advantage of polarization independency. It also exhibits angular stability up to 60° for both the horizontal polarized electric field (TE mode) and vertically polarized electric field (TM mode). A prototype of the proposed dual-band low profile FSS is fabricated. The simulation results are compared with the experimental results and are found to be in congruence with each other. [ABSTRACT FROM PUBLISHER]

In this study, a modified antipodal Vivaldi antenna (AVA) with low cross-polarisation is proposed for ultrawideband communications. The bandwidth offered by conventional single petal AVA is enhanced by adding another petal. This dual petal antenna occupies a small volume of 60 × 60 × 0.8 mm3 and provides operating bandwidth from 2.4 GHz to frequencies >14 GHz. The proposed antenna configuration provides low cross-polarisation level which is <-15 dB over the entire operational band. The designed antenna offers realised gain >5 dB and an average group delay variation of 0.5 ns. The prototype antenna is fabricated and tested to validate the simulation results. [ABSTRACT FROM AUTHOR]

A novel dual frequency, wide band textile antenna has been proposed. A slot cut out of a regular rectangular patch revealing a vertical dumbbell-shaped conducting region resonates at global positioning system (L1 and L3) and time division duplex long term evolution fourth generation bands. The radiation efficiencies of the antenna at the lower and upper resonant frequencies are 96 and 88%, respectively. The antenna is fabricated using double side silver coated conductive fabric on a denim substrate and experimentally validated. The textile antenna resonates from 1.435 to 1.81 GHz and from 2.755 to 3.19 GHz. The antenna has a bandwidth of 375 and 435 MHz, that is, fractional bandwidth of 25.08 and 12.6% at the lower and upper bands, respectively. The fabricated antenna is then subjected to bending, shear, stretching deformations and their effects on the bandwidth of the antenna are analysed using analysis of variance method. The significant factors and their percentage contribution on the bandwidth are also determined using the F-test. Finally, an empirical equation is derived for the designed antenna to compute the bandwidth and the results are validated. [ABSTRACT FROM AUTHOR]

This paper presents the design of a novel linear analog planar phase shifter deploying split-ring resonator (SRR) and complementary split-ring resonator (CSRR) structures. Based on the advantages of these structures, a triband phase shifter is designed for multiple target systems to operate at 0.85, 1.69, and 2.46 GHz bands finding applications for European RFIDs, Satellite Radio Broadcast System, Mobile Services, and ISM Band, respectively. The effect of SRR and CSRR coupling with host transmission line is also analyzed on the basis of Bloch mode theory and the modes are validated through Eigen mode analysis. The proposed phase shifter design shows a good agreement between simulated and measured results. A 90° ± 8°shift in phase is observed at lower and upper bands, and a 135° ± 8°shift is observed in center band with reasonable group delay components. [ABSTRACT FROM AUTHOR]

A novel method for achieving linear phase shift is proposed over the frequency range of 2 - 6 GHz. Dielectric characterization of FR4 substrate interfaced with air as well as water produces the phase shift. The substrate property is modified by introducing a plain rectangular packet and W-shaped packet within the FR4 substrate. The overall dimension of the proposed structure is 30 × 60 mm2. Across the entire proposed frequency range, the reflection coefficient is less than −10 dB. The proposed coplanar waveguide with water- and air-stacked FR4 substrate is simulated, fabricated, and measured for its linear phase shifting characteristics analyzed in ISM 2.45, 3.3, and 5.8 GHz bands. The analysis over the entire band depicts that the differential shift in phase is directly proportional to the effective dielectric constant of the material used. The design will be more useful in automotive anti-collision radars in military, cellular base stations, and satellite communications. [ABSTRACT FROM AUTHOR]

This communication presents the design of grid array antenna (GAA) for automotive UWB radar sensors. The proposed GAA is constructed using astroid unit cells, which concurrently achieve high gain and bandwidth. The GAA consists of 33 radiating elements and are excited using a common transmission line center fed by a 50\text-\Omega coaxial probe. Furthermore, amplitude-tapering techniques are employed to lower the sidelobe level (SLL). The prototype antenna is fabricated and experimental results are presented. The developed amplitude-tapered GAA provides 2.5 GHz effective operational bandwidth with \textVSWR \leq 2 and gain variation less than 3 dB. The measured peak gain is 13.87 dB at 24 GHz. [ABSTRACT FROM PUBLISHER]

In this article, two-element monopole multiple input-multiple output (MIMO) antenna with polarisation diversity for 4G and other applications has been presented. The designed antenna covers 16% (1701-2001 MHz) of bandwidth around the design frequency (1850 MHz) which includes both DCS-1800 and DCS-1900 bands. The two antennas are placed orthogonally and symmetrically with edge-to-edge spacing of 5.5 mm (λ0/30). With the placement of interconnected swastika-shaped resonator between the two monopole antennas, there is an isolation enhancement of 60 dB thus reducing the envelope correlation coefficient value ranging from 0.016 to 6.12 × 10-10 and improving the diversity gain ranging from 9.9 to 10 dB within the -10 dB bandwidth. A prototype has been fabricated and validated using measurements. [ABSTRACT FROM AUTHOR]

The design, development, fabrication, and testing of a wideband reflectarray antenna with a novel concentric ring element operating over Ku/K band frequencies is presented in this paper. The element characterization is performed using the infinite array approach and is inferred that the proposed unit cell offers a higher phase variation of 643° by changing the size of the concentric rings. The proposed reflectarray antenna has a circular geometry and is constructed using 437 elements with an element separation of 0.43λ0. The proposed reflectarray offers a 3 dB gain bandwidth of 35% (15–21 GHz). The aperture efficiency is estimated to be 58.78% at 16.5 GHz. The prototype reflectarray is fabricated and tested to validate the simulation results. The measured peak gain of the reflectarray is 28.4 dBi with a side lobe level of −17.6 dB. The measured cross‐polarization level is less than −32 dB. Furthermore, it is inferred that the proposed unit cell has a reduced maximum phase sensitivity of 246°/mm with a gain selectivity of 6 dB at the lowest operating frequency. The proposed broadband reflectarray with enhanced performance characteristics is suitable for application in satellite communication and aeronautical radio navigation. [ABSTRACT FROM AUTHOR]

Contemplating the advancements in communication technology, the analysis of the features of reflectarray, transmitarray, and transmit‐reflectarray becomes essential for future adaptability. This article presents a thorough review of such high‐gain antennas, presenting some of the most relevant solutions published by the scientific society in the field of antennas and wave propagation. Several examples of unit cells for array implementation and complete array designs discussed in various literatures are analyzed. The analysis is focused in identifying the unit cell layouts, such as those developed using microstrip patches, frequency selective surfaces, or metamaterials. The analysis is extended to the ways of improving bandwidth, for example, true time delay elements, phase delay lines, meander lines, and so on, and the various methods used to enable reconfiguration, for example, p‐i‐n diodes, varactor diodes, or microelectromechanical systems. In addition, some antennas, which produce bidirectional beams simultaneously, are also discussed. Finally, all the models are compared against each other in order to highlight their benefits and limitations, summarizing their main characteristics, such as the frequency of operation, bandwidth, phase range, gain, aperture efficiency, sidelobe levels, cross polarization levels, and maximum beam‐steering range. [ABSTRACT FROM AUTHOR]