Ultra-wideband Frequency Band Research Articles

Investigation of optically transparent metasurfaces for gain improvement of an ultrawideband antenna for wireless body area networks and vehicular communications

Abstract Due to higher frequencies which cause signal deterioration, 5G enabled antennas are prone to substantial attenuation. To circumvent this problem, several access points, signal repeaters, and base stations must be installed closer together on building windows, streetlights, and other infrastructure. Optically transparent antennas preserve the aesthetics of the windows by offering the requirements for access points and base stations for providing network connectivity to the cars and pedestrians passing by those buildings. Here we report an ultrawideband (UWB) high gain optically transparent antenna operating from 4-12 GHz. Indium tin oxide (ITO) coated glass has been used as an optically transparent substrate for designing the antenna and metasurface. Two optically transparent metasurfaces have been proposed for band-stop filtering action across the UWB frequency range 4-12 GHz. In absence of the metasurface, the antenna operates in the frequency band ranging from 3.8 to 15 GHz. Average gain enhancement is 5.2 dB with radiation efficiency higher than 93% across the UWB frequency band from 4-12 GHz. Numerical simulations have been carried out for analysis of the proposed antenna and metasurfaces. These simulations have been validated by experimental measurements of the fabricated prototypes.

Influence of Substrate Materials on the Performance of a Triple-Band Notched Frequency UWB Antenna

In this paper, the influence of different substrate materials on the performance of a triple-band notched frequency of ultra-wide band (UWB) antenna is presented. The antenna has a rectangular shape with dimension 31 by 24 mm and operates at UWB frequency band of 3.1GHz to 10.6GHz. The antenna was simulated using HFSS software. The effect of eight different substrate materials with different dielectric constant was examined on the antenna. Under each substrate, the performance of the antenna was investigated based on the antenna gain, directivity, radiation pattern, voltage standing wave ratio (VSWR), impedance bandwidth and S-parameter. Through thorough analysis, the results gave strong indication that UWB antenna performance is greatly affected by the type of dielectric substrate material chosen for design. The paper demonstrates the effect dielectric substrate material has on the antenna performance measurement like radiation pattern, gain, directivity and VSWR.

A compact tri-notched flexible UWB antenna based on an inkjet-printable and plasma-activated silver nano ink

The rapid development of ultrawideband (UWB) communication systems has resulted in increasing performance requirements for the antenna system. In addition to a wide bandwidth, fast propagation rates and compact dimensions, flexibility, wearability or portability are also desirable for UWB antennas, as are excellent notch characteristics. Although progress has been made in the development of flexible/wearable antennas desired notch properties are still rather limited. Moreover, most presently available flexible UWB antennas are fabricated using environmentally not attractive subtractive etching-based processes. The usage of facile additive sustainably inkjet printing processes also utilizing low temperature plasma-activated conductive inks is rarely reported. In addition, the currently used tri-notched flexible UWB antenna designs have a relatively large footprint, which poses difficulties when integrated into miniaturized and compact communication devices. In this work, a silver nano ink is used to fabricate the antenna via inkjet printing and an efficient plasma sintering procedure. For the targeted UWB applications miniaturized tri-notched flexible antenna is realized on a flexible polyethylene terephthalate (PET) substrate with a compact size of 17.6 mm × 16 mm × 0.12 mm. The antenna operates in the UWB frequency band (2.9–10.61 GHz), and can shield interferences from WiMAX (3.3–3.6 GHz), WLAN (5.150–5.825 GHz) and X-uplink (7.9–8.4 GHz) bands, as well as exhibits a certain of bendability. Three nested "C" slots of different sizes were adopted to achieve notch features. The simulation and test results demonstrate that the proposed antenna can generate signal radiation in the desired UWB frequency band while retaining the desired notch properties and having acceptable SAR values on-body, making it a viable candidate for usage in flexible or wearable communication transmission devices. The research provides a facile and highly efficient method for fabricating flexible/wearable UWB antennas, that is, the effective combination of inkjet printing processing, flexible substrates, low temperature-activated conductive ink and antenna structure design.

Simple Compact UWB Vivaldi Antenna Arrays for Breast Cancer Detection

In this study, at ultra-wideband (UWB) frequency band (3.1–10.6 GHz), we propose the use of compact 2:1 and 3:1 nonuniform transmission line Wilkinson power dividers (NTL WPDs) as feeding networks for simple 2 × 1 linear UWB Vivaldi tapered and nonuniform slot antenna (VTSA and VNSA) arrays. The 2:1 and 3:1 tapered transmission line (TTL) WPDs are designed and tested in this work as benchmarks for NTL WPDs. The VTSA array provides measured S11 < −10.28 dB at 2.42–11.52 GHz, with a maximum gain of 8.61 dBi, which is 24.39% higher than the single element. Using the VNSA array, we achieve 52% compactness and 6.76% bandwidth enhancement, with good measured results of S11 < −10.2 dB at 3.24–13 GHz and 15.11% improved gain (8.14 dBi) compared to the VNSA single element. The findings show that the NTL and Vivaldi nonuniform slot profile antenna (VNSPA) theories are successful at reducing the size of the UWB WPD and VTSA without sacrificing performance. They also emphasize the Vivaldi antenna’s compatibility with other circuits. These compact arrays are ideal for high-resolution medical applications like breast cancer detection (BCD) because of their high gain, wide bandwidth, directive stable radiation patterns, and low specific absorption rate (SAR). A simple BCD simulation scenario is addressed in this work. Detailed parametric studies are performed on the two arrays for impedance-matching enhancement. The computer simulation technology (CST) software is used for the simulation. Hardware measurement results prove the validity of the proposed arrays.

Gain enhancement of ultra-wideband hexagonal slot antenna using tessellated rhombic loops based reflector

Abstract A simple technique for gain enhancement of irregular hexagonal shaped ultra-wide band (UWB) slot antenna by inclusion of closely packed tessellated rhombic loop (TRL) based FSS is presented in this paper. The slot antenna is designed to cover entire UWB (3.1–10.6 GHz) frequency range with stable bi-directional radiation pattern. Also, it exhibits non-uniform boresight gain in zenith (θ = 0°) and nadir (θ = 180°) directions. The slot antenna is further loaded with TRL FSS at both slot and feed side separately to study distinct configurations of antenna integrated with FSS and evaluate the impact of the configurations of FSS on antenna performance. Later, an antenna and antenna loaded with TRL FSS prototype are developed for experimental validations. Through measurements it is found that the slot antenna covers entire UWB frequency band and provides a maximum of 4.31 dB gain in zenith direction while 4 dB gain in nadir direction. A gain enhancement of 2.44 dB in zenith and 3.8 dB in nadir directions are achieved when the slot antenna is integrated with TRL FSS along feed side and slot side separately. The measured results confirm the simulated results well.

An Ultra-wideband Low-power Low-noise Amplifier Linearized by Adjusted Derivative Superposition and Feedback Techniques

Ultra-wideband (UWB) applications require low-power and low-noise amplifiers (LNAs) that can operate over a wide frequency range. However, conventional LNAs often suffer from poor linearity and high-power consumption. This research work proposes a novel LNA design that uses the adjusted derivative superposition (DS) technique and feedback to improve the linearity and reduce the power consumption of UWB LNAs. The DS technique enhances the third-order intermodulation (IM3) cancellation by adjusting the bias currents of the transistors, whereas the feedback improves the stability and input matching of the LNA. The LNA is implemented using a degenerated common source topology in a 180 nm standard CMOS technology. The simulation results show that the LNA achieves a power gain of 10–12.2 dB, an input third-order intercept point (IIP3) of about 12 dBm, and a noise figure of less than 2.5 dB over the UWB frequency band of 3.1–10.6 GHz. The input reflection coefficient is less than -10 dB, and the power consumption is 11.6 mW with a 1.5 V power supply. The designed LNA offers a novel and innovative solution for UWB applications that significantly improve the performance and efficiency of UWB LNAs whereas reducing the cost and complexity of implementation.

Printable Silver Nano Ink for Bendable Ultrawideband Antenna with Triple-Notch Characteristics

Flexible antennas based on the printed flexible electronic technology are of great interest for important applications in wireless communication systems due to their distinctive features over traditional rigid-based antennas. The ultrawideband (UWB), notch characteristics, and bending capabilities of such antennas are crucial for flexible and wearable applications. Currently, only a few are focused on the printed flexible electronics technology with printable ink materials for UWB antenna applications. In addition, flexible UWB antennas with triple-notch characteristics and good bending performance are rarely reported. Thus, there is a need to make advances in this area. Here, we describe the application of a printable silver nanoparticle-based ink for rapidly fabricating an antenna with bendable and triple-notch characteristics designed for UWB communication systems. The ink, composed of monodisperse silver nanoparticles, isopropanol, and ethyl glycol, can easily produce favorable conductive patterns at a sintering temperature below 130 °C after inkjet printing. The antenna is designed on a flexible polyethylene terephthalate (PET) substrate and has a moderate size of 27 mm × 38 mm × 0.12 mm. It operates at a frequency range of 1.9–10.75 GHz, which covers the desired UWB frequency band. By loading a “U”-like slot and two “C”-like slots on the radiating patch, band rejections were generated at 3.2–3.8, 5.3–6.2, and 7.8–8.5 GHz, shielding the interference from world interoperability for microwave access, wireless local area networks, and X uplink bands. The bending results show that the antenna retains good UWB and triple-notch performance even after bending along the Y- or X-axis for different degrees. An antenna prototype was finally fabricated by inkjet printing of the silver nano ink on the PET substrate, exhibiting the desired notch characteristics and excellent bendability. The fabricated antenna prototype proved the feasibility of use as a flexible device at an ultrawide frequency band. The research provides a design guide for flexible antennas with notch features toward flexible and wearable electronics.

DESIGN OF A COMPACT BROADBAND ANTENNA USING CHARACTERISTIC MODE ANALYSIS FOR MICROWAVE APPLICATIONS

A compact broadband antenna of dimensions 27 mm x 28 mm x 1.6 mm and with good impedance matching is designed for high-bandwidth radio systems with a short range. To improve the impedance matching, two rectangular slots are created on the radiating element, and the ground plane size is reduced to extend the ultra-wideband frequency band. The antenna bandwidth and radiation performance are analysed using characteristic mode theory (TCM). The performance is compared to the desired specifications, and the shape and size are modified to produce efficient radiation and dominant radiation patterns. The findings clearly demonstrate that the six modes are resonant with (λn = 0). This implies that the eigenvalues of the six modes contribute strongly to dominant electromagnetic radiation and have high modal significance values around 1 at their respective frequencies. Furthermore, the characteristic angle indicates that the antenna resonates at 180°, since the six modes intersect the axis line at 180° at their respective frequencies. Experimental results show a bandwidth of 109.7% between 5.64 and 19.34 GHz, a maximum gain of 6.3 dB, and a maximum efficiency of approximately 86.5%. These results make this antenna a versatile and effective choice for a wide variety of communications and electronics applications and easy to install in narrow spaces due to its easy design characteristics, small size, and light weight.

A Printed U-Shaped Coplanar Waveguide Feed UWB Antenna for GPR Applications

A printed U-shaped coplanar waveguide fed (CPW) ultra-wideband (UWB) antenna is designed, fabricated, and measured in this paper for ground penetrating (GPR) applications. To enhance the working bandwidth, a set of cutoffs was introduced in different parts of the antenna. The antenna was printed on the FR4-epoxy substrate in a compact size of 0.252λ0×0.3λ0×0.015λ0 at 3 GHz. The calculated results were validated by realizing and measuring a prototype. Experimental demonstrations were done with the R& S®ZNB Vector Network Analyzer, which indicates that the antenna's working bandwidth extends from 3.09 GHz to 11.07 GHz (112.71%). Additionally, the antenna's radiation patterns were measured in an isolated anechoic chamber, which shows that the proposed antenna has omni-directional radiation patterns. Moreover, acceptable gain antenna values ranging between 1.74 and 7.04 dBi and high values of radiation efficiency of more than 80% were achieved over the whole working bandwidth. Besides, the antenna presents a stable group delay with a linear phase of S21 through the UWB frequency band. To prove the efficiency of the fabricated antenna for GPR applications, the operation of the antenna was experimentally tested in a sandy soil box. The obtained results show that the proposed antenna could be a good candidate for GPR applications.

Circular ring shaped ultra-wideband metamaterial absorber with polarization insensitivity for energy harvesting

<span>A circular ring-shaped metamaterial (CRM) absorber was designed to harvest radio frequency (RF) energy in the ultra-wideband (UWB) frequency band applications. The proposed metamaterial unit cell features a circular shaped structure, with rectangular strip lines connected in the form of a cross leaving a square shaped slot at center. The unit cell dimensions are 15×15×1.6 mm. The absorber was etched on a low cost FR4 substrate having a dielectric constant of 4.4. Ansys high frequency structure simulator (HFSS) software was used for simulation and the analysis were carried out for unit cell, 2×2, 3×3, and 4×4 array structures. The absorber parameters plotted are absorption characteristics and reflection characteristics. Also, the metamaterial parameters (μeff) and (εeff) are also retrieved from the absorber parameters and analyzed. From the analysis, the values (μeff) and (εeff) were found to be negative, leaving refractive index also negative (n<0), which proved the metamaterial property. The proposed CRM absorber showed good absorption characteristics of more than 80% and also metamaterial property in the entire UWB band (4-13 GHz). Hence the absorber proves to be a good candidate in powering low power sensors/microcontrollers for internet of things (IoT) applications.</span>

A Planar Four-Element UWB Antenna Array with Stripline Feeding Network

This paper proposes a four-element ultrawideband (UWB) planar antenna array with elliptical-shaped radiators and a stripline excitation network designed for the 6–8.5 GHz UWB frequency band allowed in Europe by the European Commission. The designed antenna array has a symmetrical structure in which the radiators are placed along one line in the central conducting layer, arranged between two layers of a dielectric. Radiating elements are fed by the stripline excitation network that provides uniform power distribution. The dimensions of the elliptical radiators’ axes are 14 mm × 16 mm. Two variants of array are proposed. The distance between the radiators’ centers is L = 19 mm for a shorter variant and L = 24 mm for a longer one. The presented antenna array structures have a size of 81 mm × 41 mm and 96 mm × 41 mm. These arrays present a measured gain of 6.4–10.6 dBi for the shorter variant and 8.5–10.8 dBi for the longer one and a fair impedance matching. The measured |S11| is less than −8.7 dB and −9.7 dB for the shorter and longer corresponding variants.

DUAL SUBSTRATE MIMO ANTENNA SYSTEM FOR COGNITIVE RADIO AND AUTOMOTIVE APPLICATIONS

A compact, planar, dual reconfigurable, substrate, multi-band, multiple-input multiple-output (MIMO) antenna system is presented. The proposed MIMO antenna is designed to operate over the entire ultra-wide-band (UWB) frequency band supporting cognitive radio (CR) and automotive applications. The dual-element MIMO antenna is integrated with a radiating element and pure ground plane to operate in two different modes. Two modes of operation are used for the MIMO antenna to sweep the frequency over a wide band especially below 1 GHz. The proposed MIMO antenna covers a wide range of frequency bands from 500MHz~10GHz. The elements of the proposed compact multilayer dual substrate MIMO antenna are placed perpendicular to each other to attain high isolation and polarization diversity which makes the antenna system best suited for CR and automotive applications. The antenna system is developed on dual substrate area of dimensions 58×61×1.6 mm3. The proposed antenna achieves multiband operation with a wide bandwidth of 2GHz within the UWB frequency band.

Vivaldi Antenna Arrays Feed by Frequency-Independent Phase Shifter for High Directivity and Gain Used in Microwave Sensing and Communication Applications.

This paper describes a novel feed system for compact, wideband, high gain six-slot Vivaldi antenna arrays on a single substrate layer using a unique combination of power splitters based on binary T-junction power splitter topology, frequency-independent phase shifter, and a T-branch. The proposed antenna system consists of six Vivaldi antennas, three on the left, and three on the right arm. Each arm connects with T-junction power divider splitter topology, given that the right arm is linked through a frequency-independent phase shifter. Phase shifters ensure that the beam is symmetrical without splitting in a radiating plane so that highly directive radiation patterns occur. The optimal return losses (S-parameters) are well enriched by reforming Vivaldi’s feeding arms and optimizing Vivaldi slots and feeds. A novel feature of our design is that the antenna exhibits the arrangements of a T-junction power splitter with an out-of-phase feeding mechanism in one of the arms, followed by a T-branching feeding to even arrays of proper Vivaldi antenna arrangement contributing high realized gain and front-to-back ratio up to 14.12 dBi and 23.23 dB respectively applicable for not only ultra-wideband (UWB) application, also for sensing and position detecting. The high directivity over the entire UWB frequency band in both higher and lower frequency ranges ensures that the antenna can be used in microwave through-wall imaging along with resolution imaging for ground penetration radar (GPR) applications. The fabricated antenna parameters are in close agreement with the simulated and measured results and are deployed for the detection of targets inside the voids of the concrete brick.

Wearable Flexible Antenna for UWB On-Body and Implant Communications

This paper describes the development and evaluation of an on-body flexible antenna designed for an in-body application, as well as on-body communications at ISM and UWB frequency bands. The evaluation is performed via electromagnetic simulations using the Dassault Simulia CST Studio Suite. A planar tissue layer model, as well as a human voxel model from the human abdominal area, are used to study the antenna characteristics next to human tissues. Power flow analysis is presented to understand the power flow on the body surface as well as within the tissues. Simulation results show that this wearable flexible antenna is suitable for in-body communications in the intestinal area, e.g., for capsule endoscopy, in the industrial, scientific, and medical (ISM) band and at lower ultra-wideband (UWB). At higher frequencies, the antenna is suitable for on-body communications as well as in-body communications with lower propagation depth requirements. Additionally, an antenna prototype has been prepared and the antenna performance is verified with several on-body measurements. The measurement results show a good match with the simulation results. The novelty of the proposed antenna is a compact size and the flexible substrate material, which makes it feasible and practical for several different medical diagnosis and monitoring applications.

An octagonal ultra-wideband double slit antenna for WiMAX and WLAN rejection

Abstract This article proposes a dual band rejected double slits-based planar octagonal microstrip antenna for Ultra-Wideband (UWB) applications. The antenna built by an edge trimmed partial ground and an octagonal microstrip patch with a horizontal and an inclined rectangular slit. The slits are made to remove the interfering frequency bands WiMAX and WLAN from UWB band. The designed antenna without slits operates on the frequency range 2.78–10.78 GHz with a fractional bandwidth of 119% which includes the UWB frequency band 3.1–10.6 GHz. The antenna with diagonal inclined slit notches the band 4.4–5.83 GHz which excluded WLAN frequency range and shift the starting frequency of UWB band to the right from 2.78 to 3.26 GHz. The antenna with both horizontal and inclined slits further shifts the starting frequency from 3.26 to 3.619 GHz, eliminating the WiMAX band. The excluded bands show the VSWR value greater than 2 dBi whereas the rest of the band has less than 2 dBi. The proposed antenna results in nearly omnidirectional radiation pattern, 6.2 dBi peak gain and 85% radiation efficiency.

A compact dual-polarized co-radiator MIMO antenna for UWB applications

AbstractIn this research study, a compact dual-polarized co-radiator ultra-wideband (UWB) multiple-input multiple-output (MIMO) antenna with improved impedance bandwidth and isolation is proposed for wireless applications. The designed co-radiator has an overall area of 0.3λo × 0.3λo mm2 (where, λo is free space wavelength corresponding to the lower cut-off frequency, i.e., 3.1 GHz). The proposed resonator comprises of a hybrid geometry which is created with the combinations of a circular-shaped patch, a square, and two rectangular stubs. It is centrally aligned between two 50 Ω micro-strip feed lines that are positioned orthogonal to each other. Further, the modified ground plane is attached with the end-loaded line which provides broadband isolation over entire UWB frequency band. The simulated results of the proposed antenna exhibit wideband characteristics with impedance bandwidth of 3.1–16.9 GHz with minimum isolation of −15 dB. Moreover, all the radiation performance parameters are analyzed and discussed. Some important diversity parameters such as envelope correlation coefficient, mean effective gain, effective diversity gain, and channel capacity loss have also been evaluated. Furthermore, all the measured results of proposed antenna agree well with the simulated results which make the proposed antenna a suitable candidate for UWB-MIMO wireless applications.

Honeycomb shaped fractal antenna with dual notch characteristic for UWB applications

The paper presents a feasible way to construct the honeycomb structured microstrip antenna for UWB (Ultra Wide-band) applications with dual notch characteristic. The antenna designed based on the concept of initial stage of honeycomb nest construction and Defected ground structure(DGS) with dual notch for Ultra Wide Bandwidth applications. The two notches for WiMAX (3.5GHz center frequency) and WLAN (5.5 GHz center frequency) are introduced by etching two asymmetrical quarter wavelength slots in the ground. The compact antenna of size 12 x 20 mm2 with simple geometry achieves very wide bandwidth of 3.1-13.8 GHz(Covers UWB and higher frequency band) with dual notch characteristic.

Dual-Functional Ultrawideband Antenna With High Fidelity Factor for Body Area Networks and Microwave Imaging Systems

Microwave Imaging (MI) and Body Area Networks (BANs) technologies are widely used in healthcare systems. A dual-functional compact ultrawideband (UWB) antenna with a high on-body and off-body fidelity factor is presented in this paper. The antenna’s design approach is based on analyzing the return loss, the antenna’s gain, the phase of S21, and the group delay over the UWB frequency band, in each designing step, to achieve the highest level of fidelity factor in both E- and H-plane. The final design (Ant. 3) consists of a circular ring with six intersecting rings in the radiating element and an elliptic ground plane with an overall size of $16\times 20\,\,mm^{2}$ . Simulated and experimental evaluations both in free space and on-body prove the excellent operation of Ant. 3 within the FCC UWB bandwidth of 3.1 to 10.6 GHz in terms of return loss and fidelity factor (greater than 0.9 at all angles). For body area communication, the final design presents the fidelity factor greater than 0.93 near the human arm. Also, for breast cancer detection applicability, a 12-element array of Ant. 3 is located around a conical breast model. The results show the antenna’s promising performance in detecting 6-mm average diameter malignant tumor and 3-mm average diameter benign tumor.

A Tree-profile Shape Ultra Wide Band Antenna for Chipless RFID Tags

In this article, a new small size planar microstrip tree profile shaped Ultra-Wide Band (UWB) antenna with partial ground plane has been presented. The antenna is designed for chipless RFID tags that are working in UWB region. The operating frequency of the antenna is between 2.72 GHz to 11.1 GHz which covers the entire UWB frequency band. The antenna exhibits comparatively high realized gain of 4.2 dBi with respect to its small size of 27 × 40 mm2 and have a gain to aperture ratio of 0.243 which is comparatively higher than other existing retransmission-based chipless RFID antennas. Another aspect of this antenna is its total efficiency which never goes below 80% throughout the entire bandwidth whereby it reaches as high as 96% at 3.5GHz. This design will motivate the chipless RFID designers to produce small size and cost effective tags.

Isolation Enhancement Using a Hybrid Technique in an Eight-Element UWB MIMO Antenna Design

A high order multiple input multiple output (MIMO) antenna assembly is designed for Ultra-Wideband (UWB) applications. The antenna configuration is based on a peculiar arrangement of the radiating elements. A defected microstrip structure is also introduced on the feedlines. The use of a novel technique, the so-called ports-shift, is here discussed. In the proposed antenna, a protruded ground branch structure is employed in combination of three parasitic stubs so as to enhance isolation and impedance matching over the UWB frequency band. The results show that the presented antenna exhibits a good impedance matching which is about -10 dB with a high mutual coupling 15 dB, and envelope correlation coefficients (ECC) smaller than 0.15. The antenna also exhibits good diversity gain of about 9.5, and a good efficiency that varied between 56% and 91% and total active reflection coefficient of less than -20 dB. Which makes it a good candidate for UWB applications.