Ultra-wideband Frequency Research Articles

Design strategies and performance evaluation of reconfigurable notch filtering in UWB Vivaldi Antennas

Abstract This paper presents a frequency reconfigurable notch band enabled Vivaldi Antenna for ultra-wideband (UWB) applications. The proposed antenna structure features a fork shaped patch embedded with a PIN diode. Patch is fed with a triangular tapered feed line and supported by a novel shaped Vivaldi ground plane consisting two exponentially tapered fins adjoining with a triangular slot. The antenna design shows a −10 dB impedance bandwidth ranging 2.17–10.97 GHz with a notch band between 4.94–5.11 GHz. With the help of BAR64 PIN diode reconfigurable notch band is achieved at 5.0 GHz frequency. Moreover, this notch frequency can be shifted to the desired frequency by adjusting the feed settings and location of the diode. The idea behind this design is to introduce a simple design, independently controlled notch parameters, simple switching operation, and high gain abilities. The developed antenna exhibits steady unidirectional radiation patterns and a peak gain of 9.3 dBi with noticeable decreases at the notched band. Almost stable gain is observed between UWB frequency range of 3.1–10.6 GHz, gain is varying from 7.05 dBi to 8.3 dBi and only 1.25 dBi gain variation is observed within this range of frequency. The simulated and fabricated results showcase a close agreement with each other. The proposed antenna improves wireless communication performance, meeting the growing demand for dependable and interference-resistant solutions.

Highly Selective Ultra-wideband Filtenna with Triple Band Notch and Wide Stop Band Rejection for UWB Communication and Sensing Applications

A compact and highly selective monopole ultra-wideband (UWB) filtenna (UFA) having triple band notch is presented in this paper. The proposed UFA covers the UWB frequency range with good matching characteristics. Defected ground structure provides good impedance matching with return loss above 10 dB. A low pass filter with wide stop band rejection is integrated in the feed line to provide high selectivity and wide rejection band at upper edge of UWB. Three folded uniform impedance resonators are integrated with the UWB radiator to suppress the effect of interference experienced in the UWB spectrum from WiMAX, WLAN, and X-bands. The proposed UFA covers the frequency bandwidth from 2.5 to 11.1 GHz with above 3 dBi gain in all the pass bands and radiation nulls at notch bands. The proposed design has been simulated and analyzed using commercially available software CST Microwave Studio and the obtained results show good agreement between simulation and measurement. The performance of this UFA makes this a suitable candidate for UWB communication and sensing applications.

Flexible ultrawide band frequency selective surface for shielding applications

Flexible ultrawide band frequency selective surface for shielding applications

Ultra-wideband and high isolation using defected ground structure modified bowtie antenna array for through wall imaging applications

The design and analysis of an ultra-wideband with high isolation characteristics, utilizing a modified bowtie antenna and coplanar waveguide feeding technique is presented in this paper. Grooves are added to the ground plane's entire structure to reduce the capacitive coupling between the patch and the ground plane. The grooves in the ground plane enhance the impedance matching and radiation efficiency across the ultrawideband frequency range. Also, defected ground structures (DGS) are used to improve isolation between the two antennas. It is novel and different in that it uses defective ground structures (DGS) to provide high isolation (−<50dB) with a high gain of 6.5 dBi and a large impedance bandwidth (155%). Compared to other documented methods, the antenna's design step is very simple, the overall size is small, larger bandwidth (13.5 GHz) and achieves high isolation due to DGS.

Microwave absorption properties and multilayer absorber design of La2FexCo14-xB with easy cone anisotropy

The effective integration of microwave attenuation capability with impedance matching is crucial for designing and optimizing microwave-absorbing materials. In this study, we investigate the microwave absorption properties of La2FexCo14-xB with easy cone anisotropy. By adjusting the filling rate of La2Fe4Co10B, we have successfully enhanced the microwave attenuation capability of the composite and optimized its impedance matching. At a filling rate of 25 vol%, La2Fe4Co10B exhibits an effective absorption bandwidth (EAB) of up to 7.5 GHz at a thickness of 1.5 mm, superior to most single-layer absorbing materials. Furthermore, we introduce a novel concentration-dependent layered structure comprising La2Fe4Co10B/paraffin composites at designated filling rates of 10 vol%, 25 vol%, and 40 vol%, respectively. This 3-layer absorber exhibits outstanding microwave absorption performance. With a total thickness of 2.9 mm, the 3-layer absorber achieves a strong absorption peak of −55.1 dB at 11.0 GHz, while also possessing an EAB of 9.8 GHz. Based on Maxwell's equations, which encompass normalized input impedance and loss analysis, it is demonstrated how the 3-layer structure efficiently utilizes the dielectric and magnetic loss properties of La2Fe4Co10B to achieve robust absorption across an ultra-wide frequency band. This study not only offers a fresh perspective on the microwave attenuation capabilities of materials but also introduces novel strategies for the design of advanced materials aimed at high-performance microwave absorption.

A split ring resonator slot based fabricated crescent microstrip patch antennas for UWB wireless system applications

This paper clarifies significant bandwidth and optimum gain for a split ring resonator slot based fabricated microstrip patch antenna for ultra wide band (UWB) wireless telecommunication system applications. The antenna has a circular slot partially cut into a circular patch and radiates in the UWB frequency range. The design system features a steady radiation pattern and an impedance bandwidth of 3.3 to 10.96 GHz. The proposed UWB notch antenna is at 4.6 GHz, 7.29 GHz, and 9.36 GHz, with an impedance bandwidth of 3.3 to 10.96 GHz. The UWB notch antenna offers linear phase response and a group delay of fewer than 1 ns. It is practical for UWB applications due to less group delay and stable radiation patterns. FR4 material with a 4.4 relative permittivity. The reported antenna is measured following the manufacturing of the prototype design using HFSS simulations. The suggested fabricated antenna minimizes return loss. The findings demonstrate that when combined with VSWR 2, the reflection coefficient covers the band ranges from 3.3-10.96 GHz.

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, 5 G 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.

Mutant amplitude modulation behavior of MIS-like structure of few-layer graphene/SiO2/p-Si in 500–750 GHz band

Graphene has great application potential in the field of electromagnetic modulation field because of its excellent physical and electronic properties. Studies have demonstrated that the properties of graphene films with different layers are also different due to the difference in energy band structure. Nowadays, the modulation mechanism of monolayer graphene (MLG) and bilayer graphene (BLG) has been gradually discovered, but for graphene with more than three layers, the mechanism of whether it is tunable remains to be explored, especially on the proving from an experimental perspective. In this study, the CVD-prepared highly homogeneous few-layer graphene (FLG) film was combined with SiO2 nanolayers and P-doped Si substrate to form an MIS-like capacitor structure, a unique electromagnetic behavior of mutant amplitude modulation exhibited by FLG film was found, which was different from that of mono- and bi-layers of graphene. The results show that the structure exhibits obvious modulation behavior in the ultra-wideband frequency of 500–750 GHz and the bias of 0.9 V, up to 3.1 dB. This study makes a new supplement to a gap in the EM modulation system of graphene series material.

RF NEMS switches based on graphene for low pull-in voltage and excellent RF performance

This study introduces a novel graphene RF NEMS capacitive switch and conducts an extensive analysis of its RF performance using CST and COMSOL Multiphysics software. The switch’s characteristic impedance matching is accomplished through a coplanar waveguide (CPW) structure, incorporating a dielectric layer topped with conductive graphene beam electrodes. Simulation results reveal that the monolayer graphene RF NEMS switch maintains an insertion loss of 0.003 ~ 0.015 dB and an isolation greater than 40 dB across an ultra-wideband (UWB) frequency range of DC ~ 140 GHz. Moreover, the switch demonstrates a switching time of 4.03 ps at a pull-in voltage of 1 V. The performance of multilayer graphene RF NEMS switches was also evaluated. The study further investigates the operational mechanism of the graphene RF NEMS switch and performs finite element analysis on the proposed design. The graphene RF NEMS switch discussed herein offers significant advantages, including minimal size, lightweight, cost-effectiveness, low pull-in voltage, rapid response time, excellent RF performance, and reduced space consumption in circuitry. Its potential applications span a range from L to F bands, encompassing data storage, communication systems, sensors, remote sensing and military uses.

A Circular Ring Patch Antenna for Breast Cancer Detection Based on Return Loss and VSWR

Breast cancer is a serious condition that affects women and requires timely identification. Various methods such as magnetic resonance imaging, mammography, digital mammography, and computer-aided detection are used for this purpose. However, these techniques have their drawbacks. To address this issue, a new approach is proposed and detailed in this paper. In this novel method, a circular patch antenna is employed to detect tumors in a breast phantom. The analysis of return loss and voltage standing wave ratio (VSWR) helps in identifying the presence of tumors. High-frequency structure simulator (HFSS) software is employed to design and simulate the antenna for an ultra-wideband (3.1 – 10.6 GHz) frequency of 5.2 GHz, along with a breast phantom with and without a tumor. The antenna is independently simulated on both the breast phantoms with and without tumors. Rogers RT/duroid 5880 (tm) dielectric material is employed to design the antenna, with overall dimensions of 30 × 20 × 0.8 mm3. It possesses a dielectric constant of 2.2, a tangent loss of 0.02, and a thickness of 0.8 mm. The ring slot and partial ground plane techniques are employed to increase the overall effectiveness of the antenna. The properties of the antenna, such as return loss and VSWR, change when simulated with and without a tumor. The presence of a tumor within the breast is clearly indicated by the alterations in return loss and VSWR. The antenna proposed exhibits remarkable efficacy in the detection of tumors owing to its inconspicuous features, straightforward design, petite dimensions, and ideal impedance matching.

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.

Circular Microstrip Antennas in 5G: Evaluating Metamaterial Integration

The rapid emergence of Fifth-Generation (5G) technologies necessitate the development of highly efficient antenna systems with compact design that can support Ultra-Wideband (UWB) frequencies. This work presents the design and enhancement of a Circular Microstrip Antenna (CMSA) for 5G UWB applications using metamaterials. The study focuses on the design of CMSA and the integration of a Complementary Split-Ring Resonator (CSRR) into the circular patch of the CMSA. The design is simulated using Computer Simulation Technology (CST) Studio 2023. The system design without metamaterials achieved a gain of 5.28 dBi and a bandwidth of 353.0 MHz. The integration of the CSRR led to an improvement in gain, 5.39 dBi at 3.8 GHz, which is above most of the literature reviewed, although there was a slight reduction in bandwidth to 135.2 MHz. The objectives of achieving a CMSA design with a gain between 5 to 10 dBi while maintaining a compact size were accomplished. Despite the slight reduction in bandwidth observed when integrating the CSRR into the CMSA, the overall results highlight the significant role metamaterials played in enhancing the performance of microstrip antennas for 5G technology applications.

Compact Ultra-Wide Band Two Element Vivaldi Non-uniform Slot MIMO Antenna for Body-Centric Applications

This work presents a novel compact two-port Vivaldi Non-uniform Slot MIMO Antenna (VNSMA) to overcome the challenges of traditional ultra-wideband (UWB) antennas, such as large size, limited bandwidth (BW), high mutual coupling, and suboptimal performance in wearable devices. Designed based on Vivaldi non-uniform slot profile antenna (VNSPA) theory, this antenna offers superior performance metrics and significantly advances wearable antenna technology. The novelty of this work is investigating different positions for the two compact UWB VNSA to get better performance with smaller sizes, wider impedance matching BW, and lower mutual coupling (MC) where side by side at an angle of 180ᵒ is determined to be the best configuration. Detailed parametric studies were performed on this configuration for better performance, where the MC was further reduced by etching the ground plane with a vertical slot between the two antennas and L slots around the Microstrip to Slot (M/S) transition, respectively. Furthermore, BW and gain enhancements were obtained by etching exponential tapered and triangular slots at its two edges. Using the Finite Integration Technique (FIT), Computer Simulation Technology (CST) software is used for the simulations in this work. The VNSMA is tested on a CST Gustav human phantom and gives excellent results with low specific absorption rate (SAR) values at several UWB frequencies. The proposed VNSMA provides good, measured outcomes of S11 < -11.08 dB with wide BW of 12.5 GHz (2.33–14.83 GHz) covering high isolation of -23 dB (for most of frequency band), moderate-high gain of 5.89 dBi, radiation efficiency of 66-90%, low Envelope Correlation Coefficient (ECC) of 0.002 and high diversity gain (DG) of 9.99 dBi, stable radiation patterns, and average group delay of 1.2 ns. This innovative design, which optimizes antenna positioning and incorporates ground plane modifications, achieves remarkable improvements in BW, which covers multiple bands, including WLAN (2.4–2.485 GHz), X-band (8-12 GHz), and part of Ku band (12-18 GHz). The findings demonstrate the antenna's potential for various high-resolution microwave imaging applications, particularly in medical diagnostics like breast and brain cancer detection, showcasing its impact in wearable technology and healthcare.

Improvement of SAW Resonator Performance by Petal-like Topological Insulator.

This article introduces a novel petal-like SAW topology insulator, which can transmit sound waves with low loss and high flexibility in an ultra-wide frequency band by simultaneously adjusting multiple structural parameters of phononic crystals. Using finite element analysis, it was found that adjusting these parameters can generate a broadband gap of 55.8-65.7 MHz. This structure can also achieve defect immunity and sharp bending in waveguide transmission. When this topology insulator is applied to resonators, compared to traditional designs, the insertion loss is reduced by 22 dB, the on-load quality factor is increased by 227%, the off-load quality factor is increased by 1024.5%, and the quality sensitivity is improved by 3.7 times compared to bare devices.

A quad port dual band notch UWB MIMO antenna using hybrid decoupling structure

A four-port dual-band notch ultrawideband (UWB) multiple input and multiple output (MIMO) antenna for automotive applications is presented. Initially, a circular patch monopole antenna is designed and optimized by embedding a rectangular stub onto the radiator and lowering the ground plane to realize the UWB frequency spectrum. The dual-band frequency notch, from 4.6 to 5.9 and 6.8–8.8 GHz, is achieved using a half wavelength slot onto the feedline and a pair of H-shaped stubs across the feedline, respectively, to cover WLAN and complete x-band satellite communication. Further, the designed dual-band notch UWB antenna is transformed to a four-port MIMO antenna with interelement spacing much smaller than λ/4 (λ at 3.1 GHz) and a size of 0.46 × 0.41 × 0.01 λ3. Isolation improvement is achieved by a hybrid decoupling technique comprising a distinctive neutralization line (NL) and defected ground structure (DGS). The average isolation of the proposed design is better than 22 dB. Characteristic mode analysis of the proposed antenna is performed to analyze the specific significant mode and their contribution to the antenna radiation. The antenna design's diversity and time-domain properties are analyzed and found suitable for automotive applications. The antenna's electromagnetic interaction with the electrically large structure is studied by mounting the antenna onto an open-source automobile model, and the gain is determined to be more than 6.1 dB at the antenna's resonant frequencies.

An Ultra-Wideband Frequency Selective Rasorber with Low Infrared Emissivity.

The paper proposes an ultra-wideband frequency selective rasorber (FSR) with low infrared emissivity for the composite detection threat of both radars and infrared sensors. Firstly, the equivalent circuit (EC) method based on transmission line (TL) theory is utilized to analyze the absorption/transmission conditions. Then, based on the analysis above, sinusoidal microstrip lines with non-frequency-varying characteristics are adopted in the design, which significantly enhances the transmission bandwidth of FSR. The FSR demonstrates an absorption band ranging from 2.65 GHz to 8.80 GHz and a transmission band ranging from 9.15 GHz to 17.71 GHz. Furthermore, an infrared shielding layer (IRSL) exhibiting low emissivity in the infrared band and high transmittance in the microwave band is applied to the FSR. The simulation and experiment results verify that the IRSL-FSR demonstrates an ultra-wide transmission band ranging from 9.16 GHz to 17.94 GHz and an ultra-wide absorption band ranging from 2.66 GHz to 8.01 GHz. Additionally, it exhibits a low emissivity value (0.23) in 8-14 μm, providing a viable solution to the formidable challenge of radar-infrared bistealth for satellites and other communication-enabled flying platforms.

Experimental validation of the horizontal resolution improvement by ultra-wideband metasurfaces for GPR systems

Achieving high horizontal resolution is crucial for general non-destructive testing (NDT) applications, and in the domain of ground penetrating radar (GPR), it can be more challenging due to inefficient transmissions of electromagnetic waves into and through complex material under test (MUT). In this study, we showcase the validation results of our recently designed ultra-wideband metasurface (UWM) in improving the horizontal resolution for GPR B-Scan images. This UWM has an ultra-wide working frequency band (100%) from 1 to 3 GHz, in which high-frequency GPR signals can be enhanced and transmitted into MUT. Our fourteen-day consecutive GPR experiments demonstrate that two buried pipes with an edge-to-edge spacing of 8 cm that are hard to distinguish by traditional GPR surveys can be visually identified by depositing the UWM atop the MUT. The underlying mechanism is the sustained and improved transmission of high-frequency signals into the MUT, enabled by the removal of transmission coupling loss by the UWM at the air–MUT interface and the resulting enhanced transmission of more high-frequency components. Our simulations also provide quantitative analysis of such enhanced behavior with a nominal transmittance increase of 30% ∼50%. We believe the horizontal resolution improvement enabled by UWM will open a new corridor for high-resolution GPR system design.

Inverse design of ultrawideband one-dimensional metamaterial photonic filters using Riccati equation constrained gradient descent.

One-dimensional photonic wave devices exhibit a pivotal role in wave engineering. Despite their relative simplicity, designing 1D wave devices that implement complex functionalities over a broad frequency range is challenging and requires careful sculpting and multiple optimizations. This paper theoretically and experimentally demonstrates a new inverse design paradigm to achieve a desired broadband frequency response efficiently. Specifically, we calculate the required dielectric profile along the device using constrained gradient descent optimization to minimize the L 2 norm between the desired and actual responses. In each optimization step, we avoid the need to solve the complete set of Maxwell equations by using Riccati's equation or its discrete ancestor as the optimization constraint for calculating the local reflection coefficient. Using this approach, we design several unorthodox filters, such as dual-band narrowband bandpass filters located within a wideband bandstop and ultrawideband first and second-order differentiators. The technique produces excellent results for ultrawideband frequency ranges, with very low computational complexity and, remarkably, with a single trivial guess for the optimization starting point. We experimentally implemented the two differentiator designs in radio frequencies using electronic circuit elements that comprise a metamaterial transmission line structure.

An absorptive coding metasurface for ultra-wideband radar cross-section reduction

In this paper, an absorptive coding metasurface (ACM) is proposed for ultra-wideband radar cross section (RCS) reduction, the design process is presented in detail, in which a lossy polarization conversion metasurface (PCM) is proposed at first. The lossy PCM is an anisotropic resistive structure with both polarization conversion and absorption performances, so that its co-polarization reflection coefficients under u- and v-polarized incidences can be kept at less than − 10 dB in magnitude in the frequency range from 7.5 to 45.2 GHz. Though the magnitude of the cross-polarization reflection coefficient cannot be very small only due to the absorption, its phase will be changed by nearly 180° when the unit-cell structure of the lossy PCM is rotated by 90°. Thus, the lossy PCM can be used as one of the two types of lossy coding elements for an ACM when its unit-cell structure is rotated by 90° or not. Based on the lossy PCM, an ACM is proposed. The simulation and experimental results show that the ACM has an excellent RCS reduction performance under arbitrary polarized incidence, it can achieve effective RCS reduction under normal incidence in the ultra-wide frequency band from 7.4 to 45.5 GHz with a ratio bandwidth (fH/fL) of 6.15:1; moreover, an ultra-wideband RCS reduction can still be achieved when the incident angle is increased to 45°, which indicates that the ACM has good stealth performance under the detection of various radars working in X, Ku, K and Ka bands, it is very practical.

An ultra-wideband reflective polarization conversion metasurface and its application in RCS reduction

ABSTRACT In this work, an ultra-wideband reflective polarization conversion metasurface (PCM) is proposed at first. Because the PCM is an anisotropic structure that is symmetric with respect to both x- and y-axes, and the reflection phase difference under x- and y-polarized incidences is close to 180° in an ultra-wide frequency range, the PCM can achieve both linear polarization conversion and circular-polarization (CP) maintaining reflection in the ultra-wide frequency band from 8.3 to 41.3 GHz except for near the frequency point of 38.8 GHz. Moreover, when its unit cell structure is rotated by 90°, its cross-polarized reflection coefficient under LP incidence, together with the co-polarized reflection coefficient under CP incidence, will be changed by almost 180° in phase. Thus, based on the PCM, an ultra-wideband coding diffusion metasurface (CDM) is further proposed for radar cross section (RCS) reduction. The simulation and experiment results indicate that the CDM can achieve effective RCS reduction in the ultra-wide frequency band of 8.2–41.7 GHz under normal incidence with arbitrary polarization; in addition, an ultra-wideband RCS reduction can still be realized under oblique incidence with an incident angle less than 45°, which shows that the CDM is of good application value in radar stealth technology.