Ultra-wide Frequency Range Research Articles

Stepwise Frequency-Shifted Optical Heterodyne for Flexible and Ultrawide Frequency Microwave Down-Conversion

A photonics-assisted method based on stepwise frequency-shifted optical heterodyne is proposed for flexible and ultrawide frequency microwave down-conversion with a low-frequency electrical local oscillator (LO). The method consists of a stepwise tunable optical carrier generator and a frequency-shifted heterodyne interferometer. A pair of coherent optical carrier with stepwise frequency spacing is modulated by the high-frequency radio frequency (RF) and the low-frequency LO, respectively. The combined optical signals heterodyne with each other and generate the desired down-converted intermediate frequency (IF) signal. The down-conversion achieves ultrawide frequency range with a low-frequency LO. Moreover, it enables flexible and configurable operation by choosing the optical carrier pairs with different frequency spacing and/or tuning the LO frequency. In the demonstration, 6.25~40-GHz RF signals are experimentally down-converted to IF signals below 1 GHz with a dc ~6.25-GHz LO.

Uneven-Layered Coding Metamaterial Tile for Ultra-wideband RCS Reduction and Diffuse Scattering

In this paper, a novel uneven-layered coding metamaterial tile is proposed for ultra-wideband radar cross section (RCS) reduction and diffuse scattering. The metamaterial tile is composed of two kinds of square ring unit cells with different layer thickness. The reflection phase difference of 180° (±37°) between two unit cells covers an ultra-wide frequency range. Due to the phase cancellation between two unit cells, the metamaterial tile has the scattering pattern of four strong lobes deviating from normal direction. The metamaterial tile and its 90-degree rotation can be encoded as the ‘0’ and ‘1’ elements to cover an object, and diffuse scattering pattern can be realized by optimizing phase distribution, leading to reductions of the monostatic and bi-static RCSs simultaneously. The metamaterial tile can achieve −10 dB RCS reduction from 6.2 GHz to 25.7 GHz with the ratio bandwidth of 4.15:1 at normal incidence. The measured and simulated results are in good agreement and validate the proposed uneven-layered coding metamaterial tile can greatly expanding the bandwidth for RCS reduction and diffuse scattering.

Metasurface base on uneven layered fractal elements for ultra-wideband RCS reduction

A novel metasurface based on uneven layered fractal elements is designed and fabricated for ultra-wideband radar cross section (RCS) reduction in this paper. The proposed metasurface consists of two fractal subwavelength elements with different layer thickness. The reflection phase difference of 180° (±37°) between two unit cells covers an ultra-wide frequency range. Ultra-wideband RCS reduction results from the phase cancellation between two local waves produced by these two unit cells. The diffuse scattering of electromagnetic (EM) waves is caused by the randomized phase distribution, leading to a low monostatic and bistatic RCS simultaneously. This metasurface can achieve -10dB RCS reduction in an ultra-wide frequency range from 6.6 to 23.9 GHz with a ratio bandwidth (fH/fL) of 3.62:1 under normal incidences for both x- and y-polarized waves. Both the simulation and the measurement results are consistent to verify this excellent RCS reduction performance of the proposed metasurface.

A micromechanical mass sensing method based on amplitude tracking within an ultra-wide broadband resonance

We propose a mass sensing scheme in which amplitude shifts within a nonlinear ultra-wide broadband resonance serve as indicators for mass detection. To achieve the broad resonance bandwidth, we considered a nonlinear design of the resonator comprised of a doubly clamped beam with a concentrated mass at its center. A reduced-order model of the beam system was constructed in the form of a discrete spring-mass system that contains cubic stiffness due to axial stretching of the beam in addition to linear stiffness (Duffing equation). The cubic nonlinearity has a stiffening effect on the frequency response causing nonlinear bending of the frequency response toward higher frequencies. Interestingly, we found that the presence of the concentrated mass broadens the resonant bandwidth significantly, allowing for an ultra-wide operational range of frequencies and response amplitudes in the proposed mass sensing scheme. A secondary effect of the cubic nonlinearity is strong amplification of the third harmonic in the beam’s response. We computationally study the sensitivity of the first and third harmonic amplitudes to mass addition and find that both metrics are more sensitive than the linearized natural frequency and that in particular, the third harmonic amplitude is most sensitive. This type of open-loop mass sensing avoids complex feedback control and time-consuming frequency sweeping. Moreover, the mass resolution is within a functional range, and the design parameters of the resonator are reasonable from a manufacturing perspective.

Glide Symmetry to Prevent the Lowest Stopband of Printed Corrugated Transmission Lines

In this letter, we demonstrate that the dispersion properties of printed double-sided parallel-strip lines can be controlled by using glide symmetry. Glide symmetry is introduced in with corrugations in both strips of a double-sided line. We demonstrate that glide symmetry eliminates the stopband between first and second propagating modes and yields to a higher propagation constant, preserving its linearity, and the broadband nature of the underlying guiding technology. Thus, the glide-symmetric double-sided line can be designed to possess a high equivalent refractive index in an ultrawide range of frequencies. These exceptional properties have been numerically and experimentally validated. Finally, we demonstrate the possibilities of this technology with a specific design, a glide-symmetric double-sided parallel-strip line with filtering properties. Potential applications are low-dispersive leaky-wave antennas and electromechanical tunable phase shifters and filters.

On time-dependence of mechanical metamaterials properties

The study focuses on wave propagation in time-periodic mechanical matamaterials, such as beams with time-modulated elastic modulus. The time-dependence of the elastic modulus results in a system with a frequency-periodic dispersion diagram. Flat bands originate at the intersections of the dispersion branches, signaling zero group velocity modes. Through an analytic approach, we obtain approximate expressions for the range of wavenumbers associated to flat bands, as well as their dependence on the modulation parameters. It is shown that the flat bands lead to unbounded growth of the displacement field, which is due to the interaction between the structure’s dynamics and the energy provided to it by means of the elastic modulus variation. If such phenomenon is properly confined over a limited time window, it provides a way to filter wave propagation over a ultra-wide frequency range by property choosing the modulation parameters. Numerical simulations, obtained by implementing a FDTD scheme, verify the theoretical findings. Finally, an experimental validation of the results is discussed, which employs piezoelectric patches and time-dependent negative capacitance shunted circuits.

Study on Dielectric Properties of Poplar Wood over an Ultra-wide Frequency Range

The dielectric properties of poplar wood (Populus deltoids cv. I-69/55) were measured using an Agilent network analyzer over the frequency range from 0.2 GHz to 20 GHz. The effects of moisture content, grain direction, temperature, and frequency on the dielectric constant and dielectric loss factor of wood were investigated. Regression equations were also established to predict the dielectric properties of wood having different grain directions and moisture contents. Results showed that the dielectric properties were strongly affected by the moisture content. As the moisture content increased from 0% to 100%, the dielectric constants of wood at longitudinal, radial, and tangential directions increased by 820.2%, 403.0%, and 434.0%, loss factors of wood at three directions increased by 8631%, 4949%, and 3404%, respectively. As frequency was increased, dielectric constant of wood decreased slowly; however, the loss factor decreased at the beginning and then increased. Dielectric properties of the wood also increased with increasing temperature. The dielectric constant in longitudinal directions was 1.2 times higher than the constant at tangential and radial directions, but the loss factor was 1.4 to 2.5 times higher. Regression equations were determined to fully describe the dielectric properties of wood at different grain dimensions and moisture contents.

Coupling-Inductor-Based Hybrid mm-Wave CMOS SPST Switch

This brief presents a hybrid CMOS millimeter-wave single-pole single-throw (SPST) switch. This newly invented hybrid structure demonstrates better tradeoffs between insertion loss and isolation compared to conventional distributed structures. The performance benefits are analyzed in detail and validated by both simulation and measurement results. Additionally, the chip area is conserved by using lump elements, the coupled inductor. Moreover, a specific bias scheme is used to further decrease insertion loss by about 0.5 dB. This SPST switch achieves higher than 35-dB isolation over an ultrawide frequency range, from 54 to 84 GHz, a minimum 1.7-dB insertion loss, and <−10-dB reflection coefficient with 0.012-mm2 chip area in 65-nm CMOS. The design achieves more than 10-dB enhancement of isolation in comparison with the state-of-the-arts while maintaining similar insertion loss.

Ultra-wideband, Wide Angle and Polarization-insensitive Specular Reflection Reduction by Metasurface based on Parameter-adjustable Meta-Atoms

In this paper, an ultra-wideband, wide angle and polarization-insensitive metasurface is designed, fabricated, and characterized for suppressing the specular electromagnetic wave reflection or backward radar cross section (RCS). Square ring structure is chosen as the basic meta-atoms. A new physical mechanism based on size adjustment of the basic meta-atoms is proposed for ultra-wideband manipulation of electromagnetic (EM) waves. Based on hybrid array pattern synthesis (APS) and particle swarm optimization (PSO) algorithm, the selection and distribution of the basic meta-atoms are optimized simultaneously to obtain the ultra-wideband diffusion scattering patterns. The metasurface can achieve an excellent RCS reduction in an ultra-wide frequency range under x- and y-polarized normal incidences. The new proposed mechanism greatly extends the bandwidth of RCS reduction. The simulation and experiment results show the metasurface can achieve ultra-wideband and polarization-insensitive specular reflection reduction for both normal and wide-angle incidences. The proposed methodology opens up a new route for realizing ultra-wideband diffusion scattering of EM wave, which is important for stealth and other microwave applications in the future.

An improved parametric analysis of CSRR loaded with microstrip line for ultra wide band frequency range

ABSTRACTIn this letter, an improved electrical parameter extraction scheme for the microstrip line loaded with complementary split ring resonator (CSSR) is proposed. A CSRR loaded with microstrip line behaves as an effective negative permittivity media. The equivalent circuit of CSRR contains four electrical quantities and it needs four different characteristic frequencies for their accurate solution which was neglected in previous studies. In this work, a four variable problem is formulated and solved which accurately gives all the electrical parameters of CSRR equivalent circuit for ultra wide frequency range. The proposed technique is used for a parametric analysis of a rectangular CSRR unit cell. © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:661–664, 2017

Compact Liquid Crystal Based Tunable Band-Stop Filter with an Ultra-Wide Stopband by Using Wave Interference Technique

A wave interference filtering section that consists of three stubs of different lengths, each with an individual stopband of its own central frequency, is reported here for the design of band-stop filters (BSFs) with ultra-wide and sharp stopbands as well as large attenuation characteristics. The superposition of the individual stopbands provides the coverage over an ultra-wide frequency range. Equations and guidelines are presented for the application of a new wave interference technique to adjust the rejection level and width of its stopband. Based on that, an electrically tunable ultra-wide stopband BSF using a liquid crystal (LC) material for ultra-wideband (UWB) applications is designed. Careful treatment of the bent stubs, including impedance matching of the main microstrip line and bent stubs together with that of the SMA connectors and impedance adaptors, was carried out for the compactness and minimum insertion and reflection losses. The experimental results of the fabricated device agree very well with that of the simulation. The centre rejection frequency as measured can be tuned between 4.434 and 4.814 GHz when a biased voltage of 0–20 Vrms is used. The 3 dB and 25 dB stopband bandwidths were 4.86 GHz and 2.51 GHz, respectively, which are larger than that of other recently reported LC based tunable BSFs.

A novel RF envelope detector with ultra-wide operation frequency range and enhanced transient response speed

A novel RF envelope detector with ultra-wide operation frequency range and enhanced transient response speed

Ferrite-based metamaterial microwave absorber with absorption frequency magnetically tunable in a wide range

A metamaterial absorber with a near-perfect absorption peak, which is tunable magnetically in an ultra-wide frequency range from 0.2 to 7.6GHz, is proposed and fabricated by combining a ferrite with a metastructure. In our design strategy, the adjustable resonance frequency of the ferrite by external magnetic field provides the tunability, while the metastructure of periodic metal strips eliminates the polarization conversion brought by the ferrite and further enhances the absorption via diffraction and interference mechanisms. The measured absorption of the as-fabricated ferrite-based tunable MMA is in good accordance with the simulation results, validating the design method. Our results here illustrate that the ingenious integration of metamaterials with traditional ferrite materials promises a way to achieve a wide frequency tuning range of a strong absorption band, especially in low frequency bands.

Preparation of a Carbon Doped Tissue-Mimicking Material with High Dielectric Properties for Microwave Imaging Application.

In this paper, the oil-in-gelatin based tissue-mimicking materials (TMMs) doped with carbon based materials including carbon nanotube, graphene ink or lignin were prepared. The volume percent for gelatin based mixtures and oil based mixtures were both around 50%, and the doping amounts were 2 wt %, 4 wt %, and 6 wt %. The effect of doping material and amount on the microwave dielectric properties including dielectric constant and conductivity were investigated over an ultra-wide frequency range from 2 GHz to 20 GHz. The coaxial open-ended reflection technology was used to evaluate the microwave dielectric properties. Six measured values in different locations of each sample were averaged and the standard deviations of all the measured dielectric properties, including dielectric constant and conductivity, were less than one, indicating a good uniformity of the prepared samples. Without doping, the dielectric constant was equal to 23 ± 2 approximately. Results showed with doping of carbon based materials that the dielectric constant and conductivity both increased about 5% to 20%, and the increment was dependent on the doping amount. By proper selection of doping amount of the carbon based materials, the prepared material could map the required dielectric properties of special tissues. The proposed materials were suitable for the phantom used in the microwave medical imaging system.

Multiband wave filtering and waveguiding in bio-inspired hierarchical composites

We investigate the elastic wave propagation in bio-inspired hierarchical composites with nacre-like and biocalcite-like architectures. These two types of architectures consist of hard mineral and soft organic phases, which are hierarchically assembled to develop multilevel of hierarchy. We numerically demonstrate that multiple band gaps and passbands, covering an ultrawide frequency range, arise in the proposed hierarchical composites with two levels of hierarchy. We further reveal that the multilevel structural hierarchy itself is responsible for this multiband characteristic. Specifically, the low frequency band gaps in the composites with two levels of hierarchy are attributed to Bragg scattering, which are intrinsically governed by the hierarchical and periodic modulation of constituent phases at the second hierarchical level. By contrast, the multiple band gaps and passbands in high frequency ranges correspond to waveguide modes, enabling the incident wave to be either trapped inside the waveguides or efficiently transmitted through the waveguides. The findings in this paper not only shed light on the mechanisms responsible for the multiband features of bio-inspired hierarchical composites, but also offer new opportunities towards the design of compact and mechanically robust phononic crystals with the capability to effectively manipulate wave propagation.

Design and Experimental Investigation of a Compact Circularly Polarized Integrated Filtering Antenna for Wearable Biotelemetric Devices.

A compact circularly polarized (CP) integrated filtering antenna is reported for wearable biotelemetric devices in the 2.4 GHz ISM band. The design is based on a mutual synthesis of a CP patch antenna connected to a bandpass filter composed of coupled stripline open-loop resonators, which provides an integrated low-profile radiating and filtering module with a compact form factor of 0.44λ(0)×0.44λ(0)×0.04λ(0). The optimized filtering antenna is fabricated and measured, achieving an S11 < -14 dB, an axial ratio of less than 3 dB and gain higher than 3.5 dBi in the targeted ISM band. With the integrated filtering functionality, the antenna exhibits good out-of-band rejection over an ultra-wide frequency range of 1-6 GHz. Further full-wave simulations and experiments were carried out, verifying that the proposed filtering antenna maintains these desirable properties even when mounted in close proximity to the human body at different positions. The stable impedance performance and the simultaneous wide axial ratio and radiated power beam widths make it an ideal candidate as a wearable antenna for off-body communications. The additional integrated filtering functionality further improves utility by greatly reducing interference and crosstalk with other existing wireless systems.

Ultrawideband RF Photonic Phase Shifter Using Two Cascaded Polarization Modulators

An ultrawideband RF photonic phase shifter implemented using two cascaded polarization modulators (PolMs) is proposed and experimentally demonstrated. The first PolM (PolM1) is employed to generate an optical carrier and two first-order sidebands that are orthogonally polarized. By aligning the polarization directions of the optical carrier and the two first-order sidebands from the first PolM with the two principal axes of the second PolM (PolM2), complementary phase modulation on the optical carrier and the first-order sidebands is produced if a DC voltage is applied to the second PolM. By selecting the optical carrier and one sideband using an optical filter and beating them at a photodetector, an RF signal with its phase that is tunable by tuning the applied DC voltage is generated. The proposed phase shifter has the advantages of fast tuning and an ultrawide frequency tunable range. An experiment is performed. A full 360° phase shift over an ultrawide frequency range from 5 to 40 GHz is demonstrated. The spurious free dynamic range of the phase shifter is also studied.

A 1.2 V CMOS COMMON-GATE LOW NOISE AMPLIFIER FOR UWB WIRELESS COMMUNICATIONS

In this paper, an ultra-wide band 0.18 μm CMOS common-gate low-noise amplifier (LNA) is presented. Designed in the ultra-wide band frequency range of 3.1–10.6 GHz, it uses a current-reused technique with modified input matching. This approach allowed obtaining a flat broadband gain of 12.75 ± 0.83 dB with an input reflection coefficient less than -5.5 dB, an output reflection coefficient less than -7 dB, and a noise figure less than 3.7 dB. Furthermore, the proposed low-power LNA consumes only 12.14 mW (excluding buffer) from a 1.2 V supply voltage.

A Printed Single-Layer UWB Monopole Antenna With Extended Ground Plane Stubs

In this letter, a compact coplanar-waveguide-fed single-layer printed antenna with an ultrawideband (UWB) rectangular monopole radiator etched with a half-elliptical slot is presented. Collaborating with the UWB radiator, two symmetrical open-circuit stubs are extended from the ground plane to jointly achieve an ultrawideband impedance match with a compact size. The proposed antenna is fabricated and tested in an anechoic chamber, showing an ultrawide operating frequency range from 3.7 to 10.1 GHz with a quasi-omnidirectional gain from 2.0 to 7.3 dBi. With the advantages of a reduced size, an improved voltage standing wave ratio (VSWR), and a monolayer configuration without any back ground plane, the proposed antenna can be used in a wide range of UWB applications.

A new class of electrically tunable metamaterial terahertz modulators

Switchable metamaterials offer unique solutions for efficiently manipulating electromagnetic waves, particularly for terahertz waves, which has been difficult since naturally occurring materials rarely respond to terahertz frequencies controllably. However, few terahertz modulators demonstrated to date exhibit simultaneously low attenuation and high modulation depth. In this letter we propose a new class of electrically-tunable terahertz metamaterial modulators employing metallic frequency-selective-surfaces (FSS) in conjunction with capacitively-tunable layers of electrons, promising near 100% modulation depth and < 15% attenuation. The fundamental departure in our design from the prior art is tuning enabled by self-gated electron layers that is independent from the metallic FSS. Our proposal is applicable to all possible electrically tunable elements including graphene, Si, MoS(2), oxides etc, thus opening up myriad opportunities for realizing high performance switchable metamaterials over an ultra-wide terahertz frequency range.