In this paper, a novel terahertz tunable bandstop filter with constant absolute bandwidth is proposed, which consists of graphene-based three-section L resonators. In order to perform bandstop property, the L resonator is used and analyzed in details based on the traditional Z matrix and ABCD matrix. With the introduction of graphene materials, the operating frequency of bandstop filter can be extended to terahertz. Moreover, the tunable performance with constant absolute bandwidth can be achieved by only loading different chemical potentials on a graphene surface. For demonstration, a terahertz tunable bandstop filter prototype is designed and simulated with chemical potentials of 0.1, 0.3, and 1 eV. The simulated results agree well with the anticipation perfectly.
A novel dual-band bandstop filter based on a square, symmetric dumbbell-shaped resonator and U-shaped slot defected ground structure is presented. First, the characteristic of the fundamental structure which adopts two dumbbell-shaped resonators and one U-shaped slot is analyzed. Simulated results demonstrate that the proposed structure induces two transmission zeros within 2-8 GHz. Then, the structure adopting four dumbbell-shaped resonators and one U-shaped slot is analyzed. Simulated results point out that the characteristic of dual stopbands is better than the fundamental structure. Based on above implementation, a dual-band bandstop filter based on eight proposed dumbbell-shaped resonators and two U-shaped slots is proposed and fabricated. Two center frequencies at 4 and 6.5 GHz are reported, corresponding to the attenuation levels of 41.9 and 26.1 dB. The return losses of center frequencies are 0.04 and 0.20 dB, respectively, and the dual stopband bandwidths with 10 dB signal attenuation are 690 MHz and 250 MHz. In addition, two transmission poles at each stopband are induced for better selectivity. Owing to the symmetric dumbbell shape, the size of the filter gets reduced. It is simple to design and quite compatible with planar construction fabrication.
In this paper, a Multiple Split Ring Resonator (MSRR) based coplanar waveguide (CPW) fed antenna for 5.8 GHz RFID application is presented. The antenna has a compact size of 15 x 21 x 0.8 mm3. The proposed antenna is designed, fabricated and tested. The simulated results are discussed and in good compliance with the measured results. Split Ring Resonator (SRR) characteristics are also studied. The proposed antenna shows good performance at the measured resonance frequency of 5.75 GHz.
This letter presents a two-port dual-band multiple-input-multiple-output (MIMO) antenna, which is achieved based on a non-radiation passive circuit. The circuit is composed of two pairs of open-ended stubs and a transmission line connecting them. The decoupling condition of S21 = 0 is deduced, thus a good isolation is achieved. Then this non-radiation circuit is further designed to be a structure with enough radiation without affecting the character of port isolation. Since the implementation of port isolation does not adopt complex decoupling network or decoupling structure, the process of design is simple and effective. The simulation and physical demonstration obtain good agreements for the proposed dual-band MIMO antenna.
Ground bounce noise (GBN) is a major concern in high speed electronic circuits. In this paper a Genetic Algorithm (GA) optimized electromagnetic band gap (EBG) structure is proposed for suppression of the GBN. The unit cell of the structure is comprised of several square patches, each having a dimension of 5 mm x 5 mm. The position of the square patches is optimized using the GA, such that the stopband is maximized. A single unit cell of the optimized structure is fabricated and tested for its stopband characteristics using the vector network analyzer (VNA). The structure is then tested for its signal integrity (SI) using the Agilent ADS software. The single unit cell of the optimized structure provides a wide band gap of 20 GHz with 30 dB isolation and a band gap of 17.4 GHz with 40 dB isolation. The results obtained are compared with the existing results. The optimized structure shows improved performance in terms of stop band gap and signal integrity (SI).
In this letter, a new compact UWB uniplanar crossover with bandpass filter characteristics is proposed and implemented. The UWB Filter-Crossover is composed of two novel UWB filters placed on the top and bottom of the substrate to obtain the crossover features. These proposed filters are based on microstrip to coplanar stripline (CPS) transitions and sections of CPS section line used as a multiple mode resonator (MMR). The simulated and measured results show a good result in terms of isolation, return loss and insertion loss in the entire UWB band.
In this paper, a simple dual-band compact slotted square ring patch antenna has been used as hyperthermia applicators in the treatment of cancerous human cells at superficial depths inside the body. The proposed antenna has the advantages of dual-band (f1=434 MHz and f2=915 MHz) operation and more compact size (124×124 mm2) than the current state-of-the-art designs without significant frequency detuning or impedance mismatch which makes it a more suitable choice for local hyperthermia. The proposed antenna provides a suitable specific absorption rate (SAR) penetration profile and shows a good resonance at two designed frequencies. We have optimized the structure so that the SAR level performed by the structure is sufficiently enough so as to meet the IEEE standard requirements for medical applications including hyperthermia. We have simulated and measured the structure with a low-profile substrate (i.e., FR4 substrate with εr=4.4 and thickness of 1.6 mm). During the design process, the simplified planar tri-layered tissue model interfaced with a water bolus is used to incorporate the main electrical effects on the antenna. The results validate the proposed antenna design.
A nonlinear metamaterial composite structure with tunable tunneling frequency is presented. Based on theoretical calculation results, a nonlinear metamaterial sandwich structure constructed by epsilon negative metamaterial (ENM), mu negative metamaterial (MNM) and nonlinear double negative metamaterial (NDNM) is designed, and its nonlinear properties are investigated. The measured results show that the tunneling frequency of the sandwich structure ENM-NDNM-MNM can be controlled conveniently by signal power.
Influence of surface impedance on radiation fields of spherical antennas excited by radially oriented electric dipole is investigated by using a Green's function for a space outside a spherical scatterer. This approach allows us to obtain analytical expressions for radiation fields of an impedance spherical antenna in the wave zone. The spherical antenna with the scatterer coated with a metamaterial layer is also considered. The surface impedance required for radiomasking of the spherical scatterer of resonant dimensions was estimated by mathematical modeling.
Usually, knowledge of material's dielectric properties, as a function of frequency, represents a key issue in scientic elds and several industrial applications. At LNE-CETIAT, in partnership with Institut Fresnel UMR 72792, a set of capacitive and coaxial cells, dedicated to the measurement of complex dielectric permittivity, have been developed. The present paper focuses on the experimental calibration and validation of two cells using low and medium dielectric loss materials. It gives the main measurement results obtained on three dierent materials: decanol alcohol, polytetra uoroethylene (PTFE) and polyvinyl chloride (PVC) in the frequency range from 3 MHz up to 2 GHz.
The radiation properties of a copper-patch antenna designed for resonating at the frequency of 0.7 THz, which is used in aerospace applications, is presented. These properties are then compared to those of a graphene-patch antenna presenting the same dimensions. We show how the use of graphene, as a tunable material, allows to dynamically modify the frequency of operation of the antenna as well as its radiation pattern. Our results show that the return loss peak reaches -29 dB, at the operating frequency, which is almost twice the value obtained with the copper patch. This increase in the return loss peak is also accompanied by an improvement in the gain of the antenna from 5.73 dB in the case of the copper patch to 7.16 dB in the case of graphene. We focus our interest on how the reconfigurable radiation properties of the graphene-patch antenna are directly related to the graphene surface conductivity.
In this work, we study a multichannel filter by using one-dimensional photonic crystal (1DPC) based on Thue-Morse sequence (TMS). We use a dielectric defect layer between binary sequence cells with a TMS structure. First, we show transmission in terms of wavelength for the structure without defect layers. Then, we plot transmission in terms of wavelength for a different number of defect layer periods (N) in normal incidence. The analysis shows that there are two photonic bang gaps (PBG) in visible and infrared regions and two defect modes in each one for N = 1. Moreover, the number of defect modes is increased by increasing N. So, by tuning them, this structure can be used as a multi-channel filter within an optical wavelength range.
This letter presents the synthesis of a broadband rat-race consisting of a miniaturized broadband rat-race hybrid and transmission line cascades. This broadband technique involves connecting a cascade of transmission lines with lengths equal to a quarter of the wavelength at the design frequency to each port of a previously proposed rat-race hybrid. Butterworth and Chebyshev performances of the broadband rat-race hybrid are also reported. The broadband rat-race hybrid was implemented on an FR4 substrate using spiral inductors and chip capacitors. For the frequency range of 420-800 MHz, which corresponds to a relative bandwidth of more than 62%, the broadband rat-race hybrid exhibited power splits of -3.8 ± 1.0 dB, return losses of greater than 19 dB, and isolation between output ports of greater than 20 dB. The phase difference between S21 and S41 was 180° ± 3°.
A hexagonal fractal antenna is presented for satellite navigation applications in this paper. The geometry of the antenna is inspired by the Sierpinski carpet and has compact dimensions, improved bandwidth, good radiation pattern due to the self-similar property of fractal geometry. The bandwidth ranging from 1.54 GHz to 1.61 GHz can work at L1 band of GPS and B1 band of Beidou satellite navigation system. The simulated and measured gains show a good agreement over the bandwidth.
This letter presents miniaturized Gysel power dividers using lumped-element components. The characteristic impedances of all the equivalent transmission lines in these dividers are fixed to the same values based on even and odd mode analysis, thus simplifying the design procedure and miniaturizing the Gysel power dividers. The ideal divider designed at a frequency of 590 MHz exhibits power splits of -3.2±0.2 dB and return losses of greater than 15 dB for the frequency range of 460 to 650 MHz. Furthermore, isolation between output ports is greater than 15 dB for the frequency range of 500 to 680 MHz. The fabricated miniaturized Gysel power divider achieves broadband characteristics and is very compact, occupying only about 15% of the area of a conventional Gysel power divider.
In this paper, a wideband differential phase shifter based on modified T- and Pi- networks is proposed. Invoking the even-odd mode analysis in this symmetric phase shifter, closed-form equations of its S-parameters are derived. The derived equations enable a generic design scheme of the phase shifter, that is, ideally the phase shifter can be designed for any differential phase requirements. To illustrate the proposed idea, design parameters for differential phases of 45˚, 60˚, 75˚, 90˚, 105˚ and 120˚ are evaluated and tabulated considering a center frequency of 3 GHz. Simulation of these examples using the Keysight ADS exhibits the intended performance. For validation, a 90˚ phase shifter has been fabricated and tested. The measurement results show a return loss better that 10 dB, an insertion loss of less than 1 dB, and a ± 7° of phase deviation from 1.18 GHz to 5.44 GHz, which is equivalent to a fractional bandwidth of 142%.
In this letter, a two-element wide-band patch antenna array with low cross-polarization is presented. The patch is excited by a magnetic-coupled loop. The two elements are placed symmetrically about the center of the array. Compared to the conventional feeding structure, the proposed feeding structure has the advantages of simple structure and much lower cross polarization. Parametric studies show the usefulness of the proposed feeding structure. Prototypes for the element and array have been fabricated and tested. The antenna array can achieve an impedance of 29.1% for VSWR <2 and a stable gain around 11.2 dBi. Unidirectional radiation patterns with low cross polarization less than -18 dB within the 3-dB beamwidths are obtained. The height of antenna is about 0.12λ(where λ is the free-space wavelength referring to the center frequency of the working band). Moreover, the proposed antenna is dc grounded, which is suitable for outdoor base station applications.
In this paper, a novel configuration for linearly polarised Dual Frequency Microstrip Antenna at S- and X-bands is presented. The proposed configuration utilises the frequency ratio of 1:3.3 between the two bands to its advantage by saving space. It uses the antenna at S-band as ground plane for a 2 x 2 antenna array at X-band without any additional requirement of separate space and ground plane. The patches are electromagnetically coupled to give measured bandwidth (|S11| <-10 dB) of 13% at S-band and 6.2% at X-band. It gives isolation better than 38 dB over the entire bandwidth of the two frequency bands. The measured antenna gain is 7.5 dB at S-band and 10.5 dB at X-band.
Recently, a new analytically regularizing procedure, based on Helmholtz decomposition and Galerkin method, has been proposed to analyze the electromagnetic scattering from a zero-thickness perfectly electrically conducting disk. The convergence of the discretization scheme is guaranteed and of exponential type, i.e., few expansion functions are needed to achieve highly accurate solutions. However, it leads to the numerical evaluation of improper integrals of asymptotically oscillating and slowly decaying functions. Asymptotic acceleration techniques allow to obtain faster decaying integrands without overcoming the problem of the oscillating nature of the integrands themselves, i.e., the convergence of the integrals becomes slower and slower as the accuracy required for the solution is higher. In this paper, by means of algebraic manipulations and a suitable integration procedure in the complex plane, an alternative expression for the scattering matrix coefficients involving only fast converging proper integrals is devised. As shown in the numerical results section, the proposed technique is very effective and drastically outperforms the classical analytical asymptotic acceleration technique.
A wideband interdigital capacitor (WIDC) is proposed and verified. By short interconnecting the open ends of interval fingers with microstrip lines etched on PCB bottom layer, the spurious spikes that limit the bandwidth of conventional interdigital capacitor (IDC) are eliminated. The bandwidth and capacitance of IDC increase more than 2800% and 100%, respectively.