Sharif Digital Repository

Superconducting devices are known to produce nonlinear effects. In planar structures, these nonlinearities depend on the current distribution on the strip, which definitely depends on the structure of device. This paper used a numerical method based on 3D-FEM to obtain the current distribution in the open-ends and gaps in the superconducting microstrip structures. This is used to present the nonlinear distributed circuit modeling of these discontinuities and its impact on the nonlinear phenomenon. This nonlinear circuit model is used in the Harmonic Balance (HB) method to analyze nonlinearity in the superconducting microwave devices. Therefore, this simple accurate enough nonlinear circuit... 

Superconducting materials are known to produce intermodulation distortion and other non-linear effects. In microstrip structures, the non-linearity depends on the current distribution on the strip which is mainly determined by the geometrical structure of the device. The current distribution in superconducting parallel-coupled microstrip lines is computed by a numerical approach based on a three-dimensional finite element method. This computed current distribution is used to produce a non-linear circuit model for parallel-coupled superconducting lines. A numerical technique based on the harmonic balance approach is used for non-linear analysis of the proposed equivalent circuit. To validate... 

There are unusual nonlinear behaviors in superconducting materials, especially at low temperatures. This paper describes the procedure to reliably predict this nonlinearity in superconducting microstrip transmission lines (SMTLs). An accurate nonlinear distributed circuit model, based on simultaneously considering of both quadratic and modulus nonlinearity dependences, is proposed. All parameters of the equivalent circuit can be calculated analytically using proposed closed-form expressions. A numerical method based on Harmonic Balance approach is used to predict nonlinear phenomena like intermodulation distortions and third harmonic generations. Nonlinear analyses of the SMTLs at the... 

In this paper, a wideband, circularly polarized patch antenna is proposed that leverages the unidirectional resonant modes of a circular patch mounted on top of a grounded dielectric-ferrite substrate. The proposed antenna is fed via the proximity coupling method and several parasitically coupled patches are placed on a dielectric superstrate to enhance the impedance bandwidth of the antenna. The resonant modes of the structure rotate only in the clockwise or counter clockwise directions. In the frequency range where the effective permeability of the ferrite layer is negative, the resonance frequencies of these modes differ significantly, which produces a large axial ratio (AR) bandwidth.... 

In this paper, distribution of voltage along a general nonuniform transmission line is expanded in an appropriate form, and by employing an approach similar to conventional and modified differential transfer matrix methods already proposed for optical structures, analytical expressions are obtained for voltage/current distributions and reflection/transmission coefficients. This method shows great accuracy in different test cases and has been found to be superior to the well-known analytical method of small reflections. Notwithstanding, the overall accuracy of proposed approach is further improved by introducing the technique of multiple divisions. In particular, lossy/lossless tapered... 

In this paper, a wideband coupled-resonator microstrip bandpass filter is designed and experimentally demonstrated in the S-Band. The filter is comprised of quarter-wavelength hair-pin resonators, reducing resonator and filter footprint compared to conventional hairpin designs. Additionally, it is considerably forgiving to fabrication tolerances and yields remarkably close matched results between theory, simulation, and measured results. One demonstration presented has minimal insertion loss ${(< 1{dB})}$ for the entire wide bandwidth of 3.4 GHz to 4.2 GHz. Wider bandwidths up to 60% are also observed using the design. The proposed filter is an attractive solution when space is a critical... 

To enhance impedance bandwidth of spherical Microstrip antenna with annular-circular patch, an air gap layer between antenna ground and substrate layer has been employed. The principle purpose of this work is to consider the effect of such layer on the impedance bandwidth and, consequently, antenna performance. To provide circular polarization, we have applied anisotropic uniaxial crystal as a substrate in spherical Microstrip antenna. Evaluating the impact of air gap layer on radiation pattern of spherical Microstrip antenna with annular-circular patch via CST program is the other goal of this correspondence for three types of substrate materials, anisotropic negative uniaxial crystal,... 

A coplanar-fed wideband antenna array system to characterize MIMO channels in the 60 GHz band is proposed. The array consists of six U-slot patch elements with half-wavelength separation and is fed independently by individual transceivers. The system is designed and simulated on fused silica substrate to be integrated easily with RFICs and to achieve fine fabrication resolution (1um) for accurate mm-wave measurements. It can provide 11dBi peak gain at broadside and beam steering up to ±40° tilted from broadside over 57-63 GHz band. A new on-wafer calibration technique is developed to balance the amplitude and phase of all transceivers at the input of the array system which realizes high... 

In this paper, a single-fed, circularly-polarized printed antenna with an elliptical slot for S-band application is suggested. The antenna structure includes a circular patch radiator having one rotated elliptical slot which feeds through a microstrip line. The circular polarization is obtained by adjusting the major axis of the elliptical slot. A metallic circular ground and four 80° slices of a wide ring-shaped patch surrounding the main radiator improve impedance matching bandwidth and circular polarization performance. The suggested antenna has a left-handed circularly polarized (LHCP) with an acceptable axial ratio that is in agreement with S-band applications. For verification of the... 

In this letter, a compact, wideband, and fully planar microstrip crossover structure is proposed. This design is based on a compact microstrip to coplanar waveguide transition, which has a measured bandwidth extending from dc to 40 GHz. At 20 GHz, the measured insertion loss, return loss, and isolation are better than 0.35, 21, and 19 dB, respectively. This circuit is ultracompact with the core size of 3 mm ×3 mm, which is 0.2λ×0.2 λ at 20 GHz. © 2012 IEEE  

Monolayer band-reject frequency selective surfaces (FSS) based on curved coupled microstrip line (CCML) resonators are proposed. Each unit cell comprises a single- or multi-loop CCML resonator, featuring single-wideband or multi-band resonance, respectively. Design guidelines for achieving various responses are demonstrated and it is shown there is a great flexibility attaining desired frequency responses versus structural parameters. For instance, it is shown that the entire microwave X-band may be rejected, using a simple single-loop structure. The FSS is particularly useful for protecting buildings against parasitic microwave signals. A visual transparency factor for the FSS, when regular... 

The bandwidth of the E-shaped microstrip antenna is optimized using the genetic algorithm (GA) based on fuzzy decision-making, The method of moments is employed for the analysis of the microstrip antenna at the frequency band of 1.8GHz to 2.6GHz by the optimization parameters of supply locations and slot dimensions. Fuzzy inference system is used for the control of the parameters of the genetic algorithm. In the implemented fuzzy system, inputs are parameters like population, and outputs are parameters such as crossover and mutation rates. Simulation results show the genetic algorithm to optimize the bandwidth of the E-shaped microstrip patch by 33.3%. The measured results of the optimized... 

Microwave filters have successfully been miniaturized using spiral resonators. One of the typical problems in wideband microwave filters, such as spiral filters, is the need for very small gaps between resonators to accomplish high external and internal coupling. These gaps cause difficulties in the physical implementation of the filter, especially at high frequencies. To avoid this problem and to enable easy fabrication of the filter, a rectangular microstrip patch was used as a coupling capacitor instead of small gaps between resonators. This technique was used both for external and for internal coupling of the filter. Additionally, this approach has another important benefit; it removes... 

A novel closed form expression is derived for spatial Green's functions of microstrip structures by expanding the spectral Green's function into a Gaussian series. This innovative method is called the Gaussian Green's function (GGF) method due to the Gaussian form in the closed form Green's function representation. The main advantage of the GGF method lies in its precision as well as rapid convergence. To demonstrate the versatility of this method, the current distribution of a microstrip antenna is achieved via the combination of the method of moments (MoM) and GGF method. It is shown that this method can be computationally very efficient with less than 1% error compared to the numerical... 

In this paper, we present an antenna array with beam steering capability to characterize MIMO channels over 57-63 GHz frequency band. This uniform linear array is built of six U-slot patch elements which are spaced half wavelength to maximize the beam scanning coverage. Each element can be fed by an individual transceiver to establish a MIMO construction. The system is implemented in fused silica technology to be integrated easily with RFICs and to achieve excellent fabrication tolerance for accurate mm-wave measurements. It can provide 11dBi peak realized gain at broadside and beam steering up to ±40° from broadside in the whole frequency band. © 2018 IEEE  

We have developed a fourth order compact finite volume method for the solution of low Mach number compressible flow equations on arbitrary nonuniform grids. The formulation presented here uses collocated grid that preserves fourth order accuracy on nonuniform meshes. This was achieved by introduction of a new fourth order method for calculation of cell and face averaged metrics. A special treatment of nonlinear terms is used to guarantee the stability of the fourth order compact method. Moreover an approach for applying this method to multi-block domains is presented for complicated geometries and parallel processing applications. Several test cases including the flow in a lid-driven cavity,... 

The performance of τ-lepton reconstruction and identification algorithms is studied using a data sample of proton-proton collisions at s = 7 TeV, corresponding to an integrated luminosity of 36 pb-1 collected with the CMS detector at the LHC. The τ leptons that decay into one or three charged hadrons, zero or more short-lived neutral hadrons, and a neutrino are identified using final-state particles reconstructed in the CMS tracker and electromagnetic calorimeter. The reconstruction efficiency of the algorithms is measured using τ leptons produced in Z-boson decays. The τ-lepton misidentification rates for jets and electrons are determined