Magnitude Of Reflection Coefficient Research Articles

Inkjet-Printed Wideband Circularly Polarized Microstrip Patch Array Antenna on a PET Film Flexible Substrate Material

In this letter, a wideband right-hand circularly polarized high-gain 4 × 4 microstrip patch array antenna on a polyethylene terephthalate (PET) film flexible substrate material is investigated. A comparison between the planar and curved surface study is also presented to show impact of curving the array on antenna performance parameters since it is employing a flexible substrate material. Due to some unknown properties of the PET material, some disagreement is noticed between the simulated and measured results in reflection coefficient magnitude, axial ratio, and gain in addition to radiation patterns. The radiation patterns are consistent with some rise in cross-polarization levels.

Uncertainty quantification and sensitivity analysis of thermoacoustic stability with non-intrusive polynomial chaos expansion

In this paper, non-intrusive polynomial chaos expansion (NIPCE) is used for forward uncertainty quantification and sensitivity analysis of thermoacoustic stability of two premixed flame configurations. The first configuration is a turbulent swirl combustor, modeled by the Helmholtz equation with an n−τ flame model. Uncertain input parameters are the gain and the time delay of the flame, as well as the magnitude and the phase of the outlet reflection coefficient. NIPCE is successfully validated against Monte Carlo simulation. It is observed that the first order expansion suffices to yield accurate results. The second configuration under investigation is a low order network model of a laminar slit burner, with the flame transfer function identified from weakly compressible CFD simulations of laminar reacting flow. Firstly the uncertainty and sensitivity of the growth rate due to three uncertain input parameters of the CFD model – i.e., flow velocity, burner plate temperature and equivalence ratio – are analyzed. A Monte Carlo simulation is no longer possible due to the computational cost of the CFD simulations. Secondly, two additional uncertain parameters are taken into account, i.e., the respective magnitudes of inlet and outlet reflection coefficients. This extension of the analysis does not entail a considerable increase in computational cost, since the additional parameters are included only in the low order network model. In both cases, the second order expansion is sufficient to model the uncertainties in growth rate.

Feasibility of using near-field microwave reflectometry for monitoring autogenous crack healing in cementitious materials

This study demonstrates the feasibility of using the near-field microwave reflectometry technique to nondestructively monitor the evolution of autogenous crack healing of mortar containing high volume of supplementary cementitious materials. Mortar samples were subjected to controlled compressive loading to generate cracks, and subsequently exposed to wetting/drying cycles to initiate the autogenous crack healing process. Test results indicate that cracked mortar samples exhibit higher point-to-point microwave reflection coefficient variations caused by cracking and moisture ingress (i.e., larger coefficient of variation (COV) values of magnitude of reflection coefficient, |Γ|, obtained from microwave reflectometry). When subjected to wetting/drying cycles, samples with higher crack healing capability are found to undergo less variation in microwave reflection coefficient. Based on the results for cracked samples, the COV trends obtained for microwave reflection properties can be divided into three parts as a function of wetting/drying cycles: part (I) corresponding to a significant point-to-point microwave reflection variations resulting from crack formation and moisture ingress after the first wetting/drying cycle; part (II) indicating the onset of the crack healing process identified by the reduction in the COV values; and part (III) representing slow-down of crack healing process for the regions exposed to microwave radiation as indicated by the relatively constant COV values during additional wetting/drying cycles. Such variations in microwave reflection properties can be linked to changes in moisture transport properties and subsequent crack healing process. To corroborate the microwave reflectometry results, concurrent ultrasonic measurements were conducted on the mortar samples during the self-healing process, and a good correlation was observed between the outcomes of these two test methods. The results of material characterization assessments including capillary water absorption, crack healing quantification, as well as X-ray diffraction and scanning electron microscopy of crack healing products were also used to quantify the crack healing evolution for the investigated mortar samples.

Frequency-Tuning Method Using the Reflection Coefficient in a Wireless Power Transfer System

In this letter, we compare two operating frequency tuning methods—the zero phase angle (ZPA) and the minimum reflection coefficient magnitude (MRCM) frequency tuning methods—to enhance the power transfer efficiency and output power in the wireless power transfer (WPT) system. For the MRCM frequency tuning method which has been introduced recently, the WPT system can be analyzed by considering the system as a matching network connected to a generator and a load. Through experiments, in the over-coupled region, the MRCM frequency tuning method has higher output power and efficiency than the ZPA frequency tuning method. Above all, the MRCM frequency tuning method does not need the information on the coupling coefficient as well as the primary and secondary resonators.

Arbitrary Antenna Arrays Without Feed Networks Based on Cavity-Excited Omega-Bianisotropic Metasurfaces

We present a design procedure for low-profile single-feed cavity-excited omega-bianisotropic metasurface antennas (CX-OBMAs), capable of generating an arbitrary desirable field distribution on their aperture. The procedure relies on a greedy algorithm that optimizes the source position inside the cavity and the magnitude and phase of the metasurface modal reflection coefficients, such that the power profile generated by the cavity fields matches the one corresponding to the specified aperture distribution. Once this local power conservation is established, we invoke previously derived analytical formulas to evaluate the (passive lossless) metasurface constituents that facilitate the required field transformation. We demonstrate this scheme by designing CX-OBMAs that generate radiation patterns with prescribed directivity and side-lobe level, for which the aperture fields can be readily stipulated using established antenna array theory. The good agreement between full-wave simulations and semianalytical predictions points out the immense potential of these novel radiators, capable of controlling near- and far-field distributions almost at will. In particular, they can emulate antenna array performance, without requiring design and implementation of complicated, expensive, and lossy feed networks.

Six-port microwave system for volatile organic compounds detection

An interdigital capacitor with resonant frequency fres ≈ 8.6GHz coated by comb polymer Pc-based thin film as a sensitive layer was investigated under exposure to different concentrations of various VOCs, such as: acetone, ethanol, methanol, isopropanol, butanol and ethylbenzene in a 0–25ppm concentration range. The measurement system has been significantly simplified due to measurement of the reflection coefficient at a single frequency f0=8GHz, at which the sensor exhibits the largest change in reflection coefficient's magnitude. For the reflection coefficient's measurement a new six-port reflectometer has been developed, which provides an enhanced measurement accuracy for the measurements of reflection coefficients having small magnitudes. The developed detector based on microwave measurements can be utilized in a portable exhaled breath analyzers.

APPROXIMATIVE COMPUTATION METHODS FOR MONOSTATIC SCATTERING FROM AXIALLY SYMMETRIC OBJECTS

Two approximation methods are presented for fast calculations of the monostatic scattering from axially symmetric scatterers coated with electromagnetic absorbers. The methods are designed for plane wave illumination parallel to the axis of rotation of the scatterer. The first method is based on simulating the scattering of a perfect electric conductor (PEC) enclosing the absorber coated scatterer, and multiplying the result with the squared magnitude of the absorber reflection coefficient in a planar scenario. The second method is based on simulating the scattering scenario in a physical optics (PO) solver, where the electromagnetic absorber is treated as reflection dyadic at the outer surface of the scatterer. Both methods result in a significant acceleration in computation speed in comparison to full wave methods, where the PO method carries out the computations in a number of seconds. The monostatic scattering from different geometries have been investigated, and parametric sweeps were carried out to test the limits where the methods yield accurate results. For specular reflections, the approximation methods yield very accurate results compared to full wave simulations when the radius of curvature is on the order of half a wavelength or larger of the incident signal. It is also concluded that the accuracy of the two methods varies depending on what type of absorber is applied to the scatterer, and that absorbers based on volume losses such as a carbon doped foam absorber and a thin magnetic absorber yield better results than absorbers based on resistive sheets, such as a Salisbury absorber. (Less)

Frequency-Scanning Planar Antenna Based on Spoof Surface Plasmon Polariton

In this letter, a frequency-scanning planar antenna composed of a phase gradient metasurface and feed structure is proposed. The phase gradient metasurface can couple the wave from the feed into a spatial radiated wave whose propagation direction is manipulated by frequency as long as the feed provides a similar electromagnetic field to that of spoof surface plasmon polariton rather than exciting the spoof surface plasmon polariton. Both the simulation and measured results demonstrate the antenna works well in the frequency range from 8.9 to 9.5 GHz, that the magnitude of reflection coefficient maintains lower than −10 dB with minimum value of −20 dB, and the gain maintains at about 10 dB. The max gain direction of the antenna changes with frequency that the beam pointing angles at 8.9, 9.1, 9.3, and 9.5 GHz are −12°, −8°, −4°,and 0°, respectively.

A radiometer of the reflection coefficient magnitude

A simple meter of integral values of the reflection coefficient magnitude in the microwave frequency band and a wide frequency band using a low-intensity noise signal is described. Its principle of operation is based on one of the modifications of the null measurement methods. On the one hand, the application of this principle increased the measurement accuracy and, on the other hand, significantly simplified the design of the meter and implemented it as a portable device. The integral error of the nonlinearity of the transfer characteristic in absolute values of the reflection coefficient magnitude did not exceed 0.003 with a measurement resolution of 0.001.

Design Tri-Band Fractal Antenna with Minkowski Island Split Ring Resonator Structures

The paper investigates the effect of Minkowski Island split ring resonator (MI-SRR) on the microstrip fractal patch antenna. Firstly, a basic Minkowski Island had been simulated in the CST Microwave Studio. Then, the addition of several sizes of the Minkowski Island split ring resonator on the substrate had been generated tri-band resonant frequencies. The optimal result of this tri-band antenna 2.394 GHz, 3.528 GHz and 5.257 GHz with a gain of 0.874 dB, 1.41 dB and 2.94 dB and the reflection coefficient magnitudes of - 21.945 dB, - 17.154 dB and – 16.536 dB. The reflection coefficient magnitudes of the simulation and fabricated antenna also had been compared. The target application for this antenna is for WLAN and WiMAX.

Printed Ultrawideband Monopole Antenna with Four Notch Band

A compact ultra-wideband planar monopole antenna with four notched bands is proposed. The antenna consists of a rectangular radiating patch with two bevels at lower edge and a modified ground plane with two bevels at upper edge. In order to realize multiple notch characteristics in the WiMAX band (3.3---3.7 GHz), the lower WLAN band (5.15---5.35 GHz), and higher WLAN band (5.725---5.875 GHz), three round shape slots are inserted in radiating patch. The fourth notch band in X-band downlink satellite communication band (7.1---7.76 GHz) is obtained by etching a pair of C-shaped slots in the ground. The proposed antenna exhibits a nearly omnidirectional radiation pattern in the H-plane, and a dipole-like radiation pattern in the E-plane for the for the entire pass band. The measured operating impedance bandwidth of proposed antenna ranges from 3.1 to more than 17 GHz having reflection coefficient magnitude less than ?10 dB with four notched bands. The effects of each individual slot on band notch characteristics are also investigated. The measured gain of the proposed quad band notched antenna is relatively stable across the operating frequency band except notched bands and thereby making the proposed antenna suitable for practical UWB applications. Proposed antenna has a compact size of 30 × 26 mm2.

A Coplanar Waveguide Rectangular Dielectric Resonator Antenna (RDRA) for 4G Applications

This paper presents the design of coplanar waveguide (CPW) rectangular dielectric resonator antenna (RDRA) with and without metallic strip, operating at 2.6 GHz for long term evolution (LTE) applications. The CPW RDRA without metallic strip produces impedance bandwidth of 51 %. Then, a metallic strip was added on top of the dielectric resonator (DR) in order to enhance the impedance bandwidth; thus give more flexibility for the system to cover more applications. A good agreement between simulation and measurement results, in terms of reflection coefficient magnitude and radiation pattern is presented. The simulated and measured impedance BWs for S11 < -6dB are 67 % (1.74-3.47 GHz) and 66 % (1.83-3.54 GHZ) respectively, with the gain of 3.12 dBi is obtained at 2.6 GHz. The mode excited for this antenna is TEy1δ1 mode.

Experimental estimation of mismatch uncertainty in radio – frequency power and attenuation measurements

In this paper, the effects of the input quantity representations in linear and complex forms are analyzed to estimate mismatch uncertainty separately for one-port and two-port components. The mismatch uncertainties in power and attenuation measurements are evaluated for direct, ratio and substitution techniques with the use of a vector network analyzer system in the range of 1 to 18 GHz. The estimated mismatch uncertainties were compared for the same device under test and these values have verified that their evaluation is dependent on the representations of input quantities. In power measurements, the mismatch uncertainty is reduced when evaluating from the voltage standing wave ratio or reflection coefficient magnitudes in comparison to the complex reflection coefficients. The mismatch uncertainty in the attenuation measurements, are found higher and linearly increasing while estimating from the linear magnitude values than those from the S -parameters of the attenuator. Thus in practice, the mismatch uncertainty is estimated more accurately using the quantities measured in the same representations as of measuring quantity.

Optical Huygens’ Metasurfaces with Independent Control of the Magnitude and Phase of the Local Reflection Coefficients

Implementation of abrupt phase discontinuities along a surface has been the theme of recent research on electromagnetic metasurfaces. Simple functionalities such as reflecting, refracting, or focusing plane waves have been demonstrated with devices featuring phase discontinuities, but optical surfaces allowing independent magnitude and phase control on the scattered waves have yet to emerge. In this paper, we propose the first true optical Huygens’ surface, which explicitly utilizes orthogonal electric and magnetic responses to realize total control on an optical surface’s local reflection coefficients. This extends the functionality of metasurfaces to an unprecedented level. We first demonstrate that a nanorod gap-surface plasmon resonator can act as a Huygens’ source. Thereafter, by properly tuning and rotating these resonators, we realize arbitrary reflection optical metasurfaces—surfaces for which the local reflection coefficients can be independently tailored in both magnitude and phase. We demonstrate the versatility of this approach through designs of a metasurface that asymmetrically reflects two copolarized beams and a Dolph-Tschebyscheff optical reflectarray.

Linear-response reflection coefficient of the recorder air-jet amplifier

Steady-state oscillations in a duct flute, such as the recorder, are controlled by (1) closing tone holes and (2) adjusting the blowing pressure or air-jet velocity. The acoustic amplitude in steady-state cannot be controlled independent of the jet velocity, because it is determined by the gain saturation properties of the air-jet amplifier. Consequently, the linear-response gain of the air-jet amplifier has only very rarely been studied [Thwaites and Fletcher, J. Acoust. Soc. Am. 74, 400–408 (1983)]. Efforts have focused instead on the more complex gain-saturated behavior, which is controlled by vortex shedding at the labium. We replace the body of a Yamaha YRT-304B tenor recorder with a multi-microphone reflectometer and measure the complex reflection coefficient of the head at small acoustic amplitudes as a function of air-jet velocity and acoustic frequency. We find that the gain (reflection coefficient magnitude) has a maximum value of 2.5 at a Strouhal number of ≈0.3 (jet transit time divided by acoustic period), independent of jet velocity. Surprisingly, the frequency where the gain peaks for a given blowing pressure is not close to the in-tune pitch of a note that is played at the same blowing pressure.

Probe-Fed linearly-polarized electrically-equivalent microstrip antennas on FR4 substrates

This paper describes a simple but efficient procedure for designing electrically-equivalent microstrip antennas on FR4 sub-strates. Radiation patterns, reflection coefficient magnitude ( |Γ| ), mutual coupling and cross-polarization level of probe-fed linearly-polarized antennas are calculated and discussed. Experimental results of |Γ| and radiation patterns of rectangular, elliptical and triangular patches validate the proposed procedure.

Characterization of Heavy Metal Contaminated Wastewater Using a Coaxial Sensor and Electromagnetic Wave Reflection Technique

Industrial wastewater control is an important issue for protection of the environment. Liquid characterization using radio frequency signal is an interesting approach for selective detection of heavy metal contaminants in industrial wastewater. A simple sensor based on open-ended coaxial structure filled with the liquid under test is proposed. Liquid samples for the experiments are copper, zinc and nickel solutions with various concentrations of 1, 10, 100 and 1000 mg/liter each. From the measurement results using a vector network analyzer (VNA) in combination with the proposed sensor, the concentration of a specific contaminant can be determined by the magnitude of the measured reflection coefficient in a frequency range lower than 2 GHz. Applying a capacitive model of the sensor, complex permittivity of the liquid under test can be calculated from the measured reflection coefficient. Obvious relationship between the imaginary part of complex permittivity and the concentration of contaminant in a frequency range lower than 2 GHz was observed. The type of contaminants in the liquid samples can be identified by the position of the resonant peaks when the magnitude of reflection coefficient is plotted in the spectrum. The frequency range for contaminant’s identification lies between 2 and 3 GHz.

Proposal of a Planar Directional UWB Antenna for Any Desired Operational Bandwidth

A novel planar directional UWB antenna is proposed. The antenna design evolves from an oblique elliptic cone antenna by applying the planar-solid correspondence to two axes. Through a simple equation, this antenna can be designed, to operate at a specific lower cutoff frequency with a bandwidth larger than 10 GHz for a reflection coefficient magnitude lower than −10 dB. This characteristic provides the antenna with a good versatility. The directional radiation pattern has an average gain of 6 dBi.

Multiband Antenna <formula formulatype="inline"> <tex Notation="TeX">${Q}$</tex></formula> Optimization Using Stored Energy Expressions

A method to compute antenna Q from a single frequency current distribution is applied to the optimization of multiband radiating structures. A genetic algorithm produces suboptimal structures in the sense of simultaneous multiband minimum Q. These structures model in a simplified manner common wireless communication devices. The comparison to the physical bounds for the considered situations shows that the suboptimal structures perform close to their limitations. Matching networks are designed using real component models with a commercial tool. These networks have less than three components and provide less than -6.5 dB reflection coefficient magnitude in all considered bands. The results show that the single-frequency Q estimation method may be useful for antenna design.

다중경로 환경에서 다중빔 탐색레이더에 적용 가능한 표적 고각오차 혼성 보정 기법

The multibeam surveillance radar is a state-of-art of 3D radar technology. It applies the stacked beams realized by a digital beamformer. In this paper, a hybrid compensation technique on elevation angle errors for low elevation angle targets over the sea in multipath radar environments is proposed. The proposed method can be applied to stacked beam radars. Double null algorithm based on maximum likelihood method in 3-D beamspace domain works well unless the phase difference between the two rays(direct and specular path) is close to 0° and the magnitude of reflection coefficient is close to 0. To overcome these problems, we propose a hybrid compensation technique which uses the selective double null algorithm and the beam-ratio compensation technique for low-elevation errors on a log scale. Results of computer simulation show that the proposed method outperform conventional monopulse method and double null algorithm only under various multipath environments.Keywords : Mutibeam Surveillance Radar(다중빔 탐색 레이더), Digital Beamformer(디지털 빔형성기), Multipath(다중경로), Monopulse(모노펄스)