S-parameters Research Articles

Wideband microwave frequency response measurement based on optical phase-locked loop

Frequency response measurement, or the forward transmission coefficient (S21) measurement for a two-port network, is the key function of a vector network analyzer (VNA). In this paper, a broadband and high dynamic range (DR) microwave S21 parameter measurement scheme based on an optical phase-locked loop (OPLL) is proposed. By heterodyning two phase-locked hybrid integrated ultra-narrow linewidth lasers, a microwave signal with low phase noise and spurious level is generated as the incident signal and reference signal, and the signal frequency can be easily manipulated over a wide range by tuning the master laser wavelength. In the receiver, the radio frequency (RF) signals are down-converted to intermediate frequency (IF) signals with the phase-locked lasers. By sampling and processing the IF signals the S21 parameter of the DUT can be acquired. A proof-of-concept experiment is performed, and with available photodetectors, phase modulators and phase-locked loops, a measurable range of 2 to 18 GHz is achieved. The demonstrated minimum frequency resolution of the OPLL-based RF signal synthesizer is 10 Hz. The system DR exceeds 68 dB at an equivalent resolution bandwidth of 1 kHz. The S21 parameters of a power divider and a bandpass filter are measured, and the results are well consistent with those of a commercial VNA. The DR and measurable range limit factors and possible extension methods are discussed. The proposed approach offers a high potential way to develop a wideband, high DR, and fully integrated VNA.

EM Radiation Thermal Effects Simulation Study on a Realistic Female Model at Some Frequencies

The purpose of research is to develop a computer simulation based mobile phone safety testing scheme that is well suited for testing any mobile phone antenna at different communication frequencies and various realistic scenarios. It has been shown how feasible the study of realistic models is, what difficulties may occur, what effects, moments appear in the modeling process. The aim of the study is also to show the need for changes in the standard of mobile phone safety testing and to investigate the possibilities of implementing these changes. It is preferable for manufacturers to perform testing using human realistic models through numerical calculations and conduct safety compliance testing under realistic conditions to produce more realistic picture. Computer modeling gives the possibility to consider various realistic models, realistic scenarios and different tissue dielectric properties according to the frequency. It was investigated how mobile phone antenna radiation parameters (S11 reflection coefficient) change according to the various positions of the hand and fingers at standard communication 2100 MHz and 3700 MHz frequencies; were estimated Specific Absorption Rate (SAR) values in the human head and their dependence on S11 parameters were studied. Based on the obtained results, it has been shown that the preferred S11 behavior should be one of the indicators in the phone safety standards. For this, manufacturers should carry out mobile phone antenna matching/S11 parameter testing with free space.

Design and Simulation of Circular Dielectric Resonator Antenna and Investigation of Structure, Microstructure, and Dielectric Properties of Mn‐Modified Sr2SnO4

Samples with compositions of Sr2Sn1−xMnxO4(SSM) with 0 ≤ x ≤ 0.10 are prepared by conventional ceramic route via heat treatment at 1350 °C. Phase and crystal structure analysis is studied using X‐ray diffraction and Rietveld refinement to confirm the crystallization of samples in the tetragonal structure under space group I4/mmm. The size‐strain plot method is employed to identify the role of Mn on crystallite size/microstrain/dislocation density. The scanning electron microscope and energy‐dispersive X‐ray spectroscopy analysis confirm a significant change in the grain size and compositional homogeneity of all samples with Mn‐doping. Dielectric properties of samples are explained in terms of interfacial and orientation polarization of dipoles . Modulus studies show the exclusion of electrode contribution from the electrical properties. The single‐segment circular dielectric resonator antenna is designed with the help of experimental dielectric parameters and showed two major resonant frequencies at 3.6 and 6.7 GHz. The reduction in the S11 parameter and −10 dB reflection coefficient bandwidth with Mn‐doping observed due to overlapping of the E‐field line suggests the application in patch array antenna for radar and satellite communication applications. This study also enables to explore Sr2SnO4‐based Ruddlesden Popper oxide for antenna and mm‐wave communication applications.

Aging characterization of dielectric materials using microstrip spiral resonator sensor: application in high frequency range, up to 18 GHz

This current work aims to propose a complete microwave procedure for dielectric materials aging characterization. To achieve this aim, a microstrip spiral resonator sensor, based on printed circuit board (PCB) technology, is designed to attend polyvinyl chloride (PVC) aging behavior through microwave measurements. The resonator is composed of a spiral microstrip, excited by coupling 50-Ohm transmission line on the top layer of the substrate; meanwhile a rectangular slot is etched in the bottom layer, behind the spiral shape to achieve high inductive effect. Structure optimization was conducted using high-frequency structure simulator (HFSS). The sensor is then used as a holder of the UV-aged PVC material while reflection (S11) and transmission (S21) coefficients are measured by vector network analyzer (VNA) in high frequency range, up to 18 GHz. The aging effect is finally perceived by observing the frequency shift of the resonance frequency between the empty and the aged-PVC loaded sensor, together with a variation in the S21 parameter amplitude. It is then found that for 864 h of UV-exposure is provided more than 0.45% frequency shift and about 4.67% decrease in electromagnetic energy transmission. Moreover, comparison between S11 and S21 results reveals that using S11 parameter is more practical to investigate material aging as it allows for simple visual checking of the frequency shift.

Modeling and Analysis of Wide Frequency Band Coaxial TSV Transmission Interconnect.

In this paper, we first build the 3D model of coaxial TSV(CTSV), RDL, and bump of the CTSV interconnect, and extract the equivalent circuit model of each part. Then, we get the S-parameters of the 3D and equivalent circuit model of the CTSV interconnect structure; the validity of the equivalent circuit model is verified by comparing the consistency of the S-parameters. The simulation results show that the maximum errors for the S11 and S21 parameters are 0.4% and 0.18%, respectively, which proves the validity of the equivalent circuit modeling in this paper. Finally, parametric analysis is performed to investigate the effect of different model parameters on the signal-transmission characteristics of the CTSV interconnect.

Experimental study on the technology optimization of clear ice thickness detection on horizontal cold plate surface by using microwave resonance

The accumulation of snow and ice has the potential to have a negative impact on numerous industries if it is not accurately detected and processed in real-time. Microwave resonators have gained interest as durable and reliable ice detectors. To detect the thickness of clear ice slices on a horizontal cold plate surface, a capacitively coupled split-ring resonant sensor was experimentally investigated. To ascertain the efficacy of the sensor, plexiglass with similar relative permittivity to ice was firstly tested. The effect of the plexiglass plate thickness on the resonance amplitude of the transmission scatter parameter was found to be monotonic in the range of 16.8 mm thickness, thereby demonstrating the ability of the sensor to accurately measure plate thickness. Then, the effect of different thicknesses of clear ice slices within 17.0 mm on the resonance parameters was tested under constant temperature. The resonant amplitude decreased by 46.55% from −4.13 dB to −6.05 dB, as the thickness of the clear ice slice gradually increased from 2.5 mm to 17.0 mm. A model for the detection of ice thickness based on the analysis of theoretical principles and experimental data was developed. The ice thickness could be detected accurately within a range of 17.0 mm at temperatures between −3 and −20 °C, with a maximum deviation of 5.66% in the detection of ice thickness. This study validates the application of the sensor to detect ice thickness, such as on ships, roads and aircraft.

Mechanical Strain, Temperature, and Misalignment Effects on Data Communication between Piezoceramic Ultrasonic Transducers.

Acoustic waves can be used for wireless telemetry as an alternative to situations where electrical or optical penetrators are unsuitable. However, the response of the ultrasonic transducer can be greatly affected by temperature variations, mechanical deformations, misalignment between transducers, and multiple layers in the propagation zone. Therefore, this work sought to quantify such influences on communication between ultrasonic transducers. The experimental measurements were performed at the frequency where power transfer is maximized. Moreover, there were four experimental models, each with its own performed setup. The ultrasonic transducers are attached to both sides of a 6 mm thick stainless-steel plate for configuring just one barrier. Multiple layers of transducers are attached to the outer side of two plates immersed in an acoustic fluid with a 100 mm thick barrier. In both cases, the S21 parameter was used to quantify the influence of the physical barrier because it correlates with the power flow between ports that return after a given excitation. The results showed that when a maximum deformation of 1250 μm/m was applied, the amplitude of the S21 parameter varied around +0.7 dB. Furthermore, increasing the temperature from 30 to 100 °C slightly affected the S21 (+0.8 dB), but the signal decayed quickly for temperatures beyond 100 °C. Additionally, the ultrasonic communication with a multiple layer was found to occur under misalignment with an intersection area of up to 40%. None of the factors evaluated resulted in insufficient power transfer, except for a large misalignment between the transducers. Such results indicate that this type of communication can be a robust alternative, with a minimum alignment of 40% between transducers and electrical penetrators.

GA optimized novel design and analysis of graphene-based antennas for THz spectroscopic security applications

The proposed research paper introduces a novel design of THz graphene-based antennas capable of countering terrorism by detecting explosive materials and drugs. The research work is subdivided into three distinct sections; the initial research entails conducting a comparative analysis of conventional and genetic algorithm-based optimised designs of terahertz antennas utilising graphene material. Subsequently, three supplementary designs are evaluated in comparison to the optimum design: one integrating a copper ground with a graphene patch, another integrating a copper patch with a graphene ground, and a third incorporating both a copper patch and ground. All four optimised designs, each resonating at a frequency of 5.6 THz, are used to detect explosive compounds like Trinitrotoluene (TNT). The optimised graphene-based antenna outshines the rest of the designs in terms of radiation efficiency, with a value of 90.03 %. It also exhibits superior performance regarding S11 parameters, with a value of −53.38 dB, and VSWR, with a value of 1.004, at the resonant frequency. The optimised antenna demonstrates superior performance concerning gain (dB) and directivity (dBi), measuring 6.56 dB and 7.02 dBi, respectively. During the final phase of the proposed research, a graphene antenna was modified to function as a tri-band antenna by incorporating a 180° mirrored f-shaped slot within the antenna’s patch. The tri-band antenna functions at resonant frequencies of 3.37 THz, 4 THz, and 5.2 THz. These frequencies detect explosives and narcotics, notably l-histidine, ammonium nitrate (NH4NO3), and PETN in PE. These resonant frequencies hold the potential to be utilised in future applications of 6G technology worldwide.

Prediction of multi-layer metasurface design using conditional deep convolutional generative adversarial networks

Designing metasurfaces is a challenging task. Traditional methodologies, which primarily depend on iterative procedures, are both time-intensive and require specialized expertise. The proposed algorithm uses conditional deep convolutional generative adversarial networks (cDCGAN) to design metasurfaces. This method instantly create a 2D image of a multi-layer metasurface using the scattering parameter S11 as the input vector. The algorithm significantly reduces the size of the training dataset by applying pre-training and post-generating steps. The pre-training step involves aliasing and modifying images using a limited color palette. The post-generating step consists of separating the color channels, converting the pixels to vector based images, and fine-tuning the borders. The algorithm is evaluated for three metasurfaces that have unique features compared to the training dataset samples: a single-band metasurface unitcell, a dual-band metasurface unitcell, and a partially trained sample improved by magnetic field analysis. The results show that the proposed algorithm can accurately predict the images of these metasurface unitcells, demonstrating its potential for fast and efficient metasurface design.

Frequency Shift in Microwave Circuits Manufactured with Circuit Board Plotters: Case Study of a Parallel Coupled Lines Filter

Board milling is one of the most widespread methods for manufacturing printed circuit boards from low frequencies to the microwave and millimeter wave range. In this contribution, the detrimental effect of defects typical of printed circuit board plotters has been investigated. In detail, a systematic frequency shift in the circuit performance has been observed both in terms of S21 and S11 parameters. The performance degradation has been analyzed and attributed to the inaccurate milling depth, which is typical of many plotters, particularly for less recent models. After the conductor removal step, the unwanted milling of dielectric material changes the electrical properties of the microstrip structure, in turn affecting the circuit performance. This circumstance has been investigated by means of electromagnetic simulations performed on the real case study of a parallel coupled lines filter. Therefore, a filter prototype has been realized and measured to confirm the simulated results. This study can be beneficial to those professionals involved in the design and realization of microwave and millimeter waves circuits with board milling machines.

Optimization design of the cavity tuning and RF input coupler for an 11 MeV superconducting cyclotron

This study addresses the compact design requirements for a 11 MeV superconducting cyclotron utilized in isotope production by proposing a design and optimization scheme for a radio frequency (RF) input coupling system. The system, comprising a coupler loop, transmission lines, and RF window, has been tailored to accommodate the spatial constraints imposed by the super conducting magnet radius, thereby facilitating efficient RF power transfer to the RF cavity and minimizing input power. Structural optimization of the coupler loop and RF window has achieved S11 parameter of -82.23 dB, significantly reducing input power while maintaining high coupling efficiency. A coaxial coupler suitable for lower frequency ranges has been designed, employing a tapered structure for the transmission line to ensure a smooth transition to reduce impedance discontinuity effects and enhance adjustability. The multi-stage design of the RF window has achieved fine impedance matching, significantly lowering the S11 parameter. In response to frequency drift caused by RF loss and temperature increase, the study utilizes perturbation theory to analyze the perturbation effect of coupling components on the resonant frequency, designing an adjustable structure with both coarse and precise tuning capabilities, realizing tuning precision at the kHz/mm level and a tuning range of several MHz. A conjectural formula has been proposed based on the impact of the tuner's structural parameters on the resonant frequency, accurately calculating the equivalent inductance of the tuner and the resonant frequency of the RF cavity post-tuner installation, with the maximum estimation error of the resonant frequency kept within 0.1%, offering significant guidance for engineering design.

The cell elastic modulus sensing based on surface acoustic wave devices

Abstract Elastic modulus is an important parameter to reflect the status of the cell. In this work, the elastic modulus of liquid and cancer cell were studied based on the delay line type surface acoustic wave (SAW) device. Firstly, the finite element method (FEM) was used to analyse and design the sensor, a cavity was etched on the propagation path. After the acoustic wave transmit through the cavity, the transmission parameter was disturbed by the material in the cavity. The phase shift of the S21 parameter of the SAW sensor was used to detect the elastic modulus of liquid or cell in the cavity.

Coupled topological rainbow trapping of elastic waves in two-dimensional phononic crystals

Rainbow trapping, observed in elastic waves, has attracted considerable scientific interest owing to its potential applications in energy harvesting, buffering, and wavelength-division multiplexing devices. However, previous approaches have often necessitated complex geometric modifications to the scatterer, such as altering dimensions or shifting along diagonals to corners, limiting practical utility. Here, we realize the coupled topological edge states (CTESs) of elastic waves in a two-dimensional (2D) solid phononic crystal (PC) with inversion center changes. Changing the inversion center along the x or y directions by a specific distance can induce the topological phase transition. The topological edge states (TESs) arise at the interface by combining PCs with different topologies positioned adjacent to each other. Furthermore, it is demonstrated that TES exhibits topological robustness against defects. By introducing a gradient into the PC structure by altering the geometrical parameters of scatterers along the interface, the topological rainbow trapping of elastic waves is achieved. Finally, the CTES are generated by the interaction between TESs of different interfaces, which can lead to coupled topological rainbow trapping in phononic heterostructures with different displacement parameters along the multiple interface gradient. Our results pave the way for manipulating the symmetric and antisymmetric topological modes of elastic waves in topologically coupled waveguides, which offers potential applications in selective filtering and multiband waveguiding.

Impact of Ho substitution on structure, magnetic and electromagnetic properties hard-soft nanocomposites

This work presented the effect of Ho substitution on magnetic and electrodynamic properties of hard-soft SrBaHoxFe12-xO19@NiFe2O4 (x ≤ 0.06) nanocomposites (H/S Ho → SBFeO@NFO NCs) which were produced through one-pot citrate sol–gel method. The structure and morphology were explored using X-ray diffractometry (XRD) and scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HR-TEM). By scrutinizing hysteresis curves at temperatures of 300 K (Room temperature, RT) and 10 K, the magnetic characteristics of H/S Ho → SBFeO@NFO (x ≤ 0.06) NCs have been investigated. These materials display smooth, open hysteresis loops at both temperatures, indicating their ferrimagnetic nature and highlighting the presence of exchange-coupling interactions within the nanocomposites. The SQR (squareness ratio) values, below 0.5 at both high and low temperatures, indicate a multi-domain structure in the H/S Ho → SBFeO@NFO (x ≤ 0.06) NCs. Magnetic parameters demonstrate fluctuations with growing Ho content. The introduction of Ho3+ ions notably reduce the coercivity of the undoped H/S Ho → SBFeO@NFO (x ≤ 0.06) NCs. Saturation magnetization (Ms) and magnetic moment show similarity between undoped and Ho-doped nanocomposites at all concentrations, except for x = 0.06, where a considerable decrease occurred at both temperatures. Our findings propose that by controlling the concentration of Ho3+ ions, the magnetic properties of H/S Ho → SBFeO@NFO NCs can be precisely adjusted. Electromagnetic properties of the H/S Ho → SBFeO@NFO NCs were investigated in the range 33–50 GHz. Frequency dispersions of the real/imaginary parts of permittivity and permeability were determined from S11 to S21 parameters. RL coefficient demonstrated intensive electromagnetic absorption with average level −16…−23 dB in this frequency range that corresponded to the absorption of the natural media.

Detection of moisture of flowing grain with a novel deep learning structure using 2D spectrogram data

In order to preserve the stored grain for a long time without deterioration, the moisture content must be accurately known. In this study, the moisture content of flowing grain was determined using radar spectrogram data and CNN structure. A free-space measurement technique-based experimental environment was established for the purpose of collecting the necessary signals to measure the moisture content. The measurement plant is composed of two horn antennas, a vector network analyzer (VNA), and a flowing grain mechanism. In the experimental environment, the S11 and S21 parameter values are recorded from the VNA. The short-time Fourier transforms (STFT) of the recorded signals were then taken, and 2D spectrogram images were created. The dataset, comprising 22,780 images, was split into 80 % for training and 20 % for testing; then, they were subjected to regression analysis using CNNs. First, the mean absolute error (MAE) values of the 27 pre-trained CNN architectures in a single epoch are calculated. Subsequently, the architecture with the best four regression results is automatically selected. The training and testing steps are performed independently for each selected architecture, and the results are recorded. The MAE, root mean square error (RMSE), mean square error (MSE) and mean absolute percentage error (MAPE) metrics are employed to assess the efficacy of the CNN architectures. Among these, ResNet50 is the architecture that yields the most favorable results. Subsequently, a subsequent architecture with fewer parameters and a more expeditious processing time is proposed. The novel deep-learning CNN architecture demonstrated superior performance compared to the pre-trained architectures. The results are as follows: MAE = 0.0411, MSE = 0.0149, RMSE = 0.122, and MAPE = 0.0397. When comparing the time spent on training and testing, the least time-consuming architecture required approximately 72 min, whereas this study was completed in approximately 325 s. The pronounced disparity is readily apparent. The results demonstrate that when the CNN is appropriately modeled and trained, the combination of CNN and appropriate signal processing can effectively determine the moisture content of grains.

Evaluation of Scatterer Parameters From Ultrasound Scattering Models Taking Into Account Scattering From Nuclei and Cells of Cell-Pellet Biophantoms and Ex Vivo Tumors.

The Quantitative Ultrasound backscatter coefficient provides the capability to evaluate tissue microstructure parameters. Tissue-based scatterer parameters are extracted using ultrasound scattering models. It is challenging to correlate ultrasound scatterer parameters of tissue structures from optical-measured histology, possibly because of inappropriate scattering models or the presence of multiple scatterers. The objective of this study is to pursue the quantification of pertinent scatterer parameters with scattering models that consider ultrasound scattering from nuclei and cells. The concentric sphere model (CSM) and the structure factor model adapted for two types of scatterers (SFM2) are evaluated for cell-pellet biophantoms and ex vivo tumors of four cell lines: 4T1, JC, LMTK, and MAT. The structure factor model (SFM) was used for comparison. CSM and SFM2 provided scatterer parameters closer to histology (lower relative errors) for nucleus and cell radii and volume fractions than SFM but were not always accompanied by lower dispersion of the scatterer distribution (lower coefficient of variation). CSM and SFM2 quantified cell and nucleus radius and volume fraction parameters with lower relative error compared to SFM. For tumors, CSM provided better results than SFM2.

System design of a microstrip antenna by dimension and substrates optimization

The microstrip antennas matured and improved over the last 25 years. Throughout these years, the limitations, and specifications of the said antennas have been overcome and significantly improved. Known to be lowprofile, suitable for mobile, and lightweight, these microstrip antennas are the focus of this research. In this paper, the researchers designed a microstrip antenna with varying lengths and substrates. They tested the changes and the effects in microstrip antennas of different lengths, along with altering substrates. To verify the differences, the researchers compared the performance parameters maximum gain (dBi), minimum gain (dBi), and S11 graph on each tested length and changed substrate. The rough set theory was used to determine the optimal design via MATLAB. From there, the researchers analyzed the results gathered and drew their respective conclusions. Additionally, they saw and compared each data result to know what antenna has the best performance parameters. From the results, a change in the dimension will result in a decrease in the said performance parameters. Furthermore, the change in substrate thickness also diminishes these changes.

Microstrip Planar Antennas for C-Band Wireless Applications

In recent years, wireless communications have evolved significantly, and many mobile devices have reduced in size. The antennas used in mobile terminals must be lowered in size to fulfil the downsizing standards. Planar antennas, like microstrip and printed antennas, have a low profile, compact size, and conformability to mounting hosts, making them particularly desirable candidates for achieving these needs. Additionally, planar antennas are also being used in communication devices for 2.4 GHz (2400 – 2484 MHz) and 5.2 GHz wireless local area network (WLAN) systems (5150). In wireless applications, an antenna is a crucial component. At the transmitter, it transforms electrical signals into RF signals, and at the receiver, it converts RF signals to electrical signals. The patch inside the antenna is made of a conducting material such as Cu (Copper) or Au (Gold), and it can be rectangular, round, triangular, or elliptical. Two unique designs of microstrip planar antennas with an operating frequency of 5.2 GHz having S11 parameters as -16.0 dB and -15.7 dB have been offered and their performance has been studied in this research article.

DGS Based CP Antenna for 5G Communication with Harmonic

Higher harmonics in antennas contribute to negative effects on antenna performance such as interference, radiation pattern distortion, impedance mismatch and increased complexity in design, commonly occurring in RF communication systems caused by the non-uniformity of the antenna structure and the presence of parasitic elements. Therefore, a patch antenna operating at 3.65GHz for 5G mobile communication that incorporates techniques to suppress unwanted higher harmonics is presented. The antenna design employs a basic rectangular patch antenna with an inset feed technique to enhance the S11 parameters at the resonant frequency. Additionally, two dumbbell defected ground structures (DGS) are employed to minimize the higher modes of harmonic distortion. To transform the antenna into a circular polarized (CP) antenna, two truncated corners and a cross slot perpendicular to the middle of the patch are introduced. The proposed antenna is able to suppress unwanted harmonics at higher resonances, demonstrating its effectiveness in mitigating harmonic distortion

Simulations and experimental study on imaging of thick defect in reusable thermal protective system using microwave NDT

Reusable thermal protective system (TPS) plays a key role for protecting space vehicles against the aerothermal heating. Thus the characterization of TPS performance becomes an important issue in their production, processing and applications. This paper demonstrates the detection and imaging of inner disbond and thick defect, which considerably compromises the performance of TPS materials within a two-layer TPS configuration (a special designed thick heat insulation tile backed by an aluminum alloy plate). The methodology employed for this investigation is a near-field microwave non-destructive testing (NDT), encompassing both simulations and experimental study. A 3D microwave model for the two-layer TPS structure containing the specified defects was established, and the magnitude and phase of the waveguide input impedance (i.e. S11 parameters) for each node within the X-band (8.2 ∼ 12.4 GHz) frequency range were obtained in the work. The simulation results reveal distinct featured amplitude and phase images of defects at various frequencies. Correlation processing algorithms were employed to make the images dimensionally reduction and featured enhancement. Finally, the results were verified by experimental measurements using an open-ended rectangular waveguide. Interestingly, the disbond defect between the two layers could be clearly identified by the phase information after correlation processing algorithms. The proposed method appears to offer a contactless, intuitive, and effective approach for characterizing defects within TPS materials.