Microwave Phase Shifter Research Articles

Enhancement of Microwave Absorption Properties of Crystal‐Engineered Perovskite Oxide Using Cobalt Ferrite

A multiferroic composite that comprises of a non‐ferromagnetic ferroelectric material with a high dielectric constant and a non‐ferroelectric ferromagnetic material with a high magnetostriction is of tremendous interest as microwave absorption material due to its applicability in tunable microwave phase shifters, resonators, filters, absorbers, etc. In the previous work, the solid solution of strontium titanate and sodium bismuth titanate (Sr0.5(Na0.5Bi0.5)0.5TiO3, SNBT50), which is observed to possess a very high dielectric constant at room temperature (Ferroelectrics, Vol 583, 252–263 [2021]), is successfully reported. Thus, in this work, a core–shell magnetoelectric composite is prepared by coating highly ferromagnetic and magnetostrictive cobalt ferrite onto a diamagnetic but strongly ferroelectric SNBT50 to enhance its magnetic properties and to investigate the modification in microwave absorption. Detailed characterization of electric and magnetic parameters in microwave frequency range (1–20 GHz) reports substantial enhancement in the magnetic permeabilities as well as the magnetic loss of the composite system, as opposed to bare SNBT50. This results in improved impedance matching in the system and enhanced microwave absorption, with a minimum reflection loss (RL) of −20.19 dB and an increased effective absorption bandwidth of 4.56 GHz at a mere 2.7 mm absorber length. Consequently, in this investigation, a promising pathway is established for the development of multiferroic composites with favorable magnetoelectric coupling at room temperature that possesses wide absorption bandwidth and suitable RL, making them highly suitable for use in multiferroic‐based microwave components.

Effect of the Polarization of Nanosized Barium Strontium Titanate Films on the Characteristics of Ferroelectric Microwave Phase Shifters

Effect of the Polarization of Nanosized Barium Strontium Titanate Films on the Characteristics of Ferroelectric Microwave Phase Shifters

Submicronic-Scale Mechanochemical Characterization of Oxygen-Enriched Materials.

Conventional techniques that measure the concentration of light elements in metallic materials lack high-resolution performance due to their intrinsic limitation of sensitivity. In that context, scanning microwave microscopy has the potential to significantly enhance the quantification of element distribution due to its ability to perform a tomographic investigation of the sample. Scanning microwave microscopy associates the local electromagnetic measurement and the nanoscale resolution of an atomic force microscope. This technique allows the simultaneous characterization of oxygen concentration as well as local mechanical properties by microwave phase shift and amplitude signal, respectively. The technique was calibrated by comparison with nuclear reaction analysis and nanoindentation measurement. We demonstrated the reliability of the scanning microwave technique by studying thin oxygen-enriched layers on a Ti-6Al-4V alloy. This innovative approach opens novel possibilities for the indirect quantification of light chemical element diffusion in metallic materials. This technique is applicable to the control and optimization of industrial processes.

Influence of growth temperature on the magnetization dynamics of sputtered CoFeB thin films on various substrates and their microwave device functionality

In the present investigation, sputtering growth of 100 nm thick Co40Fe40B20 (CoFeB) film has been investigated in a low temperature range from room temperature (RT) to 400 ℃ on silicon (Si), silicon dioxide (Si/SiO2), and sapphire (Al2O3) substrates. The film surface morphology, static and dynamic magnetization were measured as a function of growth temperature and substrate. The grown films were further tested as a potential material for microwave device functionality in terms of filter and phase shifter. Surface roughness was lowest for the film grown on Si/SiO2 substrate at 200 ℃ (0.39 nm) measured from atomic force microscopy. Static magnetic properties measured by tracing magnetic hysteresis loop suggest a soft magnetic behaviour with in-plane magnetic anisotropy. Film saturation magnetization increases with the increase in growth temperature up to 200 ℃ and then decreases from 200 ℃ to 400 ℃. This suggest that the sputtering growth from room temperature to 200 ℃ offer a moderate to low interfacial stress resulting in low defects density. Gilbert damping constant (αeff) of the thin film is obtained from the ferromagnetic resonance measurements in a broad band of microwave frequencies. Damping was lowest (5.4×10−3) in the film grown at 200 ℃ on the Si/SiO2 substrate which correlates with the roughness and magnetization data. A low value of αeff is desirable for a material to be used in energy efficient spintronics and magnonic applications. The CoFeB films were also utilized in prototype microwave band-stop filter and phase shifter device applications. The filter has been tested in the frequency range from 6GHz to 25GHz with an applied magnetic bias up to 4.0 kOe. The frequency tunability with respect to the applied magnetic bias measured to be around 3.64 GHz/kOe. The maximum attenuation of −4dB was observed for the film grown on Si/SiO2 substrate at 200 ℃. Whereas, phase shifter fabricated on Si/SiO2/CoFeB film grown at 200 ℃ shows a differential phase shift up to 75°/cm. These results indicates that the CoFeB film deposited at low growth temperature can be a potential material in spintronics and CMOS applications where low temperatures are required for device fabrications.

A CMOS Microwave Phase-Shifter With High IP1dB Employing Novel Folded VGA

A CMOS Microwave Phase-Shifter With High IP1dB Employing Novel Folded VGA

Enhanced Graphene Based Electronically Tunable Phase Shifter.

In this work, an enhanced tunable microwave phase shifter is presented. The phase shifter consists of three short circuited stubs and a tapered line. The stubs are connected to graphene pads. Graphene's tunable conductivity is varied by a DC voltage. This in turn causes a reactance variation at the input of the tapered line, which causes a phase variation. The physical parameters of the stubs are optimized for a maximum reactance variation by the help of analytical models, circuit and full wave simulations. Measurements of an optimized prototype are performed and a dynamic phase variation of 59∘ is obtained with an amplitude variation of less than 1 dB.

Investigation of wet etching technique for selective patterning of ferroelectric zirconium-doped hafnium oxide thin films for high-frequency electronic applications

This paper presents the area-selective wet etching (ASWE) method as a novel approach to have a selective patterning of a 6.8 nm-thick zirconium-doped hafnium oxide (HZO) thin film, to improve the performance of a metal ferroelectric metal (MFM)-like structure. According to the electromagnetic simulations of microwave phase shifters with patterned HZO thin films, it is underlined the importance to have selectively targeted areas covered with HZO instead of full-coverage wafers, to gain a further increase in the microwave performance of low-voltage tunable high-frequency components. The impact of the ASWE method on the morpho-structural properties was studied using various investigation tools in a non-destructive manner. X-ray reflectivity (XRR) has been employed at different immersion times, up to 120 s. Based on the extended Fast Fourier Transform (FFT) analysis, as well as from the simulation of the experimental curves in the framework of parallel-tempering algorithm, the determination of the etching rate became possible. X-ray diffraction (XRD), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) clearly indicated the complete removal of HZO after etching processes at 180 s. The method is fast, reliable, and low-cost, thus filling the actual gap in providing the necessary ferroelectric thin films exclusively in selected areas of interest.

Determination of propagation constant and impedance of non-reciprocal networks/lines using a generalized line-line method

A novel “line-line” (LL) method is generalized to determine forward and backward propagation constants (γ+ and γ−) and wave impedances (Z+ and Z−) of non-reciprocal networks/lines. It considers a reference network/line with any propagation constant, impedance, and length for this goal. A theoretical analysis is carried out to examine under which circumstance wave impedance together with propagation constant can be determined by the new general LL method. Measurements of γ+, γ−, Z+, and Z− of a microwave phase shifter (a nonreciprocal network) are conducted to validate our proposed method and examine its accuracy, through normalized root-mean-square and goodness of fit values, using uncalibrated scattering parameter measurements.

Extended Method of Lines to Model Cylindrical Graphene-Based Multilayer Structures

In this article, the method of lines (MoL) is extended to analyze 2-D multilayer structures loaded with graphene plates in cylindrical coordinates. Accordingly, the admittance transformation matrices through a 2-D interface are derived taking into account the tensor-form conductivity of the magnetized graphene plate. The transformations determine the admittance matrices on all the planes of the multilayer structure. Furthermore, a technique to obtain the characteristic equation and hence the propagation constant of the structure is proposed by matching the fields at the interfaces loaded with graphene. As a result, the proposed method is able to analyze a generic graphene-loaded multilayer structure in cylindrical coordinates. As a proof of concept, the MoL is exploited to analyze 2-D cylindrical graphene microstrip and stripline transmission lines. The proposed method is validated by comparing the results with COMSOL simulations exhibiting a good agreement. Tuning the chemical potential of the graphene plate has potential applications in tunable microwave attenuators and phase shifters.

Low-Temperature Superconductor rf-SQUIDs-Based Fully Integrated Reflective-Type Analog Phase Shifter for Quantum Applications

This article presents a low-temperature superconductor (LTS)-based microwave phase shifter. The device utilizes a superconducting hybrid coupler monolithically integrated with two tunable reflective loads. An array of radio frequency superconducting quantum interference devices (rf-SQUIDs) is used to achieve inductive tuning in reflective loads, resulting in a broadband true time delay phase shift. The rf-SQUIDs are current controlled using an on-chip dc bias circuitry. The proof-of-concept fabricated device provides excellent RF performance in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${X}$ </tex-math></inline-formula> - and Ku -band with a phase shift of 49° at 10 GHz and 67° at 15 GHz. The insertion loss is < 1.5 dB for the entire range from 8 to 18 GHz. The methods to further improve the obtained phase shift are discussed. The overall device has a chip footprint of 0.6 mm2 and is fabricated using MIT-Lincoln Lab (MIT-LL) SFQ5ee eight-layer Niobium (Nb)-based superconducting fabrication process.

Characteristic Making of Ba0.4Sr0.6TiO3 Thin Film Nanoparticles

Presently, the research on thin films is essentially useful in the world of science and technology. Therefore, this study aims to explore Barium Strontium Titanate (BST) as the basis in the making of dynamic random access memory (DRAM). This DRAM technology produces small cells that have faster operations, lower energy, longer data storage period, and are found to havemade up of Barium Strontium Titanate nanoparticles (Ba0.4Sr0.6TiO3; BST). BST applications in the form of capacitors can be used as gas sensors, temperature sensors, microwave phase shifters, tunable filters, oscillators, infrared sensors, etc.The main component of BST was showed by the sol-gel method, and the device structure constituted of Si/SiO2/RuO2/TiO2 /Ba0.4Sr0.6TiO3/Al. All the samples were annealed at 400, 450, 500, 550, 600, 650 and 700 ℃ for 60 min. The sample was annealed to see the crystalline structure of the sample.The sol gel method was chosen in the process of making thin films of Ba0.4Sr0.6TiO3 (BST) because this method was easier and cheaper than other techniques. The thin film was characterized by optical and electrical properties. The results showed that a rise in the annealing temperature increased the crystalline, grain size, thickness and surface roughness of the sample. The characterization was carried out on the device structure (Si/SiO2/RuO2/TiO2/Ba0.4Sr0.6TiO3/Al) in order to examine the optical and electrical properties, including the current density and the dielectric features. At the annealing temperature of 700 ℃, the device showed the best value, with the absorption peak at the wavelength of 688 nm. And also, with the dielectric constant (εr) of 2,500, capacitance (C) of 22.10 nF, dense alternating current (ρau) of 2.54×104 Ω.m, conductance (σau) of 1.20×10-2 1/Ω.m, and current density of 9.85×10 -5 A.cm-2 at 0.5 V. The results of characterization of this capacitor are very good to be used as an infrared sensor.&#x0D; HIGHLIGHTS&#x0D; &#x0D; The explore Barium Strontium Titanate (BST) as the basis in the making of dynamic random access memory (DRAM)&#x0D; BST applications in the form of capacitors can be used as gas sensors, temperature sensors, microwave phase shifters, tunable filters, oscillators, infrared sensors, etc.&#x0D; The results showed that a rise in the annealing temperature increased the crystalline, grain size, thickness and surface roughness of the sample&#x0D; &#x0D; GRAPHICAL ABSTRACT

Real-Time Measurement of Moisture Content of Paddy Rice Based on Microstrip Microwave Sensor Assisted by Machine Learning Strategies

Moisture content is extremely imoprtant to the processes of storage, packaging, and transportation of grains. In this study, a portable moisture measuring device was developed based on microwave microstrip sensors. The device is composed of three parts: a microwave circuit module, a real-time measurement module, and software to display the results. This work proposes an improvement measure by optimizing the thickness of paddy rice samples (8–13 cm) and adding the ambient temperatures and the moisture contents (13.66–27.02% w.b.) at a 3.00 GHz frequency. A random forest, decision tree, k-nearest neighbor, and support vector machine were applied to predict the moisture content in the paddy rice. Microwave characteristics, phase shift, and temperature compensation were selected as the input variables to the prediction models, which have achieved high accuracy. Among those prediction models, the random forest model yielded the best performance with highest accuracy and stability (R2 = 0.99, RMSE = 0.28, MAE = 0.26). The device showed a relatively stable performance (the maximum average absolute error was 0.55%, the minimum absolute error was 0.17%, the mean standard deviation was 0.18%, the maximum standard deviation was 0.41%, and the minimum standard deviation was 0.08%) within the moisture content range of 13–30%. The instrument has the advantages of real-time, simple structure, convenient operation, low cost, and portability. This work is expected to provide an important reference for the real-time in situ measurement of agricultural products, and to be of great significance for the development of intelligent agricultural equipment.

Guest Editorial Low-Cost Wide-Angle Beam-Scanning Antennas

One of the key antenna requirements in many modern wireless systems for communications and sensing is wide-angle beam-scanning <xref ref-type="bibr" rid="ref1" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[1]</xref> . The traditional method to achieve wide-angle beam-scanning is to employ mechanically controlled reflectors or lenses, which are bulky, heavy, and suffer from slow beam scanning speed. Other important limitations of mechanical scanning antennas include the lack of multi-beam scanning capability and the ability to conform with non-planar structures (conformal geometries), which are essential in a number of emerging systems requiring very low-profile antennas. An alternative technique is to employ electronically beam-scanning antennas using passive or active phased arrays <xref ref-type="bibr" rid="ref1" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[1]</xref> . Main disadvantages of phased arrays are high complexity, high power consumption, and high cost due to a large number of radio frequency (RF) or microwave phase shifters and T/R modules required. The problems worsen for phased arrays at millimeter-wave, sub-THz, and THz frequencies, due to significant losses in phase shifters and feed networks at higher frequencies combined with lower efficiency of power amplifiers <xref ref-type="bibr" rid="ref2" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[2]</xref> . The digital beamforming approach is even more costly and energy hungry due to the employment of large number of RF modules and digital devices <xref ref-type="bibr" rid="ref1" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[1]</xref> , <xref ref-type="bibr" rid="ref3" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[3]</xref> , <xref ref-type="bibr" rid="ref4" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[4]</xref> .

General line-line method for propagation constant measurement of non-reciprocal networks

A general “line-line” (LL) method is proposed for propagation constant determination (γ+ and γ−) of nonreciprocal networks using multiple reference networks. The new formalism provides flexibility in implementation of LL methods so that not only more accurate γ+ (and γ−) could be retrieved but also the effect of inaccurate length information of the non-reciprocal network on γ+ (and γ−) evaluation could be suppressed. For validation of the method, γ+ and γ− of a microwave phase shifter (a nonreciprocal network) are determined using uncalibrated scattering parameter measurements at X-band (8.2–12.4 GHz). Two different statistical analyses based on normalized root-mean-square-error and goodness of fit and based on coefficient of variation and confidence interval are individually performed to evaluate the performance and accuracy of our method.

Ultra-Sensitive Magnetoelectric Sensors of Magnetic Fields for Biomedical Applications

Composite multiferroics are materials in which electric polarization of the material is possible under the action of an external magnetic field and vice versa, a change in the magnetization of the structure when an electric field is applied. Such properties have a high practical potential for application in science and technology. Based on these materials, it is possible to manufacture a number of devices with unique properties, such as, for example, random access magnetoelectric (ME) memory, ME sensors of magnetic fields, current, magnetic nanoparticles, micromechanical ME antennas, voltage-adjustable microwave filters, resonators and phase shifters. Therefore, the search for new materials of composite multiferroics and the study of the ME effect in them is a priority and urgent task in the search and creation of new electronic devices. One of the most promising and close to practical implementation directions is the creation of highly sensitive sensors of ultra-weak magnetic fields on the basis of composite multiferroics. The absence of the need to cool such sensors is a significant technical advantage over superconducting quantum interferometers currently used for these purposes. To date, the best achieved limits for detecting magnetic fields using sensors based on composite magnetoelectrics are values of the order of pT/Hz1/2, and new works are regularly published that reduce this threshold by improving processing electronics and changing the sensor design. This threshold of sensitivity is already sufficient for reliable detection of magnetic fields induced by alpha-rhythm currents of the brain with amplitudes of units of pT (magnetoencephalography) and for detecting the magnetic activity of the human heart. The review article is devoted to composite magnetoelectric structures with a focus on sensor structures capable of detecting ultra-weak magnetic fields. The comparison of the limiting sensitivity to the magnetic field of the existing ME composite structures is carried out, the ways of increasing the sensitivity to the magnetic field are shown.

Reconfigurable second-order optical all-pass filter

Abstract The optical all-pass filter (APF), which exhibits a constant amplitude response and a variable phase response, is a key to manipulating the optical phase without inducing signal amplitude distortion. High-order APFs are significantly demanded because they can afford large time delays and phase shifts. However, to date, only first-order APFs based on lossy waveguides have been reported. Although high-order APFs can be simply obtained by cascading multiple first-order APFs, the complexity and size are increased. To solve this problem, we propose and demonstrate a second-order APF using Mach–Zehnder interferometer-assisted microring resonators. The device is fabricated based on a silicon-on-insulator platform. Based on the second-order APF, an adjustable time delay between 553 and 948 ps is obtained, and the corresponding amplitude variation is less than 1.7 dB. Meanwhile, a microwave photonic phase shifter is also obtained based on the APF. The microwave phase shift can be adjusted from 0 to 3.27π, with an RF power variation within 2.4 dB. Additionally, the second-order APF can be reconfigured to a first-order APF, which significantly enhances its flexibility. The reconfigured first-order APF can realize an adjustable time delay between 257 and 429 ps, and the amplitude variation is less than 0.9 dB. The proposed high-order APF provides a novel approach to manipulating optical signals.

Determination of Propagation Constants and Wave Impedance of Non-Reciprocal Networks From Position-Insensitive Waveguide Measurements

A microwave method is proposed to determine the forward and backward propagation constants (<inline-formula> <tex-math notation="LaTeX">$\gamma ^{+}$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">$\gamma ^{-}$ </tex-math></inline-formula>) and the wave impedance (<inline-formula> <tex-math notation="LaTeX">$z_{w}$ </tex-math></inline-formula>) of reciprocal and non-reciprocal microwave networks whose positions are not known within their measurement cells (position-insensitive). The proposed method relies purely on analytical expressions and can also evaluate the reference plane transformation distances. Scattering parameter measurements at the <inline-formula> <tex-math notation="LaTeX">$X$ </tex-math></inline-formula>-band (8.2&#x2013;12.4 GHz) of a reciprocal network (a waveguide straight) and a non-reciprocal network (a microwave phase shifter) arbitrarily positioned into their measurement cells were conducted to retrieve <inline-formula> <tex-math notation="LaTeX">$\gamma ^{+}$ </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">$\gamma ^{-}$ </tex-math></inline-formula>, and <inline-formula> <tex-math notation="LaTeX">$z_{w}$ </tex-math></inline-formula> for validation of our method and testing its position-insensitive property. The importance of the method becomes apparent when compared to conventional methods whose accuracy is based on precise determination of the reference planes.

Determination of error-corrected full scattering parameters of a two-port device from uncalibrated measurements

A methodology relying on relating terms of a two-port error network to the scattering (S-) parameters of a two-port network or device is applied to extract its full S-parameters. The new methodology has only one sign ambiguity problem (two solutions) in evaluation of S11 (and thus S22) while the similar methodology in the literature has two sign ambiguity problems (4 solutions). This ambiguity problem of our method is shown to be eliminated by applying an approach based on continuity of the argument of S11 in the frequency domain. On the other hand, our methodology, as compared with the thru-reflect-line calibration technique, does not necessitate usage of any reflection standard in determining full S-parameters of a two-port network or device. Finally, it gives information about error networks. For its validation, S-parameters of a microwave phase shifter and a polyethylene sample flushed with the left/bottom terminal of the coaxial cell were extracted.

Silicon Photonic-Based Integrated Microwave Photonic Reconfigurable Mixer, Phase Shifter, and Frequency Doubler

An integrated microwave photonic (IMWP) reconfigurable mixer, phase shifter, and frequency doubler based on the silicon photonics platform is proposed and theoretically investigated in this paper. The proposed structure consists of a novel dual-drive Mach–Zehnder modulator (DDMZM) placed in parallel with an electro-optic phase modulator (PM). The novel DDMZM is a bias-free modulator that has advantages over conventional MZMs, such as bias-free operation and tunable optical-to-carrier sideband ratio (OCSR). The proposed novel structure can be configured as an IMWP phase tunable mixer or IMWP double-balanced mixer by properly adjusting optical wavelength and choosing the proper radio frequency (RF) hybrid coupler. Besides, the proposed IMWP reconfigurable mixer has the ability to perform up-converting, down-converting, RF frequency doubling, and phase shifting. The proposed structure is theoretically analyzed and is verified by simulations.

Independent Amplitude and Phase Control of Two Orthogonal Linearly Polarised Light and Its Applications

A technique to provide independent control on the amplitude and phase of two orthogonal linearly polarised light is presented. It is based on operating a commercial dual-polarisation dual-drive Mach Zehnder modulator (DPol-DDMZM) in reverse direction that routes the input light in slow and fast axis into two different DDMZMs. The technique has the advantage of controlling the phase of the slow-axis light and the amplitude of the fast-axis light has no effect on the light travelling in the orthogonal polarisation state. It has applications in linearised microwave photonic links, frequency multipliers and microwave phase shifters. A new microwave photonic Hilbert transformer based on using the reverse operating DPol-DDMZM to alter the phase of an RF modulation sideband without affecting the orthogonally polarised optical carrier is developed. Experimental results demonstrate 24.3 dB attenuation in the fast-axis light with no change in the slow-axis light, and 0°–360° RF phase shift for only 3.3 V change in DC voltage. The new Hilbert transformer with less than 2.5° phase imbalance and 0.4 dB amplitude ripples over 4–18 GHz frequency range is also demonstrated.