Microwave Frequency Band Research Articles

L / C / X Triple band compact dipole array antenna for RADAR application

This article describes about L / C / X triple band compact dipole array antenna for RADAR communication using FR-4 Substrate. The proposed antenna is designed over a range of 1.0–10.0 GHz. The objective of the paper is to achieve appreciable basic antenna parameters for ease adaptation in Monolithic Microwave Integrated Circuits (MMIC) Technology. It is able to preserve its high recital over RADAR Communication system operating at Triple band (L, C, X – band) microwave frequency range. The proposed structure resonates at L / C / X Microwave bands and thus the antenna becomes inevitability for numerous wireless applications. The antenna is fictitious on a substrate with height of 1.6 mm, length 48mm, width 60mm and a relative permittivity of 4.2. The proposed antenna yields a VSWR of about 1.74 (1.70 GHz), 1.66 (6.70 GHz), 1.26 (8.30 GHz) and gain of 2.56 dBi (1.70 GHZ), 1.78 dBi (6.70 GHz) and 3.94 dBi (8.30 GHz) under simulation. The antenna is designed and simulated using HFSS, which helps to obtain the antenna parameters such as VSWR, gain and Return loss.

Stretching, Amplification, and Compression of Microwave Pulses Using Helically Corrugated Waveguides

We demonstrate the possible implementation of the chirped pulse amplification (CPA) method, which is widely used in optics, for the microwave frequency band. This method is based on the preliminary elongation of the incident pulse in the stretcher, sequential amplification of spectral components in a wideband amplifier, and final compression in a line with negative dispersion (compressor). A circuit is considered in which multifold, helically corrugated waveguides are used as an operating space in each section, including a stretcher, an amplifier, and a compressor. The dispersion characteristics of such waveguides can vary significantly when its geometrical parameters are changed, which makes it possible to ensure optimal dispersion characteristics in the stretcher and compressor, as well as the largest gain bandwidth in the amplifier. In addition, these dispersive elements allow us to avoid spurious reflection of the signal due to the absence of a stopband in the operating frequency range. Simulations within the framework of the coupledwave approach showed the prospects of the circuit proposed. In particular, using an experimentally realized 30-GHz gyro-TWT, the peak power of a 200-ns, 300-W incident pulse can be increased up to 4 MW, which is about six times higher than the power of the driving electron beam. With direct amplification (in the absence of a stretcher and a compressor) of the specified incident pulse in the same gyro-TWT, the output peak power does not exceed 250 kW.

Graphene-Based Microwave Antennas With Reconfigurable Pattern

This article presents a graphene-based, dynamically reconfigurable antenna with a voltage-controlled, far-field radiation pattern in the microwave frequency band. The proposed antenna consists of two radiating patches and a planar feed network mainly composed of a graphene-based attenuator and a power divider with a hybrid graphene–metal phase shifter. The output phase of the phase shifter changes by a bias voltage on the graphene. The antenna has two operating states with different beam directions when the bias voltage is between 0.7 and 5 V. The equivalent circuit model is employed to analyze the phase shift characteristic of the graphene–metal phase shifter. Then the prototype of the reconfigurable antenna is fabricated and tested. The experimental results are in good agreement with the simulated ones. This article demonstrates that in the microwave frequency band, by proper design, the graphene–metal structure can be used to realize the new type of the reconfigurable antenna, in which this kind of graphene-based tuning structure can be easily stacked with other circuits by a simple pasting technique than soldering. This feature has potential applications in flexible radio frequency system in future.

Impact of Compressive Stress on Microwave Dielectric Properties of Feldspar Specimen

As one of the most important electrical properties, the dielectric permittivity of minerals and rocks has been studied with respect to its influencing factors, such as texture, density, moisture, frequency, pressure, etc., and has aroused great interest in geophysics, mineralogy, petrology, and microwave remote sensing. However, the studies on the effect of stress on the dielectric property of rock are limited to lower frequencies, and the related mechanism is not yet clear. Considering the limitations of traditional testing methods and the complexities of compositions and structures of rock specimens, in this article, we choose the minerals of the feldspar group as specimens to investigate the impact of compressive stress on their dielectric property at a higher frequency range from 2 to 18.3 GHz. For this purpose, an open coaxial resonator probe is applied to measuring the alteration of the dielectric permittivity of the feldspar specimen in the process of increasing compressive stress using a specially designed loading device. The dielectric constants of the feldspar specimen at all of the five high-frequency points demonstrate obviously decreasing trends with increasing compressive stress. The particular discovery is that the ionic and electronic polarizations are much sensitive to the increasing compressive stress in the microwave frequency band, where the minerals behave like ionic crystals. This article implies that the variation of the microwave dielectric permittivity of rock mass under altering crustal stress due to tectonic plate movements and engineering disturbances is an important factor to be considered in applying radar investigation and microwave remote sensing for mineral exploration, geological exploration, and geo-hazard perception.

Measurement of DC and AC Response Curves of a Bipolar Transistor as a Function of Frequency

We discuss improving the reliability of measured DC and AC response curves for a bipolar transistor as a function of frequency using the mass-produced 2T937 transistor (Russia) as an example. We describe preparations for measurement and the actual measurements in considerable detail. We provide experimental response curves for the 2T937 transistor. A special test (measurement) board was developed to prevent the measured response curves from being affected in any way by the transistor mount or interface hardware (power buses, soldering leads, matching devices, adapters, etc.). A bare transistor chip was used to eliminate any effect of the transistor package on the results and improve the size and weight specifications of devices using the 2T937 transistor. The transistor chip can be directly mounted to a test board whose topology is used to connect the transistor chip to the device. The microstripline board is designed to enable measurements to be performed in the microwave frequency band using a probe station with standard calibration.

Frequency modulation, amplification and compression of microwave pulses in a system with helically corrugated waveguides as a dispersive elements

We consider the possible implementations of the Chirped Pulse Amplification (CPA) technique widely used in optics for the microwave frequency band. We propose using helically-corrugated waveguides for pulse stretching and compressing as their dispersion properties strongly depend on geometrical parameters. For stretched pulse amplification, a helical-waveguide gyro-TWT can be used as a broadband amplifier. Simulations with parameters of the experimentally realized 30 GHz gyro-TWT show that for a 300 W, 200 ps incident pulse, amplification up to 6 MW can be achieved in this system, while in the linear regime of the same gyro-TWT the output power is only about 250 kW.

Super compact ultrathin quad‐band with wide angle stability polarization independent metamaterial absorber

AbstractIn this article, a compact ultrathin polarization‐insensitive wide‐angle metamaterial‐based microwave absorber with quad‐band characteristics is presented. The designed microwave absorber provides simulated peak absorption of 99.16%, 98.21%, 98.32%, and 99.76% at 3.7 GHz, 6.4 GHz, 10.7 GHz, and 14.3 GHz, respectively. The absorption frequency lies in microwave frequency bands of S, C, X, and Ku. The unit cell of the proposed microwave absorber consists of two diagonally connected closed ring resonator (CRR) along with one metallic patch enclosed by the inner CRR. Each side of the enclosed patch is connected with inner CRR at the center of length. The unit cell of the proposed 0.0197λlowest (wavelength at lowest frequency) thick multiband absorber fits in a volume of 8 × 8 × 1.6 mm3. The proposed metamaterial‐based microwave absorber exhibits identical absorption characteristics for both transverse‐electric and transverse‐magnetic polarized radiations and also provides well peak absorption for an oblique incidence up to 75°. Finally, the absorber is fabricated and experimental result validates simulated one.

Metamaterial-based fuel sensor application with three rhombus slots

In this paper, a sensor structure operating in the microwave frequency band is used and it is aimed to determine whether fuel samples are branded or not. In the literature, the studies on the sensor applications of metamaterials (MTMs) have increased considerably in recent years. However, this study, unlike other studies, focuses on determining the changes in electromagnetic parameters of different fuel samples at X band frequencies. For this purpose, the electromagnetic properties of the branded and unbranded fuel samples are measured experimentally. Then, simulation studies are carried out using the experimental results and the dimensions of the resonators are optimized to determine the most suitable structure. Fabrication of MTM sensor structure is then performed using optimized dimensions. Finally, the experimental study is carried out using the sensor structure.

Bandwidth‐controllable band‐stop filter using spoof surface plasmon polaritons

This article presents a bandwidth-controllable band-stop filter based on spoof surface plasmon polaritons (SSPPs) transmission line in the microwave frequency band. The approach of introducing rectangular slots into the corrugation strips offers a greater degree of flexibility in the SSPPs unit cell design. Meanwhile, the high-order mode can be pulled to the low frequency segment of interest. The lower and upper edge of the stop band of this filter, therefore, can be controlled independently and conveniently. An equivalent circuit model of this unique unit cell is proposed for analyzing stop band formation and guiding the design of this SSSPs filter. Both numerical simulations and measured results demonstrate excellent stop band performance of the filter. The proposed filter may have potential applications in the SSPPs-based communication system.

RF Waveform Synthesizers With Quantum-Based Voltage Accuracy for Communications Metrology

We review our development of Josephson-junction-based programmable reference sources to synthesize spectrally pure waveforms with quantum-based voltage accuracy for characterizing and improving future communication devices and systems. The goal is to provide sources that together span the entire radio frequency band, equivalent to seven orders of magnitude in frequency (20 kHz to 300 GHz). To synthesize waveforms in the microwave frequency band, we are extending the existing Josephson arbitrary waveform synthesizer (JAWS) technology used for ac voltage metrology at audio frequencies (<;20 kHz). Using new microwave circuits and experimental techniques, we demonstrate JAWS-based synthesis of single-tone waveforms at 1 GHz, with -49 dBm output power and 79 dBc spur-free dynamic range (SFDR). To synthesize waveforms in the millimeter-wave frequency band, we are exploiting single flux quantum (SFQ) superconducting digital technology to design circuits that amplify SFQ pulses using a network of pulse splitters. With our initial SFQ-based circuit, we demonstrate synthesis of a 4-GHz sine wave with -74 dBm output power and 70 dBc SFDR.

Structure, Magnetic Properties and Electromagnetic Response of Y-Type Hexaferrites and Hexaferrite-Based Composite Materials

The paper presents a study of the phase composition, morphology, magnetic and electromagnetic properties both of Y-type hexaferrites Ba2Ni2–xCuxFe12O22 (x = 0.4, 1.0, 1.2) and composites produced therefrom. Hexaferrites are synthesized via standard ceramic method. Ferromagnetic resonance technique is applied to measure the magnetocrystalline anisotropy of synthesized hexaferrites. The spectra of permeability and permittivity and the frequency dependences of the reflection coefficients of composite materials are studied at the microwave frequency band. It is shown that these materials can be used in the production of radarabsorbing materials and coatings in the frequency range of 3.5–12.2 GHz.

Engineering morphology configurations of hierarchical flower-like MoSe2 spheres enable excellent low-frequency and selective microwave response properties

MoSe2 is a compelling narrow-band-gap semiconductor with particular lamellar crystal structure, but which is rarely used as microwave absorber filler. Owing to the analogue molecular structure with MoS2, it may be a potential dielectric dissipation candidate. The hierarchical flower-like structure has been wide accepted as attractive morphology due to its possible strong multiple scattering and reflecting abilities for microwave, thus, in this study, we employed a facile solvothermal process to fabricate the unique flower-like MoSe2 spheres for eliminating microwave interference issue. Further through the precise tuning of morphology configurations of flower-like MoSe2, the effective absorption to specific microwave frequency band can be well optimized, even including low-frequency band. The microwave absorption (MA) performance results show that the dense-flower samples could achieve full absorption in Ku-band and blooming-flower samples cover the entire X-band. The hollow-flower sample is good at absorption in low frequency of C-band and X-band. Our work not only develops outstanding microwave absorber candidates through delicate nanostructure design, but also paves a new way for tuning effective frequency band via tailoring morphology configurations.

Channel parameter acquisition in MIMO LOS systems for high capacity microwave links

Due to the increased traffic load, next generation wireless communication standards require to increase the capacity of current point-to-point (PtP) wireless backhaul links in the microwave frequency bands. Multiple-input, multiple-output (MIMO) systems are essential to multiply the link capacity, and such solutions have been already presented in the recent literature as a promising technology to increase the data rate, for line-of-sight (LOS) wireless PtP connections. In this paper, we focus on the initial acquisition scheme of a MIMO 2x2 architecture for microwave M-ary quadrature amplitude modulation (M-QAM) transceivers, based on two completely independent radio frequency (RF) chains which use different local oscillators (LOs). During the acquisition phase, a 4-QAM training preamble is considered with a joint algorithm for estimating both the MIMO gains for the interference cancellation and the timing error for initializing the clock recovery loop. A phase recovery closed loop scheme is jointly used during the acquisition phase, and the same algorithm may be used for phase error correction when the receiver switches to the tracking mode. Simulations prove the effectiveness of the proposed solutions, by considering both qualitative and quantitative results.

A superior microwave absorption material: Ni2+-Zr4+ Co-Doped barium ferrite ceramics with large reflection loss and broad bandwidth

Large reflection loss and wide bandwidth are significant targets, determining the microwave absorption ability. However, it is still a challenge to simultaneously satisfy the two conditions. As a multifunctional material, BaFe12O19 possess excellent electromagnetic properties in the microwave frequency band. Due to the natural resonance phenomenon of the material, BaFe12O19 can produce a large magnetic loss which correlates with Fe3+ content, and the microwave absorption characteristics of barium ferrite can be modulated by ion doping. As a typical magnetic metal, Ni coupled with high-valence state Zr4+ doping helps to produce double resonance peaks. In this work, Ni2+-Zr4+ co-doping M-type barium ferrites (BaFe12-2xNixZrxO19, BNZFO-x, x = 0–0.8) were prepared conveniently by solid-state reaction method. Several necessary measurements to characterize its microwave absorption property have been operated such as morphology, magnetic performance and electromagnetic parameters. The results show that reflection loss and bandwidth can be simply tuned by tailoring Ni2+-Zr4+ content. The reflection loss peak drifts from 18 GHz to 9.76 GHz, which involves a half of the studied frequency range. The maximum reflection loss achieves −60.6 dB and the corresponding bandwidth over −10 dB is 7.68 GHz for BNZFO-0.6 ceramic with only 2.1 mm thickness. Thus, the doping of Ni2+-Zr4+ ion pairs is beneficial to improve the absorbing properties of the material, and the superior microwave absorption property may originate from its inner double natural resonance in micro-scale. The excellent microwave absorption properties suggest that BNZFO-x is a promising candidate applied for designing electromagnetic shielding devices.

Compact quad-band polarization independent metamaterial absorber using circular/square metallic ring resonator

In the paper, a compact quad-band polarization-independent metamaterial absorber has been presented for different microwave frequency bands. The proposed absorber unit cell comprises of two square and two concentric circular rings and it exhibits the absorption peaks greater than 90% at 3.1 GHz, 5.5 GHz, 7.6 GHz and 10.98 GHz respectively under the normal incidence. The full width at half maximum (FWHM) bandwidth is 150 MHz (3.03–3.18 GHz), 180 MHz (5.38–5.56 GHz), 330 MHz (7.44–7.77 GHz), and 560 MHz (10.70–11.26 GHz) at the four frequency bands. The proposed absorber is polarization and incidence angle insensitive due its symmetrical. The proposed structure also shows more than 90% absorptivity up to 60° incidence angle. The absorber unit cell is compact in configuration with size of 0.12 λo × 0.12 λo and ultrathin thickness of 0.016 λo, where λo is the wavelength at lowest frequency absorption peak. To recognize the absorption phenomenon of the absorber, input impedance, E-field and surface current distribution characteristics have been demonstrated. The structure has been fabricated and it shows good agreement between simulated and measured results.

Electromagnetically induced transparency in an integrated metasurface based on bright–dark–bright mode coupling

Based on a bright–dark–bright coupling model, a classical analog of an integrated electromagnetically induced transparency (EIT) metasurface at a microwave frequency band is numerically and experimentally demonstrated. The proposed EIT metasurface structure consists of three perpendicularly connected metallic elements: two split-ring resonators (SRRs) which couple directly with normally incident wave supporting the bright modes, and the I-shaped configuration treated as the dark mode. Due to the dual coupling excitation of the middle I-shaped configuration, two anti-parallel electric dipoles were formed in the upper and lower SRRs, resulting in the destructive interference. In addition, the wide-angle incidence and the different polarization-angle incidence of the proposed metasurface were calculated and studied. The group index is extracted and calculated to verify the slow light property within the transparent window. The research in this work reveals that the scheme based on multi-mode coupling is of referable value for constructing EIT-like metamaterials or high transmission bandpass filters.

Design of the Gradual Patch Spiral Dipole Complementary Gap Composite Ultra Wideband Antenna

According to the performance requirements of the multi band compatible antennas for microwave frequency band multi network integration system, the present paper originally combines gradual patch spiral dipole antenna, complementary gap antenna, polyethylene terephthalate film, ceramics thin slice and ferrite coating, designed a gradual patch spiral dipole complementary gap composite ultra wideband antenna. The result of test indicates that this antenna has a better anti-jamming ability. When the antenna is placed near metal objects and various microwave signal sources, the radiation performance of the antenna is almost unaffected and the antenna can work normally. This antenna completely covered all working frequency bands of the second generation to the fifth generation mobile communication, the frequency bands of the radio frequency identification system, the frequency band of the ultra wideband system, and the frequency band of the mobile digital TV system. This antenna has high radiation intensity and large performance redundancy, so it has broad application prospects.

Broadband extremely close-spaced 5G MIMO antenna with mutual coupling reduction using metamaterial-inspired superstrate.

A metamaterial structure, which has positive and negative permeability over a wide microwave frequency band, has a proposed structure that can be employed as a superstrate for reducing the mutual coupling of a MIMO antenna system. This MIMO antenna system consists of two extremely close-spaced antenna elements. The proposed structure's decoupling mechanism is verified by both the full-wave electromagnetic simulations and experiments, and the simulated and measured results agree very well with each other. The two-element MIMO antenna system, when loaded with the metamaterial-inspired superstrate, shows a high isolation (S21<-15 dB) within a broad matching band of 22.3% from 4.2 to 5.25 GHz covering the 5G frequency band of 4.8-5 GHz with an extremely close edge-to-edge space of just 1 mm (corresponding to 0.017λ at 4.9 GHz). The MIMO antenna system's measured largest isolation with the metamaterial-inspired superstrate is 29 dB. This isolation is characterized by a maximum improvement of 23 dB, compared to the original case. Furthermore, after loading the superstrate, the measured gain is enhanced by more than 0.5 dB in the whole matching band as well, with a 3.2 dB maximum gain improvement.

Effect of magnetic iron(III) oxide particle addition with MWCNTs in kenaf fibre-reinforced epoxy composite shielding material in ‘E’, ‘F’, ‘I’ and ‘J’ band microwave frequencies

Mechanically toughened electromagnetic shielding composite material was prepared with MWCNTs and Iron(III) oxide nano particles. The principal aim of this research work is explicating the advantage of magnetic particle addition along with conductive MWCNTs in EMW shielding. The kenaf fibre, MWCNTs and Iron(III) oxide particles were surface-treated by APTMS for effective dispersion and adhesion on matrix medium. The EM wave shielding composites were prepared using hand layup method. The mechanical results shows addition of kenaf fibre increased the tensile, flexural and impact properties. Similarly additions of MWCNTs and iron(III) oxide particles increased the electrical permittivity and magnetic permeability of epoxy matrix. The hysteresis graphs showed improved magnetization and retentivity in epoxy composites. The maximum EM wave shielding effectiveness of 82.5% (14.5 dB) was observed for composite designation ‘E’ in J band microwave frequency. The SEM images showed improved adhesion of fibre and dispersion of particle in epoxy matrix.

Exploitation of RF-MEMS Switches for the Design of Broadband Modulated Scattering Technique Wireless Sensors

The use of RF microelectromechanical systems (RF-MEMS) switches for the design of broadband modulated scattering techniques (MSTs) wireless sensors has been investigated in this letter. In an MST sensor, the antenna is loaded with different resistive loads to produce a modulation in the backscattered field by means of an electronic switch. At microwave frequency bands, the RF switches are quite expensive, moreover, they are quite narrowband. The narrowband behavior of MST sensors is one of their major drawbacks. The adoption of RF-MEMS microwave switches could be a good opportunity to overcome this problem. In particular, MEMS switches are able to perform good up to 110 GHz with a reduced dimension and complexity. In this letter, an MST sensor prototype based on MEMS switches and able to work in the whole X -band from 8 to 12 GHz has been designed, fabricated, and experimentally assessed. The obtained results are quite good and they demonstrate the feasibility of such kind of sensors. In particular, the MEMS switches demonstrate that they could play a key role for the design of millimetric and submillimetric frequencies bands MST sensors, where the standard microwave switches technologies cannot operate.