Ku-band Frequency Research Articles

Poly(vinylidene fluoride)-Based Flexible and Lightweight Materials for Attenuating Microwave Radiations

Two unique materials were developed, like graphene oxide (GO) sheets covalently grafted on to barium titanate (BT) nanoparticles and cobalt nanowires (Co-NWs), to attenuate the electromagnetic (EM) radiations in poly(vinylidene fluoride) (PVDF)-based composites. The rationale behind using either a ferroelectric or a ferromagnetic material in combination with intrinsically conducting nanoparticles (multiwall carbon nanotubes, CNTs), is to induce both electrical and magnetic dipoles in the system. Two key properties, namely, enhanced dielectric constant and magnetic permeability, were determined. PVDF/BT-GO composites exhibited higher dielectric constant compared to PVDF/BT and PVDF/GO composites. Co-NWs, which were synthesized by electrodeposition, exhibited saturation magnetization (Ms) of 40 emu/g and coercivity (Hc) of 300 G. Three phase hybrid composites were prepared by mixing CNTs with either BT-GO or Co-NWs in PVDF by solution blending. These nanoparticles showed high electrical conductivity and significant attenuation of EM radiations both in the X-band and in the Ku-band frequency. In addition, BT-GO/CNT and Co-NWs/CNT particles also enhanced the thermal conductivity of PVDF by ca. 8.7- and 9.3-fold in striking contrast to neat PVDF. This study open new avenues to design flexible and lightweight electromagnetic interference shielding materials by careful selection of functional nanoparticles.

Wideband, High-Efficiency Quasi-Planar Antenna Array For Ku-Band DBS Reception Systems

We propose a compact, high-efficiency antenna configuration, which is 18 cm in diameter and has average gain of 24.1 dBi for automotive applications of satellite TV systems operating at Ku band. To achieve high aperture efficiency, hybrid microstrip, and waveguide feed network with low-loss microstrip-to-waveguide transition is designed and validated. The array antenna is wideband and covers entire downlink Ku-band frequencies (10.8–12.75 GHz) for simultaneous reception from multiple transponders. Vertical polarization panel is built and tested for reception quality. Carrier-to-noise ratio of 6.2 dB was observed the target transponder (42°E) at 11.9 GHz using intermediate frequency loop-out of the receiver. The antenna can be used on small vehicles or automobiles for satellite TV reception.

Electromagnetic shielding materials and coatings derived from gelation of multiwall carbon nanotubes in an LCST mixture

Thermally induced demixing in an LCST mixture, polystyrene (PS)/poly[vinyl methyl ether] (PVME), was used as a template to design materials with high electrical conductivity. This was facilitated by gelation of multiwall carbon nanotubes (MWNTs) in a given phase of the blends. The MWNTs were mixed in the miscible blends and the thermodynamic driven demixing further resulted in selective localization in the PVME phase of the blends. This was further confirmed by atomic force microscopy (AFM). The time dependent gelation of MWNTs at shallow quench depth, evaluated using isochronal temperature sweep by rheology, was studied by monitoring the melt electrical conductivity of the samples in situ by an LCR meter coupled to a rheometer. By varying the composition in the mixture, several intricate shapes like gaskets and also coatings capable of attenuating the EM radiation in the microwave frequency can be derived. For instance, the PVME rich mixtures can be molded in the form of a gasket, O-ring and other intricate shapes while the PS rich mixtures can be coated onto an insulating polymer to enhance the shielding effectiveness (SE) for EM radiation. The SE of the various materials was analyzed using a vector network analyzer in both the X-band (8.2 to 12 GHz) and the Ku-band (12 to 18 GHz) frequency. The improved SE upon gelation of MWNTs in the demixed blends is well evident by comparing the SE before and after demixing. A reflection loss of −35 dB was observed in the blends with 2 wt% MWNTs. Further, by coating a layer of ca. 0.15 mm of PS/PVME/MWNT, a SE of −15 dB at 18 GHz could be obtained.

Performance Evaluation of Rain Attenuation Models in a Tropical Station

The non-uniformity of rainfall in both the horizontal and vertical directions makes the estimation of slant path attenuation complex. At frequencies above 10 GHz, the effects of attenuation and noise induced by rain are quite significant. One year satellite attenuation data were sourced from Malaysia East Asia Satellite at Ku frequency band; using ASTRO beacon signals to monitor and measure the slant path rain rate and attenuation at Universiti Teknologi Malaysia, Skudai. Four years’ one minute rain rate ground data at 0.01% of time exceeded were collected using rain gauge. The attenuation exceeded for other percentages of the time was obtained using statistical methods. Different rain attenuation prediction models were investigated and their performances compared. The validation results clearly suggested that the Breakpoint attenuation prediction model produced better results when compared with other models of interest. DOI: http://dx.doi.org/10.11591/ijece.v4i5.6583

Measurement of a Weak Satellite Beacon Level at 27.5 GHz with a Dual Circular Antenna Array [Measurements Corner

The rapid increase of available Ka-band and Ku-band transponders in orbit proves that these frequency bands will be in common use in the near future. However, compared to the Ku band and lower frequencies, Ka-band transmission is much more sensitive to atmospheric moisture. To determine its impact, we have measured the beacon (27.5 GHz) signal of the communication satellite KA-SAT with high precision on the ground. In this paper, we describe and discuss the concept and the results of our measurements.

Design of a Low-Profile, High-Gain Fabry-Perot Cavity Antenna for Ku-Band Applications

A Fabry-Perot resonator cavity antenna for Ku-band application is presented in this paper. The Fabry-Perot cavity is formed by a ground plane and a frequency selective surface (FSS) made of a circular hole array. The cavity resonance is excited by a single-feed microstrip patch located inside the cavity. The measured results show that the proposed antenna has an impedance bandwidth of approximately 13% (<TEX>$VSWR{\leq}2$</TEX>) and a 3-dB gain bandwidth of approximately 7%. The antenna produces a maximum gain of 18.5 dBi and good radiation patterns over the entire 3-dB gain bandwidth. The antenna's very thin profile, high directivity, and single excitation feed make it promising for use in wireless and satellite communication applications in a Ku-band frequency.

The Influence of CNT Contents on the Electrical and Electromagnetic Properties of CNT/Vinylester

Characterizing electrical and electromagnetic properties of carbon nanotube (CNT)-based nanocomposites is conducted as an important issue in their development process for the space applications. The properties of CNT/Vinylester are experimentally investigated including alternative current and direct current electrical conductivities, permittivity, transmission and reflection coefficients, loss tangent, and skin depth in the Ku frequency band (12.4–18 GHz). The investigated nanocomposites were fabricated using an in␣situ polymerization method. A vector network analyzer is employed for measuring electrical properties. The wt.% of incorporated CNT are chosen between 0.1% and 3% evaluating the influence of CNT contents on the investigated properties. Finally, the equivalent circuit model is used to describe the observed behavior on the basis of a semi-empirical approach.

Electromagnetic interference shielding properties of butyl rubber-single walled carbon nanotube composites

Abstract Butyl rubber (BR)-single walled carbon nanotube (SWCNT) (BR-SWCNT) composites were prepared by solution mixing process to evaluate its electromagnetic interference (EMI) shielding efficiency in the X and Ku band (8.2–18 GHz) frequency range for flexible electrostatic discharge shielding applications. Shielding properties of BR improved with SWCNT addition and EMI shielding effectiveness of about 9–13 dB was obtained for the composite with 8 phr of SWCNT loading in the measured frequency range. The experimental results reveal that absorption was the dominating shielding mechanism. The dielectric properties, conductivity and skin depth of BR-SWCNT composite were found to increase with SWCNT loading and were observed to be significant factors influencing EMI shielding properties of the developed composite.

Microwave dielectric properties of lanthanum based complex perovskites

The present investigation discusses the synthesis and dielectric properties of three series of oxides of the formula La2BaTi2M1−xCuxO9 (where M=Mg, Zn and Cd). The reactions have been carried out via solid state method and all the compositions crystallize in the disordered cubic perovskite structure. Suitable substitution at both A and B sites lead to enhancement in the dielectric properties at high frequencies. The relative permittivity and loss tangent have been measured at X-band (8.2–12.4GHz) and Ku-band (12.4–18GHz) frequencies. The oxides show a dielectric constant of 20–30 while the dielectric loss is quite low in the order of 10−3–10−4 (at 500kHz) and 10−2 at X and Ku-band. There is scope for further investigations in these systems to realize useful materials for microwave applications.

Development and performance analysis of satellite communication system for real-time river monitoring

K-water uses its Koreasat No. 5-based communications network for remote acquisition and provision of hydrological information on rainfall, water levels, water quality, and warnings via its hydrological observation network. The satellite is greatly affected by the rainfall attenuation during heavy rainfall seasons and typhoons since it is using the Ku-band frequency. K-water used the site diversity (SD) technology and developed a duplexing system that involved the setup of its main hub station at its headquarters and its auxiliary hub station at Gunnam Dam located at 200 km away, to smoothly use its data during rainfall attenuation and satellite malfunctions. In this paper, we proposed an online monitoring SD system in the communications satellite equipment and manual/automatic switching algorithms. We examined the SD effects in the projected site to improve the stability and reliability of K-water’s hydrological communications satellite. Data reliability was found to be improved to 96.7% through the comparative study of the existing and SD systems, in which present data observation failure occurred in all 418 terminal stations, but proposed method occurred only in 14 terminals.

Effect of Nd Substitution on Magnetic and Microwave Absorption Properties of Nanocrystalline Sr(MnSn)0.5Fe11O19

The preparation of Sr1-xNdx(MnSn)0.5Fe11O19 M-type hexaferrites powders by a citrate sol-gel method was investigated. The samples were determined by X-ray diffraction (XRD) and transmission electron microscope (TEM). Microwave absorption properties of hexaferrite- acrylic resin composites were measured using SWR (standing-wave-ratio) method in the range of 12 to 20 GHz. It was shown that small amounts of Nd+3 substitution could significantly modify the microwave electromagnetic parameters. Furthermore, the investigation indicated that substitution of Nd+3 ions for Sr+2 ions in Sr(MnSn)0.5Fe11O19 resonant frequency would move toward higher frequency. The results showed that the powder possesses excellent microwave absorption properties. A minimum reflection loss of –43 dB was observed for the composite, where x = 0.03. A broad bandwidth of microwave absorption (with a –10 dB reflection loss as a reference) is predicted in the composite samples containing the ferrite powders of x=0.02, and x=0.03 in Ku-band frequencies. Keywords: Chemical synthesis, magnetic materials, magnetic properties, nano crystalline materials.

Low Profile Wideband Antenna Array With Hybrid Microstrip and Waveguide Feed Network for Ku Band Satellite Reception Systems

Wideband, planar and low profile antenna array is proposed and designed for Ku band direct broadcast from satellite reception for mobile systems. Contrary to earlier designs, the array antenna covers entire downlink Ku-band frequencies (10.8-12.75 GHz) for simultaneous reception from multiple transponders. The array antenna exhibits 16.5% bandwidth and has 30 dBi average gain for both vertical and horizontal polarizations. To achieve high efficiency, hybrid waveguide microstrip feed network is proposed. H-plane waveguide T-junctions with reduced waveguide height and disk loaded coaxial probe for microstrip to waveguide transition are designed. Loss in the array is formulated as an optimization problem and it is minimized for subarray and array configuration. Overall height of the planar antenna with waveguide feed network is under 25 mm. The antenna is built and tested for reception quality. Carrier-to-noise ratio of 9.5 dB was observed for the target transponder (42 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> E) at 11.9 GHz using IF loop-out of the receiver.

Microwave absorption in X and Ku band frequency of cotton fabric coated with Ni–Zn ferrite and carbon formulation in polyurethane matrix

The present study highlights various microwave properties, i.e. reflection, transmission, absorption and reflection loss, of the coated cotton fabric [formulation: Ni–Zn ferrite (Ni 0.5Zn0.5Fe2O4) and carbon black (acetylene black) at concentrations of 30, 40, 50, 60 and70g of ferrite and 5g carbon in each 100ml polyurethane] evaluated at 8–18GHz frequency. The uniform density of filling materials in coated fabrics (dotted marks in SEM micrograph) indicates homogeneous dispersion of conducting fillers in polyurethane and the density of filling material cluster increases with increase in ferrite concentration. SEM images also show uniform coating of conducting fillers/resin system over individual fibers and interweave spaces. The important parameters governing the microwave properties of coated fabrics i.e. permittivity and permeability, S-parameters, reflection loss, etc. were studied in a HVS free space microwave measurement system. The lossy character of coated fabric is found to increase with increase of ferrite content; the ferrite content decreases the impedance and increases the permittivity and permeability values. The 1.6–1.8mm thick coated fabric sample (40wt% ferrite, 3wt% carbon and 57wt% PU) has shown about 40% absorption, 20% transmission and 40% reflectance in X (8.2–12.4GHz) and Ku (12–18GHz) frequency bands. The reflection loss at 13.5GHz has shown the highest peak value (22.5dB) due to coated sample optical thickness equal to λ/4 and more than 7.5dB in entire Ku band. Owing to its thin and flexible nature, the coated fabric can be used as apparel in protecting human being from hazardous microwaves and also as radar camouflage covering screen in defense.

Implementation of ARIMA model to predict Rain Attenuation for KU-band 12 Ghz Frequency

Satellite communication systems operating at Ka band and Ku band frequencies must affect the problem of propagation impairments which includes fading due to rain, clouds, snow for obtaining the required performance. Rain affects the signal most and involved is absorption & scattering. Auto-Regressive Integrated Moving Average (ARIMA) model is used to generate and predict the time series values for rain attenuation. The predicted values obtained for different window size of the ARIMA model and analysis is done in terms of error matrix

A broadband transmission absorption polarization-independent metamaterial absorber

In this paper, we propose a new metamaterial absorber based on magnetic absorbing material. This absorber has the characteristics of low-frequency transmission and high-frequency broadband absorption. The transmission coefficient of the metamaterial absorber is-0.5 dB at 1 GHz: the good low-frequency transmission property can realize intercommunication between the low-frequency signals. The absorptivity is greater than 80% in the frequency range above 8.4 GHz, which almost covers all the X-band and Ku-band frequencies. In addition, the metamaterial absorber is polarization-independent due to the fourfold rotational symmetry of the unit cell metallic periodic structure. The metamateiral absorber has the advantages of simple design, strong practicability, and high potential application value.

Assessing the critical concentration of NH2 terminal groups on the surface of MWNTs towards chain scission of PC in PC/SAN blends: effect on dispersion, electrical conductivity and EMI shielding

The localization and dispersion quality of as received NH2 terminated multiwall carbon nanotubes (MWNT-I) and ethylene diamine (EDA) functionalized MWNTs in melt mixed blends of polycarbonate (PC) and poly(styrene-co-acrylonitrile) (SAN) were assessed in this study using rheo-electrical and electromagnetic interference (EMI) shielding measurements. In order to improve the dispersion quality and also to selectively localize MWNTs in the PC phase of the blends, EDA was grafted onto MWNTs by two different strategies like diazonium reaction of the para-substituted benzene ring of MWNTs with EDA (referred to as MWNT-II) and acylation of carboxyl functionalized MWNTs with thionyl chloride (referred to as MWNT-III). By this approach we could systematically vary the concentration of NH2 functional groups on the surface of MWNTs at a fixed concentration (1 wt%) in PC/SAN blends. XPS was carried to evaluate the % concentration of N in different MWNTs and was observed to be highest for MWNT-III manifesting in a large surface coverage of EDA on the surface of MWNTs. Viscoelastic properties and melt electrical conductivities were measured to assess the dispersion quality of MWNTs using a rheo-electrical set-up both in the quiescent as well as under steady shear conditions. Rheological properties revealed chain scission of PC in the presence of MWNT-III which is due to specific interactions between EDA and PC leading to smaller PC grafts on the surface of MWNTs. The observed viscoelastic properties in the blends were further correlated with the phase morphologies under quiescent and annealed conditions. Electromagnetic interference (EMI) shielding effectiveness in X and Ku-band frequencies were measured to explore these composites for EMI shielding applications. Interestingly, MWNT-II showed the highest electrical conductivity and EMI shielding in the blends.

Tailored polyaniline/barium strontium titanate/expanded graphite multiphase composite for efficient radar absorption

The present paper reports the synthesis of a high-performance microwave absorbing material using a simple, cost-effective and scalable method by encapsulating barium strontium titanate (BST) and expanded graphite (EG) in a polyaniline (PANI) matrix. One of the formulations (higher content of BST) shows shielding effectiveness due to absorption of more than 50 dB (>99.9999% attenuation) with minimum reflection loss (≤1 dB) in the Ku-band (12.4–18 GHz) frequency range. Another formulation (higher content of EG) shows a total shielding effectiveness of more than 81 dB with a reflection loss of 10 dB. In order to probe the relationship between the observed shielding response and the electromagnetic attributes, dielectric and permeability parameters have been calculated from the measured scattering parameters (S11, S22, S12, S21) using the Nicolson–Ross–Weir algorithm. The synthesised formulations were characterized thoroughly using XRD, FTIR, TGA, UV, Raman spectroscopy, SEM and HRTEM.

E-Shaped Linear Array Antenna for Ku Band on Alumina Substrate

An E-Shaped Linear Array Antenna design for Ku band is presented here on Alumina Substrate. The substrate made with Aluminum Oxide (Al2O3) has high dielectric constant (9.8) and is 1.5mm thick. The patch's dimension is 3.5mm x 5.0mm for miniaturized antenna and the slots of unequal width 2.8mmx1.5m and 3mmx2mm are introduced here for gain maximization. The finite element method is used to design and analyse the presented antenna array. The impedance bandwidth for this array antenna comes out to be approximately 2.8GHz (46.67% of entire Ku band). This proposed antenna is able to give a gain of 4.48 dB for the Ku band frequency range and almost a stable radiation pattern throughout the 12~18GHz frequency range. The projected antenna array is designed and simulated by using Ansoft's 3D full-wave electromagnetic field software HFSS.

Preliminary Analysis of Dust Effects on Microwave Propagation Measured in Sudan

Dust storms are meteorological phenomena which occur for a percentage of time in arid and semi arid areas especially at African Sahara and Middle East. Measurements at existing microwave links have showed dust storms can potentially result in serious attenuation in signal level especially at Ku band and higher frequencies with direct impact on telecommunications system performance. Only a limited amount of research has been carried out and the available data was very scarce. Few prediction models have been developed to estimate microwave signal attenuation during the dust storm based on scattering theory and approximation of dust properties. However, real dust storm is a complex phenomenon which is difficult to be described by theoretical physical or mathematical models [5–6]. In this paper, an evaluation of the existing attenuation prediction models has been done based on the measured dust storm properties and measured attenuation in Sudan.

Microwave properties of Al and Mn doped nickel ferrites at Ku band frequencies

To investigate the influence of aluminum and manganese doping on structural, electrical, magnetic and microwave behavior of nickel ferrites, the samples were prepared by citrate sol–gel method. Samples were characterized by X-ray diffractometer using Rietveld refinement technique and are found to have cubic structure with space group Fd3¯m. A systematic investigation of magnetization, permeability, permittivity and microwave properties such as isolation, insertion loss and return loss was undertaken at Ku band (12–18GHz) frequencies. A qualitative explanation for the various observed phenomena was given.