Ku-band Frequency Research Articles

Experimental assessment of excess loss prediction models for satellite‐to‐Earth radio links shadowed by single in‐leaf trees

This study presents an experimental verification of the excess path loss for a satellite-to-Earth radio link shadowed by a single tree for elevation angles in the range from 20° to 40°. A measurement campaign was carried out in scale inside an anechoic chamber with five different species of trees at the X (8–12 GHz) and Ku (12–18 GHz) frequency bands to obtain the signal level variation as a function of the distance. It was discriminated the effect of the ground receiver terminal location with respect to the tree that affects the elevation angle value perceived by the receiver and the shadowing introduced by the tree. Results were discussed comparing with excess loss predicted by different vegetation scattering models aiming to characterise the goodness of their performance in terms of the excess signal loss predicted for short thickness of vegetation. In general, the models show a good agreement with measurements far away from the tree, however failing to describe the signal level variation if the terminal is near the tree. Nevertheless, it was determined that the models can be used to establish and upper and a lower limit to the excess signal loss.

Outstanding electromagnetic interference shielding effectiveness of polyvinylbutyral–polyaniline nanocomposite film

In this study, we studied the electromagnetic interference (EMI) shielding property of a solution processed polyvinylbutyral–polyaniline nanocomposite (PVBPN) film in the X-band (8.2–12.4 GHz) and Ku-band (12.4–18 GHz) frequency.

Ku대역 전파고도계 체계점검장비 개발

For performance improving of C-band radar altimeter used in a missile system, Ku-band radar altimeter is developed. To utilize the time delay devices which are used in testing C-band radar altimeter, we proposed C-band and Ku-band frequency conversion method and implemented it as a part of missile system test equipment. In this paper we present design contents, development results and test application results of radar altimeter test equipments.

Conductive, dielectric and amalgamated obstacles coupled waveguide based highly selective multiband bandpass resonators

This paper demonstrates transverse nonplanar resonators consisting of symmetrically placed obstacles (posts which made up of same or different type of materials) coupled into rectangular waveguide. Introducing posts inside a waveguide in proposed structure creates discontinuity and become a cavity resonator. Resonance is created at X band, Ku band and Ka band frequencies are reported. Simulation results demonstrates that resonators's results are matched to free-space as well as having a superior insertion loss and better return loss of conductive posts compare to dielectric posts. Moreover, obstructing the E-field (using conductive posts) compare to the H-field (using dielectric posts) are given better insertion loss and impedance match- ing characteristics. However, insertion of amalgamated obstacles into rectangular waveguide generates good transmission and reflection zeros compared to other two topologies at resonant frequencies which are described here. Posts coupled waveguide resonators having high power handling capacity so it can be utilized for Base transceiver station, Satellite Communication, Space applications, sensors as well as the fusion plasma diagnostics system. All the proposed structures are simulated with Ansoft's finite-element High Frequency Structure Simulator (HFSS) tool to demonstrate the characteristics of the resonators using a rectangular waveguide with center frequency of 11.2 GHz for X-band. In addition, the equivalent model of resonator is simulated in ADS (Advance designing system). It is observed that offered topologies are very sensitive to the parameters devia- tion (Post coupled waveguide resonator performance depends on diameter of conductive post, elevation of post and detachment between posts).

English

The dielectric properties of the leaves due to presence of water in varying quantities can be detected using microwave methods. Microstrip L - section λ/2 rejection filter can be used to investigate the effect of leaf moisture on their response. The investigations are reported in Ku band. An approximate estimate of the effective dielectric constant of the leaf has been made using overlay technique. It is felt that thin film λ/2 rejection filter can be used to monitor the moisture status of leafy vegetation in Ku band frequency range.

RF MEMS and CSRRs-based tunable filter designed for Ku and K bands application

AbstractThis paper presents the design and simulation of a reconfigurable stop-band filter on a silicon substrate based on the combination of RF microelectromechanical system and metamaterial-based technologies. The device is implemented on coplanar waveguide structure by embedding complementary split-ring resonators on the central line and an RF MEMS varactor bridge supporting the neighboring ground planes. The response characteristics of this metamaterial-based filter can be dynamically tuned, thus enhancing its usefulness. The device operates within a frequency range of 16.5–19.5 GHz, giving a tuning range of 15%, and can be tuned from Ku-frequency band to K-frequency band. It works with a comparative low pull-in voltage of 17.42 V and a faster switching time of 0.138 µs. A thorough electromechanical analysis has been done by varying various structural and material parameters. Moreover, a comparative electrical performance of silicon and glass has been shown to overcome the cons of silicon by high-resi...

Excellent improvement in the static and dynamic magnetic properties of carbon coated iron nanoparticles for microwave absorption

Carbon coated iron nanoparticles were synthesized, using a simple arc-discharge method. The morphology and the internal structure of the core/shell nanoparticles were studied, using field emission scanning electron microscopy and transmission electron microscopy. X-ray diffraction analysis showed that both magnetic α-Fe and nonmagnetic γ-Fe phases existed in the as-prepared particles. In order to improve the static and dynamic magnetic properties of the core/shell nanoparticles, the produced nanocapsules were annealed in argon atmosphere at two different temperatures. Hysteresis loops revealed that the value of the saturation magnetization (MS) increased more than 4.1 times of its original value by annealing and this led to 70% increase in the imaginary part of the permeability. Phase analysis showed that heat treatment eliminated the nonmagnetic γ-Fe phase completely. The reflection loss plots were studied for composite layers containing 20vol% of the annealed and not annealed nanocapsules. One of the absorber layers which contained annealed nanocapsules showed at least −10dB loss in the whole G, C, X and Ku frequency bands and the optimal absorption exceeded −37dB at 5.8GHz for the as-prepared sample with a thickness of 3.2mm. The results revealed that the magnetic properties of the arc-made Fe/C core/shell nanoparticle can be improved significantly by annealing in argon.

Ku대역 무인항공기 데이터 링크 설계를 위한 강우감쇠 분석

강우에 취약한 특성을 갖는 Ku대역을 이용한 통신 링크 설계 시에는 반드시 정확한 데이터와 정밀한 예측모델을 이용하여 도출한 강우감쇠 값을 반영하여 링크 마진을 분석하여야 한다. 따라서 본 논문에서는 최근 TTA에서 제시한 국내 강우강도 분포를 분석하여 Rec. ITU-R PN.837-1 및 Crane 모델에서의 지역별 강우강도와 비교하고, 우리나라의 최근 강우강도 분포와 유사한 지역을 선택하여 Ku대역 주파수에 대한 해당 지역의 강우감쇠를 Rec. ITU-R P.618-8와 Crane 강우감쇠 예측 모델을 통해 무인항공기와 지상통신장비의 통신 링크 거리 및 연 시간율 (%)에 따라 분석한다. It is necessary to apply an exact data and a precise prediction model for a rain attenuation to design the link margin for a data link using Ku-band with the serious effect by rain. In this paper, we investigate the regional rainfall-rate distribution of Korea proposed in TTAK.KO-06.0122/R1 and compare it with the distribution provided by Rec. ITU-R PN.837-1 and Crane. And, the rain rate climate regions similar with the rainfall-rate distribution of Korea in Rec. ITU-R PN.837-1 and Crane model are selected. Finally, using Rec. ITU-R P.618-8 and Crane rain attenuation prediction model, we derive and analyze the rain attenuation for Ku-band frequency according to the time percentage of an average year and the distance of wireless communication link between unmanned aerial vehicle (UAV) and ground data terminal (GDT).

Designing Of MWCNT/ Ferrofluid/ Flyash Multiphase Composite As Safeguard For Electromagnetic Radiation

Utilization of flyash which is produced at large scale in coal based thermal power plant is a challenge. In this regard, our investigation provides distinctive way of utilizing flyash for designing and preparing high-performance EMI shielding materials. Herein, we report synthesis and characterization of multiwalled carbon nanotubes (MWCNT) based multiphase composites. The multiphase composites were synthesized by in-situ co-precipitation with conductive filler (MWCNT) and magnetic filler (Ferrofluid). Scanning electron microscopy results confirm the presence of fly ash particles covered with Ferrofluid nanoparticles along with MWCNTs. Multiphase composites show total shielding effectiveness of 48 dB (>99.998 % attenuation) in the Ku-band (12.4–18 GHz) frequency range. 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 synthesized multiphase composites were characterized using XRD, FTIR, VSM and SEM. The results suggested that the MPC composites showed great potential as a radar absorbing material.

Application of the Mode Matching Technique to Determine the Complex Permittivity of Each Layer for a Bi-Layer Dielectric Material at Microwave Frequency

A new technique is presented to determine the complex permittivity of each layer for a bi-layer dielectric material. The bi-layer material sample is loaded in a Ku-band rectangular waveguide and its two port S-parameters are measured as a function of frequency using the E8634A Network Analyzer. Also, by applying the mode matching technique, expressions for the S-parameters of the bi-layer dielectric material as a function of complex permittivity of each layer are developed. To estimate the complex permittivity of each layer’s dielectric material, the square sums of errors between the measured and calculated S-parameters are minimised using a nonlinear optimization algorithm. The complex permittivity of each layer for a bi-layer dielectric material such as FR4-Teflon, FR4-Delrin and Delrin-Teflon are determined at the Ku-band frequencies, and the average relative errors between the individual dielectric materials and those of each individual layer of the bi-layer dielectric materials are calculated.

Carbon black/ polyurethane nanocomposite-coated fabric for microwave attenuation in X & Ku-band (8–18 GHz) frequency range

In the present study, coating formulations based on carbon nanoparticle (125–150 nm) and two component polyurethane resin [Polyester polyol-8 and hexamethylene diisocyanate [C8H12N2O2 (NCO-(CH2)6–NCO)] have been prepared in concentration of 5,6,7,8, 9 and 10 g of carbon black in 100 ml of polyurethane solution and was applied on cotton fabric adopting knife over roller coating technique. The coated fabrics were evaluated for surface resistivity and relevant microwave properties i.e. permittivity, scattering parameters, reflection, transmission, absorption, reflection loss and electromagnetic interference shielding in HVS free-space microwave measurement system. It is observed that increasing the carbon content increases the permittivity values and decreases the impedance. It is seen that with increase of carbon content up to 7 g, absorption increases due to increase of permittivity while with further increase of carbon content from 8 to 10 g, absorption decreases due to increase of conductivity and thereby increased reflection. The coated fabric at 6.55 wt% carbon and 93.45 wt% PU in thickness of 1.3 mm has shown about 46% absorption, 29.49% transmission and 24.5% reflectance in X (8.2–12.4 GHz) and Ku (12–18 GHz) frequency band. When electrical thickness of coated fabric equals λ/4, a peak of reflection loss is observed due to Salisbury absorption mechanism. Highest reflection loss of –31.39 dB at 17 GHz, more than 20 dB in bandwidth of 16–18 GHz and more than 10 dB in entire Ku- band is achieved. Coated fabric may be used as apparel for protecting human being from hazardous microwave and for radar absorbing structural materials for defence applications.

Estimation of Material Damping Coefficients of AlN for Film Bulk Acoustic Wave Resonator

AlN has been widely used as the piezoelectric thin film layer in film bulk acoustic wave resonator (FBAR). The performance of FBAR is influenced by various geometrical parameters and losses from piezoelectric material such as thermoelastic damping and material damping. This research focuses on the estimation of material damping coefficients (α and β) of the AlN by using the Akhieser approximation to estimate more accurate values of the coefficients, thus a more realistic value of the quality (Q) factor is achieved for FBAR operating at Ku-band frequency ranges (12 GHz-18 GHz).

Occupational EMF exposure from radar at X and Ku frequency band and plasma catecholamine levels.

Workers in certain occupations such as the military may be exposed to technical radiofrequency radiation exposure above current limits, which may pose a health risk. The present investigation intended to find the effect of chronic electromagnetic field (EMF) exposure from radar on plasma catecholamines in the military workforce. In the study, 166 male personnel selected randomly were categorized into three groups: control (n = 68), exposure group-I (X-band, 8-12 GHz, n = 40), and exposure group-II (Ku-band, 12.5-18 GHz, n = 58). The three clusters were further divided into two groups according to their years of service (YOS) (up to 9 years and ≥10 years) to study the effect of years of radar exposure. Enzyme immunoassay was employed to assess catecholamine concentrations. EMF levels were recorded at different occupational distances from radar. Significant adrenaline diminution was registered in exposure group-II with no significant difference in exposure group-I when both groups were weighed against control. Nor-adrenaline and dopamine levels did not vary significantly in both exposure groups when compared to controls. Exposure in terms of YOS also did not yield any significant alteration in any of the catecholamines and in any of the exposure groups when compared with their respective control groups. The shift from baseline catecholamine values due to stress has immense significance for health and well-being. Their continual alteration may prove harmful in due course. Suitable follow-up studies are needed to further strengthen these preliminary observations and for now, exposures should be limited as much as possible with essential safeguards.

Design of Ku‐band transformer‐based cross‐coupled complementary LC‐VCO

A transformer-based cross-coupled complementary LC voltage-controlled oscillator (VCO) is investigated which is capable of operating at the Ku-band frequency range with low power consumption. The VCO simultaneously achieves low phase noise and low power consumption. The VCO demonstrates a measured tuning range of 12.1–13.1 GHz and a phase noise of −116.4 dBc/Hz at 1 MHz at a centre frequency of 12.4 GHz. The VCO consumes 0.96 mW from a 0.45 V supply voltage with a figure of merit of 198.4. It is implemented in a standard 0.13 µm CMOS process with an area of 0.23 mm2.

Reflectarray Antennas for Dual Polarization and Broadband Telecom Satellite Applications

A reflectarray antenna with improved performance is proposed to operate in dual-polarization and transmit-receive frequencies in Ku-band for broadcast satellite applications. The reflectarray element contains two orthogonal sets of four coplanar parallel dipoles printed on two surfaces, each set combining lateral and broadside coupling. A 40-cm prototype has been designed, manufactured, and tested. The lengths of the coupled dipoles in the reflectarray cells have been optimized to produce a collimated beam in dual polarization in the transmit and receive bands. The measured radiation patterns confirm the high performance of the antenna in terms of bandwidth (27%), low losses, and low levels of cross polarization. Some preliminary simulations at 11.95 GHz for a 1.2-m antenna with South American coverage are presented to show the potential of the proposed antenna for spaceborne antennas in Ku-band.

SMOS soil moisture retrievals using the land parameter retrieval model: Evaluation over the Murrumbidgee Catchment, southeast Australia

The land parameter retrieval model (LPRM) is a methodology that retrieves soil moisture from low frequency dual polarized microwave measurements and has been extensively tested on C-, X- and Ku-band frequencies. Its performance on L-band is tested here by using observations from the Soil Moisture and Ocean Salinity (SMOS) satellite. These observations have potential advantages compared to higher frequencies: a low sensitivity to cloud and vegetation contamination, an increased thermal sampling depth and a greater sensitivity to soil moisture fluctuations. These features make it desirable to add SMOS-derived soil moisture retrievals to the existing European Space Agency (ESA) long-term climatological soil moisture data record, to be harmonized with other passive microwave soil moisture estimates from the LPRM. For multi-channel observations, LPRM infers the effective soil temperature (Teff) from higher frequency channels. This is not possible for a single channel mission like SMOS and therefore two alternative sources for Teff were tested: (1) MERRA-Land and (2) ECMWF numerical weather prediction systems, respectively. SMOS measures brightness temperature at a range of incidence angles, different incidence angle bins (45°, 52.5° and 60°) were tested for both ascending and descending swaths. Three LPRM algorithm parameters were optimized to match remotely sensed soil moisture with ground based observations: the single scattering albedo, roughness and polarization mixing factor. The soil moisture retrievals were optimized and evaluated against ground-based data from the Murrumbidgee Soil Moisture Monitoring Network (OzNet) in southeast Australia. The agreement with single-angle SMOS LPRM retrievals was close to the official SMOS L3 product, provided the three parameters were optimized for the OzNet dataset, with linear correlation of 0.70–0.75 (0.75–0.77 for SMOS L3), root-mean-square error of 0.069–0.085m3m−3 (0.084–0.106m3m−3 for SMOS L3) and small bias of −0.02–0.01m3m−3 (0.03–0.06m3m−3 for SMOS L3). These results suggest that the LPRM can be applied successfully to single-angle SMOS L-band observations, but further testing is required to determine if the same set of parameters can be used in other geographic areas.

Carbothermally synthesized core–shell carbon–magnetite porous nanorods for high-performance electromagnetic wave absorption and the effect of the heterointerface

A high-performance microwave absorbing composite based on heterostructured nanorods with porous magnetite core and carbon shell was realized by combining a hydrothermal carbonization (HTC) coating process and a controlled carbothermal reduction. Goethite nanorods as the precursor for magnetite nanorods were successfully prepared by an ethylenediaminetetraacetic acid-assisted hydrothermal process with high efficiency, low cost, morphology tunability and mass production capability. The X and Ku frequency bands were completely covered with a minimum suitable RL of −10dB by composite layers with the thicknesses being less than 2mm; with increasing the thickness, other frequency bands were also acceptably covered. The heterostructured magnetite nanorods exhibited more enhanced EM properties than simple magnetite nanorods and other similar structures. The excellent EM properties arose from effective complementarities between the magnetic loss and the dielectric loss. The formation of carbon shells on the nanorods during the controlled carbothermal reduction process tailored the dielectric constants in a manner that increased the dielectric loss and the impedance matching of the composites, conjointly. In this regard, multiple interfacial polarization relaxations at core–shell and nanorod–matrix interfaces were effectively involved. These results indicated that the fabrication of heterostructured magnetite nanorods by HTC coating and controlled carbothermal reduction could be a promising method to manufacture highly efficient and economic EM wave absorbing materials.

ANALYSIS AND COMPENSATION OF SUBREFLECTOR DISPLACEMENT FOR THE PARABOLIC ANTENNA OF A RADIO TELESCOPE

A subreflector system in the parabolic antenna of a 65 m radio telescope has been installed for compensating the gravitational deformation of the supporting frame in the antenna. This paper investigates the influence caused by the displacement of subreflector on the performance of the antenna and the corresponding compensation method. The investigation focuses on Ku-band frequencies and a new fitting formulation which is different from that of low-frequency bands is proposed to reduce the fitting error in the Y direction. In addition, the pointing deviation caused by the offset of the subreflector is analyzed and the model of pointing deflection caused by the displacement of subreflector is established, which can be used to improve the pointing accuracy. The model can determine the position and attitude of the subreflector with elevation and an extensive test shows that it can effectively improve the efficiency of the antenna at each elevation.

Pulsed EPR dipolar spectroscopy at Q- and G-band on a trityl biradical.

Pulsed electron paramagnetic resonance (EPR) spectroscopy is a valuable technique for the precise determination of distances between paramagnetic spin labels that are covalently attached to macromolecules. Nitroxides have commonly been utilised as paramagnetic tags for biomolecules, but trityl radicals have recently been developed as alternative spin labels. Trityls exhibit longer electron spin relaxation times and higher stability than nitroxides under in vivo conditions. So far, trityl radicals have only been used in pulsed EPR dipolar spectroscopy (PDS) at X-band (9.5 GHz), Ku-band (17.2 GHz) and Q-band (34 GHz) frequencies. In this study we investigated a trityl biradical by PDS at Q-band (34 GHz) and G-band (180 GHz) frequencies. Due to the small spectral width of the trityl (30 MHz) at Q-band frequencies, single frequency PDS techniques, like double-quantum coherence (DQC) and single frequency technique for refocusing dipolar couplings (SIFTER), work very efficiently. Hence, Q-band DQC and SIFTER experiments were performed and the results were compared; yielding a signal to noise ratio for SIFTER four times higher than that for DQC. At G-band frequencies the resolved axially symmetric g-tensor anisotropy of the trityl exhibited a spectral width of 130 MHz. Thus, pulsed electron electron double resonance (PELDOR/DEER) obtained at different pump-probe positions across the spectrum was used to reveal distances. Such a multi-frequency approach should also be applicable to determine structural information on biological macromolecules tagged with trityl spin labels.

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.