Browsing by Author "Kumar, A. V. Praveen"

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Analysis and control of wakefields in X-band crab cavities for Compact Linear Collider
(Elsevier, 2011-11) Kumar, A. V. Praveen
The Compact Linear Collider requires a crab cavity on each beamline prior to the interaction point to rotate the bunches before collision. The cavities are X-band travelling wave type and are located close to the final doublet of the beam delivery system. This makes the beam very sensitive to transverse momentum imparted by wakefields; hence the wakefields must be tightly controlled. Of special concerns are the orthogonal polarisation of the operating mode and the fundamental monopole mode of the crab cavity. The former mode is at the same frequency as the operating mode of a cylindrically symmetric cavity and the latter one is at a lower frequency and hence is difficult to damp using a single means. In this paper major problematic modes of the crab cavity are investigated and damping requirements for them are calculated. Possibility of meeting the required wakefield control using waveguide damping and choke damping is thoroughly investigated. As a comparison, damped-detuning is also investigated.
Application of a Cylindrical Dielectric Resonator as an Angular Displacement Sensor
(IEEE, 2020) Kumar, A. V. Praveen
Authors investigate the application of a cylindrical dielectric resonator (CDR) for detecting the angular displacement with the help of numerical simulations. The CDR is made bisymmetric by attaching a metal strip diametrically on its top-face to enable angular sensing in the range of 0 - 90°. The CDR is coupled to a single microstrip line for reflection mode measurement, while it is coupled to two microstrip lines for transmission mode measurement. Identically in both the configurations, the CDR resonates at the HEM 11δ mode frequency of ≈3.5 GHz, with the magnitude of the respective S-parameters varying with the strip angle. The CDR configurations provide nearly identical sensitivities and quasi-linear ranges of ≈0.26 dB/°, and 70° respectively for the reflection mode, while ≈0.3 dB/° and 60° respectively for the transmission mode operation.
Application of HEM11δ Mode in DR based Linear Displacement Sensor
(IEEE, 2023) Kumar, A. V. Praveen
Presented a numerical investigation on the application of HEM 11δ mode in a dielectric resonator (DR) sensor. A simple two-port network is implemented by placing two microstrip lines opposite to each other for full transmission. A dielectric resonator (DR) is placed between them to detect the coupling w.r.to its displacement. Proposed transmission mode operated DR excite HEM 11δ mode at~ 3.7 GHz. Here, the DR positional movement produces identical results in both directions (+dx/ -dx) due to the structural bisymmetry. This single frequency operated Transmission circuit provides 1.78 dB/mm sensitivity in the 0 - 9 mm range.
BST@Copper Nanowire/Epoxy composites with excellent microwave absorption in the X-band
(Elsevier, 2024-09) Kumar, A. V. Praveen; Etika, Krishna Chitanya
In this work, hybrid epoxy nanocomposites containing varying loading of copper nanowires (CuNW), Ba0.7Sr0.3TiO3 (BST), and BST@CuNW hybrid nanoparticles were prepared and analyzed for their microwave absorption characteristics. The nanoparticles used in this study were prepared using a facile co-precipitation and hydrothermal methodology. The synthesized nanoparticles were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD) for their morphology and phase determination. While the XRD results confirmed the presence of BST and CuNW, the SEM micrographs obtained on the hybrid BST@CuNW nanoparticles show BST anchored on the CuNW surfaces. A series of epoxy composites containing varying loading of synthesized nanoparticles were prepared and characterized for their microwave properties, such as complex permittivity, shielding effectiveness, and power coefficients. The results indicate that nanocomposites containing BST@CuNW hybrids exhibited enhanced dielectric loss and more significant microwave power absorption compared to samples with equivalent CuNW and/or BST loading. The best composite sample, i.e., a one-millimeter-thick epoxy containing 10:15 (wt/wt) CuNW: BST hybrid nanoparticles with an estimated density of 1.49 g/cc attenuated 99.1 % of incident microwave power and exhibited a shielding effectiveness value of 21.2 dB in the X-band (8–12 GHz) of the microwave frequency spectrum. These lightweight polymer composites with high microwave absorption in the X-band are useful for military and civilian applications.
CLIC crab cavity design optimisation for maximum luminosity
(Elsevier, 2011-11) Kumar, A. V. Praveen
The bunch size and crossing angle planned for CERN's compact linear collider CLIC dictate that crab cavities on opposing linacs will be needed to rotate bunches of particles into alignment at the interaction point if the desired luminosity is to be achieved. Wakefield effects, RF phase errors between crab cavities on opposing linacs and unpredictable beam loading can each act to reduce luminosity below that anticipated for bunches colliding in perfect alignment. Unlike acceleration cavities, which are normally optimised for gradient, crab cavities must be optimised primarily for luminosity. Accepting the crab cavity technology choice of a 12 GHz, normal conducting, travelling wave structure as explained in the text, this paper develops an analytical approach to optimise cell number and iris diameter.
Coaxial fed hexagonal dielectric resonator antenna for circular polarization
(Wiley, 2006-01) Kumar, A. V. Praveen
A coaxial-fed hexagonal dielectric resonator antenna (HDRA) producing circular polarization is investigated experimentally. Circular polarization is achieved by exciting the orthogonal HE11δ modes of the HDRA in phase quadrature. The return-loss, impedance, and radiation characteristics are studied. The results show that the antenna produces circular polarization in the elevation plane with an axial ratio less than 3 dB over a bandwidth of 14.84% and a beam width of 66°.
Comparative Analysis of Dielectric Resonator based Linear Displacement Sensor with Various Microwave Feeding Techniques
(IEEE, 2022) Kumar, A. V. Praveen
The authors presents the comparative analysis of a dielectric resonator (DR) based linear displacement sensor with various microwave feeding techniques. A cylindrical DR excited by common feeding techniques such as the coaxial probe feed, microstrip slot feed, microstrip line feed, and coplanar waveguide feeds is numerically investigated using ANSYS HFSS. Single-port or reflection mode sensor characteristics such as the frequency shift, displacement sensitivity, linearity, and dynamic range are found to be highly dependent on the feeding technique.
Conducting sheets-loaded slot antenna for high gain and wide 3 dB gain-band operation
(Wiley, 2022-03) Kumar, A. V. Praveen
This article presents the design and analysis of a high-gain rectangular slotantenna with an operating band (intersection between the 10 dB impedanceband and the 3 dB gain band) of 6–10 GHz with peak gain of ~12 dBi. Toachieve this, an offset fed slot antenna is loaded with two pairs of conductingsheets—a reflector-superstrate pair, and a pair of side sheets. The offset feedingof the slot provides wideband bidirectional radiation; subsequent reflector-sup-erstrate loading enables directional beam with higher gain and wider imped-ance bandwidth, and finally, the side sheet loading equalizes the gain overfrequency band, resulting in a wider operating 3 dB gain-band. The opti-mized antenna has size 2.28λ0 1.34λ0 0.46λ0at the mid-band fre-quencywhichinmeasurementprovides a 3 dB gain-band of 6.03–9.77 GHz(47.34%) with 12.04 dBi peak gain, verifying the simulation. This widegain-band antenna is superior to existing wideband-high-gain antennas asit provides high-peak gain and wide gain-band, which is more than 90% ofthe impedance band.
Conducting Side Sheet Loading to Enhance the Bidirectional Gain of a Wide Rectangular Slot Antenna in the 6–8.5 GHz Band
(Taylor & Francis, 2021-11) Kumar, A. V. Praveen
Bidirectional gain of a wide rectangular slot antenna resonating over the 6 − 8.5 GHz band is enhanced by loading a pair of conducting sheets on the ground plane edges. These sheets are vertically loaded with respect to the slot antenna for meeting two purposes – (i) to appropriately converge the oblique radiation of the slot towards the broadside direction for enhanced gain and (ii) to retain the original impedance band (reflection coefficient ≤ −10 dB) of the slot by avoiding the formation of a resonant cavity (as in the case of superstrate loaded antennas). Optimized antenna using FR-4 substrate of side 50 mm has an overall size of 2.2λ0 × 1.2λ0 × 0.5λ0, where λ0 is the free-space wavelength at the mid-band frequency of the operating band. Measurements of fabricated antenna prototype demonstrate an impedance band of 5.97–8.53 GHz with bidirectional radiation pattern, with peak in-band gain of 5.52 dBi. The average gain improvement in the band is 3.99 dB, relative to the wide-slot antenna without sheet loading. The main attraction of the proposed method is its non-resonant nature, which enables almost uniform gain enhancement throughout the original impedance band, with bidirectional radiation pattern.
Coupler induced monopole component and its minimization in deflecting cavities
(APS, 2013-06) Kumar, A. V. Praveen
Deflecting cavities are used in particle accelerators for the manipulation of charged particles by deflecting or crabbing (rotating) them. For short deflectors, the effect of the power coupler on the deflecting field can become significant. The particular power coupler type can introduce multipole rf field components and coupler-specific wakefields. Coupler types that would normally be considered like standard on-cell coupler, waveguide coupler, or mode-launcher coupler could have one or two rf feeds. The major advantage of a dual-feed coupler is the absence of monopole and quadrupole rf field components in the deflecting structure. However, a dual-feed coupler is mechanically more complex than a typical single-feed coupler and needs a splitter. For most applications, deflecting structures are placed in regions where there is small space hence reducing the size of the structure is very desirable. This paper investigates the multipole field components of the deflecting mode in single-feed couplers and ways to overcome the effect of the monopole component on the beam. Significant advances in performance have been demonstrated. Additionally, a novel coupler design is introduced which has no monopole field component to the deflecting mode and is more compact than the conventional dual-feed coupler.
Dielectric characterization of common edible oils in the higher microwave frequencies using cavity perturbation
(Taylor & Francis, 2019-02) Kumar, A. V. Praveen
Dielectric constants and loss tangents of four common edible oils – mustard oil, olive oil, sesame oil and canola oil are measured in the 9–15 GHz range using cavity perturbation. Accuracy of the measurement is enhanced by determining the sample volume through mass and density measurements, instead of dimensional measurements. Results show that the dielectric properties vary with oil type at a given frequency and also with frequency for a given oil. In addition, the impact of repeated heating of the oils to the smoke point is also studied, which demonstrates changes in the dielectric properties with smoking, for all the oils under consideration.
Differentially-Fed Half-Cylindrical Dielectric Resonator Antenna for Dual-Mode Applications
(IUP, 2016-02) Kumar, A. V. Praveen
Differentially-fed half-Cylindrical Dielectric Resonator Antenna (CDRA) enables two different modes to be excited at the proper phase difference between the two feed lines. For a differential phase of 00, TE0 mode is excited, while for a phase of 1800, HEM12 mode is excited. The cut-plane of the half-CDRA is so placed on the ground plane-backed substrate that the above modes obey the respective boundary conditions. With minor design changes, the DRA can be operated either in single mode or in dual mode. In dual-mode operation, the maximum directivities are 6.9 dB and 4.3 dB, respectively for a differential phase of 00 and 1800, respectively.
First Test Results of the 4-rod Crab Cavity, IPAC2013, China
(CERN, 2013) Kumar, A. V. Praveen
The first compact prototype crab cavity with the 4rod geometry has undergone surface treatment and cold testing. Due to the complex geometry and unique fabrication procedure, RF validation of the field at beyond the nominal operating voltage at a sufficiently high Q0 is an important pre-requisite. Preliminary results of the first cold tests are presented along with cavity performance at different stages of the cavity processing is described.
A Fixed-Frequency Angular Displacement Sensor Based on Dielectric-Loaded Metal Strip Resonator
(IEEE, 2021-02) Kumar, A. V. Praveen
A fixed-frequency angular displacement sensor using a dielectric-loaded metal strip resonator is proposed. The dielectric body on which the strip resonator is attached is a cylinder having a high dielectric constant (e r ≫ 1). The resulting resonator operates at the half-wave resonant frequency of the quasi-TEM mode of the loaded strip, which is much lower than the nominal resonant frequency of the strip. To enable angle sensing, the resonator is placed symmetrically between two 50 Ω, open-ended microstrip lines, so that the magnitude of the transmission coefficient(|S 21 |) between the lines varies with the strip angle, i.e., 0° ≤ θ ≤ 90°. Also, this configuration ensures constant resonant frequency operation for all angles. Simulations show that although the |S 21 | versus angle curve varies exponentially in the range of 0° ≤ θ ≤ 90°, the corresponding coupling coefficient varies quasi-linearly in 10° ≤ θ ≤ 80°. A laboratory prototype for ~ 2.4 GHz resonant peak is fabricated and the simulation results are verified through prototype measurement. The advantages of the proposed sensor are that it is compact, has a simple design, and operates at a fixed frequency, enabling a low-cost, robust angular sensor.
Hexagonal dielectric resonator antenna for 2.4 GHz WLAN applications
(Wiley, 2006-11) Kumar, A. V. Praveen
A dielectric resonator antenna (DRA) with hexagonal geometry for WLAN applications is proposed. The antenna is excited with a simple 50 Ω microstrip transmission line. The proposed antenna produces an impedance bandwidth of 105 MHz from 2.395 to 2.50 GHz, which covers the 2.4 GHz wireless local area networks band (WLAN: 2.4–2.485 GHz). The radiation patterns are measured and are found to be omnidirectional. An average gain of 5.4 dBi is measured in the operating band.
High gain broadside mode operation of a cylindrical dielectric resonator antenna using simple slot excitation
(Cambridge University Press, 2020-06) Kumar, A. V. Praveen
In this work, the authors report the operation of a cylindrical dielectric resonator antenna (CDRA) in the high gain HEM13δ mode, for the first time. This mode, excited with a standard microstrip slot, radiates in the broadside direction with gain in the range of 8−10 dBi. It is shown that through feed optimization, the HEM13δ mode can be excited dominantly by suppressing the fundamental HEM11δ mode of the CDRA. Detailed simulation studies show that the HEM13δ mode is supported by cylindrical dielectric resonators with an aspect ratio (radius to height ratio or a/d) >1, and it resonates at a frequency approximately 2.2 times that of the fundamental HEM11δ mode. The above features of the HEM13δ mode CDRA can be used as approximate design rules. For a CDRA with dielectric constant ɛr = 24, diameter 2a = 19.43 mm, and height d = 7.3 mm (a/d = 1.3), the HEM13δ mode is excited at 6.125 GHz with a peak gain of 10.14 dBi in simulation. Corresponding values from prototype measurement are 5.981 GHz and 9.62 dBi, respectively for the resonant frequency and the gain, verifying the simulation.
High Gradient Testing of an X-band Crab Cavity at XBox2
(2015) Kumar, A. V. Praveen
CERN’s Compact linear collider (CLIC) will require crab cavities to align the bunches to provide effective head-on collisions. An X-band quasi-TM11 deflecting cavity has been designed and manufactured for testing at CERN’s Xbox-2 high power standalone test stand. The cavity is currently under test and has reached an input power level in excess of 40MW, with a measured breakdown rate of better than 10⁻⁵ breakdowns per pulse. This paper also describes surface field quantities which are important in assessing the expected BDR when designing high gradient structures
Impact of the Design Parameters on the Microwave Displacement Sensor Performance
(IEEE, 2023) Kumar, A. V. Praveen
The investigations have been conducted on the involved design parameters to analyze the behavior of the microwave displacement sensor output characteristics. To implement this, a dielectric resonator loaded to a reflection mode operated microstrip line circuit is proposed. For the proposed reflection mode sensor, the sensor features like resonant frequency, impedance matching position, sensitivity, and dynamic range are sensitive to the displacement of DR to microstrip line. The impact of the substrate shape and size, and resonators geometrical properties are numerically analyzed and experimentally validated by using VNA. The sensor analysis shows good matching between both HFSS simulations and VNA measurements.
Investigation on the aspect ratio of conducting superstrates in deciding its function as a gain enhancer/suppressor for wideband slot antenna
(ACM Digital Library, 2022-09) Kumar, A. V. Praveen
This paper presents an investigation on the effect of the aspect ratio (AR or width-to-length ratio) of a conducting sheet for radiation control i.e., gain enhancement or suppression, leading to useful applications for wireless communication. A wideband slot antenna working in 6–8.5 GHz band is adopted as the basic antenna. It is found that for the sheet AR < 1, the boresight (θ = 0°) gain in the entire band is enhanced, while for AR > 1, boresight gain suppression is achieved. For an optimum AR such that AR(enhancement) = 1/AR(suppression), the same sheet can serve the above dual purposes according to its azimuthal orientation with respect to the slot. For ϕ = 0° orientation with respect to the slot, the sheet acts as a gain enhancer, while for ϕ = 90° orientation, it suppresses the radiation, both in θ = 0°. Practically, the sheet orientation can be easily controlled manually. Antenna measurements demonstrate an impedance band of 6–8.66 GHz with bidirectional radiation pattern, and 1.11 dBi boresight gain at 7.25 GHz. A conducting sheet of size 1.45λ0 × 0.29λ0 where λ0 is the free-space wavelength at 7.25 GHz, is loaded above the slot which improves the boresight gain by 5.77 dB, and when rotated by ϕ = 90°, suppresses the gain by 8.78 dB, both relative to the original slot antenna.
Investigation on the aspect ratio of conducting superstrates in deciding its function as a gain enhancer/suppressor for wideband slot antenna
(Springer, 2022-07) Kumar, A. V. Praveen
This paper presents an investigation on the effect of the aspect ratio (AR or width-to-length ratio) of a conducting sheet for radiation control i.e., gain enhancement or suppression, leading to useful applications for wireless communication. A wideband slot antenna working in 6–8.5 GHz band is adopted as the basic antenna. It is found that for the sheet AR < 1, the boresight (θ = 0°) gain in the entire band is enhanced, while for AR > 1, boresight gain suppression is achieved. For an optimum AR such that AR(enhancement) = 1/AR(suppression), the same sheet can serve the above dual purposes according to its azimuthal orientation with respect to the slot. For ϕ = 0° orientation with respect to the slot, the sheet acts as a gain enhancer, while for ϕ = 90° orientation, it suppresses the radiation, both in θ = 0°. Practically, the sheet orientation can be easily controlled manually. Antenna measurements demonstrate an impedance band of 6–8.66 GHz with bidirectional radiation pattern, and 1.11 dBi boresight gain at 7.25 GHz. A conducting sheet of size 1.45λ0 × 0.29λ0 where λ0 is the free-space wavelength at 7.25 GHz, is loaded above the slot which improves the boresight gain by 5.77 dB, and when rotated by ϕ = 90°, suppresses the gain by 8.78 dB, both relative to the original slot antenna.