D. Chadha

Bio: D. Chadha is an academic researcher from Indian Institutes of Technology. The author has contributed to research in topics: Dielectric & Planar. The author has an hindex of 4, co-authored 11 publications receiving 44 citations.

Field Theory of Planar Helix Traveling-Wave Tube

Abstract: A pair of unidirectionally conducting screens, conducting in different directions, constitute a planar helix. The planar helix is proposed as a slow-wave structure for application in a traveling-wave tube (TWT). Field theory is applied to analyze the behavior of the planar helix in the presence of a flat electron beans present between the two screens. Results indicate the presence of three modes, with one mode having a negative attenuation constant, as in the case of the usual helix-type TWT. Curves are shown for a typical proposed planar TWT. Also, the effect of beam current is indicated.

Study of planar-helix slow-Wave structure for application to travelling-wave tubes

Abstract: A planar helix, constituted of a pair of unidirectionally conducting screens conducting in different directions, is suggested as a slow-wave structure for application in a travelling-wave tube (TWT). Circuit parameters, such as interaction impedance and space-charge parameter, are derived for the suggested planar-helix TWT. Computed results for the planar helix indicate a performance comparable with that of its circular helix counterpart. Also, the change in interaction impedance and the dispersion characteristics of the planar helix, are considered in the presence of dielectric substrates and a metal shield. Results are obtained for a few different possible configurations of the planar helix on dielectric substrates with or without a metal shield. The phase velocity and interaction impedance reduce, both as the substrate thickness increases and as the metal shields are brought closer to the planar helix. However, the resulting degradation in the characteristics of the structure with commonly used substrate materials, for example alumina and beryllia, is less severe than in the case of the circular helix.

Modes of a shielded conductor-backed coplanar waveguide

Abstract: The dispersion characteristics of conductor backed coplanar waveguide (CBCPW) in a metal enclosure, including higher order modes, are obtained by means of an efficient numerical technique, namely the method of lines (MoL). Knowledge of higher order modes is essential for estimating 'singlemode' bandwidth and for characterising discontinuities. >

Energy efficient design for Green optical core network

Abstract: In recent years Green technologies are emerging as important research efforts to develop strategies to reduce the energy consumption in the network and also to develop energy efficient architecture for the optical networks. In this work we have considered typical optical backbone network architecture, and have minimized the operational power primarily for provisioning techniques. Typically, operational power depends on strategy operations, and route. Traffic grooming is being considered as a key functionality of WDM networks, in which, multiple low-speed traffic requests are groomed onto a single, high-capacity lightpath. Various approaches viz. direct lightpath, optical by-pass, traffic grooming, dynamic routing; have been discussed and evaluated. The work amply brings out the advantage of using dynamic routing, in conjunction with traffic grooming, in greening the optical backbone.

Coupled mode analysis of finlines on anisotropic substrates

Abstract: Coupled mode theory has recently been applied to study finlines loaded inhomogenously with a dielectric or a ferrite. In this letter we report the results of the application of the coupled mode theory to obtain the propagation constants of finlines on anisotropic substrates.

Coplanar waveguide circuits, components, and systems

Abstract: Preface Introduction Conventional Coplanar Waveguide Conductor-Backed Coplanar Waveguide Coplanar Waveguide with Finite-Width Ground Planes Coplanar Waveguide Suspended Inside A Conducting Enclosure Coplanar Striplines Microshield Lines and Coupled Coplanar Waveguide Attenuation Characteristics of Conventional, Micromachined, and Superconducting Coplanar Waveguides Coplanar Waveguide Discontinuities and Circuit Elements Coplanar Waveguide Transitions Directional Couplers, Hybrids, and Magic-Ts Coplanar Waveguide Applications References Index

On the use of vias in conductor-backed coplanar circuits

Abstract: Ground planes of conductor-backed coplanar waveguides (CBCPWs) behave like overmoded patch antennas supporting parallel-plate modes and show numerous resonances. For typical monolithic-microwave integrated-circuit chip sizes, these unwanted resonance frequencies lie within the microwave and millimeter-wave frequency region. Due to this feedback mechanism, today's coplanar millimeter-wave amplifiers operating up to 250 GHz require special packaging techniques for stable operation. The use of vias is one method of suppressing parallel-plate modes. The effect of via-holes within a ground plane and the effect of an open or a shorted ground-plane periphery on the parallel-plate modes of CBCPWs were investigated in depth up to 200 GHz for quartz and GaAs substrates. It is shown that the placement of the vias within the coplanar-waveguide structure is crucial for the suppression of parallel-plate modes. If properly placed, vias are an effective means to suppress these unwanted modes over a chosen frequency range.

Dispersion Characteristics of a Rectangular Helix Slow-Wave Structure

Abstract: A special type of helical slow-wave structure encompassing a rectangular geometry is investigated in this paper, and the slow-wave characteristics are studied taking into account the anisotropically conducting helix. By using the electromagnetic integral equations at the boundaries, the dispersion equation and the interaction impedance of transverse antisymmetric modes in this structure are derived. Moreover, the obtained complex dispersion equation is numerically calculated. The calculation results by our theory agree well with the results obtained by the 3-D EM simulation software HFSS. The numerical results reveal that the phase velocity decreases and interaction impedance increases at higher frequencies by flattening (increasing the aspect ratio of) the rectangular helix structure. In addition, a comparison of slow-wave characteristics of this structure with a conventional round helix is made.

Planar Helix With Straight-Edge Connections in the Presence of Multilayer Dielectric Substrates

Abstract: A planar slow-wave structure consisting of a planar helix with straight-edge connections has been studied in the context of application in traveling-wave tubes. The effects of several practical modifications to the basic structure are examined. These modifications comprise a vacuum tunnel, metal shield, and multilayer dielectric substrates. A modified effective dielectric constant method is proposed to obtain the dispersion characteristics for different possible configurations. Furthermore, coupling impedance for the different configurations has been calculated using the corresponding 2-D approximations. It is shown that, far from cutoff, the phase velocity and coupling impedance values calculated in this manner match very well with the simulation results obtained from CST Microwave Studio. The effects of variations in aspect ratio, metal shield distance, and dielectric constant of the substrates on phase velocity and coupling impedance are studied. A coplanar waveguide feed has been designed for one of the possible configurations. The measured S-parameters and phase velocity values for this proof-of-concept configuration agree well with the simulated results and confirm the ease of fabrication, low loss, and the wideband potential of the planar helix with straight-edge connections.

Analysis of the Mixed Coupling in Bilateral Microwave Circuits Including Anisotropy for Mics and Mmics Applications

Abstract: Higher integration and smaller layout size, two major trends in today’s industry, lead to more prominent electromagnetic coupling with direct applications in the RF/microwave area such as directional couplers, filters, multiplexers, shifters, delay lines, etc. In the present work, an efficient hybrid-mode method is presented for a rigorous characterization of the coupling in multilayer bilateral microwave circuits including anisotropy effects. Various types of planar configurations were considered including microstrip, finline and coplanar structures, but the proposed approach can easily be extended to any form of coupled lines. To fully characterize bilateral multilayer circuits in millimetre wave region with an arbitrary number of conductors, closed forms of dyadic Green’s functions were determined in the spectral domain, with use of the Galerkin technique. The computed results show good agreement with data available in the literature. Furthermore, two original configurations based on three line bilateral couplers were computed and validated using neural network models.