DRDO Grant by Dr Naveen Babu | Shiv Nadar University
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DRDO Grant by Dr Naveen Babu

19 Mar 2018

Dr. G Naveen Babu, Assistant Professor, Department of Electrical Engineering received Extramural Research and Intellectual Property Rights (ER & IPR) from Defence Research and Development Organisation (DRDO), Government of India. He has been awarded the grant of ₹ 12.14 Lakhs for a duration of two years (2017- 2019) for a research project entitled: “Large Signal Field Analysis of an O-Type Travelling Wave Amplifier using a Tape-Helix Model for the Slow- Wave Circuit”.

Brief Outline of the project


The large- signal field theory of an O-type travelling wave amplifier developed for the sheath- helix model is proposed to be generalized to the present case of a tape helix.


The large signal field theory of a TWT amplifier, expounded in earlier works, is based on a coupled Eulerian-Lagrangian formulation, that is, the boundary value problem for the Maxwell’s equations is formulated in Eulerian coordinates whereas the electron ballistic equations are formulated in Lagrangian coordinates. The key step in the solution procedure was a representation of the electromagnetic field components as nonlinear functionals of the electron- arrival time through a sequence of Green’s functions for the slow- wave circuit. Substitution of this functional representation for the axial electric field component into the electron ballistic equation made it possible to recast the latter into the fixed-point format for a nonlinear operator in a suitable function space. The fixed point, and therefore the solution for the electron- arrival time, and hence the solution for the electromagnetic fields could be obtained by the method of successive substitutions. Numerical computation of the amplifier parameters could then be readily carried out once the solution for the field vector was available.


The proposed generalization of the above approach to the problem at hand is highly non trivial because of the following intrinsic difficulties of a technical nature associated with the tape- helix geometry:


i.      A tape helix is not an axially symmetric structure; a finite- length helix is not even a periodic structure. Lack of axial symmetry implies that the field will be functions of all the three spatial coordinates. Lack of periodicity implies that Floquet’s theorem is no longer available thereby necessitating an expansion of each field component and the convection current density in a double Fourier series with respect to the axial and the azimuthal coordinates.

ii.      Enforcing the boundary condition of zero tangential electric field along the winding direction over the entire width of the tape surface is a crucial, nevertheless highly nontrivial, intermediate step in the analysis. A judicious use of yet another orthogonal expansion with respect to the axial and the azimuthal coordinates is required to tackle this step.