Radiation Analysis of a Coated Axially Slotted Cylindrical Antenna in Microwave Regime

Abstract

Axially Slotted Cylindrical Antennas (ASCA) are popular for their versatility, compact design, and unique properties that make them suitable for various applications. This dissertation examines the radiation characteristics of coated ASCA operating within the microwave frequency range. The study aims to systematically investigate the impact of different coating materials and metamaterials on ASCA placed in diverse environments. The main goal is to establish a comprehensive theoretical framework that can lay down foundations for improving the design of ASCA by employing a suitable coating layer to optimize for future applications in areas such as space communication, remote sensing, medical diagnostics, and treatment. A semi-analytic cylindrical wave expansion technique is employed to represent the electromagnetic fields in various regions and the coefficients are computed by using a computer program. The radiated fields in regions filled by inhomogeneous material are written in terms of modified Bessel and Hankel functions of non-integer order. The eccentricity is mathematically incorporated by employing Graf’s addition formula and the graphene conductivity is described according to the local random phase approximation of the Kubo formula. This dissertation presents extensive investigation into the gain characteristics of ASCA coated with various materials and embedded in different host media, with a particular focus on inhomogeneous coatings, eccentric layers and the inclusion of graphene layers. The gain properties of ASCA clad with an inhomogeneous dielectric material is studied when placed in either non-magnetic lossless or lossy plasma material. The radiation characteristics of an ASCA on a conducting cylinder with an eccentric coating of radially inhomogeneous material embedded in a lossy medium are examined. The study of radiations from ASCA coated with both homogeneous and inhomogeneous materials, with an additional layer of graphene. Various novel coating materials, including double positive (DPS), double negative (DNG), mu negative (MNG), and epsilon negative (ENG), are considered in the analysis. The effects of variation of different parameters like coating thickness, inhomogeneity parameter, and lossless/lossy plasma background on gain characteristics of an axial slot have been discussed. The study explored the influence of inhomogeneity parameters, finding their pivotal role in shaping gain characteristics, especially in the forward direction. Additionally, it demonstrated the ability to control radiation patterns from isotropic to directive by selecting suitable inhomogeneity profiles and eccentricity parameters. Notably, when ASCA were embedded in zero index media, the exponent of the profile function directly correlated with the number of main lobes in the radiation pattern. The study revealed that coating thickness significantly impacts the gain pattern, making it more direct in lossless plasma materials and exhibiting a mixed behavior in lossy media. iii ABSTRACT Overall, this research contributes valuable insights into enhancing the performance of ASCA in various applications by tailoring their gain patterns and directivity. iv