0018-926X (c) 2018 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/TAP.2018.2869612, IEEE Transactions on Antennas and Propagation Excitation of Space-Wave, Leaky-Wave and Creeping-Waves in Cylindrical Media Mahesh Singh, Student Member, IEEE, Bratin Ghosh, Senior Member, IEEE, and Kamal Sarabandi, Fellow, IEEE Abstract—The discrete and continuous spectrum in a cylindrical dielectric rod is rigorously characterized taking into account the TE-TM coupling and the longitudinal wavenumber for a ˆ z , ˆ ρ and ˆ φ -directed source. Pattern characteristics corresponding to the space and leaky-waves are investigated for all source-polarizations with variation in rod-parameters. It is observed that the rod can function as a high-gain antenna and support proper and improper surface-waves depending on rod- parameter values. The phase and attenuation characteristics of the axially propagating leaky-waves are also investigated delineating the radiating and guided-wave regions of the rod. The beam scanning characteristics for the space and leaky-waves with variation in rod-parameters are also investigated. The complex azimuthal propagation characteristics of the creeping-waves are examined to obtain an insight into propagation regions where such waves are strongly excited. Index Terms—Cylindrical media, space-wave, branch-cut, steepest descent path, leaky-wave, guided-wave, creeping-wave. I. INTRODUCTION The printed planar dipole antenna configuration has attracted considerable research attention in the past and present [1]-[10]. It is known that the leaky-wave can never exist by itself but is always associated with the continuous spatial spectrum and usually in conjunction with a single or multiple surface-wave modes. The power distribution between the surface and space-waves for a grounded dielectric slab excited by a horizontal electric dipole (HED) is addressed in [2]. Excitation of TE and TM leaky and surface waves for a line source in a grounded dielectric slab topped by a metallic strip grating was investigated in [11]. Leaky wave radiation due to a 2D periodic structure of narrow metallic patches over a grounded dielectric slab excited by a slot was presented in [12]. Directive leaky-wave radiation from a grounded wire- medium slab excited by a horizontal electric dipole was reported in [13]. A leaky wave configuration based on a reactance sheet over a grounded uniaxial dielectric substrate was investigated in [14] for obtaining a prescribed pattern. Investigations on the HED embedded in a superstrate / substrate antenna configuration was reported in [3], [4]. Parametric variation with respect to the dielectric layer permittivities, the dielectric slab thicknesses and the location of the HED were discussed. Resonance conditions and subsequent gain enhancement for a HED using multiple superstrates is investigated in [5], [6]. A leaky-wave analysis of a multilayer printed antenna configuration was presented in [7] to provide additional physical insight into the radiation mechanism of such antenna configurations. A broadband Fabry-Perot leaky wave antenna structure using a double-layer partially reflecting surface over a ground plane was proposed in [15]. An efficient approach for the calculation of the propagation and leakage constants was developed in [8] by using the transverse resonance technique [30]. Closed-form evaluation of the continuous spectrum for an infinite line- source embedded in a substrate-superstrate structure was reported in [9] by expressing it in terms of contributions of two leaky-wave pole singularities. Polarization characteristics of a planar multilayer antenna structure excited by a linearly polarized source was investigated in [10]. Substrate integrated waveguide based leaky-wave configurations with transverse and H-shaped slots on the ground plane were reported in [16] and [17]. Printed antenna configurations in cylindrical structures have also attracted considerable research attention in view of their applications in missile bodies, bullet surfaces, aerodynamic structures and borehole in geophysics. Electromagnetic radiation from conducting cylindrical structures is discussed in [18]. The determination of the far- field from a current-source in the vicinity of a metallic cylinder has been reported using the Green’s function technique [18]- [20] and the plane wave scattering solution using the principle of reciprocity [21], [22], with the saddle- point integration for computing the far-field. However, it is known that the TE and TM modes are coupled for the case of the dielectric cylinder. A two-dimensional treatment for the dielectric cylinder problem excited by a line source has been discussed in [20], with no variation along the axial direction. In addition, the TE-TM mode coupling has not been considered. The lowest order TM surface-wave excitation with a circular filament of magnetic current in a dielectric cylinder was investigated in [23]. The effect of different source polarizations, particularly from higher order modes that involve TE-TM mode coupling and which contribute significantly to the space-wave have not been considered. Propagation characteristics of creeping-waves for a dielectric-coated circular cylinder excited by ˆ z -directed electric / magnetic line sources is investigated in [24], [25]. The creeping, leaky and surface-wave propagation wavenumbers for the dielectric-coated cylinder are compared with the leaky and surface-wave characteristics for a grounded dielectric slab in [25]. For the cylindrical leaky-wave treatment in [25], however, the longitudinal wavenumber z k has not been considered. A cylindrical microstrip leaky-wave antenna configuration on a coated PEC cylinder has been investigated in [26] with a high gain and wide-band characteristic for the configuration, similar to planar leaky- wave antennas. A conformal subwavelength leaky-wave antenna using thin cylindrical metamaterial shells was proposed in [27]. In the following work, the space-wave, leaky-wave and creeping-waves excited by different source polarizations in a cylindrical dielectric medium is investigated. The treatment is rigorous, considering the mode coupling between the TE and TM modes together with the longitudinal wavenumber. The TE-TM mode coupling is observed to be particularly relevant for space-wave excitation for the ˆ ρ and ˆ φ -directed sources together with the creeping-wave excitation due to the