Analysis of leaky characteristics for NRD guide with arbitrary profile of cross-section

Abstract

The leaky wave characteristics of a nonradiative dielectric waveguide (NRD) guide having irregular cross-section profile are known to be not amenable to an exact field analysis, even for a relatively simple geometric profile. Therefore, one must resort to an approximate but accurate modal analysis. In particular, a method is required that should be generally applicable to different profiles of the structure. A method using the staircase approximation and combining multimode network theory with the mode-matching procedure can be effectively applied to the analysis of leaky wave structures of any profile. In the analysis, the arbitrary continuous profile is discretised by a staircase approximation; evidently, in the limit of vanishing step size, the piecewise constant profile will approach the continuous one. With such an approximation, mathematical analysis and physical interpretation of the potential mode coupling phenomena related to the leaky wave structure can be kept simple and clear. The new antenna structures with an arbitrary profile of cross-section provide more degree of freedom for the design of a leaky wave antenna by flexibly changing the geometric dimensions of the structures. On the other hand, these antennas may be more practical because keeping an exact regular shape in manufacturing sometimes is very difficult. The analysis given thus permits one to gain an insight into the qualitative effects produced by some geometric size and also to determine how large the size change can be acceptable before it influences significantly the transmission properties of the NRD guide when used as a millimeter wave guiding structure.