Intermodal Coupling at the Junction Between Straight and Curved Waveguides

In a microwave system for guiding electromagnetic waves, often there are bends formed by connecting straight and continuously curved rectangular waveguides (see Fig. 1). Precise numerical computations and extensive analytical investigations of the angular propagation constants for the various electromagnetic modes in the curved section alone have been published by Cochran and Pecina. 1 The propagation constants and modal fields which may exist in the straight sections alone are trivial. To understand propagation of electromagnetic waves through these waveguide bends, therefore, requires a complete comprehension of the intermodal coupling that takes place at the various junctions and discontinuities. This paper investigates the coupling that occurs where straight and continuously curved rectangular waveguides join. This type of structure has been studied to some extent by others. 2259 2260 T H E BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1969 Fig. 1 -- Waveguide bends formed by connecting straight and continuously curved rectangular waveguides, (a) E-plane bend, (b) H-plane bend.