A review of electromagnetic scattering analysis for inlets, cavities, and open ducts

This paper is a review of all methods that have been used in the literature for the solution of a very important and challenging set of problems, namely electromagnetic scattering from inlets, cavities, and open ducts. The techniques examined have been grouped together according to their fundamental principles, so that easy and direct comparisons among them are facilitated. The complexity and difficulty of the problems are clearly inferred from the very long list of references, which includes several very recent articles. The purpose of the paper is to highlight the advantages and limitations of the techniques invoked, draw useful conclusions, and trigger initiatives for future improved approaches to the topic.

1. Introduction

One of the most challenging problems in modern applied electromagnetics, with extensive military and civilian applications, is the scattering characterization of aircraft configurations. Closely related topics of interest include non-cooperative target recognition, radar cross section (RCS) reduction and “stealth” (low-observable) technology, evaluation of target visibility for detection/tracking studies, etc. Among the various contributors to the RCS, measurements have shown that the jet-engine inlets have a very significant impact on the overall signature of the airplane structure. Indeed, most aircraft types exhibit significantly different scattering behaviors when measured with covered or uncovered engine intakes. As a result, over the years, numerous studies have been carried out for the analysis of jet-engine inlets and their components. Early studies have expectedly been of theoretical nature, focusing on very simple geometrical models, such as mere circular cylinders. However, the complexity of the configurations has been steadily increasing, leading to reliable computational results for fairly realistic structures. The great interest of the scientific, technical, and defense communities in the problem is clearly demonstrated by the large number of PhD dissertations and MSc theses [1]–[13] that have been completed on this topic at prestigious academic institutions with solid backgrounds in electromagnetics. Such institutions include, among others, the Ohio State University (Columbus, Ohio), University of Michigan (Ann Arbor, Michigan), and University of Illinois (Urbana-Champaign, Illinois).