Coaxial waveguides are frequently used in order to feed and
interconnect a wide variety of microwave and millimeter wave
devices (filters, diplexers, multiplexers, etc.). As a
consequence, the rigorous and efficient characterization of the
coaxial excitacion of waveguide structures is a very important
topic that has been widely studied in the technical literature.
However, a few number of these contributions investigate this
problem from a multimodal point of view.

The main objective of this work is the efficient multimodal
characterization of the coaxial excitation of waveguide components
using the 3D BI-RME (Boundary Integral - Resonant Mode
Expansion) method. In particular, two types of configurations
widely used in practical applications are discussed: the classical
coaxial excitation, and the coaxial excitation based on an
end-launcher configuration. The end-launcher configuration is
commonly used to feed comb-line filters, which are also
investigated in this work. Concretely, a very efficient CAD tool
for the analysis and design of comb-line filters has been
developed.

The analysis and design of compensated waveguide junctions using
partial-height metallic posts is also a main objective of this
investigation. Following the 3D BI-RME method, we present the
design of a great variety of compensated waveguide junctions
(right-angled bends, T junctions, magic T junctions, and turnstile
junctions) with an optimum electrical performance. Moreover, we
demonstrate that the relative position of the metallic post in the
structure is a very important design parameter that has not been
taken into account in previous works concerning compensated
junctions using partial-height metallic posts.