here to go to our main page on transmission lines
New for March 2010! Professor
Bharathi Bhat was one of the principal researchers in establishing
the theory and application of finline. She literally wrote
the book on finline!
This page was writen with the
help of Dr. S. Raghavan, the last Ph.D. scholar of Prof. B. Bhat
and a Senior Professor, National
Institute of Technology, Trichirappalli, India. Thanks!
Finline is similar to slotline,
but the finline structure is bounded within a rectangular waveguide.
It solves the problem of how to install components such as diodes
into rectangular waveguide. It is a close relative of double-ridged
End view of unilateral
Finline was first proposed by
Meier in 1972, and ideally suited for use in millimeter frequency
applications. It can be used from 30 GHz to 110 GHz. Basically it
consists of a partially metalized dielectric substrate shielded
by a rectangular metal enclosure. The metallization can be in the
form of fins and/or isolated strip conductors of arbitrary widths
placed in symmetric or antisymmetric positions on the substrate.
The types of finline include unilateral finline (fins on only one
side of the substrate with slot in the centre or off-centered) symmetrical
and asymmetrical, bilateral finline (fins located on both sides
of substrate, broadside coupled double-dielectric finlines employing
two symmetrically positioned substrates with an intervening air
gap between them), asymmetric broad side coupled double dielectric
finline, edge coupled finline, antipodal finline and insulated finline.
Antipodal finline is useful to act as transitions between two kinds
of planar transmission lines. The useful applications are filters,
hybrid rings, power dividers, phase shifters, mixers and transitions.
Finline got its name because
it resembles a fin of a fish. This is the only structure having
planar transmission line in E-plane inserted in a waveguide. These
kind of quasi-planar structures combine the advantageous features
of planar technology in terms of amenability to circuit integration
and mass production, and of waveguide technology in terms of low
impedance (Z0) range that can be realized in finline spans 10 to
400 ohms, which is much greater than what is practical in microstrip
or stripline. The dominant mode of propagation is a hybrid mode.
Commonly used substrates include RT-Duroid, Cuflon and Kapton. An
exhaustive analysis of finline is reported in B. Bhat and S. K.
Koul, Analysis, Design and Application of Finlines, Artech
House, MA 1987.