COPLANAR WAVEGUIDE TRANSMISSION LINES

Report
COPLANAR WAVEGUIDE
TRANSMISSION LINES
Who invented CPW and why
was it introduced?
C.P. Wen introduced CPW (Titled it based
on its initials) to overcome the limitations of
microstrip transmission lines
Limitations of Microstrip Transmission
Lines
Grounding can be obtained by accessing the backside
ground by a via through the substrate( this leads to high
amount of undesirable associated inductance at higher
frequencies)
Microstrip is difficult to use when the substarte thickness is
significant , in this case energy easily radiates to the
adjacent structures.
Dispersion is also high for microstrip
Design and Strucure of CPW’S
CPW
ECPW
Discontinuities in CPW’s
CPW discontinuities are an integral part of
practical CPW circuits
The CPW short-end and open-end series stubs
are two important structures for filter
applications.
The CPW short-end series stub was modeled as
a series inductor and the open-end series stub
was modeled as a series capacitor.
These can be attributed to their bandstop and
bandpass response respectively. However, both
these stubs are asymmetric and their resonant
nature is valid only for small stub lengths
T-Junction and Cross Junction designs
simulation result
Circuit Layout Examples
Undesired modes of Operation
The first of these is excitation of the coupled slotline mode
due to the three-conductor nature of CPW.
The second is the excitation of the parallel plate
waveguide mode if a backside ground plane is
introduced.
The third arises in ungrounded CPW when the dimension
of the total ground plane becomes large enough that it
resonates
Calcualtion of Parameters
Characteristic Impedence Z0 :-
Conductor Losses:-
Total Attenuation Losses:Conductor Losses + Dielectric Losses
Application of CPW in real time :In Aviation Industry CPW transmission lines are being
developed to use in RF MEMS Switches (
Microelectromechanical Systems)for missile seeker system
It involves fabrication of CPW transmission lines on one
wafer and piezolectrically actuated stuctures on another
wafer by thermocompression bonding
Limitations of CPW
Design could be challenging due to limited
design and layout available in market
Packaging may also be challenging since we
have to look for parallel plate mode supression
References:-
“A flip-chip MMIC design with coplanar waveguide transmission line
in the W-band”
“Coplanar Waveguide Basics for MMIC and PCB Design”
“Design, fabrication and testing of coplanar waveguide transmission
lines for use in RF MEMS switches”
“characterization of a coplanar waveguide open stub-based
discontinuity for mmics and filter applications”
“Characteristics of Coplanar Transmission Lines on Multilayer
Substrates: Modeling and Experiments”
“Modeling of Elevated Coplanar Waveguides for High Speed Digital
Circuits “
Queries ?

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