Waveguide Transitions

Waveguide Transitions
by Manfred Thumm and Werner Wiesbeck
Forschungszentrum Karlsruhe
in der Helmholtz - Gemeinschaft
Universität Karlsruhe (TH)
Research University•founded 1825
Transitions
It is often necessary to transfer from strip line components to other
waveguide types, e.g. to attach a coaxial antenna feed cable or to feed
the HF-power generated in a stripline circuit into a waveguide mixer.
How such transitions are implemented with as little attenuation and
reflection as possible is shown in the next section.
Transitions introduce different, usually undesired effects:





losses, attenuation
series impedances L,C,
parallel impedances L,C,
coupling to other components
influence on phase
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Microwave Line Characteristics
criteria
line
type
production
cost
weight
size
losses
preferred
application
complicated
high
high
big
low
high power,
low loss
moderate
flexible,
subsystem
connections
low
large scale
production,
semiconductor
integration
waveguide
coaxial line
moderate
moderate
moderate
small
microstrip line
easy
low
moderate
very
small
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Typical Microwave Line Transitions
fields non-symmetric
Task for transitions:
Matching of the fields
fields symmetric
fields non-symmetric
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Coaxial Line - Microstrip Line Transition
In the following only the problems encountered in the transitions
between coaxial and microstrip lines are discussed, since these occur
most frequently in practice. The arising difficulties are:



good contact formation (low transition resistance)
all round contacting of the substrate (with housing assembly)
no detours for the ground current path
For a connection with a ground loop, the following simplified
equivalent circuit diagram can be assumed:
solder well
ground
current
avoid
ground gap
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Unpackaged Coaxial-Microstrip Transition
If no housing assembly is to be made, then two different techniques are
principally used: soldering and the clamping technology.
Soldered Contact
Clamped Contact
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Housed Coaxial-Microstrip Transition Assembly
Ground Contact:
Connector
Housing
Microstrip Ground
a) Clamps; b) Clamps with spring plate; c) Soldering or glueing with line adhesive;
d) Soldering on Invar or Kovar intermediate carriers.
Invar:
Fe – Ni – C (63,8% - 36% - 0,2%)
Kovar:
Fe – Ni – Co (54%
- 28% - 18%)
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Center Conductor Transition (abrupt, narrowband)
Narrowband Low-Pass Compensation
SMA Connector
a) Clamping
technology with
contact spring
(f  18 GHz);
b) Like
(a) but with plastic
thrust piece;
c) Like (a), but with
sprung stamp fitted;
d) Soldered center
conductor (f  1 GHz);
e) Welded strip
(f  0.5 GHz);
f) Welded bond wire
(f  0.2 GHz).
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Center Conductor Transition (continuous, broadband)
Further designs of reflectionpoor transitions of 3/7-coaxial
cable (di = 3 mm, da = 7 mm) or
SMA coaxial cable (di = 1.3 mm,
da = 4.3 mm) on microstrip line
on ceramic substrate
S: Substrate (thickness:
25 mil = 0.635 mm, r = 9.8)
K: Contact spring inner line
B: Housing floor
D: Dielectric
a) with inserted air line
b) with graduated cross
sectional adjustment
c) with continuous cross
sectional adjustment
d) multiply stepped
e) eccentric coaxial cable
transition
f) hermetically sealed transition
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Field Distribution of the H10-Wave (TE10-Wave)
b
a
Ey, Hx
a
Hz
x
z/2
y
x
z
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Transitions Coaxial Line - Waveguide
c)
a)
H/4
b)
d)
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Transitions Microstrip Line - Waveguide
a)
conductor
r
b)
c)
slot in -strip
ground plane
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Special Forms of Microstrip Line - Waveguide Transitions
Transitions of rectangular
waveguides to striplines:
a) E-probe feed coupling
of suspended substrate
line (15% bandwidth)
b) Stepped transformer
transition to microstrip
line (20% bandwidth)
Balun: Balanced – unbalanced – Transition
c) Finline transition to
microstrip line
(36% bandwidth)
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