Contents

1
Contents
This discusses the major types of transmission
lines involved in fabrication procedures across
the world- microstrip, CPW, stripline and
Suspended substrate Stripline(SSSL)

• Pl. Trans. Lines
• Substrate Materials
• Dist. Ct. Elements
• Solid State Dev.
• Mixers
• Others

2
Contents
This discusses the variety of options any
engineer has when he fabricates the device of his
choice. It talks about the conventional quartz,
alumina and sapphire and also on the latest
composites that are being used.

• Pl. Trans. Lines
• Substrate Materials
• Dist. Ckt. Elements
• Solid State Dev.
• Mixers
• Others

3
Contents
This provides a birds eye view of the the
variety of distributed circuit elements one has
at his disposal, the related uses, equations etc.

• Pl. Trans. Lines
• Substrate Materials
• Dist. Ckt. Elements
• Solid State Dev.
• Mixers
• Others

4
Contents
This builds a grounding in the various solid
state devices that are being used, gives their
frequency ranges, uses, characteristics and also
the visualization diagrams showing their cross
sections.

• Pl. Trans. Lines
• Substrate Materials
• Dist. Ckt. Elements
• Solid State Dev.
• Mixers
• Others

5
Contents
Discusses the common types of mixers available,
their characteristics and the various
applications they are being used for. It also
gives diagrammatical representations of the same.

• Pl. Trans. Lines
• Substrate Materials
• Dist. Ckt. Elements
• Solid State Dev.
• Mixers
• Others

6
Planar transmission Lines
7
Planar transmission Lines
MICROSTRIP The great majority of planar circuits
are realized in microstrip. Microstrip is a
practical medium for a wide variety of components
and is a natural choice for large, integrated
systems. Microstrip, like most planar circuits,
is a "quasi- TEM" transmission line. This means
that it is usually treated as a TEM line at
frequencies low enough for dispersion to be
negligible. At higher frequencies, dispersion
corrections are usually necessary. Again, a
number of methods exist. One of the most popular
and most accurate is that of Kirschning and
Jansen. Another good one is by Wells and
Pramanick. A simple approximate expression for
the cutoff frequency of the lowest non- TEM mode
is 75/h(k-1)0.5. where this is got in GHz and h
is in mm.
8
Planar transmission Lines
CPW For many purposes CPW is a good alternative
to microstrip. In CPW the ground surfaces are
alongside the strip conductor instead of
underneath it. This configuration causes many
characteristics to differ from those of
microstrip. First, the fields are not as fully
contained in the dielectric and extend farther
into the air above the substrate. This causes
dispersion and radiation to be worse in CPW than
in microstrip. Second, the currents are more
strongly concentrated in the edges of the
conductors. Because the edges are likely to be
much rougher than the surfaces, losses are higher.
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Planar transmission Lines
Nevertheless, CPW has significant advantages over
microstrip for monolithic circuits. The most
important is that ground connections can be made
on the surface of the substrate there is no need
for "via" holes, which are used to make ground
connections in microstrip circuits. CPW grounds
usually have much less inductance than
microstrip, an important consideration for many
types of high-frequency circuits. Another
important advantage is size. CPW conductors can
be very narrow, even with low characteristic
impedances. Low-impedance microstrip lines often
are impractically wide. Finally, CPW is much less
sensitive to substrate thickness than microstrip,
so the thinning of the monolithic substrate is
much less critical. CPW monolithic circuits often
are not thinned at all)
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Planar transmission Lines
STRIPLINE Strip line is one of the oldest types
of planar transmission media, developed in the
late 1950s and originally called triplate. Of the
lines listed in Table 1.1,stripline is the only
true TEM transmission line. As such, it is
non-dispersive, but it is not immune to moding,
especially if the strip conductor is not centered
evenly between the ground planes. Strip line
components invariably use composite substrates.
One technique is to create a sandwich of two
substrates, one having a ground plane and a strip
conductor, the other having only the ground
plane. These two substrates are clamped firmly
together to prevent the formation of an air gap,
which would create variations in the dielectric
constant of the medium between the ground planes.
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Planar transmission Lines
Stripline is a great medium for directional
couplers. This is virtually impossible in
microstrip or CPW, which can use only edge
coupling. The homogeneous dielectric of stripline
makes its even-mode and odd-mode phase velocities
equal, resulting in high directivity. Broadside
coupling is also possible in suspended-substrate
stripline. Stripline is not a favored
transmission medium these days, probably because
it is not really suitable for components that
include chip diodes, transistors, or other
discrete circuit elements, and it does not
integrate well with the media that do.
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Planar transmission Lines
One possibility is suspended-substrate stripline
(SSSL). It has many of the properties of
stripline but can be realized with either a hard
or a soft substrate. The non homogeneous
dielectric gives SSSL a very low effective
dielectric constant, close to LO, and slightly
lower loss than stripline. It is, however,
slightly dispersive. The enclosure also is
subject to waveguide-like modes, so its
cross-sectional dimensions must be kept
comfortably less than one-half wavelength in both
width and height. An approximate expression for
the lowest cutoff frequency fc of such modes, in
GHz, is
150/a(1-(h(k-1)/bk)0.5 where a and b are the
width and the height of the channel in
millimeters, h is the substrate thickness, and k
is the dielectric constant.
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Substrate Materials
Commonly used substrate materials are shown
14
Substrate Materials
Silica Loosely called quartz, its single-crystal
form, fused silica has a number of very good and
very bad properties. It is one of the few
high-quality materials that have a low dielectric
constant. Its dielectric constant is 3.78, much
lower than other hard substrates but not as low
as the composite materials. This low dielectric
constant, combined with low loss and good
smoothness, makes fused silica seemingly ideal
for millimeter-wave circuits. Unfortunately,
fused silica is also very brittle, making it
difficult to handle and to fabricate, and its
smoothness makes good metal adhesion difficult to
obtain. Fused silica has a low thermal expansion
coefficient it is matched only to Invar or
Kovar, metal alloys that are expensive and
difficult to machine. Metallizations consist of
a very thin sputtered adhesion layer with a top
layer of plated gold.
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Substrate Materials
Alumina is the ceramic form of sapphire (see
below). It is a moderately expensive substrate
but still the least expensive of the "hard"
substrates. It is very hard, temperature-stable,
and has good thermal conductivity. Although its
thermal expansion coefficient is not well matched
to brass or aluminum, alumina is so strong that
it does not crack easily when bonded to a
thermally mismatched surface, even at extreme
temperatures. Alumina can be polished to high
smoothness, if necessary, and metal adhesion is
good. Although hard, alumina can be cut easily
with a diamond substrate saw or a laser holes
can be made with a laser or a carbide
tool. Alumina has a high dielectric constant,
usually 9.5 to 10.0The most common metallization
is gold. A very thin adhesion layer is used
between the gold and the substrate.
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Substrate Materials
Sapphire Sapphire is the crystalline form of
aluminum oxide (Al2O4). It is relatively
expensive. Its only advantage over alumina is its
extreme smoothness, which minimizes conductor
loss, and slightly lower dielectric loss.
Sapphire is electrically anisotropic its
dielectric constant depends on the direction of
the electric field in the material. It is 8.6 in
a plane and 10.55 in the direction parallel to
that plane. Sapphire usually is cut so that the k
8.6 plane is parallel to the ground plane. This
makes the characteristics of microstrip lines
independent of their orientation, but it causes
the difference between even- and odd-mode phase
velocities in coupled lines to be Worse than in
an isotropic material. The metallization is
invariably gold with an adhesion layer.
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Substrate Materials
Composite Materials Composite materials often
are called "soft substrates," because they are
usually made from flexible plastics. The most
common form is poly-tetra-fluoro-ethylene (better
known by its trade name, Teflon), loaded with
glass fibers or ceramic powder. This is both an
advantage and disadvantage the soft material is
easy to handle and inexpensive to fabricate, but
the mechanical and thermal properties are not as'
good as those of "hard" substrates. The thermal
conductivity may be very low.
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Substrate Materials

• The following are some concerns
• Tolerance of the dielectric constant
• Variation of the dielectric constant and loss
  tangent with frequency and temperature
• Electrical anisotropy
• Thermal expansion coefficient and Moisture
  absorption
• Volume and surface resistivity.

19
Distributed Circuit Elements
20
Distributed Circuit Elements

• A stub is a length of straight transmission line
  that is short- or open-circuited at one end and
  connected to a circuit at the opposite end. Stubs
  can approximate inductors, capacitors, or
  resonators. High- or low-impedance series lines
  also approximate series inductors or shunt
  capacitors, respectively
• . Stubs are used almost exclusively as shunt
  elements. Although they could, in theory, be used
  to realize series elements, there are a couple of
  problems in doing so. First, the stub would have
  to be realized by a parallel-coupled line. The
  even mode on such a line would introduce shunt
  capacitance, so the stub would not be a series
  element. Second, such structures often are
  difficult to realize both mechanically and
  electrically. Usually they just don't work.
• Shortcircuit stub Zin jZo tan(ßl)
• Opencircuit stub Zin jZo cot(ßl)

21
Distributed Circuit Elements
A radial stub is an open-circuit stub realized in
radial transmission line instead of straight
transmission line. It is a very useful element,
primarily for providing a clean (no spurious
resonances) broadband short circuit, much broader
than a simple open-circuit stub. It is especially
useful on bias lines in high-frequency amplifiers
and similar components. Radial stubs are used
almost exclusively in microstrip circuits they
could be used in stripline as well. Although
radial stubs are shorter than uniform stubs, they
cannot be folded or bent therefore they take up
a lot of substrate area. For this reason radial
stubs are used primarily at high frequencies,
where they are relatively small.
22
Distributed Circuit Elements
A radial stub commonly used
in microstrip.
23
Distributed Circuit Elements
Series Lines. The expressions are valid when
mod(ß) n/4, and under these conditions
tan(mod(ß)) mod(ß). We should also quantify
what we mean by high and low impedances we mean
that they are high or low compared to the
impedances locally in the circuit. For example, a
filter designed for SOQ terminations requires Zo
SOQ or Zo SOQ. Series lines do not provide
very good approximations of shunt capacitors or
series inductors unless the capacitance or
inductance is fairly low. Even then, the
discontinuities introduced by cascading low- and
high-impedance sections, as would exist in a
low-pass filter, for example, can be difficult to
characterize accurately.
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Solid State Devices
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Solid State Devices
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Solid State Devices
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Solid State Devices
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Solid State Devices
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Solid State Devices
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Solid State Devices
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Solid State Devices
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Solid State Devices
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A Study of Mixers
sss
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A Study of Mixers
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A Study of Mixers
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A Study of Mixers
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A Study of Mixers
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A Study of Mixers