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Design Dengan Microstrip
Sukiswo
[email protected]
Elektronika Telekomunikasi, Sukiswo ST, MT
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Outline
 Pengertian
 Design Dengan Microstrip
 Microstrip sebangai saluran transmisi (line
transmission)
 Microstrip as Equivalent Componen
 Distributed Equivalent Component Design
Elektronika Telekomunikasi, Sukiswo ST, MT
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Pengertian
 Microstrip is a type of electrical
transmission line which can be fabricated
using printed circuit board [PCB]
technology, and is used to convey
microwave-frequency signals.
 It consists of a conducting strip separated
from a ground plane by a dielectric layer
known as the substrate.
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Pengertian
Cross-section of microstrip geometry.
Conductor (A) is separated from ground plane (D)
by dielectric substrate (C). Upper dielectric (B) is
typically air.
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Pengertian
Band Stop Filter 1 GHz
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Pengertian
Power Divider 1 GHz
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Pengertian
 Microwave components such as antennas,
couplers, filters, power dividers etc. can be
formed from microstrip, the entire device
existing as the pattern of metallization on
the substrate.
 Microstrip is thus much less expensive than
traditional waveguide technology, as well as
being far lighter and more compact.
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Pengertian
 The disadvantages of microstrip compared with waveguide
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are the generally lower power handling capacity, and
higher losses.
Also, unlike waveguide, microstrip is not enclosed, and is
therefore susceptible to cross-talk and unintentional
radiation.
For lowest cost, microstrip devices may be built on an
ordinary FR4 (standard PCB) substrate.
However it is often found that the dielectric losses in FR4
are too high at microwave frequencies, and that the
dielectric constant is not sufficiently tightly controlled.
For these reasons, an alumina substrate is commonly used.
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Pengertian
 On a smaller scale, microstrip transmission lines
are also built into monolithic microwave
integrated circuits [MMIC]s.
 Microstrip lines are also used in high-speed digital
PCB designs, where signals need to be routed
from one part of the assembly to another with
minimal distortion, and avoiding high cross-talk
and radiation.
 Microstrip is very similar to stripline and coplanar
waveguide [CPW], and it is possible to integrate
all three on the same substrate.
Elektronika Telekomunikasi, Sukiswo ST, MT
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Design With Microstrip
 At microwave frequencies, microstrip is employed not only
as a transmission line on PCBs, but also as equivalent
passive components, tuned circuits, and high-Q microwave
filters and resonators.
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Design With Microstrip
 Microstrip transmission line is used in microwave
applications due to its low loss, low cost, small size, ease of
implementation, and the ability to mount components, such
as surface-mount capacitors, resistors, and transistors,
directly onto the microstrip itself.
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Design With Microstrip
 Most microstrips are unbalanced transmission lines and, because of
their unshielded nature, can radiate some RF.
 However, radiations from properly terminated microstrips are fairly
small.
 Stripline (Fig. 1.42) is similar to microstrip, but is placed between the
metallization layers of a PCB and, due to these balanced twin
groundplanes, does not radiate.
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Design With Microstrip
 The characteristic impedance of microstrip transmission
line is governed by the width of the conductor, the
thickness of the dielectric, and the dielectric constant; with
low impedance microstrip lines being wide, and high
impedance microstrip lines being narrow
 But the most important attribute of terminated microstrip as
transmission line is that its impedance does not change with
frequency, or with length.
 The normal characteristic impedances of microstrip and
stripline are designed to be anywhere between 10 to 110 Ω,
with 50 Ω being the universal norm for RF transmission
line use.
 Microstrip is very common in frequencies of operation at
250 MHz and above
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Microstrip as Transmission Line
 A 50-Ω microstrip is utilized in microwave circuits to
prevent reflections and mismatch losses between
physically separated components, with a calculated
nominal width that will prevent the line from being either
inductive or capacitive at any point along its length.
 In fact, with a source’s output impedance matched to the
microstrip, and the microstrip matched to the input
impedance of the load, no standing or reflected waves will
result.
 Consequently, there will be no power dissipated as heat,
except in the actual resistance of the copper and dielectric
as I2R losses.
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Microstrip as Transmission Line
 In microstrip, the dielectric constant (Er) of the
PCB’s substrate material will not be the sole Er
that the microstrip transmission line itself “sees.”
 This is due to the flux leakage into the air above
the PC board, combined with the flux penetrating
into the dielectric.
 So the actual effective dielectric constant (EEFF),
which is the true dielectric constant that the
microstrip will now see, will be at some value
between the surrounding air and the true dielectric
constant of the PCB.
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Microstrip as Transmission Line
 Due to the small RF field leakage that emanates
from all microstrips, these types of transmission
lines should be isolated by at least two or more
line widths away from other traces and circuits in
order to decrease any mutual coupling effects.
 To lower the chances of crosstalk even further an
isolation ground trace may possibly be necessary
between two such lines.
 To decrease any impedance bumps at high
microwave frequencies, microstrip should always
be run as short and as straight as possible, with
any angle using a mitered or slow round bend
(Fig. 1.43)
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Microstrip as Transmission Line
 Another issue to watch for when designing microwave circuits with microstrip
transmission lines is the waveguide effect (see RF Shielding Resonances): Any
metal enclosure that is used to shield the microstrip, or its source or load
circuit, may act as a waveguide, and drastically alter the circuit’s behavior.
 This effect can be eliminated by changing the width of the shield to cover a
smaller area, or by inserting a special microwave foam attenuator material
within the top of the enclosure.
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Design with Microstrip
 Use the following equation to plug in different
microstrip widths to obtain the desired impedance:
Where
ZO = characteristic impedance of the microstrip, Ω
W = width of the microstrip conductor (use same units as h below)
h = thickness of the substrate between the groundplane and the microstrip
conductor (use same units as W)
Er = dielectric constant of the board material
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Microstrip as Equivalent Componen
 Distributed components, such as inductors and
capacitors, can be formed from microstrip
transmission-line sections on PCBs at microwave
frequencies.
 A series or shunt inductor can be formed from a
thin trace (Fig. 1.44),
 A shunt capacitor can be formed from a wide trace
(Fig. 1.45),
 And even a transformer can be formed by varying
the width of the microstrip (Fig. 1.46).
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Microstrip as Equivalent Componen
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Microstrip as Equivalent Componen
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Microstrip as Equivalent Componen
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Microstrip as Equivalent Componen
 Distributed equivalent microstrip works in replicating a
lumped component because high impedance (thin)
microstrip traces possess very little capacitance (due to the
small surface area of the structure), but possessing a useful
amount of inductance.
 This inductance is caused by the current flowing through
the constricted microstrip element, which is both thin and
long.
 In other words, we are taking a normal 50-Ω microstrip,
with its built-in distributed inductance and capacitance that
makes the microstrip line 50 Ω throughout its entire length,
and simply minimizing the capacitance, while maximizing
its inductance.
Elektronika Telekomunikasi, Sukiswo ST, MT
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Microstrip as Equivalent Componen
 The reverse is also true if we want to create a distributed
capacitor, since the 50-Ω microstrip can now be formed as
a wide strip, with the PCB’s copper groundplane and its
dielectric being located directly beneath it.
 Thus, the much larger surface area of this fatter microstrip
(over its 50-Ω configuration) appears as a capacitor at RF
frequencies.
 However, we cannot accurately, nor with any value above
1 pF or so, replicate series capacitors in distributed form,
so we should select an appropriate lumped matching
network that is devoid of any such series capacitors, and
then convert it to a distributed structure.
Elektronika Telekomunikasi, Sukiswo ST, MT
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Microstrip as Equivalent Componen
 The accuracy of the equivalency itself will only be exact
for frequencies that are less than 30° long across the
distributed equivalent shunt component.
 Equivalency is still possible with longer lengths, but
keeping all equivalent component elements at less than 30°
will supply the best performance.
 Maintaining this shorter length in the distributed
component design will sometimes demand compensating,
which we can do by narrowing the distributed inductor’s
trace width (increasing impedance), or widening the
distributed capacitor trace width (decreasing impedance),
to keep the total length under 30°.
 Due to the increased losses and the lack of width
repeatability during board fabrication, we cannot normally
use equivalent inductors that are narrower than 6 mils.
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Distributed Equivalent Component Design
 As stated above, it is important to strive to make a
distributed component shorter than 30° out of the 360° of
an entire wavelength, or the equivalent component effect
will begin to depart more and more from that of an ideal
lumped component.
 To calculate how long 30° is out of 360°, simply divide 30
by 360, then multiply this value by the actual wavelength of
the signal on the PCB, keeping in mind that the signal’s
wavelength in the substrate will not be the same as if it
were traveling through a vacuum.
 To find the actual wavelength of the signal, which is being
slowed down by the PCB’s substrate material, calculate the
microstrip’s velocity of propagation (VP).
 First, find the effective dielectric constant (EEFF) of the
microstrip, since the signal will be partly in the dielectric
and partly in the air above the microstrip, which affects the
propagation velocity through this combination of the two
dielectric mediums.
Elektronika Telekomunikasi, Sukiswo ST, MT
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Distributed Equivalent Component Design
 First, find the effective dielectric constant (EEFF) of the
microstrip, since the signal will be partly in the dielectric
and partly in the air above the microstrip, which affects
the propagation velocity through this combination of the
two dielectric mediums.
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Distributed Equivalent Component Design
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Distributed Equivalent Component Design
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Distributed Equivalent Component Design
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Perhitungan Microstrip
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Perhitungan Microstrip
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Perhitungan Microstrip
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Perhitungan Microstrip
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Perhitungan Microstrip
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Perhitungan Microstrip
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Perhitungan Microstrip
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Perhitungan Microstrip
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