Upload
others
View
12
Download
1
Embed Size (px)
Citation preview
CONFIDENTIAL 1
Presented by: John Coonrod
Design Considerations and Tradeoffs for Microstrip, Coplanar and Stripline Structures at Millimeter-wave Frequencies
Webinar
CONFIDENTIAL 2
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
Agenda:
• Elementary transmission line theory• General theory• Millimeter-wave concerns
• Basic structure overview• Microstrip• Coplanar• Stripline
• Structure comparisons across a wide range of frequencies
• PCB variables to consider that affect RF performance (e.g. etching tolerance and plated finish)
CONFIDENTIAL 3
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
Elementary transmission line theory
General theoryMillimeter-wave concerns
CONFIDENTIAL 4
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
Elementary transmission line theory, general theory
Waves
Microwave and millimeter-wave engineers frequently refer to “waves” and their properties
Plane wave: wave propagation direction is perpendicular to the forces that create it
Electric field is perpendicular to Magnetic field and also is perpendicular to wave direction
CONFIDENTIAL 5
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
Wavelength (λ) is the physical length from one point of a wave to the same point on the
next wave
Long wavelength = low frequency
Short wavelength = more waves in the same time frame
Amplitude is the height of the wave and often related to power
High electric field = High magnetic field = High amplitude = High power
Waves
Elementary transmission line theory, general theory
CONFIDENTIAL 6
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
Transverse ElectroMagnetic (TEM) wave
Electric field varies in z axis
Magnetic field varies in x axis
Wave propagation is in y axis
TEM wave propagation is most common in PCB technology, but there are other waves
Waves
Elementary transmission line theory, general theory
CONFIDENTIAL 7
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
Waves
Other wave propagation modes are:
TE (transverse-Electric) or H wave; magnetic field travels along with wave
TM (transverse-Magnetic) or E wave; electric field travels along with wave
TEM or quasi TEM waves are typically the intended wave for a transmission line
Some PCB design scenarios will have problems with “modes” or “moding”
Moding issues are when the intended TEM wave is interfered with another wave mode
such as TE or TM modes; this is a spurious parasitic wave or unwanted wave
Elementary transmission line theory, general theory
CONFIDENTIAL 8
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
Properties
Relative permittivity (εr) or dielectric constant (Dk):The property of material which alters the electric field in the waveVery important property for microwave PCB designMaterials used in PCB technology generally have Dk from 2 to 10The imaginary component of complex permittivity is Df (dissipation factor)Df is the amount of dielectric loss the material imparts on the wave
Relative permeability (μr)The property of material which alters the magnetic field This property is rarely used in microwave PCB applicationsMost PCB materials have μr = 1Some plated finishes used on PCB’s have ferromagnetic properties (μr >> 1)Ferromagnetic issues can cause more conductor loss
Elementary transmission line theory, general theory
CONFIDENTIAL 9
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
Circuit with low Dk Circuit with high Dk
Dk effect on wavelength
Elementary transmission line theory, general theory
CONFIDENTIAL 10
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
Conductivity (σ): Copper is typically the conductor for PCB’sMost plating finishes in PCB technology have lower conductivity than copperLower conductivity causes:
more conductor lossdeeper skin depth in the conductor
A copper surface which is rough will cause more conductor losses than smooth
Skin depth is how deep the current density will be in the conductor
At DC (0 Hz) the current will used the entire conductor
At a higher frequency the current will use the “skin” of the conductor
skin depthμ permeabilityσ conductivity
Elementary transmission line theory, general theory
CONFIDENTIAL 11
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
• There are many kinds of transmission lines
• Wires
• Cables
• Printed circuit boards (PCB)
Elementary transmission line theory, general theory
CONFIDENTIAL 12
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
• Example of a transmission line with 3 dB insertion loss
• 3 dB is a loss of half of the power
• The load receives half of the power that the generator sent
Elementary transmission line theory, general theory
CONFIDENTIAL 13
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
2-port system, transmission line
Signal Flow Diagram
Port 1 Port 2
S parameters are an easy way to analyze loss
S21 is insertion lossS21 is the energy at port 2 that came from port 1
S11 is return loss or loss due to reflections at port 1S11 is the energy received at port 1 that came from port 1
Elementary transmission line theory, general theory
CONFIDENTIAL 14
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
Elementary transmission line theory, general theory
Example of wideband insertion loss curve
CONFIDENTIAL 15
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
αT is total insertion lossαC is conductor lossαD is dielectric lossαR is radiation lossαL is leakage loss
Dielectric loss (αD) is mostly due to the substrate, prepreg or soldermask
Conductor loss (αC) is due to several issues related to the conductor of the circuit
Radiation loss (αR) is due to many issues related to energy radiating off of the circuit
Leakage loss (αL) is mostly due to electrical leakage, through the dielectric and between conductor layers
Elementary transmission line theory, general theory
CONFIDENTIAL 16
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
• The dominate loss component can be different, for the different circuit thicknesses
• Three circuit sets made from same material but different thicknesses
• Circuit material used was RO4350B™ laminate
Elementary transmission line theory, general theory
CONFIDENTIAL 17
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
frequency radiation loss
• There are many variables regarding radiation loss
• Radiation loss is:
• Frequency dependent
• Circuit thickness dependent
• Dielectric constant (Dk) dependent
• Radiation loss can vary magnitude due to:
• Circuit configuration (microstrip, coplanar, stripline)
• Signal launch
• Spurious wave mode propagation
• Impedance transitions and discontinuities
thickness radiation loss
Dk radiation loss
Elementary transmission line theory, millimeter-wave concerns
CONFIDENTIAL 18
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
Elementary transmission line theory, millimeter-wave concerns
A thinner laminate is necessary for minimizing spurious modes at mmWave frequencies
Thin laminates are better for reducing radiation losses
Radiation losses at mmWave (millimeter-wave) frequencies can be a major concern
However a drawback of the thinner laminate is more conductor losses
CONFIDENTIAL 19
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
Elementary transmission line theory, millimeter-wave concerns
Resonances can set up between the signal conductor and the ground plane
Resonances can set up between opposite edges of the signal conductor
• When W is ½ or ¼ wavelength, resonances will occur and a resonance can generate its’ own EM wave
• The resonance generated EM wave will be a spurious wave that can interfere with the intended quasi-TEM wave; a good design limit is no feature > 1/8 wavelength
W
W
CONFIDENTIAL 20
Thickness comparisons, microstrip insertion loss; thicker laminate has more issues at higher frequencies
CONFIDENTIAL 21
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
Elementary transmission line theory, millimeter-wave concerns
Thickness can be a concern, but typically conductor width is more significant
This example: conductor width is 0.036”
1/4 wavelength (λ) is 0.036” at 46.5 GHz
1/8λ is 0.036” at 23.8 GHz
The insertion loss curves after 1/8λ has increasing amounts of noise
1/8λ
1/4λ
CONFIDENTIAL 22
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
Elementary transmission line theory, millimeter-wave concerns
Signal launch
• Signal launch is extremely critical to get the energy from one interconnect (coaxial cable) to another interconnect (transmission line PCB)
• Example using a microstrip transmission line
• Microstrip is a 2 copper layer PCB having a signal layer and ground layer
• The transition from coax to microstrip can be plagued with mismatch issues
CONFIDENTIAL 23
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
Elementary transmission line theory, millimeter-wave concerns
• Signal launch for high frequency RF PCB is the transition from one electric field orientation to another
• Electric fields in the coaxial domain of the connector are cylindrical• Electric fields in the PCB are planar
• Signal launch is also a wave propagation mode transition
• The coaxial connector is a pure TEM mode• A microstrip or grounded coplanar waveguide PCB will have a quasi-TEM mode
• Additionally, there is a change in field distribution and field line length in the signal launch area
• The Effective-Dk of the PCB is typically much different than the Dk of the coax
CONFIDENTIAL 24
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
Elementary transmission line theory, millimeter-wave concerns
• The coaxial medium uses a TEM wave propagation mode where the phase velocity doesn’t change with frequency (no transmission line dispersion)
• The microstrip transmission line circuit uses a quasi-TEM mode which does change phase velocity with frequency
• Thinner circuit has less dispersion; using 10mil RO4350B laminate it would be 0.97 @ 50 GHz
• Using high Dk materials and the phase velocity curve shown here will be much more dramatic; using 25mil RT/duroid® 6010.2LM material, normalized Vp would be 0.87 @ 50 GHz
• Example of 2.4mm coaxial cable and a microstrip transmission line circuit using 30mil RO4350B™ 5E laminate
CONFIDENTIAL 25
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
Basic structure overview
MicrostripCoplanarStripline
CONFIDENTIAL 26
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
Basic structure overview, Microstrip
Most common transmission line used in the microwave PCB industry
It is simple, cheap to construct, good reliability and easy for assembly
Wave propagation: Quasi - TEM mode (dominate wave propagation mode)
Due to the wave using air and substrate there is an “effective Dk”
The effective Dk is the Dk which the wave experiences (air+substrate)
Since the wave will have different phase velocity in air than the substrate:
the wave is not a pure TEM wave, but a quasi-TEM wave
there will be some dispersion (wave property changes with frequency)
microstrip SubstrateSignal layerGround layer
Cross-sectional view
CONFIDENTIAL 27
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
Basic structure overview, Microstrip
Dielectric loss:
mostly due to dissipation factor of the substrate
soldermask will typically increase dielectric loss
Conductor loss and is due to several issues:
skin effect (frequency dependent), surface roughness[1], plated finish
surface roughness will also affect the wave propagation constant[1]
The copper surface roughness; rougher copper will cause more conductor loss and
slows the phase velocity. A slower phase velocity is perceived as a higher Dk
RO4003CTM
Exaggerated surface roughness example
CONFIDENTIAL 28
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
Basic structure overview, Microstrip
Radiation loss:
energy radiated and lost from the circuit
microstrip is more susceptible to radiation loss than other RF structures
frequency dependent (higher frequency has more radiation loss)
substrate thickness dependent (thinner has less radiation loss)
Dk dependent (higher Dk has less radiation loss)
CONFIDENTIAL 29
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
Basic structure overview, GCPW
There are several types of coplanar circuits
Mostly used at microwave frequencies is the grounded coplanar waveguide (GCPW) or the conductor back coplanar waveguide (CBCPW)
GCPW circuits need PTH (plated through hole) via’s to connect the ground planes on the top layer (coplanar layer) to the bottom ground plane
Via hole placement is critical for obtaining the desired impedance and loss performance
CONFIDENTIAL 30
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
Basic structure overview, GCPW
GCPW circuits have an effective Dk like microstrip
Dispersion is much less for GCPW than microstrip
Radiation losses are significantly better with GCPW than microstrip
Less dispersion and radiation loss: capable of higher frequency ranges
Dominate wave mode propagation is quasi-TEM
Suppressing spurious wave propagation modes is significantly more efficient with GCPW as compared to microstrip
Signal launch issues are significantly better for GCPW than microstrip
CONFIDENTIAL 31
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
Basic structure overview, GCPW
Losses and fields:
Dielectric loss:Mostly due to dissipation factor of the substrateSoldermask will have more effect on dielectric loss than on microstrip
Conductor loss:Same issues as microstripOverall there are more conductor loss for GCPW than microstripConductor losses due to finish plating are worse for GCPW
Radiation loss:When designed properly these can be extremely small or negligible
CONFIDENTIAL 32
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
Basic structure overview, GCPW
Via location and pitch can be critical to RF performance for GCPW
If the PTH via is far from the edge of the coplanar ground plane (left picture), there is more parasitic parallel plate inductances which increases impedance and conductor loss
If the PTH via has a length axis pitch of ¼ wavelength or larger then resonances can occur on the coplanar plane and spurious wave mode interference can be present
Distance from edge of via to coplanar ground edge
Distance from edge of via to coplanar ground edge
CONFIDENTIAL 33
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
Basic structure overview, Stripline
Probably the second most common
transmission line used in the PCB industry
More complex to fabricate, moderate in cost, moderate reliability and more difficult for
assembly as compared to microstrip or GCPW
Has the capability for extremely wideband (wide frequency range) applications
If all substrate material has the same Dk:
will have a true TEM wave mode propagation
extremely little or no dispersion
When designed correctly, there will be not radiation loss
Balance stripline
Unbalance stripline
CONFIDENTIAL 34
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
Basic structure overview, Stripline
Losses and fields:
Dielectric loss:Mostly due to dissipation factor (Df) of the substrateCan be more difficult to correct evaluate when using prepreg and cores with different Df
Conductor loss:Skin effects, copper surface roughnessConductor losses due to copper surface roughness is much more difficult to model for
stripline due to 4 copper-substrate interfaces which often have different roughness
Generally a 50ohm stripline can have higher loss than microstrip and some GCPW, mostly due to conductor loss, however there are exceptions.
Magneticfields
Electricfields
CONFIDENTIAL 35
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
Basic structure overview, Stripline
Via placement can be critical for stripline
Via pitch should ideally be a distance less than 1/8 the wavelength of the highest operating frequency (same as GCPW)
Via distance (3X) from the signal shown above is a general rule to avoid coplanar effects
Signal launch is very problematic for striplineThe signal launch via can have increased inductance or capacitance depending on designThe launch via can have a stub which can cause radiation and reflectionsThe design of the signal launch via has stepped impedance changes as the via goes down
through different material layers
CONFIDENTIAL 36
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
Basic structure overview, Stripline
Multilayer PCB Example of signal launch issues
Effects of the signal path from the connector to the signal plane of the circuit:
Transition from connector to circuit has an air-substrate Dk difference
Dk difference causes some reflection
When the signal via diameter is less than the connector pin diameter the via will be seen as inductive
The connector-circuit transition copper design can be coplanar, with a smaller space adding capacitance to offset the inductive signal via
Moving down the signal via: the impedance will increase in the prepreg area, the GCPW effect on layer 2 will decrease impedance, then then impedance will increase in the area between layer 2 and layer 3, etc.
The high / low impedance transitions moving down the via need to be minimized to improve signal launch
Ideally, the signal launch via should be removed (back drilled) from bottom of the signal plane to bottom of the circuit
CONFIDENTIAL 37
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
Structure comparisons across a wide range of frequencies
CONFIDENTIAL 38
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
Structure comparisons across a wide range of frequencies
Current density (red) comparisons of microstrip and GCPW circuits
Copper surface roughness of the laminate has more impact on microstrip than GCPW
Changing from a rough copper to a smooth copper on GCPW has less significant improvement in conductor loss as on microstrip
Tightly coupled GCPW is less impacted by copper surface roughness than loosely coupled GCPW
Current density uses less of the roughened copper surface on a the GCPW than the microstrip
CONFIDENTIAL 39
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
Structure comparisons across a wide range of frequencies
Tightly and loosely coupled GCPW with two different copper surface roughness
Copper surface roughness difference is 2.3 microns RMS and 2.9 microns RMS
The coplanar conductor width (w) is 18mils and 21mils. The coplanar space (s) 12mils and 6 mils
Loosely coupled GCPW is more impacted by copper surface roughness difference
Tightly coupled GCPW is w18s6Loosely coupled GCPW is w21s12
CONFIDENTIAL 40
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
Structure comparisons across a wide range of frequencies
CONFIDENTIAL 41
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
Structure comparisons across a wide range of frequencies
Microstrip insertion loss comparing very smooth copper (rolled copper) to rough copper (ED)
Rolled copper has surface roughness average of 0.35 microns RMS
This particular ED copper has average surface roughness of 2.0 microns RMS
CONFIDENTIAL 42
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
Structure comparisons across a wide range of frequencies
Unwrapped phase angle vs. Frequency
This shows the difference between phase angle using smooth copper and ED copper, while using the same lot of substrate There is a 61° phase angle
difference at 77 GHz
CONFIDENTIAL 43
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
PCB variables to consider that affect RF performance (e.g. etching tolerance and plated finish)
CONFIDENTIAL 44
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
PCB variables to consider that affect RF performance
Material and circuit fabrication variables which impact impedance
The most significant variables for microstrip impedance differences are:
1. Substrate thickness2. Conductor width3. Copper thickness4. Dk
Thinner circuits are more influenced by conductor differences
CONFIDENTIAL 45
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
PCB variables to consider that affect RF performance
The most significant variables at mmWavefrequencies for phase angle differences are:
1. Copper thickness2. Dk3. Conductor width4. Substrate thickness
• Thinner circuits are typically used at mmWave frequencies
• Phase angle variation can be critical to many mmWave applications
• Radar sensors at 77 GHz are especially sensitive to phase angle differences
Material and circuit fabrication variables which impact phase angle
CONFIDENTIAL 46
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
PCB variables to consider that affect RF performance
• A study was done using the same sheet of material 2 different GCPW circuit designs• Tightly coupled GCPW; small space between coplanar Ground-Signal-Ground• Loosely coupled GCPW; wide space
• Additionally, circuits were purposely made to have significantly different copper thickness• Thin copper plated• Thick copper plated
Tightly coupled GCPW with thin copper Tightly coupled GCPW with thick copper
CONFIDENTIAL 47
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
PCB variables to consider that affect RF performance
• Wider conductor has lower loss• Thick copper increases height of conductor sidewalls and more air is used (lower loss)
All circuits evaluated in this study used 10mil thick RO4350BTM laminate with standard ½ oz. ED copper
Tightly coupled GCPW is w18s6 which means 18mil conductor with 6mil coplanar space
Graph is from article on Microstrip vs. Coplanar[2] performance
CONFIDENTIAL 48
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
PCB variables to consider that affect RF performance
• RF testing procedure for determining Effective Dielectric Constant
• Effective dielectric constant (Eff_εr) is the dielectric constant which the circuit realizes and is the combination of substrate and air
• Tightly and loosely coupled GCPW will have fields which use air used more or less and this will causes differences in constant Eff_εr even when using the same substrate
• Two circuits are measured for phase angle (Φ) and the phase response formula adjusted for two circuits which are identical except for physical length (ΔL)
CONFIDENTIAL 49
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
PCB variables to consider that affect RF performance
• The tightly coupled circuits will have concentrated electric fields in air (air is lowest dielectric constant)
• Thicker copper will cause the conductor walls to be taller and more air is used
• The lowest Eff_εr circuit has thick copper and is tightly coupled
• Graph is from article on Microstrip vs. Coplanar[2]
performance
CONFIDENTIAL 50
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
PCB variables to consider that affect RF performance
• Most final plated finish is less conductive than copper
• Due to this fact, when most final plated finish is added to copper the conductor loss will increase, which increases the insertion loss
• The exception is silver
• Typically the silver used in the PCB industry is applied very thin so the skin effects benefit of silver may not be obvious unless at very high frequencies
Conductivity of pure metals
CONFIDENTIAL 51
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
PCB variables to consider that affect RF performance
Microstrip, final plated finish impacts the conductor loss due to high current density at the edge of the conductor
Grounded coplanar waveguide (GCPW) has fields and current densities using 4 edges of the ground-signal-ground conductor
Since GCPW has 4 edges using the plated finish, it will have more conductor loss (and insertion loss) due to the finish than microstrip
CONFIDENTIAL 52
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
PCB variables to consider that affect RF performance
The increased loss due to the final plated finish, depends on the thickness of the circuit
A thinner circuit will be dominated by conductor loss more than a thick circuit
When final plated finish is added to the copper it adds to the conductor loss
CONFIDENTIAL 53
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
PCB variables to consider that affect RF performance
CONFIDENTIAL 54
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
PCB variables to consider that affect RF performance
CONFIDENTIAL 55
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
PCB variables to consider that affect RF performance
Plated finishes have impact in frequency region where skin depth of the composite metal is changing quickly with a change in frequency
At low microwave frequencies the impact of plated finish is in order of plated finish composite conductivity
When this same study is done on thicker substrate the Dk differences are reduced
56
Become a Member of the Technology Support Hub for additional technical tools & information
Access:
Microwave Impedance Calculator
ROG Mobile App
Electrical & Thermal Calculators
Engineering Support
Technical Papers
Videos
Sign up to receive email updates to be kept up to date on recently released products.
CONFIDENTIAL 57
Design Considerations and Tradeoffs for Microstrip, Coplanar
and Stripline Structures at Millimeter-Wave Frequencies
References
[1] J. W. Reynolds, P. A. LaFrance, J. C. Rautio, A. F. Horn III, “Effect of conductor profile on the insertion loss, propagation constant, and dispersion in thin high frequency transmission lines,” DesignCon 2010.
[2] John Coonrod, “Managing Circuit Materials at mmWave Frequencies”, Microwave Journal, Vol 58. No. 7, July 2015
The Rogers’ logo, RO3003, RO4350B, LoPro, RO4003C, RT/duroid and Helping power, protect, connect our world are trademarks of Rogers Corporation or one of its subsidiaries.
©2017 Rogers Corporation