Suppose you have a slab of FR4 with copper on both sides, standard
ebay stuff. Now shear off a long thin slice. That's a balanced
transmission line.
air
__________________ copper
.........................................fr4
__________________ copper
air
What's that called?
Does anyone know of a calculator that handles this case?
Suppose you have a slab of FR4 with copper on both sides, standard
ebay stuff. Now shear off a long thin slice. That's a balanced
transmission line.
air
__________________ copper
.........................................fr4
__________________ copper
air
What's that called?
Does anyone know of a calculator that handles this case?
On 9/06/2025 12:58 am, john larkin wrote:
Suppose you have a slab of FR4 with copper on both sides, standard
ebay stuff. Now shear off a long thin slice. That's a balanced
transmission line.
air
__________________ copper
.........................................fr4
__________________ copper
air
What's that called?
Does anyone know of a calculator that handles this case?
Neither of my transmission line textbooks say anything about that. It's clearly a kind of transmission line, but presumably not a useful one -
it's going to be dispersive, just like microstrip. If it was useful you
would presumably be able to buy reels of it.
On 6/8/2025 11:39 AM, Bill Sloman wrote:
On 9/06/2025 12:58 am, john larkin wrote:
Suppose you have a slab of FR4 with copper on both sides, standard
ebay stuff. Now shear off a long thin slice. That's a balanced
transmission line.
air
__________________ copper
.........................................fr4
__________________ copper
air
What's that called?
Does anyone know of a calculator that handles this case?
Neither of my transmission line textbooks say anything about that. It's
clearly a kind of transmission line, but presumably not a useful one -
it's going to be dispersive, just like microstrip. If it was useful you
would presumably be able to buy reels of it.
Used that way it's called a "parallel plate line" and the essential >characteristics for ye olde Telegrapher's Equation are given in Pozar:
<https://imgur.com/a/gAbKJgk>
Suppose you have a slab of FR4 with copper on both sides, standard
ebay stuff. Now shear off a long thin slice. That's a balanced
transmission line.
air
__________________ copper
.........................................fr4
__________________ copper
air
What's that called?
Does anyone know of a calculator that handles this case?
On Sun, 8 Jun 2025 11:41:19 -0400, bitrex <user@example.net> wrote:
On 6/8/2025 11:39 AM, Bill Sloman wrote:
On 9/06/2025 12:58 am, john larkin wrote:
Suppose you have a slab of FR4 with copper on both sides, standard
ebay stuff. Now shear off a long thin slice. That's a balanced
transmission line.
air
__________________ copper
.........................................fr4
__________________ copper
air
What's that called?
Does anyone know of a calculator that handles this case?
Neither of my transmission line textbooks say anything about that. It's
clearly a kind of transmission line, but presumably not a useful one -
it's going to be dispersive, just like microstrip. If it was useful you
would presumably be able to buy reels of it.
Used that way it's called a "parallel plate line" and the essential
characteristics for ye olde Telegrapher's Equation are given in Pozar:
<https://imgur.com/a/gAbKJgk>
Except that between the plates is FR4, dielectric constant near 4.
I could test that case experimentally, TDR some strips of copperclad.
Another case that I'm interested is a 5-layer board where the parallel conductors are on layers 2 and 4.
air
.........................................fr4
__________________ copper
.........................................fr4
__________________ copper
.........................................fr4
air
Or even
air
.........................................fr4
__________________ copper
.........................................fr4
__________________ copper
air
Yes, I guess I'll have to crank up ATLC, which is rather a nuisance to
drive.
The goal is to build some high-voltage transmission-line transformers
using pot cores with stacked layers of PCBs as the windings, sort of
like the Coilcraft planar transformers.
PCBs with odd numbers of layers are, well, odd.
Am 08.06.2025 um 16:58 schrieb john larkin:
Suppose you have a slab of FR4 with copper on both sides, standardhttps://saturnpcb.com/saturn-pcb-toolkit/
ebay stuff. Now shear off a long thin slice. That's a balanced
transmission line.
air
__________________ copper
.........................................fr4
__________________ copper
air
What's that called?
Does anyone know of a calculator that handles this case?
On 6/8/2025 1:01 PM, john larkin wrote:
On Sun, 8 Jun 2025 11:41:19 -0400, bitrex <user@example.net> wrote:
On 6/8/2025 11:39 AM, Bill Sloman wrote:
On 9/06/2025 12:58 am, john larkin wrote:
Suppose you have a slab of FR4 with copper on both sides, standard
ebay stuff. Now shear off a long thin slice. That's a balanced
transmission line.
air
__________________ copper
.........................................fr4
__________________ copper
air
What's that called?
Does anyone know of a calculator that handles this case?
Neither of my transmission line textbooks say anything about that. It's >>>> clearly a kind of transmission line, but presumably not a useful one - >>>> it's going to be dispersive, just like microstrip. If it was useful you >>>> would presumably be able to buy reels of it.
Used that way it's called a "parallel plate line" and the essential
characteristics for ye olde Telegrapher's Equation are given in Pozar:
<https://imgur.com/a/gAbKJgk>
Except that between the plates is FR4, dielectric constant near 4.
It's okay, in those equations epsilon prime is defined as e_r*e_0, and
then epsilon double prime is related to the loss tangent of the
dielectric is related as tan(delta) = (omega*e'' + sigma)/omega*e'
air
__________________ copper
.........................................fr4
__________________ copper
air
ir
__________________ copper
.........................................fr4
__________________ copper
air
Suppose you have a slab of FR4 with copper on both sides, standard
ebay stuff. Now shear off a long thin slice. That's a balanced
transmission line.
air
__________________ copper
.........................................fr4
__________________ copper
air
What's that called?
Am 08.06.2025 um 21:29 schrieb john larkin:
air
__________________ copper
.........................................fr4
__________________ copper
air
The formulars are for 2 symmetrically lines in picture 4.20.1-3 on the
2nd page of the *.pdf
... have fun ...
On Sun, 08 Jun 2025 07:58:14 -0700, john larkin <jl@glen--canyon.com>
wrote:
Suppose you have a slab of FR4 with copper on both sides, standard
ebay stuff. Now shear off a long thin slice. That's a balanced
transmission line.
air
__________________ copper
.........................................fr4
__________________ copper
air
What's that called?
Double-strip transmission line or dual stripline.
air
__________________ copper
.........................................fr4
__________________ copper
air
On Sun, 8 Jun 2025 15:19:18 -0400, bitrex <user@example.net> wrote:
On 6/8/2025 1:01 PM, john larkin wrote:
On Sun, 8 Jun 2025 11:41:19 -0400, bitrex <user@example.net> wrote:
On 6/8/2025 11:39 AM, Bill Sloman wrote:
On 9/06/2025 12:58 am, john larkin wrote:
Suppose you have a slab of FR4 with copper on both sides, standard >>>>>> ebay stuff. Now shear off a long thin slice. That's a balanced
transmission line.
air
__________________ copper
.........................................fr4
__________________ copper
air
What's that called?
Does anyone know of a calculator that handles this case?
Neither of my transmission line textbooks say anything about that. It's >>>>> clearly a kind of transmission line, but presumably not a useful one - >>>>> it's going to be dispersive, just like microstrip. If it was useful you >>>>> would presumably be able to buy reels of it.
Used that way it's called a "parallel plate line" and the essential
characteristics for ye olde Telegrapher's Equation are given in Pozar: >>>>
<https://imgur.com/a/gAbKJgk>
Except that between the plates is FR4, dielectric constant near 4.
It's okay, in those equations epsilon prime is defined as e_r*e_0, and
then epsilon double prime is related to the loss tangent of the
dielectric is related as tan(delta) = (omega*e'' + sigma)/omega*e'
But all the capacitance is assumed to be confined into the central
rectangle, with the rest of the universe having e=0.
That's maybe good enough if the dielectric constant of the stuff
between the plates is high, and the w/t ratio is large. But it ain't
right.
Please take another picture of the second page.
Please take another picture of the second page.
And broadside coupled stripline.What's that called?Double-strip transmission line or dual stripline.
What impedance is being calculated? Top line against dotted one below?
It occurred to me that if I drive my top and bottom lines out of
phase, which I will, there will be an equipotential plane midway
through the board. So I could sneak a ground plane in there and
nothing would change. With the ground plane, it becomes two
microstrips, and there are lots of microstrip solvers.
Am 08.06.2025 um 21:29 schrieb john larkin:
air
__________________ copper
.........................................fr4
__________________ copper
air
The formulars are for 2 symmetrically lines in picture 4.20.1-3 on the
2nd page of the *.pdf
... have fun ...
Am 08.06.2025 um 22:42 schrieb Joe Gwinn:
Please take another picture of the second page.
sorry - it is a very thick book, I cannot do it better with my A4-scanner
john larkin wrote:
Suppose you have a slab of FR4 with copper on both sides, standard
ebay stuff. Now shear off a long thin slice. That's a balanced
transmission line.
air
__________________ copper
.........................................fr4
__________________ copper
air
What's that called?
Does anyone know of a calculator that handles this case?
It's just a parallel plate waveguide.
For the TEM mode Z0 = 377*sqrt(ur/er)*(d/w).
ur/er - substrate permeability/permittivity (relative)
d - dist between copper
w - width copper strip
Formulas for the higher modes also exist.
But I'd have to look them up.
On Sun, 08 Jun 2025 07:58:14 -0700, john larkin <jl@glen--canyon.com>
wrote:
Suppose you have a slab of FR4 with copper on both sides, standard
ebay stuff. Now shear off a long thin slice. That's a balanced
transmission line.
air
__________________ copper
.........................................fr4
__________________ copper
air
What's that called?
Does anyone know of a calculator that handles this case?
It's just a parallel plate waveguide.
For the TEM mode Z0 = 377*sqrt(ur/er)*(d/w).
ur/er - substrate permeability/permittivity (relative)
d - dist between copper
w - width copper strip
Formulas for the higher modes also exist.
But I'd have to look them up.
JM wrote:
john larkin wrote:
Suppose you have a slab of FR4 with copper on both sides, standard
ebay stuff. Now shear off a long thin slice. That's a balanced >>>transmission line.
air
__________________ copper
.........................................fr4
__________________ copper
air
What's that called?
Does anyone know of a calculator that handles this case?
It's just a parallel plate waveguide.
For the TEM mode Z0 = 377*sqrt(ur/er)*(d/w).
ur/er - substrate permeability/permittivity (relative)
d - dist between copper
w - width copper strip
Formulas for the higher modes also exist.
But I'd have to look them up.
Your free space impedance is easier for me to comprehend than the one >contained in Chemandy's calculator:
<https://chemandy.com/calculators/microstrip-transmission-line-calculator.htm>
Danke,
On Tue, 10 Jun 2025 07:53:38 -0700, john larkin <jl@glen--canyon.com>
wrote:
On Tue, 10 Jun 2025 13:33:57 -0000 (UTC), "Don" <g@crcomp.net> wrote:
JM wrote:
john larkin wrote:
Suppose you have a slab of FR4 with copper on both sides, standard >>>>>ebay stuff. Now shear off a long thin slice. That's a balanced >>>>>transmission line.
air
__________________ copper >>>>>.........................................fr4
__________________ copper
air
What's that called?
Does anyone know of a calculator that handles this case?
It's just a parallel plate waveguide.
For the TEM mode Z0 = 377*sqrt(ur/er)*(d/w).
ur/er - substrate permeability/permittivity (relative)
d - dist between copper
w - width copper strip
Formulas for the higher modes also exist.
But I'd have to look them up.
Your free space impedance is easier for me to comprehend than the one >>>contained in Chemandy's calculator:
<https://chemandy.com/calculators/microstrip-transmission-line-calculator.htm>
Danke,
And that one assumes an infinite ground plane.
I suspect that all such formulas are wrong, except in a few rare cases
like a coax. EM simulation is better.
Get Cadence to come along and demonstrate Alllegro + Clarity to you.
The days of using formulas to calculate these things are long gone.
On Tue, 10 Jun 2025 07:51:38 -0700, john larkin <jl@glen--canyon.com>
wrote:
On Tue, 10 Jun 2025 07:57:03 +0100, JM
<sunaecoNoChoppedPork@gmail.com> wrote:
On Sun, 08 Jun 2025 07:58:14 -0700, john larkin <jl@glen--canyon.com> >>>wrote:
Suppose you have a slab of FR4 with copper on both sides, standard
ebay stuff. Now shear off a long thin slice. That's a balanced >>>>transmission line.
air
__________________ copper
.........................................fr4
__________________ copper
air
What's that called?
Does anyone know of a calculator that handles this case?
It's just a parallel plate waveguide.
For the TEM mode Z0 = 377*sqrt(ur/er)*(d/w).
ur/er - substrate permeability/permittivity (relative)
d - dist between copper
w - width copper strip
Formulas for the higher modes also exist.
But I'd have to look them up.
That assumes that all the capacitance is confined to the rectangle
between the plates. Actually, that's good enough for what I'm doing
now, just making a txline transformer.
It's good enough for typical impedances used in PCB's (120 ohm or
less) where w/d > 1.
What Z0 do you need.
On Tue, 10 Jun 2025 20:54:38 +0100, JM
<sunaecoNoChoppedPork@gmail.com> wrote:
On Tue, 10 Jun 2025 07:51:38 -0700, john larkin <jl@glen--canyon.com>
wrote:
On Tue, 10 Jun 2025 07:57:03 +0100, JM
<sunaecoNoChoppedPork@gmail.com> wrote:
On Sun, 08 Jun 2025 07:58:14 -0700, john larkin <jl@glen--canyon.com>
wrote:
Suppose you have a slab of FR4 with copper on both sides, standard
ebay stuff. Now shear off a long thin slice. That's a balanced
transmission line.
air
__________________ copper
.........................................fr4
__________________ copper
air
What's that called?
Does anyone know of a calculator that handles this case?
It's just a parallel plate waveguide.
For the TEM mode Z0 = 377*sqrt(ur/er)*(d/w).
ur/er - substrate permeability/permittivity (relative)
d - dist between copper
w - width copper strip
Formulas for the higher modes also exist.
But I'd have to look them up.
That assumes that all the capacitance is confined to the rectangle
between the plates. Actually, that's good enough for what I'm doing
now, just making a txline transformer.
It's good enough for typical impedances used in PCB's (120 ohm or
less) where w/d > 1.
What Z0 do you need.
I need to put a fast kilovolt pulse into a 50 ohm load. I can use a
GaN fet and a transmission line step-up/isolation transformer.
I'd like to make the windings from PCBs with roughly 50 ohm
differential impedances, but if the txline windings are short compared
to rise time, it doesn't matter much.
I was just interested that this geometry is not included in any pcb
impedance programs that I know of. The imaginary equipotential plane
is a workaround.
Supposedly that's exactly _why_ this specific geometry is not
explicitly included.
Am 11.06.2025 um 11:36 schrieb Jeroen Belleman:
Supposedly that's exactly _why_ this specific geometry is not
explicitly included.
The text in my book states that this line geometry is unstable. Other
lines and geometries in the vicinity have a significant disruptive
influence on Z.
On 6/11/25 05:12, john larkin wrote:
On Tue, 10 Jun 2025 20:54:38 +0100, JM
<sunaecoNoChoppedPork@gmail.com> wrote:
On Tue, 10 Jun 2025 07:51:38 -0700, john larkin <jl@glen--canyon.com>
wrote:
On Tue, 10 Jun 2025 07:57:03 +0100, JM
<sunaecoNoChoppedPork@gmail.com> wrote:
On Sun, 08 Jun 2025 07:58:14 -0700, john larkin <jl@glen--canyon.com> >>>>> wrote:
Suppose you have a slab of FR4 with copper on both sides, standard >>>>>> ebay stuff. Now shear off a long thin slice. That's a balanced
transmission line.
air
__________________ copper
.........................................fr4
__________________ copper
air
What's that called?
Does anyone know of a calculator that handles this case?
It's just a parallel plate waveguide.
For the TEM mode Z0 = 377*sqrt(ur/er)*(d/w).
ur/er - substrate permeability/permittivity (relative)
d - dist between copper
w - width copper strip
Formulas for the higher modes also exist.
But I'd have to look them up.
That assumes that all the capacitance is confined to the rectangle
between the plates. Actually, that's good enough for what I'm doing
now, just making a txline transformer.
It's good enough for typical impedances used in PCB's (120 ohm or
less) where w/d > 1.
What Z0 do you need.
I need to put a fast kilovolt pulse into a 50 ohm load. I can use a
GaN fet and a transmission line step-up/isolation transformer.
I'd like to make the windings from PCBs with roughly 50 ohm
differential impedances, but if the txline windings are short compared
to rise time, it doesn't matter much.
I was just interested that this geometry is not included in any pcb
impedance programs that I know of. The imaginary equipotential plane
is a workaround.
Supposedly that's exactly _why_ this specific geometry is not
explicitly included.
Jeroen Belleman
Am 11.06.2025 um 11:36 schrieb Jeroen Belleman:
Supposedly that's exactly _why_ this specific geometry is not
explicitly included.
The text in my book states that this line geometry is unstable. Other
lines and geometries in the vicinity have a significant disruptive
influence on Z.
Am 11.06.2025 um 23:21 schrieb Jeroen Belleman:
On 6/11/25 14:30, Leo Baumann wrote:
Am 11.06.2025 um 11:36 schrieb Jeroen Belleman:
Supposedly that's exactly _why_ this specific geometry is not
explicitly included.
The text in my book states that this line geometry is unstable. Other
lines and geometries in the vicinity have a significant disruptive
influence on Z.
That is true for any geometry that does not confine the fields.
So we lay coaxial cables and waveguides.
On 6/11/25 14:30, Leo Baumann wrote:
Am 11.06.2025 um 11:36 schrieb Jeroen Belleman:
Supposedly that's exactly _why_ this specific geometry is not
explicitly included.
The text in my book states that this line geometry is unstable. Other
lines and geometries in the vicinity have a significant disruptive
influence on Z.
That is true for any geometry that does not confine the fields.
On 6/12/25 00:26, Leo Baumann wrote:
Am 11.06.2025 um 23:21 schrieb Jeroen Belleman:
On 6/11/25 14:30, Leo Baumann wrote:
Am 11.06.2025 um 11:36 schrieb Jeroen Belleman:
Supposedly that's exactly _why_ this specific geometry is not
explicitly included.
The text in my book states that this line geometry is unstable.
Other lines and geometries in the vicinity have a significant
disruptive influence on Z.
That is true for any geometry that does not confine the fields.
So we lay coaxial cables and waveguides.
Sure, but what will you do on a PCB?
Am 11.06.2025 um 23:21 schrieb Jeroen Belleman:
On 6/11/25 14:30, Leo Baumann wrote:
Am 11.06.2025 um 11:36 schrieb Jeroen Belleman:
Supposedly that's exactly _why_ this specific geometry is not
explicitly included.
The text in my book states that this line geometry is unstable. Other
lines and geometries in the vicinity have a significant disruptive
influence on Z.
That is true for any geometry that does not confine the fields.
So we lay coaxial cables and waveguides.
Am 12.06.2025 um 00:34 schrieb Jeroen Belleman:
On 6/12/25 00:26, Leo Baumann wrote:
Am 11.06.2025 um 23:21 schrieb Jeroen Belleman:
On 6/11/25 14:30, Leo Baumann wrote:
Am 11.06.2025 um 11:36 schrieb Jeroen Belleman:
Supposedly that's exactly _why_ this specific geometry is not
explicitly included.
The text in my book states that this line geometry is unstable.
Other lines and geometries in the vicinity have a significant
disruptive influence on Z.
That is true for any geometry that does not confine the fields.
So we lay coaxial cables and waveguides.
Sure, but what will you do on a PCB?
I usually do it with asymmetrical lines.
---------------------------------- line
////////////////////////////////// FR4
********************************** Ground plane
On Wed, 11 Jun 2025 14:30:33 +0200, Leo Baumann <ib@leobaumann.de>
wrote:
Am 11.06.2025 um 11:36 schrieb Jeroen Belleman:
Supposedly that's exactly _why_ this specific geometry is not
explicitly included.
The text in my book states that this line geometry is unstable. Other
lines and geometries in the vicinity have a significant disruptive
influence on Z.
Same as microstrip.
Am 08.06.2025 um 21:29 schrieb john larkin:
ir
__________________ copper
.........................................fr4
__________________ copper
air
www.leobaumann.de/newsgroups/Stripline_without_Groundplane.pdf
Leo Baumann:
schrieb john larkin:
ir
__________________ copper
.........................................fr4
__________________ copper
air
www.leobaumann.de/newsgroups/Stripline_without_Groundplane.pdf
It is necessary to determine the effective material permittivity of the geometry.
Leo Baumann wrote:
Leo Baumann:
schrieb john larkin:
ir
__________________ copper
.........................................fr4
__________________ copper
air
www.leobaumann.de/newsgroups/Stripline_without_Groundplane.pdf
It is necessary to determine the effective material permittivity of the
geometry.
OK. It's easy enough for me to mentally model the stripline as a
complexly constructed capacitor.
Open question: Is it possible to view the stripline as unterminated long
wire antenna with a length longer than one or two wavelengths? In this
case the radiation pattern's major lobe constricts to increasingly align
with the antenna axis.
Danke,
On Thu, 19 Jun 2025 13:30:55 -0000 (UTC), "Don" <g@crcomp.net> wrote:
Leo Baumann wrote:
Leo Baumann:
schrieb john larkin:
ir
__________________ copper
.........................................fr4
__________________ copper
air
www.leobaumann.de/newsgroups/Stripline_without_Groundplane.pdf
It is necessary to determine the effective material permittivity of the
geometry.
OK. It's easy enough for me to mentally model the stripline as a
complexly constructed capacitor.
With inductance.
Open question: Is it possible to view the stripline as unterminated long >>wire antenna with a length longer than one or two wavelengths? In this
case the radiation pattern's major lobe constricts to increasingly align >>with the antenna axis.
Danke,
People don't usually include radiation in calculating transmission
line behavior, even though some geometries probably do radiate. I'd
expect that copper and dielectric losses are a lot worse than
radiation, and we usually ignore them too.
Stripline between ground planes shouldn't radiate, at least into free
space.
Some really fast txlines have serious losses, like later gen PCIe and
such. They need adaptive equalizing.
I was at the microwave show in San Francisco yesterday. A guy from R+S
was demonstrating an ADC chip that digitizes at 64 Gbps
On Tue, 10 Jun 2025 20:06:13 -0700, john larkin <jl@glen--canyon.com>
wrote:
On Tue, 10 Jun 2025 21:00:37 +0100, JM
<sunaecoNoChoppedPork@gmail.com> wrote:
On Tue, 10 Jun 2025 07:53:38 -0700, john larkin <jl@glen--canyon.com> >>>wrote:
On Tue, 10 Jun 2025 13:33:57 -0000 (UTC), "Don" <g@crcomp.net> wrote:
JM wrote:
john larkin wrote:
Suppose you have a slab of FR4 with copper on both sides, standard >>>>>>>ebay stuff. Now shear off a long thin slice. That's a balanced >>>>>>>transmission line.
air
__________________ copper >>>>>>>.........................................fr4
__________________ copper
air
What's that called?
Does anyone know of a calculator that handles this case?
It's just a parallel plate waveguide.
For the TEM mode Z0 = 377*sqrt(ur/er)*(d/w).
ur/er - substrate permeability/permittivity (relative)
d - dist between copper
w - width copper strip
Formulas for the higher modes also exist.
But I'd have to look them up.
Your free space impedance is easier for me to comprehend than the one >>>>>contained in Chemandy's calculator:
<https://chemandy.com/calculators/microstrip-transmission-line-calculator.htm>
Danke,
And that one assumes an infinite ground plane.
I suspect that all such formulas are wrong, except in a few rare cases >>>>like a coax. EM simulation is better.
Get Cadence to come along and demonstrate Alllegro + Clarity to you.
The days of using formulas to calculate these things are long gone.
We have lots of programs and web sites that use the formulas!
I'm having to do some EM simulations at the moment for some fast stuff
(13ps rise time) so thought I'd also check the accuracy of that
equation I gave.
Although it agrees with the one posted by Leo Baumann from his
reference book (for sensible trace widths and heights) the impedance
it calculates is nowhere near that given by simulation. If I do a
parametric sweep on the width of the return conductor, by the time
it's x10 or so that of the trace conductor the resulting impedance
agrees with that given by the likes of the Saturn toolkit, or the
website linked to by Don, so my simulation is probably correct.
If I have time I'll bend some copper tape over some Kapton tape and
cut off a few slices of varing widths to do a TDR measurement on as a
reality check.
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