Hi there,

I am currently working on a project which leads to simulate EMC Field
coupling to printed circuits. The Field couples into the circuitry
through (unwanted) loops and di/monopoles.
I started with modeling a simple loop and a stub. I experienced no
problems for the loop, but the stub is driving me crazy:
In order to calculate the output voltage of a PCB antenna for a given
geometry and EM-Field at a desired frequency, I need to know the
output impedance for this antenna. I didn't find anything on the web
on calculating/extracting it.
This brings up the question, wether it is possible or not? If yes, how
can i perform the calculation? Do you have any suggestions? If I am am
totally wrong, please feel free to correct me.

Thanks in Advance

Greets

Daniel

"Daniel" wrote in message
om...
Hi there,

I am currently working on a project which leads to simulate EMC Field
coupling to printed circuits.

Well, that sentence makes little sense, but let's plow onward:

The Field couples into the circuitry
through (unwanted) loops and di/monopoles.
I started with modeling a simple loop and a stub. I experienced no
problems for the loop, but the stub is driving me crazy:
In order to calculate the output voltage of a PCB antenna for a given
geometry and EM-Field at a desired frequency, I need to know the
output impedance for this antenna. I didn't find anything on the web
on calculating/extracting it.

Most good antenna theory is contained in an old fashioned item called books.
Learn what they are and how to read them. Kraus, Johnson, Balanis, and many
others. Even Terman, whose forte was starting Silicon Valley, had lots of
good information.

This brings up the question, wether it is possible or not? If yes, how
can i perform the calculation? Do you have any suggestions?

Well, you should have paid attention in fields and waves class. If you
didn't have that class, you shouldn't be expected to work on the project you
tried to describe in the first sentence.

If I am am
totally wrong, please feel free to correct me.

Thanks in Advance

Greets

Daniel

--
Crazy George
Remove N O and S P A M imbedded in return address

On 20 Oct 2003 02:14:38 -0700, (Daniel) wrote:

Hi there,

I am currently working on a project which leads to simulate EMC Field
coupling to printed circuits.

Without discussion of a frequency or band of frequencies, you are sure
to be either deeply disappointed or vastly rewarded in results.

The Field couples into the circuitry
through (unwanted) loops and di/monopoles.

Certainly, this is true at all scales. Your problem is not that so
much as it is a matter of degree. As this turns on the same issue of
what frequency, it also turns on the issue of what size? Beyond that,
it becomes a problem of how near (or how far). You may note that
there is a lot of dimensionality here that is wholly lacking in your
question.

I started with modeling a simple loop and a stub. I experienced no
problems for the loop, but the stub is driving me crazy:
In order to calculate the output voltage of a PCB antenna for a given
geometry and EM-Field at a desired frequency, I need to know the
output impedance for this antenna. I didn't find anything on the web
on calculating/extracting it.

This, in fact, is one of the easiest things to determine - if you know
the frequency and physical dimension.

This brings up the question, wether it is possible or not? If yes, how
can i perform the calculation? Do you have any suggestions? If I am am
totally wrong, please feel free to correct me.

Thanks in Advance

Greets

Daniel

Hi Daniel

How? The clues above give a significant indication.

73's
Richard Clark, KB7QHC

Hi again,

thanks for the quick answers. First of all, I have to apologize for
bad explaination. As you would guess, I am not a natural english
speaker, and so have difficulties to explain exactly what I am looking
for.

Hi there,

I am currently working on a project which leads to simulate EMC Field
coupling to printed circuits.

Without discussion of a frequency or band of frequencies, you are sure
to be either deeply disappointed or vastly rewarded in results.

What i want to simulate is a common EMC-Test. Put a PCB with the
circuitry in a shielded EMC-room (I dont know the english word) and
put a 10V/m E-Field around it in 3m distance from the sending antenna.
Frequency band is 80MHz to 1GHz


The Field couples into the circuitry
through (unwanted) loops and di/monopoles.

Certainly, this is true at all scales. Your problem is not that so
much as it is a matter of degree. As this turns on the same issue of
what frequency, it also turns on the issue of what size? Beyond that,
it becomes a problem of how near (or how far). You may note that
there is a lot of dimensionality here that is wholly lacking in your
question.

I know that, and i took in into account in my calculation. this was
not the question, its just to explain what i am doing.

I started with modeling a simple loop and a stub. I experienced no
problems for the loop, but the stub is driving me crazy:
In order to calculate the output voltage of a PCB antenna for a given
geometry and EM-Field at a desired frequency, I need to know the
output impedance for this antenna. I didn't find anything on the web
on calculating/extracting it.

This, in fact, is one of the easiest things to determine - if you know
the frequency and physical dimension.

This was the question! unfortunately
This, in fact, is one of the easiest things to determine - if you know
the frequency and physical dimension.
doesn't help me.... I know the physical dimension (PCB Layout, 93mm
length, 2mm Strip width, 0.035mm hight) The freqeuncy band is given
above.
The only thing antenna books are talking about (the ones i read) are
wire antennas, where a radius is given for calculating the
Waveresistance(? correct word ?)ZL. As i dont have a radius (stripline
is rectangular) I am not sure what to do. Is it possible to say the
area of the stripline is 0.035mm*2mm (crossection), and therefore
build up the equation 0.035mm*2mm=2*pi*r^2 and then follow for the
radius: r=sqrt((0.035mm*2mm)/(2*pi)). I think this is rather wrong,
how else can I determine the waveresistance and with it the Impedance
of the antenna?
I was thinking of a 2D FEM in order determine the unit per length
parameters L' and C' and then i can calculate the waveresistance, too.
What do you think?

thanks

Daniel

"Crazy George" wrote in message ...
"Daniel" wrote in message
om...
Hi there,

I am currently working on a project which leads to simulate EMC Field
coupling to printed circuits.

Well, that sentence makes little sense, but let's plow onward:

The Field couples into the circuitry
through (unwanted) loops and di/monopoles.
I started with modeling a simple loop and a stub. I experienced no
problems for the loop, but the stub is driving me crazy:
In order to calculate the output voltage of a PCB antenna for a given
geometry and EM-Field at a desired frequency, I need to know the
output impedance for this antenna. I didn't find anything on the web
on calculating/extracting it.

Most good antenna theory is contained in an old fashioned item called books.
Learn what they are and how to read them. Kraus, Johnson, Balanis, and many
others. Even Terman, whose forte was starting Silicon Valley, had lots of
good information.

This brings up the question, wether it is possible or not? If yes, how
can i perform the calculation? Do you have any suggestions?

Well, you should have paid attention in fields and waves class. If you
didn't have that class, you shouldn't be expected to work on the project you
tried to describe in the first sentence.

If I am am
totally wrong, please feel free to correct me.

Thanks in Advance

Greets

Daniel


thanks for flaming... next time you have to say something dispensable - please don't

Bye

"Daniel" wrote in message
m...
Hi again,

thanks for the quick answers. First of all, I have to apologize for
bad explaination. As you would guess, I am not a natural english
speaker, and so have difficulties to explain exactly what I am looking
for.

Hi there,

I am currently working on a project which leads to simulate EMC Field
coupling to printed circuits.

Without discussion of a frequency or band of frequencies, you are sure
to be either deeply disappointed or vastly rewarded in results.

What i want to simulate is a common EMC-Test. Put a PCB with the
circuitry in a shielded EMC-room (I dont know the english word) and
put a 10V/m E-Field around it in 3m distance from the sending antenna.
Frequency band is 80MHz to 1GHz


Not wanting to dampen your enthusiasm, but I think you'll find that the
modeling is quite limited in predicting what really happens in the above
scenario.

First, a real circuit board usually has far too many variables for a model,
and that's assuming you can even recognize all the variables. Second, the
exposure within an RF semi-anechoic enclosure is never quite so clean as you
posit. Support structures, such as tables (maybe not as RF invisible as you
assume) and cables, all add to the general fuzz. And the shielded chamber's
lining is SEMI anechoic, that is, not a perfect absorber. At 80 MHz, the
typical 24" pyramidal loaded-foam absorber will yield a return loss of less
than 10 dB, which is a significant reflection for your modeling effort.

Most board designers make some attempts at modeling EMC performance, but
they usually run into the concept of diminishing returns quite soon. The
pressure of costs and schedule usually limits the modeling effort anyway,
and the board gets designed more by rules of motherhood and sin than precise
modeling.

Finally, few electronic assemblies exist wholly unto themselves, life gets
very messy once you factor in the IO, command & control, and power
attachments. These externals are usually the path of more problems than
responses directly attributable to board components, especially in very
low-level RF fields like 10 V/M.

Ed

On 21 Oct 2003 01:59:07 -0700, (Daniel) wrote:
What i want to simulate is a common EMC-Test. Put a PCB with the
circuitry in a shielded EMC-room (I dont know the english word) and
put a 10V/m E-Field around it in 3m distance from the sending antenna.
Frequency band is 80MHz to 1GHz

English is perfect. Specification is too.

I started with modeling a simple loop and a stub. I experienced no
problems for the loop, but the stub is driving me crazy:
In order to calculate the output voltage of a PCB antenna for a given
geometry and EM-Field at a desired frequency, I need to know the
output impedance for this antenna. I didn't find anything on the web
on calculating/extracting it.

This, in fact, is one of the easiest things to determine - if you know
the frequency and physical dimension.

This was the question! unfortunately
This, in fact, is one of the easiest things to determine - if you know
the frequency and physical dimension.
doesn't help me.... I know the physical dimension (PCB Layout, 93mm
length, 2mm Strip width, 0.035mm hight) The freqeuncy band is given
above.
The only thing antenna books are talking about (the ones i read) are
wire antennas, where a radius is given for calculating the
Waveresistance(? correct word ?)ZL. As i dont have a radius (stripline
is rectangular) I am not sure what to do. Is it possible to say the
area of the stripline is 0.035mm*2mm (crossection), and therefore
build up the equation 0.035mm*2mm=2*pi*r^2 and then follow for the
radius: r=sqrt((0.035mm*2mm)/(2*pi)). I think this is rather wrong,
how else can I determine the waveresistance and with it the Impedance
of the antenna?

You are working too hard. Round wire compared to flat stripline is
not that different. The difference, for the broad range of frequency,
will be overwhelmed by other things.

I was thinking of a 2D FEM in order determine the unit per length
parameters L' and C' and then i can calculate the waveresistance, too.
What do you think?

thanks

Daniel

Hi Daniel,

Think of doing this by parts. The first approximation will be close.
The second approximation will improve it a little. Being perfect will
not matter.

For overall dimension of dipole/monopole/loop, wavelengths less than 1
and more than 0.1 can be found in many antenna reference books.

Let's look a some simple approximations for a loop:
Ra = 320 · pi^6 · (radius / wavelength)^4
for
radius = 0.046 M
wavelength = 3 M
then
Ra = 0.017 Ohm

for
radius =0.046 M
wavelength = 0.3M
then
Ra = 170 Ohm

Let's look a some simple approximations for a dipole:
Ra = 80 · pi² · (length / wavelength)²
for
length = 0.186 M
wavelength = 3 M
then
Ra = 3 Ohm

for
length = 0.186 M
wavelength = 0.3M
then
Ra = 304 Ohm

Now, be warned. These formulas only work for length wavelength and
for radius wavelength. The last evaluation for a nearly halfwave
dipole reveals 304 Ohms for what is actually closer to 70 Ohms.

So for your range, for your largest dimension (93mm) the radiation
resistance will vary between roughly 1 Ohm and 100 Ohms (I am
discounting the loop too). This is for "free space." Your board will
limit that severely. This again suggests high evaluations will be
modified (and closer to my 1 - 100).

This is a first approximation. A second approximation will not alter
this more than 30%. Nearby components will significantly alter it
through proximity.

Trying to compute the reactances will meet similar issues.

73's
Richard Clark, KB7QHC

Thanks all for your help,

English is perfect. Specification is too.

thanks :-D

You are working too hard. Round wire compared to flat stripline is
not that different. The difference, for the broad range of frequency,
will be overwhelmed by other things.

I like to hear that - I hope my boss is reading it
This is exactly what I was looking for - Thanks for this advice. As I
just finished my studies, i don't have the experience to know what i
can neglect and what not - I am just uncertain. Trial and error is one
way - to ask experienced people another...

Think of doing this by parts. The first approximation will be close.
The second approximation will improve it a little. Being perfect will
not matter.

I am aware of never beeing able to create perfect models. What I am
doing is a brief desciption of what to expect.
Thanks again

Bye

Daniel


Richard Clark wrote in message . ..
On 21 Oct 2003 01:59:07 -0700, (Daniel) wrote:
What i want to simulate is a common EMC-Test. Put a PCB with the
circuitry in a shielded EMC-room (I dont know the english word) and
put a 10V/m E-Field around it in 3m distance from the sending antenna.
Frequency band is 80MHz to 1GHz

English is perfect. Specification is too.

I started with modeling a simple loop and a stub. I experienced no
problems for the loop, but the stub is driving me crazy:
In order to calculate the output voltage of a PCB antenna for a given
geometry and EM-Field at a desired frequency, I need to know the
output impedance for this antenna. I didn't find anything on the web
on calculating/extracting it.

This, in fact, is one of the easiest things to determine - if you know
the frequency and physical dimension.

This was the question! unfortunately
This, in fact, is one of the easiest things to determine - if you know
the frequency and physical dimension.
doesn't help me.... I know the physical dimension (PCB Layout, 93mm
length, 2mm Strip width, 0.035mm hight) The freqeuncy band is given
above.
The only thing antenna books are talking about (the ones i read) are
wire antennas, where a radius is given for calculating the
Waveresistance(? correct word ?)ZL. As i dont have a radius (stripline
is rectangular) I am not sure what to do. Is it possible to say the
area of the stripline is 0.035mm*2mm (crossection), and therefore
build up the equation 0.035mm*2mm=2*pi*r^2 and then follow for the
radius: r=sqrt((0.035mm*2mm)/(2*pi)). I think this is rather wrong,
how else can I determine the waveresistance and with it the Impedance
of the antenna?

You are working too hard. Round wire compared to flat stripline is
not that different. The difference, for the broad range of frequency,
will be overwhelmed by other things.

I was thinking of a 2D FEM in order determine the unit per length
parameters L' and C' and then i can calculate the waveresistance, too.
What do you think?

thanks

Daniel

Hi Daniel,

Think of doing this by parts. The first approximation will be close.
The second approximation will improve it a little. Being perfect will
not matter.

For overall dimension of dipole/monopole/loop, wavelengths less than 1
and more than 0.1 can be found in many antenna reference books.

Let's look a some simple approximations for a loop:
Ra = 320 · pi^6 · (radius / wavelength)^4
for
radius = 0.046 M
wavelength = 3 M
then
Ra = 0.017 Ohm

for
radius =0.046 M
wavelength = 0.3M
then
Ra = 170 Ohm

Let's look a some simple approximations for a dipole:
Ra = 80 · pi² · (length / wavelength)²
for
length = 0.186 M
wavelength = 3 M
then
Ra = 3 Ohm

for
length = 0.186 M
wavelength = 0.3M
then
Ra = 304 Ohm

Now, be warned. These formulas only work for length wavelength and
for radius wavelength. The last evaluation for a nearly halfwave
dipole reveals 304 Ohms for what is actually closer to 70 Ohms.

So for your range, for your largest dimension (93mm) the radiation
resistance will vary between roughly 1 Ohm and 100 Ohms (I am
discounting the loop too). This is for "free space." Your board will
limit that severely. This again suggests high evaluations will be
modified (and closer to my 1 - 100).

This is a first approximation. A second approximation will not alter
this more than 30%. Nearby components will significantly alter it
through proximity.

Trying to compute the reactances will meet similar issues.

73's
Richard Clark, KB7QHC