NAME
design_coupler - for designing directional couplers (part of the atlc
package)
SYNOPSIS
design_coupler [-C][-d][-e][-H height][-L length][-q]
[s fstep][-Z Zo] CF fmin fmax
WARNING
This man page is not a complete set of documentation - the complexity
of the atlc project makes man pages not an ideal way to document it,
although out of completeness, man pages are produced. The best
documentation that was current at the time this version was produced
should be found on your hard drive, usually at
/usr/local/share/atlc/docs/html-docs/index.html
although it might be elsewhere if your system administrator chose to
install the package elsewhere. Sometimes, errors are corrected in the
documentation and placed at http://atlc.sourceforge.net/ before a new
release of atlc is released. Please, if you notice a problem with the
documentation - even spelling errors and typos, please let me know.
DESCRIPTION
design_coupler is used to design directional couplers. It it not used
to analyse couplers for which you know the dimensions. Instead, it is
used but when you require a coupler to have specific properties, but
don’t know the required odd and even mode impedances or the required
physical dimensions that will achieve those required properties.
As a minimum the user must specify the coupling factor CF in dB, the
minimum frequency fmin in MHz and the maximum frequency fmax in MHz.
With this information, the design_coupler will
a) Tell you the required odd and even mode impedances Zodd and Zeven
assuming the coupler is for 50 Ohms and assuming the coupler is is a
quarter wave long, which might be an impractical length. There a
numerous ways of making a coupler having those impedances and
design_coupler does not (without the addition of options mentioned
later), tell you how to make such a coupler. b) Given you the
frequency response of the coupler, making the assumptions about the 50
Ohm impedance and quarter-wave length. The frequency response is
calculated at 5 points in the range specified by fmin and fmax.
By use of the -Z ’Zo’ and -L ’length’ and -f ’fstep’ options it it
posible to specify different a different characteristic impedance,
length and different frequency steps to display the frequency response.
The computed values of Zodd and Zeven required are valid no matter how
the coupler is design physically. So no matter whether it’s implemented
on a PCB, air spaced or whatever, the above impedances are correct and
the frequency response is correct.
The -d option causes design_coupler to not only report the required odd
and even modem impedances but also the physical dimensions of a coupler
that achieves these properties! Currently, the only stucture for which
it is possible to compute the physical dimentions is two wide edge-
coupled striplines between two wide plates like this:
----------------------------------------------------- ^
| | |
| Er | |
| | |
| ----------- ----------- | H
| <----w----><--s--><----w----> | |
| | |
| | |
| | |
----------------------------------------------------- v
<-------------------------W------------------------->
The width W must be much greater than the height of the coupler and
generally it is assumed that this width will at least 2*w+s*5*H,
otherwise the calculations will be incorrect. In order to calculate
these dimenisions an analytical method is used, which is only valid if
the width W is infinity, but should be resonably good assuming W is at
least 2*w+s+5*H.
It is later intended to enable design coupler to use other structures,
which migth be more suitable for construction, such as microstrip
couplers on PCBs, but for now at least, it is only possible to compute
the physical dimensions of the coupler using the above stucture. For
strong coupling (less than 20 dB or so), the dimenions calculated might
be impractical, as the spacing s will be so small. However, for weak
coupling, the physcical dimensions are practical.
OPTIONS
-C
print copyright, licensing and copying information.
-d
Design a coupler, using two edgle-coupled stiplines inside a wide
4-sided rectangular enclosure.
-e
Priont an example of how to use design_coupler
-H height
Specify the height of the enclosure in some convenient unit. By
default, a height of 1 unit is assumed, but by use of this option it is
possible to specify any height you want. Since its the ratio of
dimensions that is important, not the absolute values, this just scales
all the other dimensions by the specified height. It is just a
conveneince for the user.
-L length
Specifies the coupler length in metres. By default the coupler is
assumed to be a quarter-wave, but this allow any length you want. Don’t
chose a length that is a multiple of a half-wave though, as this will
make it impossible to couple any power out. -q
This is the ’quite’ switch and causes design_coupler to print out less
information. One can use -qq to cause the even less output.
-s fstep Causes design_couler to print out the frequency response at
different steps from the default 5 values. fstep must be in MHz. The
default value of fstep is obviously (fmax-fman)/5.
Z Zo
Causes design_coupler to compute properties of an impedance Zo
(shecified in Ohms). The default value for Zo is 50 Ohms.
EXAMPLES
Run design_coupler gives examples of its use. However, here are those
same examples.
Here are a examples of how to use design_coupler In the examples, the %
sign is used in front of anything you must type which is what you will
probably see when using the csh or tcsh as a shell. It would probably
be a $ sign if using the sh or bash shell.
To find the odd and even mode impedances and frequency response of a 50
Ohm coupler, covering 130 to 170 MHz, with a coupling coefficient of 30
dB:
% design_coupler 30 130 170
Note the frequency response is symmetrical about the centre frequency
at 0.192 dB below that wanted. You may wish to redesign this for a
coupling coefficient of about 29.9 dB, so the maximum deviation from
the ideal 30.0 dB never exceeds 0.1 dB Note the length suggested is 0.5
m (nearly 20") is a quarter wave at the centre frequency of 150 MHz.
You might find this a bit too long, so let’s specify a length of 0.25
m.
% design_coupler -L 0.25 30 130 170
What you may notice is that while the coupling to the coupled port is
exactly 30 dB below the input power at the centre frequency (150 MHz)
it is no longer symmetrical about the centre frequency. Also,
deviations from the ideal 30 dB are now much larger, with a maximum
error of 1.012 dB Unlike the case when the length is the default
quarter wave, there is not much you can do about this, since the
deviations occur in both directions.
Now assume you are reasonably happy with the response when the length
is 250 mm but would like to see the response at every 2.5 MHz. This can
be done using the -s option to design_coupler.
% design_coupler -L 0.25 -s 2.5 30 130 170
Assuming the performance is acceptable, the dimensions of the coupler
can be determined by adding the -d option. This will design a coupler
that must look like the structure below. The two inner conductors,
which are spaced equally between the top and bottom edges of the outer
conductor, must be very thin. These are placed along the length of a
box of width W, height H and of a length L determined by the user,
which in this case is 250 mm.
----------------------------------------------------- ^
| | |
| Er | |
| | |
| ----------- ----------- | H
| <----w----><--s--><----w----> | |
| | |
| | |
| | |
----------------------------------------------------- v
<-------------------------W------------------------->
The program reports: H = 1.0, ; w = 1.44 ; s = 0.44 The height of the
box H must be small compared to the length L, (perhaps no more than 7%
of the length), or 17.5 mm in this case, with a length of 250 mm,
otherwise fringing effects will be significant. The width of the
structure W should be as large as possible. The program suggests making
this 5*H+2*w+s. The 7% and 5*H+2*w+s are educated guesses, rather than
exact figures. There is no problem in making the width larger than
5*H+2*w+s. The length L must be kept at 250 mm. The RATIO of the
dimensions H, w and s (but not L or W must be kept constant. W just
needs to be sufficiently large - it is uncritical.
If you happened to have some 15 mm square brass available, then using
that for the side-walls would require that H becomes 15*1.0 = 15 mm, w
= 15*1.44 = 21.6 mm and s = 15*0.44 = 6.6 mm
There is no need to compute the above scaling with a calculator, as
using The -H option allows one to specify the height H. The program
then reports the exact dimensions for the length L, height H, w, s and
suggests a minimum width for W.
In summary we have:
30 dB coupler +1.02 dB / -0.78 dB for 130 to 170 MHz
Length L = 250 mm, height H = 15 mm, stripline spacing s = 6.3 mm
stripline width w = 21.6 mm enclosure width W >= 124 mm
By default, design_coupler prints a lot of information to the screen.
This can be reduced by the -q option or reduced to only one line with
-qq Other options include -Z to change the impedance from the default
50 Ohms and -C to see the fully copyright, Licensing and distribution
information
FILES
No files are created at all.
SEE ALSO
atlc(1)
create_bmp_for_circ_in_circ(1) create_bmp_for_circ_in_rect(1)
create_bmp_for_microstrip_coupler(1) create_bmp_for_rect_cen_in_rect(1)
create_bmp_for_rect_cen_in_rect_coupler(1)
create_bmp_for_rect_in_circ(1) create_bmp_for_rect_in_rect(1)
create_bmp_for_stripline_coupler(1)
create_bmp_for_symmetrical_stripline(1)
find_optimal_dimensions_for_microstrip_coupler(1)
readbin(1)
http://atlc.sourceforge.net - Home page
http://sourceforge.net/projects/atlc - Download area
atlc-X.Y.Z/docs/html-docs/index.html - HTML docs
atlc-X.Y.Z/docs/qex-december-1996/design_coupler.pdf - theory paper
atlc-X.Y.Z/examples - examples