Ubuntu Manpage: design_coupler - for designing directional couplers (part of the atlc package)

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.