## 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 documen-
         tation - 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 dimen-
         sions. 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 fre-
         quency  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 characteris-
         tic 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 cou-
         ple 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  cou-
         pled port is exactly 30 dB below the input power at the cen-
         tre 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  calcu-
         lator,  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