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design_coupler(1)	    General Commands Manual	     design_coupler(1)

       design_coupler  -  for designing	directional couplers (part of the atlc

       design_coupler [-C][-d][-e][-H height][-L length][-q]
       [s fstep][-Z Zo]	CF fmin	fmax

       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	 docu-
       mentation that was current at the time this version was produced	should
       be found	on your	hard drive, usually at
       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	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.

       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	numer-
       ous 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-cou-
       pled striplines between two wide	plates like this:

       -----------------------------------------------------  ^
       |						   |  |
       |		  Er				   |  |
       |						   |  |
       |	    -----------	      -----------	   |  H
       |	    <----w----><--s--><----w---->	   |  |
       |						   |  |
       |						   |  |
       |						   |  |
       -----------------------------------------------------  v

       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,	other-
       wise  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 cou-
       plers 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 im-
       practical,  as  the  spacing s will be so small.	However, for weak cou-
       pling, the physcical dimensions are practical.

       print copyright,	licensing and copying information.
       Design a	coupler, using	two  edgle-coupled  stiplines  inside  a  wide
       4-sided rectangular enclosure.

       Priont an example of how	to use design_coupler
       -H height
       Specify	the  height  of	 the enclosure in some convenient unit.	By de-
       fault, 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	dimen-
       sions 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  as-
       sumed  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  (sheci-
       fied in Ohms). The default value	for Zo is 50 Ohms.

       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

       % 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 cou-
       pling  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,	devia-
       tions 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

       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,  oth-
       erwise 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	dimen-
       sions 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 us-
       ing 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 sug-
       gests 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

       No files	are created at all.

       create_bmp_for_circ_in_circ(1)	create_bmp_for_circ_in_rect(1)	  cre-
       ate_bmp_for_microstrip_coupler(1)    create_bmp_for_rect_cen_in_rect(1)
       create_bmp_for_rect_cen_in_rect_coupler(1)			  cre-
       ate_bmp_for_rect_in_circ(1)     create_bmp_for_rect_in_rect(1)	  cre-
       ate_bmp_for_stripline_coupler(1)		      create_bmp_for_symmetri-
       cal_stripline(1)	find_optimal_dimensions_for_microstrip_coupler(1)
       readbin(1)		  - Home page	  - 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

Dr. David Kirkby	   atlc-4.4.2 10th Sept	2003	     design_coupler(1)


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