1 .TH design_coupler 1 "atlc-4.4.2 10th Sept 2003" "Dr. David Kirkby"
4 \fBdesign_coupler\fR - for designing directional couplers (part of the \fBatlc\fR package)
6 \fBdesign_coupler [-C][-d][-e][-H height][-L length][-q]
8 [s fstep][-Z Zo] CF fmin fmax \fR
11 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.
12 The best documentation that was current at the time this version was produced should be found on your
13 hard drive, usually at
15 /usr/local/share/atlc/docs/html\-docs/index.html
17 although it might be elsewhere if
18 your system administrator chose to install the package elsewhere. Sometimes, errors are corrected
19 in the documentation and placed at http://atlc.sourceforge.net/ before a new release of atlc is
20 released. Please, if you notice a problem with the documentation - even spelling errors and typos,
24 \fBdesign_coupler\fR is used to design directional couplers. It it \fBnot\fR
25 used to analyse couplers for which you know the dimensions. Instead, it
26 is used but when you require a coupler to have specific properties, but don't know the
27 required odd and even mode impedances or the required physical dimensions
28 that will achieve those required properties.
30 As a minimum the user must specify the coupling factor CF in dB, the
31 minimum frequency fmin in MHz and the maximum frequency fmax in MHz.
32 With this information, the \fBdesign_coupler\fR will
34 a) Tell you the required odd and even mode impedances Zodd and Zeven
35 assuming the coupler is for 50 Ohms and assuming the coupler is is a
36 quarter wave long, which might be an impractical length. There a numerous
37 ways of making a coupler having those impedances and \fBdesign_coupler\fR does
38 not (without the addition of options mentioned later), tell you how to
40 b) Given you the frequency response of the coupler, making the
41 assumptions about the 50 Ohm impedance and quarter-wave length. The frequency
42 response is calculated at 5 points in the range specified by fmin and
45 By use of the -Z 'Zo' and -L 'length' and -f 'fstep' options it it posible to
46 specify different a different characteristic impedance, length and
47 different frequency steps to display the frequency response.
49 The computed values of Zodd and Zeven required are valid no matter how
50 the coupler is design physically. So no matter whether it's implemented
51 on a PCB, air spaced or whatever, the above impedances are correct and
52 the frequency response is correct.
54 The -d option causes \fBdesign_coupler\fR to not only report the
55 required odd and even modem impedances but also the physical
56 dimensions of a coupler that achieves these properties! \fBCurrently\fR,
57 the only stucture for which it is possible to compute the physical
58 dimentions is two wide edge-coupled striplines between two wide plates like
62 ----------------------------------------------------- ^
70 | ----------- ----------- | H
72 | <----w----><--s--><----w----> | |
80 ----------------------------------------------------- v
82 <-------------------------W------------------------->
85 The width W must be much greater than the height of the coupler and
86 generally it is assumed that this width will at least 2*w+s*5*H,
87 otherwise the calculations will be incorrect. In order to calculate
88 these dimenisions an analytical method is used, which is only valid if
89 the width W is infinity, but should be resonably good assuming W is at
92 It is later intended to enable design coupler to use other structures,
93 which migth be more suitable for construction, such as microstrip
94 couplers on PCBs, but for now at least, it is only possible to compute
95 the physical dimensions of the coupler using the above stucture. For
96 strong coupling (less than 20 dB or so), the dimenions calculated
97 might be impractical, as the spacing s will be so small. However, for
98 weak coupling, the physcical dimensions are practical.
103 print copyright, licensing and copying information.
107 Design a coupler, using two edgle-coupled stiplines inside a wide
108 4-sided rectangular enclosure.
112 Priont an example of how to use \fBdesign_coupler\fR
116 Specify the height of the enclosure in some convenient unit. By default,
117 a height of 1 unit is assumed, but by use of this option it is possible
118 to specify any height you want. Since its the ratio of dimensions that
119 is important, not the absolute values, this just scales all the other
120 dimensions by the specified height. It is just a conveneince for the
125 Specifies the coupler length in metres. By default the coupler is
126 assumed to be a quarter-wave, but this allow any length you want. Don't
127 chose a length that is a multiple of a half-wave though, as this will
128 make it impossible to couple any power out.
131 This is the 'quite' switch and causes \fBdesign_coupler\fR to print out
132 less information. One can use -qq to cause the even less output.
135 Causes \fBdesign_couler\fR to print out the frequency response at
136 different steps from the default 5 values. fstep must be in MHz. The
137 default value of fstep is obviously (fmax-fman)/5.
141 Causes \fBdesign_coupler\fR to compute properties of an impedance Zo
142 (shecified in Ohms). The default value for Zo is 50 Ohms.
145 Run \fBdesign_coupler\fR gives examples of its use. However, here are
148 Here are a examples of how to use \fBdesign_coupler\fR
149 In the examples, the % sign is used in front of anything you must type
150 which is what you will probably see when using the csh or tcsh as a shell. It
151 would probably be a $ sign if using the sh or bash shell.
153 To find the odd and even mode impedances and frequency response of a 50 Ohm
154 coupler, covering 130 to 170 MHz, with a coupling coefficient of 30 dB:
156 % design_coupler 30 130 170
158 Note the frequency response is symmetrical about the centre frequency at 0.192 dB
159 below that wanted. You may wish to redesign this for a coupling coefficient of
160 about 29.9 dB, so the maximum deviation from the ideal 30.0 dB never exceeds 0.1 dB
161 Note the length suggested is 0.5 m (nearly 20") is a quarter wave at
162 the centre frequency of 150 MHz. You might find this a bit too long, so
163 let's specify a length of 0.25 m.
165 % design_coupler -L 0.25 30 130 170
167 What you may notice is that while the coupling to the coupled port is exactly
168 30 dB below the input power at the centre frequency (150 MHz) it is
169 no longer symmetrical about the centre frequency. Also, deviations from the
170 ideal 30 dB are now much larger, with a maximum error of 1.012 dB
171 Unlike the case when the length is the default quarter wave, there is not much
172 you can do about this, since the deviations occur in both directions.
174 Now assume you are reasonably happy with the response when the length is 250 mm
175 but would like to see the response at every 2.5 MHz. This can be done using the
176 -s option to design_coupler.
178 % design_coupler -L 0.25 -s 2.5 30 130 170
180 Assuming the performance is acceptable, the dimensions of the coupler can
181 be determined by adding the -d option. This will design a coupler that must look
182 like the structure below. The two inner conductors, which are spaced equally
183 between the top and bottom edges of the outer conductor, must be very thin.
184 These are placed along the length of a box of width W, height H and of
185 a length L determined by the user, which in this case is 250 mm.
187 ----------------------------------------------------- ^
195 | ----------- ----------- | H
197 | <----w----><--s--><----w----> | |
205 ----------------------------------------------------- v
207 <-------------------------W------------------------->
210 The program reports: H = 1.0, ; w = 1.44 ; s = 0.44
211 The height of the box H must be small compared to the length L, (perhaps no
212 more than 7% of the length), or 17.5 mm in this case, with a length of 250 mm,
213 otherwise fringing effects will be significant. The width of the structure W
214 should be as large as possible. The program suggests making this 5*H+2*w+s. The
215 7% and 5*H+2*w+s are educated guesses, rather than exact figures. There is
216 no problem in making the width larger than 5*H+2*w+s. The length L must be
217 kept at 250 mm. The RATIO of the dimensions H, w and s (but not L or W
218 must be kept constant. W just needs to be sufficiently large - it is
221 If you happened to have some 15 mm square brass available, then using that
222 for the side-walls would require that H becomes 15*1.0 = 15 mm,
223 w = 15*1.44 = 21.6 mm and s = 15*0.44 = 6.6 mm
225 There is no need to compute the above scaling with a calculator, as using
226 The -H option allows one to specify the height H. The program then reports the
227 exact dimensions for the length L, height H, w, s and suggests a minimum width
232 30 dB coupler +1.02 dB / -0.78 dB for 130 to 170 MHz
234 Length L = 250 mm, height H = 15 mm, stripline spacing s = 6.3 mm
236 stripline width w = 21.6 mm enclosure width W >= 124 mm
238 By default, design_coupler prints a lot of information to the screen.
239 This can be reduced by the -q option or reduced to only one line with -qq
240 Other options include -Z to change the impedance from the default 50 Ohms
241 and -C to see the fully copyright, Licensing and distribution information
244 No files are created at all.
248 create_bmp_for_circ_in_circ(1)
249 create_bmp_for_circ_in_rect(1)
250 create_bmp_for_microstrip_coupler(1)
251 create_bmp_for_rect_cen_in_rect(1)
252 create_bmp_for_rect_cen_in_rect_coupler(1)
253 create_bmp_for_rect_in_circ(1)
254 create_bmp_for_rect_in_rect(1)
255 create_bmp_for_stripline_coupler(1)
256 create_bmp_for_symmetrical_stripline(1)
257 find_optimal_dimensions_for_microstrip_coupler(1)
262 http://atlc.sourceforge.net - Home page
264 http://sourceforge.net/projects/atlc - Download area
266 atlc-X.Y.Z/docs/html-docs/index.html - HTML docs
268 atlc-X.Y.Z/docs/qex-december-1996/design_coupler.pdf - theory paper
270 atlc-X.Y.Z/examples - examples
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