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  1.         I.  EXAMPLES
  2.  
  3.         a.  LOWPASS FILTER
  4.  
  5.          Let's begin the examples with a simple five-pole lowpass
  6.     filter, having a cutoff frequency of 1 GHz and a maximally flat
  7.     passband response.  Using commonly found design tables, we de-
  8.     rive the following circuit:
  9.  
  10.                                         ELEMENT         PARAMETER
  11.                                        TYPE  NUM   #1      #2      #3
  12.                                      1  CPP  1    1.967
  13.                                      2  INS  2    12.875
  14.                                      3  CPP  3    6.366
  15.                                      4  EQU  4    2
  16.                                      5  EQU  5    1
  17.                                      6  CAX  6    1       5
  18.                                      7  END  6
  19.  
  20.          Note that the EQU (equivalent) command has been used for
  21.     the last two elements.  We can do this as the filter is symmet-
  22.     rical.  This saves execution time as we are using the previous-
  23.     ly calculated S-parameters of elements 1 and 2 rather than cal-
  24.     culate them again.  Now, let's see how this filter performs
  25.     from .1 to 2 GHz in .1 GHz steps (see the chapter on response
  26.     for instructions on how to enter analysis frequencies).
  27.  
  28.                        FREQ     S11     S21     S12     S22
  29.                       in GHz   in dB   in dB   in dB   in dB
  30.                       0.1     -99.81  0       0       -99.81
  31.                       0.2     -69.85  0       0       -69.85
  32.                       0.3     -52.27  0       0       -52.27
  33.                       0.4     -39.79  0       0       -39.79
  34.                       0.5     -30.1   0       0       -30.1
  35.                       0.6     -22.21  -0.03   -0.03   -22.21
  36.                       0.7     -15.61  -0.12   -0.12   -15.61
  37.                       0.8     -10.13  -0.44   -0.44   -10.13  
  38.                       0.9     -5.88   -1.3    -1.3    -5.88
  39.                       1       -3.01   -3.01   -3.01   -3.01
  40.                       1.1     -1.42   -5.55   -5.55   -1.42
  41.                       1.2     -0.65   -8.57   -8.57   -0.65
  42.                       1.3     -0.3    -11.7   -11.7   -0.3
  43.                       1.4     -0.15   -14.76  -14.76  -0.15
  44.                       1.5     -0.07   -17.68  -17.68  -0.07
  45.                       1.6     -0.04   -20.45  -20.45  -0.04
  46.                       1.7     -0.02   -23.06  -23.06  -0.02
  47.                       1.8     -0.01   -25.54  -25.54  -0.01
  48.                       1.9     -0.01   -27.89  -27.88  -0.01
  49.                       2       0       -30.1   -30.1   0
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  56.                                     - 18 -
  57.