There are at least two ways to compute cutoff-frequencies with GdfidL. The easiest way is to compute resonant fields in a short section of the waveguide. When the proper boundary conditions are applied, the resulting fields and frequencies are the resonant fields at cutoff and their cutoff-frequencies.
The easiest is just to apply periodic boundary conditions with a phase shift of zero, although this is not the most computational efficient. While we are at waisting CPU-cycles, we do not even consider symmetries in the geometry of the waveguide. The computation of the cutoff-frequencies in an elliptical waveguide then is:
gd1 < waveguide.gdf | tee out
After some seconds we get a list of frequencies like:
i freq(i) acc(i) cont(i) 1 122.4760e+6 1.2263639315 0.4112620337 # "grep" for me 2 2.2297e+9 0.0000035244 0.0000021997 # "grep" for me 3 4.0480e+9 0.0000000681 0.0000000812 # "grep" for me 4 4.4089e+9 0.0000015489 0.0000098211 # "grep" for me 5 4.7150e+9 0.0000012703 0.0000029069 # "grep" for me 6 5.7555e+9 0.0000000273 0.0000000753 # "grep" for me 7 5.8907e+9 0.0000003628 0.0000035260 # "grep" for me 8 6.1920e+9 0.0000000138 0.0000000484 # "grep" for me 9 7.0729e+9 0.0000002350 0.0000009870 # "grep" for me 10 7.6704e+9 0.0000000257 0.0000001639 # "grep" for me 11 7.7208e+9 0.0000001496 0.0000008549 # "grep" for me 12 8.4049e+9 0.0000000052 0.0000000316 # "grep" for me 13 8.5090e+9 0.0000000066 0.0000002716 # "grep" for me 14 8.5653e+9 0.0000000160 0.0000000900 # "grep" for me 15 9.3371e+9 0.0000000107 0.0000000643 # "grep" for me 16 9.3944e+9 0.0000000482 0.0000005784 # "grep" for me 17 9.7872e+9 0.0000000188 0.0000002359 # "grep" for me 18 9.9837e+9 0.0000000028 0.0000000718 # "grep" for me 19 10.0480e+9 0.0000000123 0.0000000657 # "grep" for me 20 11.0034e+9 0.0000000107 0.0000000613 # "grep" for me 21 11.0735e+9 0.0000000032 0.0000002290 # "grep" for me 22 11.1497e+9 0.0000000023 0.0000000642 # "grep" for me 23 11.3516e+9 0.0000000020 0.0000000512 # "grep" for me 24 11.5672e+9 0.0000000006 0.0000000049 # "grep" for me 25 12.2768e+9 0.0000000036 0.0000000307 # "grep" for me 26 12.4153e+9 0.0000000038 0.0000001697 # "grep" for me 27 12.4677e+9 0.0000000004 0.0000000200 # "grep" for me 28 12.5967e+9 0.0000000024 0.0000001197 # "grep" for me 29 12.6975e+9 0.0000000010 0.0000000626 # "grep" for me 30 12.7606e+9 0.0000000009 0.0000000088 # "grep" for me 31 13.3912e+9 0.0000000012 0.0000000132 # "grep" for me 32 13.6535e+9 0.0000000003 0.0000000085 # "grep" for me 33 13.8491e+9 0.0000000030 0.0000001071 # "grep" for me 34 13.9047e+9 0.0000000011 0.0000000236 # "grep" for me 35 14.2239e+9 0.0000000031 0.0000000697 # "grep" for me 36 14.4204e+9 0.0000000076 0.0000002782 # "grep" for me 37 14.5021e+9 0.0000000142 0.0000004646 # "grep" for me 38 14.7227e+9 0.0000000058 0.0000001524 # "grep" for me 39 15.0025e+9 0.0000000064 0.0000001735 # "grep" for me 40 15.1974e+9 0.0000000197 0.0000007736 # "grep" for me 41 15.3650e+9 0.0000000651 0.0000015631 # "grep" for me 42 15.6836e+9 0.0000005207 0.0000117680 # "grep" for me 43 16.0273e+9 0.0046087858 0.1073045033 # "grep" for me 44 16.0768e+9 0.0039905447 0.6498775793 # "grep" for me 45 16.1235e+9 0.0047293597 0.3225176260 # "grep" for me 46 16.2417e+9 0.0027525493 0.0795671401 # "grep" for me 47 16.5221e+9 0.0069169406 0.2046412339 # "grep" for me 48 16.6937e+9 0.0606064395 0.9964082399 # "grep" for me 49 17.2006e+9 0.0274154940 0.4583279318 # "grep" for meThe inputfile for this cavity is waveguide.gdf
We start the postprocessor, gd1.pp, and use him interactively:
Input for gd1.pp:
-general, infile= @last -3darrow fcolour= 7, eyeposition= ( 1, 2.3, 3 ), scale= 5 quantity= ere solution= 2 doit
------- Thats it.