Hi, Gib, it appears there are two resonant modes relatively close in frequency (separated by 1/4 of their center frequency, as you wrote). You may wish to set the 'width' to some reasonable value so that the spectrum of the source is narrower. http://ab-initio.mit.edu/wiki/index.php/Meep_Reference
Of course, there is also the possibility to run the simulation for longer time, so that the ringing decays, or to use the frequency-domain solver. Both could be especially useful if you were interested what the resonances stem from. Filip 2015-03-31 4:01 GMT+02:00, Gib Bogle <g.bo...@auckland.ac.nz>: > I appreciate that most Meep users, those who post on this mailing list > anyway, are working in optics, while my project is in the microwave range > (5-6 GHz), but there may be someone who can throw some light (ha!) on my > question. > > I am exciting a slot antenna, which is supposed to be resonant at 5.8 GHz, > with a continuous plane wave at that frequency, and logging the electric > field Ey in the gap at the end of the waveguide. After a couple of periods > the Ey signal displays the expected sinusoidal shape - almost. There is a > low frequency modulation, about 4x the wavelength, that is gradually > decaying but still obvious after 20 periods. This makes it hard to get a > good estimate of the amplitude of the antenna response - my goal. > > I haven't been able to find out what is creating this persistent low > frequency wave. My best guess is that it is somehow triggered by the sudden > onset of the sinusoidal forcing by the plane wave. Is there a way to ramp > up the forcing signal? Is this likely to be the cause? > > Thanks > Gib > _______________________________________________ meep-discuss mailing list meep-discuss@ab-initio.mit.edu http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss
