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
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