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Finite-width excitation source
Posted 12 mag 2016, 13:45 GMT-4 RF & Microwave Engineering Version 5.2 1 Reply
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Dear users,
I would like to define a plane wave source which does not extend throughout the entire computational domain. In order to do it, I start with a square air box embedded into a larger square PML domain. Later, I define a plane wave source in the air, launch my wave and look at the E-field distribution. My wave is polarized out-of-plane.
For the plane wave, I would expect to have a wave which propagates parallel to the source and is getting absorbed by the PMLs. However, as you can see in the attached figure my field starts to expand to the left and right.
Is there a way to define it the way I want?
Best regards,
Andrzej
I would like to define a plane wave source which does not extend throughout the entire computational domain. In order to do it, I start with a square air box embedded into a larger square PML domain. Later, I define a plane wave source in the air, launch my wave and look at the E-field distribution. My wave is polarized out-of-plane.
For the plane wave, I would expect to have a wave which propagates parallel to the source and is getting absorbed by the PMLs. However, as you can see in the attached figure my field starts to expand to the left and right.
Is there a way to define it the way I want?
Best regards,
Andrzej
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1 Reply Last Post 23 mag 2016, 19:50 GMT-4
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Posted:
8 years ago
Updated:
7 years ago
1. Sorry, but a wave that does not extend to infinity in all directions perpendicular to its direction of propagation is not a true plane wave. So... the short answer to your question is no, you can't define a "plane wave" that is limited in width as you describe. However, do not give up hope, since this doesn't mean you can't define something similar, and sort-of limited in width, such as a wave with a Gaussian cross-section (as one example). Such a Gaussian beam is not properly called a "plane wave," but there is a good chance it might be what you actually want, and if you make it wide enough, it can be a fair approximation to a plane wave in the middle part of the beam.
2. The wave expands because of diffraction. It is unavoidable. If you make the aperture wider, your beam will expand with a smaller angle (assuming your aperture has uniform (or nearly uniform) amplitude and phase). By the way, such an aperture is properly called an "antenna." So if want to make a particular beam, you might want to look up what kinds of beams you can expect from various antennas. Of course, you don't need an explicit/physical antenna to make a beam in Comsol Multiphysics, you just need to set up the right boundary conditions. But once you understand antennas better, you'll have a better feeling for the kind of boundary conditions you need.
2. The wave expands because of diffraction. It is unavoidable. If you make the aperture wider, your beam will expand with a smaller angle (assuming your aperture has uniform (or nearly uniform) amplitude and phase). By the way, such an aperture is properly called an "antenna." So if want to make a particular beam, you might want to look up what kinds of beams you can expect from various antennas. Of course, you don't need an explicit/physical antenna to make a beam in Comsol Multiphysics, you just need to set up the right boundary conditions. But once you understand antennas better, you'll have a better feeling for the kind of boundary conditions you need.