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Input Port Excitation Power for 2D RF Simulation

Posted Jan 15, 2013, 11:50 a.m. EST RF & Microwave Engineering Version 4.3 3 Replies

aCOMSOLuser
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Hello, I'm having difficulty understanding exactly what the input power is for the port in the RF module in COMSOL 4.3. The unit is declared as watt, but unless there's some predefined thickness, the unit doesn't make sense (I would expect watt/m).

Just as an example, I tried simulating a silicon waveguide and set a line integration variable on the input where I measured the emw.Poavx (perpendicular to the line) at different lines on the waveguide and multiplied this value (which is in watt/m) by my expected thickness and got values that were much smaller than what I expected for what I put in as my input power.

Does this mean that the unit for input power in the port excitation is in fact watt/m? If so, that would explain some discrepancies in my other results I've been simulating.
3 Replies Last Post Mar 22, 2017, 11:40 a.m. EDT
Sergei Yushanov Certified Consultant
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Posted: 1 decade ago Jan 15, 2013, 1:06 p.m. EST
Input power in 2D is defined per unit thickness, t.e. per 1m thickness in the out-of plane direction:

n.Pav=P0[W]/b[m]/1[m],

where

Pav[W/m^2] is Poynting vector, b is port width, and n is the unit vector to the port.

For TE mode, port field amplitude is calculated based on the specified port power P0 as following:

n.Pav=|E|^2/(2*Z_TE), where Z_TE=omega*mu/beta => |E|=sqrt(2*Z_TE*P0[W]/b[m]/1[m]).


For TM mode, port field amplitude is calculated based on the specified port power P0 as following:

n.Pav=|nxE|^2/(2*Z_TM), where Z_TM =beta/omega/epsilon => |E|=sqrt(2*Z_TM* P0[W]/b[m]/1[m]).

where beta is propagation constant NORMAL to the port boundary.

One should be very careful if port input wave is oblique.


Regards,
Sergei
Input power in 2D is defined per unit thickness, t.e. per 1m thickness in the out-of plane direction: n.Pav=P0[W]/b[m]/1[m], where Pav[W/m^2] is Poynting vector, b is port width, and n is the unit vector to the port. For TE mode, port field amplitude is calculated based on the specified port power P0 as following: n.Pav=|E|^2/(2*Z_TE), where Z_TE=omega*mu/beta => |E|=sqrt(2*Z_TE*P0[W]/b[m]/1[m]). For TM mode, port field amplitude is calculated based on the specified port power P0 as following: n.Pav=|nxE|^2/(2*Z_TM), where Z_TM =beta/omega/epsilon => |E|=sqrt(2*Z_TM* P0[W]/b[m]/1[m]). where beta is propagation constant NORMAL to the port boundary. One should be very careful if port input wave is oblique. Regards, Sergei
Stuart Earl
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Posted: 1 decade ago Feb 27, 2013, 10:39 p.m. EST
And what about for 3D normal excitation? If I have a port of known area a [m^2] and input irradiance I [W/m^2], am I correct in using Pin=a*I [W] ?

I'm running 4.3a and getting some funny results, I just want to check that the input power of a port BC is defined as I expect it to be. Excitation is linearly polarised


And what about for 3D normal excitation? If I have a port of known area a [m^2] and input irradiance I [W/m^2], am I correct in using Pin=a*I [W] ? I'm running 4.3a and getting some funny results, I just want to check that the input power of a port BC is defined as I expect it to be. Excitation is linearly polarised
Nathan Woodard
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Posted: 8 years ago Mar 22, 2017, 11:40 a.m. EDT
Great Answer Sergei! Very helpful. Thanks for posting.
Great Answer Sergei! Very helpful. Thanks for posting.

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