Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Microstrips lines radiation loss is bigger for thin or thick lines?

Status
Not open for further replies.

Terminator3

Advanced Member level 3
Joined
Feb 25, 2012
Messages
806
Helped
71
Reputation
142
Reaction score
67
Trophy points
1,308
Activity points
9,042
I am not sure if the question is correct. I know that in thicker substrates radiation loss is higher. What about line width, is there any relation?
 

volker@muehlhaus

Advanced Member level 5
Joined
Apr 11, 2014
Messages
2,672
Helped
1,010
Reputation
2,026
Reaction score
1,011
Trophy points
1,393
Activity points
17,149
I just checked with Sonnet EM for a simple through line with 0.1mm, 1mm and 2mm width. The radiated field for 2mm wide line is about 10dB larger than the field for the thin 0.1mm line.

So it seems than going for a thinner substrate has both direct and an indirect effect (narrower lines for same Z0) that reduce radiation.
 

catherine_smith

Junior Member level 1
Joined
Jul 11, 2014
Messages
17
Helped
11
Reputation
22
Reaction score
11
Trophy points
3
Activity points
128
I am not sure if the question is correct. I know that in thicker substrates radiation loss is higher. What about line width, is there any relation?

a) Thicker substrate is better as a radiator: If the substrate is thinner, the signal line and ground are closer to each other, providing tight coupling of the fields between them, making it a better guiding structure..if substrate thickness is high, the coupling of fields between signal to ground is not that strong, and also the fringing field from sides is comparable as well..so its more radiation prone.

b) Lower dielectric constant is better radiator: Permittivity is a quantifier which states how much a dielectric permits electric fields through it.. So higher epsilon will have more fields through substrate and less fringe fields through air, helping in better guiding structure..

c) Higher width is a better radiator: If the line width is high, it provides greater radiating edge for the fringing fields to be excited.. More the fringing fields, more the radiation..
 

vfone

Advanced Member level 5
Joined
Oct 10, 2001
Messages
5,391
Helped
1,560
Reputation
3,123
Reaction score
1,170
Trophy points
1,393
Activity points
34,167
Decreasing the height of the substrate reduce the radiation loses but make the microstrip line thinner, with higher ohmic loss.

Increasing the height of the substrate, the fringing fields from the edges increase, make the effective length of the line longer, and the input impedance of the line become slightly more inductive.
 

volker@muehlhaus

Advanced Member level 5
Joined
Apr 11, 2014
Messages
2,672
Helped
1,010
Reputation
2,026
Reaction score
1,011
Trophy points
1,393
Activity points
17,149
but make the microstrip line thinner, with higher ohmic loss.

Because of skin effect it is not that simple. At GHz frequencies with a few µm skin depth, most current flows at the edges of the conductor and there is very little current in the middle of the lines.
 

vfone

Advanced Member level 5
Joined
Oct 10, 2001
Messages
5,391
Helped
1,560
Reputation
3,123
Reaction score
1,170
Trophy points
1,393
Activity points
34,167
It is true, but the skin effect in this situation (which might help by theory) causes the effective resistance of the conductor to change with frequency.
 

volker@muehlhaus

Advanced Member level 5
Joined
Apr 11, 2014
Messages
2,672
Helped
1,010
Reputation
2,026
Reaction score
1,011
Trophy points
1,393
Activity points
17,149
It is true, but the skin effect in this situation (which might help by theory) causes the effective resistance of the conductor to change with frequency.

Yes, the effective series resistance does change a lot with frequency.

I didn't mean that skin effect helps, but it's there. And it does cause a certain lower limit in resistance if we go to wider lines. At that point, the RF resistance doesn't decrease because the extra width in the center doesn't carry RF current.
 
Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top