Waveport Size in Driven Terminal

[jianke]

Hi everyone,

I am not sure how to choose the size of waveport in Driven Terminal. Can anyone give me some suggestion?
The dimensions of my structure (see the attached picture or HFSS file):
Height of substrate, h=0.762mm;
Width of microstrip line, w=1.98mm;
Operation frequency, f=14.25GHz;
Wavelength=21.053mm; Wavelength/2=10.526mm, Wavelength/4=5.263

According to the HFSS manual (w>h),
Height of waveport = 6h~10h
Width of waveport = 10w=19.8mm
However, the height and width of waveport cannot exceed the Wavelength/2 (10.526mm)!!!

Thus, I choose 6.762mm as waveport height, and 10mm as waveport width.
The operation frequency is f=14.25GHz, and I want to sweep from 1GHz to 25GHz.
Whether the waveport size I choosed is correct, espically the width?
View attachment Shield.rar

 

[Tucco]

Hi,
1) the rule of Wavelength/2 is true but the effective value seen by your transmission line , not the value in vacuum. --> not 10mm but maybe 6 ou 7 mm if er = 3 (I supposed)

2) 5 h / 5 w are enough in many case .Be careful to boundary conditions around port.

3) Your case in very special, Wstrip is very heigth relative to frequencies, Height of the substrate too -->
You may have big radiation losses problem. For me, max frequency for this circuit is 10-12 GHz.

 

[jianke]

Hi Tucco, Thanks so much for your suggestions. The effective value of wavelength you mentioned should be about the effective dielectric constant of the microstrip line, rather than in vacuum or substrate. I am not very sure about it.

Another question is if the microstrip line enclosed in a metal box. The boundary conditions of the air box is PEC, rather than radiation. How can I set a lumped port for the line?
- I drew a rectangle from the line end to the ground, and set it as lumped port. However, since this rectangle overlaps with the metal box while the line, ground and metal are all PEC, the simulation is wrong. The error is that "Too few conductors were found."
- Although the waveport is available, I want to simulate this shielding box using lumped port in Driven Terminal. Do you know how I can avoid this problem and set right for the lumped port?

 

[Umar608]

Hi,
In a similar simulations, I have used a lumped port which was equal to substrate height and microstip line width. So it was actually attached to the side of substrate between ground and microstip line. The box with PEC walls start from the substrate height and there was no overlap. The simulation worked fine.

 

[Tucco]

Lumped port are not allowed in the boundary box of your model. You need to place lumped port inner that induce posible modification
in your layout...When I can use wavaport I don't hesitate. And reserve luimped only for special cases (IC in packaging for example).