# Microstrip Port Design in Hfss

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#### haast36

##### Newbie level 1
Can anyone please tell me what would be the ideal dimensions for a port in HFss using microstrip. I am analysing a basic structure of microstrip and need to know the effects of a fintie ground plane, however there seems to be no propagation from my input wave port. What is the diffrence btw a Waveport and a Port?

#### adel_48

##### Full Member level 6
In microstrip circuits you ill have to define a port with a certain specifications since otherwise you won't be able to get the expected 50 ohms C/Cs impedance. to read more about this subject read HFSS manual available on the forum.

BR
Adel_48

#### maverick09

##### Member level 4
Hi,

Two ports can be defined: 1. Gap source port
2. Conventional port.

A gap source port can be just a simple rectangle between the trace and the ground plane. We need to specify the port impedance and an impedance line(integration line).

For conventional port, HFSS calculates the port impedance for you. Thus this kind of port should be large enough to provide room for fringing fields around the trace. So a rectangle is constructed with port width ten times the trace width, port height 5 times the substrate thickness and the port height and port width should not differ by a factor 10 or more.

If the port is a little smaller or larger, the port impedance is insensitive to the changes. However if you make the port smaller and smaller, at some point you will squeeze the fields and notice an impedance change. If you make port larger and larger , at some point a waveguide mode may fit the rectangle and you get incorrect results.

Often, you can use the face of the model to define port. However, if the face is very large compared to teh trace width or substrate thickness, use rectangle to define the ports..

Hope this is of your help...........

Andryuha and safura

### safura

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### Andryuha

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