# Circuit-HFSS Dynamic Link Port Excitation

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• Last Post 13 December 2018
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Julia posted this 11 December 2018

Hello,

I have a 5 lumped port loop antenna in HFSS. I want to excite port 1 with 1W at 2.4GHz and port 2 with 1W at 127.7MHz from the circuit designer and push the excitations to HFSS. The other three ports I wish to model as series capacitors. I am setting the AC mag of the source excitation in the circuit schematic as 1V and the frequency at each port as either 127MHz or 2.4GHz. Can I assign the input power instead of the voltage? If I can't assign 1W input power from the circuit, would the dynamically linked components still hold if I changed the input power magnitude in HFSS as a post-processing step instead?

Thanks,

Julia

Peter Serano posted this 11 December 2018

Hi Julia,

First, you can push both excitations simultaneously from a Circuit Model but keep in mind you can only view the fields one frequency at a time in HFSS. It might be simpler to create two separate Linear Network Analysis solution setups and analyse and push them separately.

To model your series capacitors properly, be sure to modify the pinouts of you HFSS N-Port block in Designer to have separate reference ports. Then wire the capacitor between these two connections for each respective port. The ports that drive your excitations will then have a GND symbol attached to their reference ports.

To assign a 1W excitation in Designer from a voltage you can back calculate the voltage amplitude since the port source impedance is fixed at 50 ohms. P = V^2/R; 1 = V^2/50; V = sqrt(50) = 7.071 V. - Keep in mind this is incident power and the actually power entering into the system will be scaled by the reflection coefficient of the port.

HFSS is a linear field solver - the power level can always be scaled linearly as a post-processing operation in HFSS by editing the value in the 'Fields -> Edit Source' menu... Keep in mind here that if you setup the circuit simulation to push multiple frequencies at once you will lose the ability to scale the fields from within HFSS - they will show up as a dynamically linked function in the 'Edit Sources' dialog... If you push excitations at just one frequency point, you will be able to see the actual power values pushed into each port and have the ability to edit them if needed...

Best,

Peter Serano - Senior Application Engineer - High Frequency Products

Julia posted this 11 December 2018

That was very helpful, thank you!

This is an example of a schematic (with only one feed port for the 127MHz and not including the 2.4GHz port). However, is this the correct way to model the series capacitors and excitations at the feed ports using the reference pins to ground? Or should the capacitors be connected across the ports?

Peter Serano posted this 11 December 2018

No, you should connect the capacitors directly between the ports' respective terminals; e.g. C4 will connect between C1:1 and C1:1_ref and R5 can be deleted (unless you want to add in the ESR of the capacitors to your model).

Is this for an MRI application? Before joining ANSYS I worked for many years using HFSS for MRI Applications! - https://scholar.google.com/citations?user=Ur7DHqEAAAAJ&hl=en

Peter Serano - Senior Application Engineer - High Frequency Products

Julia posted this 13 December 2018

That makes sense, thank you!

That's great - this is for an MRI application as well! I've been learning how to use HFSS for MR/antenna applications so it's helpful to hear and read about the work others have done.