Calculation of track impedance in Sonnet

Hi to all.
I'm new to this sort of stuff , so excuse the ignorance
I'm just playing around with Sonnet 12.52.(lite)
Ive made a project with a 16cm track(give or take) connected to the side of the box.
It is about 1/4 wavelength at 433MHz , so I'd assume it would be around 37 ohm impedance(real) ,
but Sonnet shows it as almose 0 ohms at 433MHz.
What am I doing wrong?
I'm sure Sonnet is giving me the correct answer , but I've made a mistake somewhere.
I'm going to attach the project file.
Cheers
Rob

There is no Sonnet Lite version 12.52

Sorry , 12.53

Hello neddie ,

you not properly defined the substrate stackup such as the dielectric constant, thickness or height & loss tangent, etc...
Also more importantly is it microstrip trace or suspended microstrip or stripline trace?
Again define conductor material properties including conductor thickness....

Then analyze you will get the expected input impedance...

---manju---

It's just supposed to be a quater wave antenna. ie a piece of wire . There is no copper below or above the track.
A quater wavelength piece of wire as an antenna is about 37 ohms , so I assume a length of track in the same
enviroment will exhibit the same characteristics. I'm assuming the "box" will provide the ground for the antenna.
Basically a piece of wire in free space.
Ned

Hello neddie ,

Then set the Box Cover boundary conditions as "Free Space" instead of "Lossless" metals...
Also make sure the X grid size is around 0.25 mm & then simulate...
Make sure your conductor width is properly setup (you used 2mm) & conductor thickness...
You should get desired impedance, once you set the above......
I am getting around 147 ohms...


---manju---

Thanks , that is exactly what I was looking for. Getting numbers that make sence now :0)
How come having the box a lossless metal caused the impedance to be 0(approx) ohms.
Would that be the case in real life..
Cheers
Ned

Antenna needs free space for radiating the energy.

If you have a quarter wave stub radiatiating into a metal box, you will get the same results in measurement. With lossless metal on all sides, and lossless dielectric, there is nothing in the model to absorbe any energy. This is why you get total reflection.

One general comment: For such wire antennas, you should use some NEC-based simulator. Sonnet is designed for circuit analysis, not for wire antennas.

Thanks for the tip!
I would actually like to use Sonnet to model a pcb antenna for a small 433MHz transmitter(keyfob). The antenna is basically
a track(about 6-10cm) around the edge of the PCB. I want to get the track impedance , so I can do matching calcs.
I'm not trying to get radiation patterns at this stage. Is Sonnet ok for this type of application?
Cheers
Ned

Yes.
http://muehlhaus.com/wp-content/uplo...op-antenna.pdf

Thanks , you are a star!
Just the type of thing I'm looking at :0)
At least I'm on the right track , although I fear its a long and winding track :0)
Cheers
Ned