short questions on CST MWS

Hello,

I will write some short questions and annotations on CST MWS. In hope anyone
will give me some response.

1) My energy curves are sometimes round and sometimes edgy?

2) Waveguide ports must be sized carefully. Too short means low accuracy,
too big leads to higher order modes disturbing the calculation.
Isnt it a good idea to look at the line impedance Zline while increasing the
port size. Should we see a constant Zline if the port is big enough ?

3) Physics: Whats wrong with line resonance. We get a reflection coefficient near zero, means there is no reflected wave. Is it the phase ? If the resonance setting
does not destroy the structure, where is the problem. A good way to match
the system ?

Any comment is helpfull. Thanks. elektr0

Hi electr0,
about the second question, your structure is a planar one?
A microstrip for example?
If you work on a planar stucture the size of the waveguide port should not
affect the line impedance. Generally speaking, line impedance depends on the
width of the line and the dielectric material based on (height and εr).So I
think that you should see a constant line impedance.
For the correct port size have a look at the documentation of CST MWS.
It says that the width of the port should be 10 times the width of the microstrip line
and the height 5 times the height of the substrate.
Hope I helped

Well elektr0 for your second question..

I've been working on planar antennas both in Microstrip and co-planar technologies for somehow a long time. I'm pretty sure of what I'm going to tell you now..

YOU ALWAYS HAVE TO LOOK AT THE LINE IMPEDANCE to make sure that your port's size is appropriate that when Maxwell equations are solved with its size, the line impedance can produce near 50 Ohms value. That's confirmed..
Beside all this, you need to set the Microstrip line or the coplanar feeding line to proper dimensions according to their design equations to get a good PRACTICAL matching, which leads to good results!
Because, for an instance, you can set any value for the Microstrip line in simulation, and then set the wave guide port again to get nearly 50 Ohms again! so be careful..

Good luck

i recommend for avoiding the waveguide port dimension that u could use the discrete port
it already provide u with 50 ohm without any dimension,just need only 2 points
regards

The discrete port is NOT accurate in all cases. The results gotten by the waveguide port are more realistic especially for planar structures having a significant width and a ground. That's the reason why they have a "waveguide port" choice, otherwise it will be useless! So he elektr0 should be careful in choosing the port type depending on the design. Yet, many designs are best excited by discreet ports.

I hope it was clear :)