phase center of open waveguide antenna
I am calculating the phase center of horn antennas and open waveguides (WR10, W-band).
It seems, the phase center is centered within the aperture and first moves backward with frequency. Further increase of frequency then shifts it forward.
My simulations are within the mono-mode operation of the waveguides.
Is this physical behaviour ? Any good explanation for this phenomenon available ?
backward=against direction of propagation
forward = direction of propagation
Thanks
-e
my empiracal data at C band is that the phase center is right at the face of the waveguide (or horn) opening. I do not remember a frequency component to it.
Hi biff44, well phase center acutally does change with frequency.
This is pretty much a problem if antennas are part of distance sensors or tracking/imaging sensors.
I am just wondering why the dependency is not "straight". It moves back and forth...
http://www.nsi-mi.com/images/Technic...Adjustment.pdf
Hi,
attached is the result of a 3D simulation with CST time domain solver (FIT).
The phase center (coordinate=direction of propagation) of an open waveguide (WR10, W-band).
If you want to use the measured reflection coefficient (phase of S11) to extract the distance of your target, the phase center movement constitutes a direct source of error.
Dims=mm
What's the unit of phase shift in the diagram?
Too few frequency points to read a systematical behavior into the measurements, I think It might be an oscillating phase.
It is not a phase shift, it is the phase_center in x-direction versus frequency. Dimensions=milli-meter.
x-direction, is also the direction of propagation. The phase center is located in the center of the WR10 wavguide and moves with frequency back and forth.
I suspect that your waveguide em-excitation mode changes. Are you sure it is not (upper freq is almost twice of lower one).
Maybe looking at EM-field for two frequency points with rapid change of phase center help find the cause.
My first impression is that the Centre of Phase (CoP) should move monotonically vs frequency. How do you compute the CoP ? what angular range (field of View) are you considering ? Did you look at the pattern phase once the output system coordinate is place in the computed CoP ?
Thanks.
@Terminator3: Other simulations from 75 to 110 GHz (mono mode operation) give the same results.
@juppydu: Calculationof CoP is done by CST. Angular range is not a parameter, but angle-step=1 degree.
I will check the phase ...
Uhmmmm... you must define a FOV, the CoP is strong function of FOV, what about if you have side lobes, ie phase jumps, in the FOV ?
Hello juppydu,
normally I use HFSS, but I found the angular range (see pic). It is 30 deg around direction of propagation. This should be fine, no side lobes included.
Just to understand, what is e-field boresigth ? Can you select the linera polarization under test ? Can you provide the initial phase plot at least on the two main planes? It also seems to me that the software works only on the two main planes, that in general is not a good choice. The software could use a simplifies formula that take inti acciunt just the boresight phase and the ohase at the edge of fov, even if I do not belive that works in this way.
Dear juppydu,
I will try to find out what is going on and discuss these things internally first.
I come back to you next week. Thank you very much for your time and comments.
-e
Dear juppydu,
boresight means CST will use the main field component that is alligned to the theta (elevation) direction - should be fine for our setup.
We use +/-15 degree=30 degree around the main propagation direction.
The phase center calculation differs for elevation and azimuth (E- and H-plane), using the setting EH (both) just gives the mean value (see attachment).
After all, I think the calculations are correct.
Thanks, -e
good. you can check visually moving accordingly with the results the coordinate system of output beam.
one interesting thing....if you are transmitting with a quarterwave monopole over a ground plane, and the receivig antenna dipps below that plane, there is a sudden 180 degree phase shift. That surprised me the first time i saw it.
Can you further clarify what you see ?