The importance of phase center for UWB

Hi

Please help me know why phase center is relatively more important for UWB and is it related to phase of S21.

Moreover how to visualize that it is linear for a given frequency response.

Thanks

Well, if you think in the time domain, if you are trying to transmit a narrow time width voltage pulse, you want all of the various frequency components of that energy to arrive at the receiving antenna at the same instant of time. If you used an antenna that had a phase center near the tip for higher frequencies, and nearer the base for lower frequencies, then the higher frequency components would arrive first, and the lower frequency components would arrive later. You pulse will be widened, and its apparent time would shift over a little due to the broadening of the pulse. You can only stand so much of that before you have system troubles.

I see this issue similarly. The phase center in itself is not important. Moving the phase center is like increasing or decreasing the antenna separation. It changes the propagation delays but that is not in itself damaging.

There is the issue of signal dispersion and a frequency dependant phase center will effect dispersion. I think if the differenences in the response of a LPD vs. a Vivaldi. The literature points to LPD's as being much more dispersive than Vivaldi's. I suspect that a "good" UWB antenna is one that has very linear phase response vs frequency.

Thinking of this as a linear phase s21 is the way I see the issue. (I know we do not have s21 in an antenna with only one port. I don't want to get distracted by that debate.) Maybe we could call it "insertion phase".

This issue is more adressed for DS communication in UWB that uses single pulse for the whole bandwidth. However for OMFDM in UWB phase center is not important.
I saw few paper (Directional UWB) that talk about phase center and all of them just mention it. IS the phase center is more important for directional UWB antenna?

Omni or directional I see no impact either way for the phase center. That is a literal answer to your question. Can you focus the concern more? Why do you see a potential problem?

Both biff44 and I see a potential connection to an increased dispersion if the position of the phase center is frequency dependent. Is that your concern? The antenna biff44 mentioned is probably a LPD with some degree of directivity.

What UWB technique do you have in mind? As you say, a pulse based system has different requirements when compared to OFDM.

I could see your concern going another direction as well if you are looking at an array and want to locate the phase center for element spacing. Or you could be looking at a reflector antenna and are fooling with feed positioning.

It comes down to where are you going with the question?

Thanks for your concerns. You look tooo good but I am not good that why i ask the questions and frankly the question i asked was "how to visualize that it is linear for a given frequency response?"