antenna group delay

Hello all

My question regards simulating an antenna and calculating the group delay/group delay varaiation from the simulation results.
(btw: I'm using CST but i'd like to hear all users' suggestions)

In case i'd like to find the group delay between 2 antennas I would normally simulate them and derive ΔΦ/Δω from S21 phase.

BUT what if i need a general group delay of a single (transmitting) antenna without the frequency deformation of the receiving antenna?

Please share your suggestions with me,
Best regards,
P.

I think you just have to build two identical antennas and split/2 the result

pl

I'm assuming this is for UWB antennas since that is mostly what I hear about when group delay is mentioned these days. In general, you would like the antenna gain to be flat across the band of interest for a good group delay. I agree with the first response that you should be able to simulate the same antenna for receive and transmit and then divide the group delay by two. This is done in measurements as well.

Hi,

I have some basic questions.
-How much the distance should be between these two identical antennas?
-Good group delay means linear ? or zero ? or ?

Regards

The distance should be sufficiently large so that the antennas are not coupling in the near field (which is reactive coupling). Group delay is a metric which shows the phase linearity across a given bandwidth and is an far-field parameter, so the separation between the two antennas needs to be large enough so they are in each other's far field region. The far field of an antenna is usually taken as 2D^2/lambda where D is the largest dimension of the antenna.

As the original poster mentioned, group delay is the negative derivative of the phase response with respect to frequency. A good flat group delay means that the phase response is linear and therefore there will be no or little distortion of a transmitted pulse. One way to think of it is as characterizing the transfer function of the system. Good group delay is constant across the band.

See these links for more info:

http://www.uwbgroup.ru/pdf/26mohammadian.pdf

http://www.slac.stanford.edu/cgi-wra...-pub-11749.pdf

http://media.wiley.com/assets/350/15/UWB_Article.pdf

http://mtlweb.mit.edu/researchgroups...SAP_paper2.pdf

Thanks alot,

I think these articles will be helpful,

P.

Thanks a lot. I'm fully understand the situation now.
So, could we simulate two identical antennas in CST and calculate in some way the group delay between them?

Regards

Draw 2 antennas but use symmetry plan between to reduce the problem.

pl

Hi again,

How much the acceptable ripple in the group delay for good performance of the antenna?
Is there any dependance on frequency of working ? and what's the relation between this ripple in the group delay with BER?

I mean by the ripple: the chage in group delay inside the bandwidth of interest.

Its being very fruitfull discussion regrading group delay and i would like to share my experience with few questions :D. At first i would like to tell very good resource for GD
h**p://www.microwaves101.com/encyclopedia/groupdelaymeasurements.cfm.

Group delay is essential for UWB as it tells about the distortion/dispersion of the transmitted signal. But one should know that GD is only paramete for which smoothining is allowed(During Measurement) and different Network anlyzers have their own techniques. Thats why its little tricky. CST results are quite different from measurement becoz of smothining.

Now my question is that what is the difference b/w group delay measured from S11 to that from S21(using same antenna for transmisison and measurement).

Regards

Hello,

My understanding for the group dealy is: The derivative of the phase relative to frequency difference for transmitted signal. So, it should be for S21, not for S11 at all.
Correct me if I'm wrong please....

I thing that since S11 contains phase infoamtion and group delay reffers with respect to transmitted signal so it S11 which accounts for group delay (Am i right/it look reasonable). Moreover, group delay accounts for the degree of dispersion of the transmitted single which can be seen by overlapping the transmittes single with the received one. So in this case one needs receiving antena.

As an observation we can measure group delay in simulation software like CST with only one antenna.

What ur opinion now

Please look at the follwoing thesis (Google search)
Antenna Design for Ultra Wideband Radio


I have see some papers with group delay results calculated from S11. So does someoday has any idea. the difference in group dealy if measured from S11 and S21.

How to simulate antenna's S21 using 2 identical antenna?

Hi Freqzt
Design two antenna with some distance among them (open space), feed both of the antenna and run the simulation.

I note that the original thread has been around for a while.

That being said, these guys used to have several interesting white papers on the subject as well as an interesting discussion of transmit vs. receive reciprocity.

h**p://www.picosecond.com (Picosecond Labs)

You might poke around on their site to see if you can find anything useful.

Relative to UWB change in group delay is one interesting debate. Another is trying to decide if one wants constant gain with frequency in the antenna(s) or is preconditioning in the amplifiers a better tactic.

Is it valid for any simulator?

well you can use only one antenna
place an E field probe in the far field, and when the result appears, click on the probe from NT and you can see arg(p) which is the phase response.
once you got that,, use any post processing software like Matlab to get the derivative of the phase responce which gives you the group delay.

Hi, All of them.

I saw this board, and I realize everybody confuse about the group delay.

the group delay from S11 and S12 is used based on the application.

If you are radar engineer, you need the group delay from S12. Sometimes, from S11 (mono case)

If you are antenna desinger, you need show the group delay from S11.

the group delay from S12 is varied in terms of the environment, distance, angle, and so on.
Therefore, Even I usually concern the group delay from S12 due to my project in my lab, I first look at the group delay from S11. It is the reference.

Please, don't confuse the group delay.