dielectric properties of materials illuminated by UWB antennas

Since dielectric properties are frequency dependent, which dielectric properties are we supposed to use for materials illuminated by UWB antennas? UWB antennas bandwidth spans different frequencies. Which frequency do we pick to find the dielectric property of the material that will be illuminated by the UWB antenna? Do we pick the center frequency? If so, would that be accurate?

I read a paper about estimating the "average" frequency-dependent dielectric properties of dielectric materials illuminated by UWB. It's not clear exactly on how the average will be calculated.

Thank you.

I think the problem is that the properties of some materials have not been determined for the full frequency coverage over UWB band. If you use FR-4 or similar generally used material for microwave PCBs, then its dielectric properties are quite well known. Other materials simply have not been measured yet, so one can take some "average" value for permittivity, etc., and correct the prototype.

To elaborate, I am not talking here about the dielectric properties of the antenna itself. I am talking about the dielectric properties of the object that is right next to the antenna and will be illuminated by it. For example, in the application of SAR, you have an antenna radiating next to the head.

My question is: What numbers to use for the dielectric properties of the head when the dielectric properties are frequency dependent and you are using a UWB antenna?

Thanks.

Dear Sir:

This is an excellent example how the problem(s) stand. Determining parameter properties is a developing science. You may want an easy answer to seemingly easy question but there is none. You have to study and make experiments. There is no place to find a direct answer.

Now you added another dimension: a living tissue. Again, a tough problem, and not easy answers. I would recommend you a PhD dissertation by Mr. C.M.Alabaster, done at the Cranfield University, UK, in 2004. You can get it via Google. Mr.Alabaster measured microwave properties of tissue and other lossy dielectrics. I like his quite concise analytic methods as well as experimental results.

Be ready for a tough ride!

can somebody shed more light on this subject?

Thanks.

It looks like it is your turn to answer your questions. Go for a Ph.D. on this subject!