antenna-theory.com

[adnan]

any one on this forum kindly help in my project. i want to evaluate concrete slab for cracks in my project. For this purpose i crated a microstrip patch antenna on hfss using fr4 substate at 1.2 ghz freq in hfss.

q1) is microstrip good for concrete evaluation as other antennas are not available in my country?

q2) should i insert U slot to make wide band?

q3) how to find lengths of u slot when using fr4 substrate read many research papers could not find any formulas by hit and trial its not working.
the return loss required is <-10 but inserting U slot wont give the required return loss.

q4) After antenna is designed on hfss what should i do next as i have to implement on hardware also. our supervisor says we have to get resolution of concrete cracks how do we get resolution?

q)5 As project is not gpr. i want to have tx and rx antennas which should strike concrete and after reflection it should be received.

q)6 how should i give power to tx and rx antennas. should i use oscilloscope or any modules?

waitng for reply. (new sorry for my bad english).

[helix]

a microstrip patch antenna might be an OK choice, the principle drawback is going to be narrow bandwidth. the long "ringdown" time of a very narrow band antenna may have an impact on your ability to receive the signal you're looking for.

of course if you can build a patch, you can build a planar monopole/dipole antenna on FR4. itoh has a paper on "quasi-yagi" (look it up) that might be a nice solution for you, too. it has a semi-directional pattern but you can get a fair bit of bandwidth out of it.

if you're above 1GHz, FR-4 is questionable for a patch due to its relatively high loss tangent. loss in the substrate will make the impedance BW appear broader than it otherwise would be, but the antenna efficiency will be lower. unless you're actually building an air-patch (e.g., with plastic standoffs separating the patch element from the ground plane). then with respect to loss you're probably fine. if you're literally building a patch on a solid FR-4 substrate then the patch height is probably pretty thin, 62 or 128 mils (these are common FR-4 thicknesses) and the best way to improve BW is not with a U-slot but by simply increasing substrate thickness. if you use standoffs to increase the patch thickness, then basically it is an air cavity and the lowering of the epsilon towards 1 (from ~4.5 for FR-4) will increase the BW as well. aperture feeding (rather than probe feeding) the patch can also help achieve broad bandwidth (with the help of a matching stub on the feedline beyond the aperture).

what do you mean by "resolution"? downrange or crossrange or something else? this is likely a RF systems design issue, not an antenna issue per se.

sounds a lot like GPR to me -- how is it different?

what do you mean by "power to the tx and rx antennas"? DC power or RF power?