What kind of antennas can be used in undergound communication?

What do you mean: underground antenna for usual air communications or antenna for in tunnel radio communications? Both of them are exist but are not the same.

I want to know what kind of antennas can be used in the deep earth.As far as I know,there are only dipole.magnetic dipole. linear arrays,and some kinds of slot antennas can be used for communication or reconnoitre in the ocean or deep earth. I want to know if there are other kinds of antennas can be used,such as microstrip antennas.
As I am still a college student,I am not skilled in this area.So I want to know what should be considerd in designing this kind of antennas.

Submarine's use LF band in the sea. But they have to be near to the surface for comminications. and some metal detectors use dipoles and LF band too. But i dont understand how to communicate within the earth?

oh ,thanks.In some papers,two holes should be diged so as to put two antennas into the earth,but there still some problems should be considerd,such as efficiency,radiation pattern,frequency ect.
So,if you are good at this problem,especially what kind of antennas can be used in this domain.please help me.

for submarine

http://en.wikipedia.org/wiki/Communi...ith_submarines

for metal detector

http://www.gi.alaska.edu/~jesse/trea...wdetector.html

ok,thanks

I saw antennas for tunnels and for underground placing in order to hide them. All of them were wire type. Antennas for tunnels were much longer than hidden underground.

I am not sure whether other antennas(microstrip antennas,slot antennas .ect) can be used in lossy medium(undergound,or sea).What should be consided in designing antennas in such case.
I find it is difficult to get something imformation about this.

Yes, it is hard to find. I remember that I saw information on hidden underground antennas in ham radio books from ARRL. You may try to heck these books. I am to busy now but later may try to check my library for these antennas. I just cannot promise to do it for sure.

ok,thanks.
In my school library,there is a book named<antennas in matter>,and I find the antenns that introduced in this book are wire antennas,and the book was pressed in the 1980's.So I hope to find some new materials.