GPR RADAR  (Price 850 $)
In this kind of Radar "TRS" technique is used.

It means that, instead of using one antenna for sending and receiving of waves, because of few distances between target and antenna, it uses

two simultaneous and separated units.

Generally, in this kind of Radar, frequency of operation, determines type of target and power of transmitter, range of system. It means that whatever power of system become more, range of system increases too and for example, a GPR with 1KhZ frequency, is more sensitive than (in relation to) metals and a GPR with 100KhZ frequencies is more sensitive than water

Verification Code of Metal Detectors More Details