Two planar dipoles embedded in a conductor-backed thin dielectric layer were suggested as a subsurface antenna. Since the transmitting planar dipole is closely located to the conducting plane, the radiation efficiency is rather poor.
The feeding waveguides coupled through a cut-off dielectric waveguide are proposed to improve the radiation efficiency without increasing the decoupling. The input impedance of transmitting and receiving antenna is analyzed and compared with the measured data, which shows good agreement. The direct coupling and radiation power are measured in the frequency range from 100MHz to 1000MHz. The measured data indicate that we can guarantee the direct coupling lower than -50dB in the frequency range from 100MHz to 1000MHz, especially lower than -80dB in the frequency range from 100MHz to 500MHz.
