Choke Rings for Pattern Shaping of a GPR Dipole Antenna

This paper establishes that a choke ring-a common pattern-shaping structure in GPS antennas-can also be effective when employed in ground-penetrating radar (GPR) as a shielding device to isolate GPR antennas from the above-ground environment. A choke ring shield is compared to similar cavity structures in response to a wideband pulse excitation, and it is shown that in addition to its pattern-shaping ability, good time-domain performance can be achieved through the inclusion of an absorber within the choke ring's central cavity. Wideband performance measures are developed, and measured data are in generally very good agreement with simulations. The choke ring is shown to provide a 3-5 dB redirection of radiated power from the back to the front of the shield, while the inclusion of the absorber ensures less than -40 dB of late-time clutter.