Some experience with the use of spiral antennas for a GPR for landmine detection

Ground penetrating radars for detection of antipersonnel landmines operate in a UWB domain from 400 MHz up to 5 GHz. One of the radar concepts for this kind of application is a stepped frequency CW radar. The requirements on the antenna for this radar is, that it shall have a stable phase centre, frequency independent gain, ultra-wide band, high isolation between the two antennas in a bi-static arrangement and other more common requirements like a low VSWR. The antenna selected for the application is an Archimedean spiral. Such an antenna has a wide beam width and a radiation pattern only slightly dependent on frequency. A basic problem to the use of a spiral antenna when it is elevated above the ground is that the small contribution of the anti personnel mine is surged by the strong reflection off the air/ground interface. This paper is addressing this effect by analysing the impact of the size of the antenna footprint on the SAR-synthesised three dimensional image of the subsurface. Experimental results like the ones presented here are not available to the authors´ knowledge elsewhere in the open literature.