We want an antenna which can be used off ground, not only for safety reasons but also to improve the mobility of the sensor. As a consequence, the antenna must have a high directivity so that it can still couple sufficient energy into the ground to achieve a penetration depth of 20 cm in any soil. Another criterion to guarantee high mobility is the dimensions and weight of the antenna. Mine fields have often a rough surface and are covered with a lot of vegetation. Only little antennas can guarantee a sufficient flexibility in such scene.
Little antennas are also better for hand-held applications.
The antenna properties must be independent of the ground properties. This criterion is automatically achieved when using the antenna off the ground. The antennas must be cheap in production. One of the most promising antennas which can meet these design goals is the traveling wave TEM horn. Such an antenna can take various forms.