Dielectric measurements of stone materials with a wideband microwave sweep

Ground penetrating radars (GPR) are increasingly used for the quality assessment of asphalt work on road construction and measurements are needed to focus only on surface layers of the road. Two different aggregate slabs and reference plastic sheet were measured with the vector network analyzer to investigate the depth resolution issues of the classic electromagnetic field reflection problem in the case of chained dielectric layers. We found that tests of stone material are inadequate at 4 GHz sweep width, which equals a GPR pulse of around 300 ps. The widest sweep from 6.5 to 18 GHz, corresponding to about 100 ps pulses in time domain radar, seems to give both repeatable and reliable information and should be used.