Currently for landmine detection, metal detector (MD) and ground penetrating radar (GPR) are the most popular sensor. Both of the sensors are based on the electromagnetic field. ALIS (Advanced Landmine Imaging System) is a novel hand-held sensor system combined with MD and GPR and can offer subsurface visualization information, and can show the MD sensor output in real time. The system has a sensor position tracking system that needs only one CCD camera attached on the sensor handle. The GPR of the system is a stepped frequency radar system whose RF component is a newly developed compact vector network analyzer. Based on the diffraction electromagnetic waves of subsurface targets, we combined migration algorithm into GPR system that can improve signal-clutter ratio and can image buried objects clearly. Considering the effects of ground surface and inhomogeneous soil to diffraction field, we optimize the migration aperture based on the comparison between migration trajectory and diffraction surface of the electromagnetic waves. Some field test for landmine detection sensors including ALIS had been carried out in 2006 from February to March at Benkovac test site in Croatia. The evaluation tests are organized by the Japan Science and Technology Agency (JST) and the Croatian Mine Action Center - Center for Testing, Development and Training (HCR-CTRO). In the test, ALIS can detect 100% shallow landmines.