Ground Penetrating Radar (GPR) is an important non-destructive tool to detect landmines. It radiates radar pulses to probe the ground that contains a variety of media, including landmine, sand, soil, clay, water, etc. and a large number of clutter items like burrows, cracks, discarded waste, branches and roots, metal wire, and so on. The subsurface is in such a complex and unidentified condition, that it will impact the performance of the GPR system considerably. This brings a big challenge for the system developers to control and understand the GPR system, especially during the early stage of the design. Therefore, a simpler and less time-consuming simulation method for GPR than the real-field test is essential for engineers to have an overview and a clear grasp of the whole GPR system. This paper uses gprMax, an open-source software using the Finite-Difference Time-Domain (FDTD) method, to explore the parameter tradeoffs for a transmitter-receiver pair of bowtie antennas operating at different spacing and heights above the ground for target at different depths.