We employ plane and cylindrical wave expansions with the fast Fourier transform to solve scattering problems involving a circular cylinder buried in soil. The illumination is provided by a three-dimensional source located in air above ground. Plane wave expansions describe transmitted and reflected fields at the air-soil interface, and cylindrical wave expansions describe the fields scattered by the cylinder. The two types of expansions are joined by employing explicit expressions that relate cylindrical and plane waves. We neglect multiple interactions between the cylinder and the interface. The cylinder and soil can have frequency-dependent permittivities and conductivities. With the formulas cast in a special form the scattered fields can be computed rapidly for fixed-offset configurations in which the location of the source is different for each observation point. Fixed offset is the most commonly used transmitter-receiver configuration for ground-penetrating radar (GPR). Numerical simulations involving time domain fields and fixed-offset configurations determine the radar responses of various types of pipes and conductive soils encountered in GPR.