Abstract: An earth-penetrating synthetic image radar system includes a frequency generator, a transmitter, a microprocessor-based timing and frequency controller, a reference receiver, a parallel polarized receiver, an orthogonal polarized receiver, a digitizer, a calibration processor, a position measurement reference, and an image processor. A plurality of frequency synthesizers are utilized within a single frequency generator to transmit a fast-stepped synthetic image containing a series of discrete frequencies. A switch is used to select between the outputs of the synthezisers for control of the transmitter's frequency output. With a first synthesizer of a frequency f.sub.1 selected, a second synthesizer is being directed digitally to change to the next step in the frequency stepping sequence, frequency f.sub.2.