Many geophysical parameters can be determined with the aid of a passive microwave sensor. To achieve a high spatial resolution in passive microwave imaging the method of aperture synthesis can be applied. Narrowband radiometric measurements within a wide frequency range allow extracting more surface information on observed objects or materials and it is possible to obtain depth information on layered structures. Furthermore, the advantages of using a range of different center frequencies, i.e., a higher spatial resolution with increasing frequency and a higher penetrating capability at lower frequencies, can be combined in many cases to enhance the overall imaging capabilities. Thus our recent interest is focused on the development of an experimental system offering those features but keeping the costs affordable. In This work the basic system concept is outlined.