Based on a systematic analysis the design and experimental studies on a composite dual-frequency feed with a single radiating aperture are presented. The criterion for selecting the ratio of the diameter of the corrugated guide excited at the lower frequency in the dominant mode to that of the dielectric rod, axially located within the guide and excited at the higher frequency in the dominant mode, is discussed. The constructional features of a typical dual-frequency feed designed for operation at S and X bands (with 2.68 GHz and 9.375 GHz as center frequencies, respectively) are outlined. The measured radiation patterns show good symmetry and sidelobe suppression over 20-percent bandwidth in S and X bands and are in good agreement with calculated patterns. Copyright © 1979 by The Institute of Electrical and Electronics Engineers, Inc.