A new type of dual-frequency antenna using a hollow-fin trough waveguide is described. The hollow fin is used as a

mode waveguide with sidewall radiating elements. These Sidewall radiating elements constitute the high-frequency section of the antenna. The low-frequency section consists of a thick hollow-fin trough waveguide antenna. The attenuation due to radiation and waveguide wavelength of the trough waveguide section are analyzed. This analysis shows good agreement with experimental measurements. Existing data may be used as a guide in the design of the high-frequency section of this antenna, and the data presented may be used as a guide in the design of the low-frequency section.