Low-profile helical antenna with a cavity

A two-turn low-profile helical element backed by a cavity is investigated using frequencies within the Ku band. It is found that the beam width is sensitive to the cavity diameter D_cav; as the D_cav is decreased, the beam width increases. It is also found that the beam width is not sensitive to a cavity height of more than 0.2 wavelength. Further investigation reveals that the helical antenna has a frequency bandwidth of approximately15% for a 3-dB axial ratio criterion. Across this bandwidth, the input impedance and gain are relatively constant. A dielectric layer (ε_r = 2.1) attached to the top of the cavity does not significantly affect the antenna characteristics, as long as its thickness B is less than 0.04 wavelength.