Radiation from an open ended eccentric annular waveguide

The radiation from an open ended eccentric annular waveguide is examined here. The region between the two circular conductors is assumed to have either symmetrical or anti-symmetrical TE field distribution. Cutoff wavenumber is first calculated and the unknown coefficients in the field are then obtained. It is found that for anti-symmetric field distribution the radiation pattern in the H-plane has a null which can be widely scanned by displacing the conducting core from the central axis. For the symmetrical field distribution a pair of symmetrical nulls in the E-plane are slightly scanned with the displacement of the conducting core. This type of waveguide antenna is useful for applications in phased and adaptive arrays which require null scanning.