A.D. Olver

Transverse Coupling Between Two Surface Wave Antennas

A method has been devised to derive the coupling coefficient between two infinitely long perfectly conducting surface-wave antennas such as disc-on-rod antennas. This method is based on the Lorentz reciprocity theorem and on the equivalence principle. The theoretical derivation of a general expression for the coupling coefficient as well as numerical results for disc-on-rod antennas are presented in this paper. Results based on this method have been found to be in good agreement with those obtained from an analysis of element interaction in a broadside array of traveling-wave end-fire antennas.

Compact dielectric feeds for prime focus reflector antennas

It is argued that small-diameter circular waveguides partially filled with dielectric can be used as compact and efficient feeds for prime focus reflector antennas. Both singlemode and multimode designs are briefly reviewed and evaluated. Results are given for a case where the HE/sub 11/ mode and EH/sub 11/ mode propagate in the dielectric and where the diameter and permittivity have been chosen so that the cross-polar power is minimized.<<ETX>>

Mode conversion in dielectric loaded horns

The dielectric-cone-loaded horn creates a balanced hybrid mode by the inhomogeneously filled conical horn. Analytical models based on a single hybrid mode predicted a crosspolarization level which was greater than the measured result. The authors now show that good horn performance is caused by the presence of higher-order modes in the aperture. For a horn with a semiflare angle of 12 degrees , an aperture diameter of 154 mm, a dielectric with relative permittivity of 1.13, and air gap of 12 mm, the power at the aperture is made up of 77% HE/sub 11/ cylindrical mode, 16% HE/sub 12/ cylindrical mode and the remainder of the other higher order modes. This shows that a substantial amount of higher-order mode is present. To understand the mechanism for the mode conversion, the power in the first three cylindrical hybrid modes was computed and is shown as a function of radius for the horn. The mode conversion is partly due to the throat region and partly due to the inhomogeneous dielectric horn; the first component can be reduced by smoothly tapering the transition from the waveguide to the horn.<<ETX>>