The scalar feed

The radiation and crosspolarisation characteristics of a longitudinally slotted conical horn antenna with small flare angle, excited in the modified TE11 mode, are investigated. To this end the electromagnetic wave propagation in a longitudinally slotted circular waveguide is studied first, Using a wall reactance model. Because of the need to introduce mode-dependent wall reactances in the present structure, conditions for orthogonality are given. Propagation characteristics and field line patterns are presented. It turns out that the modified TE11 mode in this guide, used as an aperture antenna, produces a main radiation lobe which can be made nearly symmetrical around the axis over a wide frequency range, namely by a proper choice of the slot depth. As a typical example the maximum crosspolarisation level in the main lobe is lower than-30 up to-45 dB, dependent on slot depth and frequency range. Experiments carried out with a slotted conical horn antenna with small flare angle confirm the theoretical results.

Longitudinally slotted conical horn antenna with small flare angle

A slotted flange mounted on a waveguide has been studied for use as a feed with deep reflectors. The E -plane patterns have large beamwidths and are reasonably square. A comprehensive device, consisting of a slotted flange mounted on a square aperture, has been designed and fabricated using the optimum slot width values of the slotted flange waveguide system. The amplitude, phase, and bandwidth characteristic of this device satisfy the requirements of a feed for deep reflectors.

Experimental study of a flange mounted waveguide as a device for square radiation pattern

The calculation of aperture radiation patterns

Corrugated conical horns are extensively used as radiators where a relatively broadband and symmetrical radiation patterns are needed. The properties of these horns were investigated by many workers, both theoretically and experimentally. In some works frequency variation of groove wall admittance was ignored, while in others certain approximations were used. In this work the characteristic equation for the corrugated conical horn is numerically solved without an approximation for the wall admittance. The results obtained for the mode order variation with frequency is compared with other two frequency dependent solutions and the difference is clearly shown.

Frequency Dependence of Corrugated Horn Mode Order

The radiation pattern of a small corrugated conical horn with a wide flare angle has been calculated by means of a Kirchhoff-Huygens integration. An assumption was made about the phase relationbetween the TE and the TM parts of the spherical hybrid mode in the horn. The solutions of the characteristic equation became dependent on the electrical length of the horn. Calculations and experiments showed a good agreement.

M.E.J. Jeuken

Papers

Small corrugated conical-horn antenna with wide flare angle