Broadbanding of corrugated conical horns by means of the ring-loaded corrugated waveguide structure

Broadbanding of corrugated conical horns is investigated with the ring-loaded corrugated circular waveguide (RCWG) structure devised by the authors. The useful frequency bandwidth in which the corrugated horn is effective for the improvement of antenna properties is limited by the frequency characteristics of the horn-aperture field and input VSWR of the horn. By the precise analysis of the RCWG, the maximum frequency range in which the desirable field is obtained is much wider than that in the conventional corrugated circular waveguide, and is achieved almost independent of ring thickness, when ring width is about 20 percent of slot depth. The characteristic impedance of the RCWG is nearly equal to that of the homogeneous circular waveguide when ring thickness becomes large. Therefore, a good transformer between the RCWG and the homogeneous circular waveguide is achieved by increasing ring thickness from the RCWG toward the homogeneous waveguide. From the above investigations, it is found that in the ring-loaded corrugated horn, the useful bandwidth is 1.35 times broader than that in the conventional corrugated horn. The theoretical results are verified by the experimental results.