Beam Mode Expansion of Corrugated Conical Horns with Phase Correcting Lens: Application to Radioastronomy Receivers

• Published in: Experimental astronomy 2003, Vol.15 (3), p.173-193
• Main Authors: García, E., De Haro, L., O'Sullivan, C., Cahill, G., Fernández, J. A. López, Tercero, F., Galocha, B., Besada, J. L.
• Format: Article
• Language: English
• Subjects: Apertures; Beams (radiation); Corrugating; Focusing; Horns; Lenses; Phase error; Receivers
• ISSN: 0922-6435; 1572-9508
• DOI: 10.1023/B:EXPA.0000038613.38191.5d

A classical radioastronomy receiver is fed with a corrugated horn and an independent lens, both placed in a cryostat to lower the noise temperature. The beam is focused and directed using a combination of elliptical and plane mirrors. This paper proposes modifying the initial feeding system by placing the lens onto the horn aperture, thereby allowing a size reduction of the horn and lens, and a simplification of their mechanical design. The profiled lens is shaped to correct the phase error on the horn aperture. A quasi-optical model of the horn-plus-lens system has been developed using a Beam Mode Expansion (BME). Results using both a hyperbolic-planar lens and a spherical-elliptical lens, as well as results obtained by using Geometrical Optics (GO) with a Kirchoff-Huygens integration to get the far-field pattern, have been compared with measurements. As a direct application, a full focusing system for the new 40-m radiotelescope at the 'Centro Astronomico de Yebes' is presented for the 22, 30 and 45 GHz bands. This paper has developed a QO model for a corrugated conical horn with a phase-correcting lens.