Hybrid mode feeds which are capable of handling very wide bandwidths. In the present feed arrangements, a dominant TE11 mode is converted to the HE11 hybrid mode which is then launched. The TE11 to HE11 mode conversion is achieved by inserting a circular dielectric rod (12) into a flared end (11) of a smooth-walled cylindrical feedhorn until a small cylindrical section of the dielectric rod engages with the inner wall (15) of the unflared portion of the feedhorn. In one feed arrangement, the other end of the dielectric rod is similarly inserted into a flared end (21) of a corrugated cylindrical feedhorn section (22) until a short longitudinal section of the cylindrical portion of the rod is concentric with the corrugations of an unflared section of the feedhorn to provide a transition for the HE11 mode into the corrugated waveguide for subsequent launch. In a second feed arrangement, the dielectric rod at the aperture of the smooth-walled flared feedhorn is flared outward to end in a curved configuration which is shaped to minimize reflections back into the dielectric rod and provide a predetermined wavefront at the aperture of the feed.

Wide bandwidth hybrid mode feeds

The coupler comprises a principal corrugated waveguide (10) and four identical secondary waveguides (11) regularly disposed on the perimeter of the principal waveguide and in such a way that the five axis are parallel. Coupling units (12) allow transfer of energy between principal and secondary waveguides. Due to reactance boundary conditions and size, only the HE11 mode in the higher frequency band and the EH11 mode in the lower frequency band can propagate in the principal waveguide. This perserves the polarization characteristics. Directional filtering is obtained by close agreement of phase constants in the different waveguides and 90o phase change between two successive coupling units in the higher frequency band, and evanescence or very low phase constant in the secondary waveguides in the low frequency band.

Directional coupler for separation of signals in two frequency bands while preserving their polarization characteristics

This paper proposes overview of the multiband feed system for reflector-type antennas. Coaxial, multimode Potter's type structures, multiband corrugated and dielectric loaded feed horns is discussed below.

Recent progress in development of multiband feed horns (Review)

This paper presents the results of a study to determine the satellite capacity enhancement obtainable by using syllabic compandors. Syllabic companding applied to the speech channels of tDDM-rm carriers can increase satellite capacity by as much as 100 percent, depending on the number of channels per carrier. Syllabic compandors presently produced by integrated circuit technology are small and inexpensive. Compandors permit a higher level of satellite circuit noise and hence an FM index (and bandwidth) which is smaller than that required for uncompanded channels. The results presented in the paper are based on compandor advantage measurements and singleand multi-channel amplitude distribution measurements for both companded and uncompanded speech signals. For data transmission, it is estimated that about 2-dB degradation may be encountered when long terrestrial access circuits are interconnected via a companded satellite circuit for international transmission. *This paper is based upon work performed at COMSAT Laboratories under the sponsorship of the International Telecommunications Satellite Organization (INTELSA r).

Enhancement of FDM-FM satellite capacity by use of compandors

A broadband corrugated horn radiator including a hybrid mode exciting member whose inner cross section is constant over its entrie length and a transition member from the cross section of the hybrid mode exciting member to the cross section of the horn aperture. The length and the inner cross section of the hybrid mode exciting member are dimensioned such that the waveguide mode entering this excitation member is converted completely only to the desired hybrid mode type, the pitch of the wall of the transition member is such that no interference waves are able to exist therein, and the corrugation grooves in all members of the horn radiator are matched, by appropriate dimensioning, to the same transmission bandwith.

E. Carpenter

Papers

A dual-band corrugated feed horn