# US 4,398,200 A · Feed apertures with crosspolarization compensation for linear polarization > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 4,398,200 A - Document ID: US4398200A - Status: Granted - Kind: A - Application number: 06/319,389 - Filed: 1981-11-06 - Granted: 1983-08-09 - Earliest claimed: 1980-07-10 - Assignees: General Electric Company - Inventors: Raymond J. Meier - Web page: https://patentgrep.com/patent/US4398200A ## CPC - H01Q 19/028: {for reducing the cross polarisation} - H01Q 19/08: for modifying the radiation pattern of a radiating horn in which it is located {(corrugated horns H01Q13/0208; producing a circular polarisation H01Q13/0241)} - H01Q 25/001: {Crossed polarisation dual antennas (orthomode horns H01Q13/0258; cross-polarised rear feeds H01Q19/136; orthomode transducers H01P1/161)} - H01Q 25/007: {using two or more primary active elements in the focal region of a focusing device (for operation on different wavebands H01Q5/22)} - H01Q: ANTENNAS, i.e. RADIO AERIALS (radiators or antennas for microwave heating H05B6/72) ## Abstract The crosspolarization components radiated by adjacent orthogonally linearly polarized feed horns of a reflector antenna system are compensated by structural modifications incorporated in the feed horns. In a first embodiment, the modified feed horns have curved walls and included shaped septa. Other embodiments involve the use of shaped walls or shaped septa only. In the case of an offset reflector, asymmetric modifications of the wall shape and septa are employed. For flared feed horns with rectangular cross section, the crosspolarization compensation is provided by curving the forward edges of the horn walls convexly or concavely as required. ## Claims ### Claim 1 An antenna system, comprising: a reflector; at least a pair of feed horns located in the focal region of said reflector, said feed horns being positioned adjacent each other with the axis of each horn pointed at said reflector; means for radiating beams in the same frequency band from said pair of feed horns at said reflector effective to reflect a pair of corresponding beams from said reflector; and compensation means incorporated in the structure of each of said feed horns, each of said compensation means being configured to alter the beam radiated from its feed horn in a manner which reduces crosspolarization components in the corresponding reflected beam, said reduction of crosspolarization components being effective to provide substantially linear polarization in said pair of reflected beams in mutually orthogonal directions. ### Claim 2 (depends on 1) An antenna system as recited in claim 1, wherein the axes of said feed horns are pointed toward the vertex region of said reflector. ### Claim 3 (depends on 1) An antenna system as recited in claim 1, wherein the axes of said feed horns are offset from the vertex of said reflector. ### Claim 4 (depends on 2, 3) An antenna system as recited in claim 2 or 3, wherein said compensation means comprise mutually spaced septa positioned within each of said feed horns. ### Claim 5 (depends on 4) An antenna system as recited in claim 4, wherein said septa of each feed horn extend between one pair of opposite feed horn walls. ### Claim 6 (depends on 5) An antenna system as recited in claim 5, wherein at least some of said septa are curved. ### Claim 7 (depends on 6) An antenna system as recited in claim 6, wherein an odd number of septa extend between said pair of opposite feed horn walls including a substantially planar central septum, the septa on opposite sides of said planar central septum curving away from the latter. ### Claim 8 (depends on 7) An antenna system as recited in claim 7, wherein the cross section of each of said feed horns normal to said feed horn axis is substantially uniform throughout the length of each of said feed horns. ### Claim 9 (depends on 8) An antenna system as recited in claim 8, wherein each of said feed horns has planar walls and said cross section is rectangular throughout. ### Claim 10 (depends on 8) An antenna system as recited in claim 8, wherein said compensation means of each of said feed horns further comprises curved feed horn walls, said curved walls and septa of each feed horn being configured to cooperatively provide said substantially linearly polarized reflected beam. ### Claim 11 (depends on 10) An antenna system as recited in claim 10, wherein a first pair of opposite feed horn walls in each of said feed horns is convex and the second pair of opposite feed horn walls is concave. ### Claim 12 (depends on 3) An antenna system as recited in claim 3, wherein said compensation means of each of said feed horns comprises curved feed horn walls and mutually spaced, curved septa positioned within said feed horn and extending between one pair of opposite feed horn walls, said curved walls and septa of each feed horn being configured to cooperatively provide said substantially linearly polarized reflected beam and being asymmetric to correct for said offset. ### Claim 13 (depends on 2, 3) An antenna system as recited in claim 2 or 3, wherein the cross section of each of said feed horns normal to said feed horn axis is substantially uniform throughout the length of said feed horn. ### Claim 14 (depends on 2, 3) An antenna system as recited in claim 2 or 3, wherein the walls of each of said feed horns are planar throughout. ### Claim 15 (depends on 2, 3) An antenna system as recited in claim 2 or 3, wherein the cross section of each of said feed horns normal to said feed horn axis increases along the length of said feed horn. ### Claim 16 (depends on 15) An antenna system as recited in claim 15, wherein each of said feed horn cross sections is rectangular. ### Claim 17 (depends on 16) An antenna system as recited in claim 16, wherein the walls of each of said feed horns are planar throughout. ### Claim 18 (depends on 17) An antenna system as recited in claim 17, wherein said compensation means of each of said feed horns comprises curved edges on said feed horn walls. ### Claim 19 (depends on 18) An antenna system as recited in claim 18, wherein said edges are curved convexly. ### Claim 20 (depends on 18) An antenna system as recited in claim 18, wherein said edges are curved concavely. ### Claim 21 An antenna system, comprising: a reflector; a feed horn located in the focal region of said reflector, said feed horn being positioned with its axis pointed at said reflector; means for radiating a beam from said feed horn at said reflector effective to reflect a beam from the latter, said radiated beam having a dominant linear polarization accompanies by spurious crosspolarization; and compensation means incorporated in the structure of said feed horn, said compensation means being configured to provide said radiated beam with a polarization modification adapted to reduce crosspolarization components in said reflected beam to an extent where said reflected beam is substantially linearly polarized. ### Claim 22 (depends on 21) An antenna system as recited in claim 21, wherein said feed horn axis is pointed toward the vertex region of said reflector. ### Claim 23 (depends on 21) An antenna system as recited in claim 21, wherein said feed horn axis is offset from the vertex of said reflector. ### Claim 24 (depends on 22, 23) An antenna system as recited in claim 22 or 23, wherein said compensation means comprises mutually spaced septa positioned within said feed horn. ### Claim 25 (depends on 24) An antenna system as recited in claim 24, wherein said septa extend between one pair of opposite feed horn walls. ### Claim 26 (depends on 25) An antenna system as recited in claim 25, wherein at least some of said septa are curved. ### Claim 27 (depends on 26) An antenna system as recited in claim 26, wherein an odd number of septa extend between said pair of opposite feed horn walls including a substantially planar central septum, the septa on opposite sides of said planar central septum curving away from the latter. ### Claim 28 (depends on 27) An antenna system as recited in claim 27, wherein the cross section of said feed horn normal to said feed horn axis is substantially uniform throughout the length of said feed horn. ### Claim 29 (depends on 28) An antenna system as recited in claim 28, wherein said feed horn has planar walls and said cross section is rectangular throughout. ### Claim 30 (depends on 28) An antenna system as recited in claim 28, wherein said compensation means further comprises curved feed horn walls, said curved walls and septa being configured to cooperatively provide said substantially linearly polarized reflected beam. ### Claim 31 (depends on 30) An antenna system as recited in claim 30, wherein a first pair of opposite feed horn walls is convex and the second pair of opposite feed horn walls is concave. ### Claim 32 (depends on 23) An antenna system as recited in claim 23, wherein said compensation means comprises curved feed horn walls and mutually spaced, curved septa positioned within said feed horn and extending between one pair of opposite feed horn walls, said curved walls and septa being configured to cooperatively provide said substantially linearly polarized reflected beams and being asymmetric to correct for said offset. ### Claim 33 (depends on 22, 23) An antenna system as recited in claim 22 or 23, wherein the cross section of said feed horn normal to said feed horn axis is substantially uniform throughout the length of said feed horn. ### Claim 34 (depends on 22, 23) An antenna system as recited in claim 22 or 23, wherein the walls of said feed horn are planar throughout. ### Claim 35 (depends on 22, 24) An antenna system as recited in claim 22 or 24, wherein the cross section of said feed horn normal to said feed horn axis increases along the length of said feed horn. ### Claim 36 (depends on 35) An antenna system as recited in claim 35, wherein said feed horn cross section is rectangular. ### Claim 37 (depends on 36) An antenna system are recited in claim 36, wherein the walls of said feed horn are planar throughout. ### Claim 38 (depends on 37) An antenna system as recited in claim 37, wherein said compensation means further comprises curved edges on said feed horn walls. ### Claim 39 An antenna system as recited in claiim 38, wherein said edges are curved convexly. ### Claim 40 (depends on 38) An antenna system as recited in claim 38, wherein said edges are curved concavely.