Title of Invention

A DEVICE AND METHOD OF MAKING MECHANICALLY ACTIVE PARABOLIC MICROWAVE ANTENNA

Abstract

The invention relates to a method of making mechanically active parabolic microwave antennae having polycarbonate reflector skins. It consists of metal beams disposed at 900 from each other. The beams have actuatable piezoelectric bimorphs disposed thereon and means for holding flat antenna body when the flat body is mounted and the piezoelectric body is actuated, parabolic bending of the body results.

Full Text

FIELD OF INVENTION The present invention relates to a device and a method for making parabolic reflector skins for microwave antennae. The invention further relates to bending the parabolic reflector skins made thereby mechanically active antennae having reflector skins made of polycarbonate film is also a part of this invention. BACKGROUND OF INVENITON Piezoelectric actuation has been studied by various researchers on wide gamut of structural systems namely, beams plates and shells. Recently, it has also been demonstrated that the aperture antenna can have their performance enhanced by employing shape control on the antenna surface. Some researchers have studied the Polyinlydine Fluoride (PVDF) material and observed the far field radiation pattern. Some researchers have also studied the radiation modes with respect to the vibration modes. Other researchers have highlighted the use of Piezo ceramic Unimorph actuators (PZT) and found them to be more robust in the applications domains of aperture antennae. Some researches have recently mooted out the concept of using curved Unimorph actuators pasted on the convex side of the skin of the reflectors to develop inward / outward movements of the re-configurable reflectors. But the displacements of the reflector skin obtained by this fashion are quite insignificant from the practical utility point of view for real life re-configurable spacecraft reflectors. The present invention relates to generating one order higher displacements for the poly carbonate reflector skin which has lot of practical utility in the development of futuristic re-configurable reflectors capable to compensate for on orbit thermal distortions and can be augmented to cater to beam shaping and beam steering of the futuristic re-configurable spacecraft reflectors for Geo-stationary satellites. SUMMARY OF INVENTION The object of the present invention is to provide a novel method of bending the parabolic reflector skin made up of polycarbonate material using smart backup metal beams preferably Aluminum beams with Series / Parallel type flat Bimorphs Piezo patches. Microwave antenna reflectors up to 1m in diameter can be made with the help of the device designed according to this invention. It has potential applications in antenna beam shaping and beam steering in futuristic re-configurable antennas for space programs. When a piezoelectric actuator is attached to metal preferably Aluminum beams fixed 90° apart behind the reflector surface, the converse effects develops a bending moment in the structure making the reflector show displacements inward or outward under an electrical field. With the usage of polycarbonate material, the results with respect to the reflector tip displacement are found to be encouraging in both reflector form & discrete beam form. The investigations with respect to the tip displacements on beams pinned in the center and with Piezo patches on one side on the backup beams, pave the way as a solution to balance the thermal distortions of the spacecraft reflectors. For microwave antenna applications copper / Aluminum metalized polycarbonate reflectors have to be used along with the proposed mechanically active backup beam concept. The advantages of the present invention are as follows: 1. The PZTs need not be curved, tailor-made / customized as per the skin profile of the proposed application. 2. The PZTs need not be high capacity patches to get the inward movement of the reflector skin. 3. Flat Bimorphs can be used to get the similar bending effect with less fabrication complexities. BRIEF DESCRIPTION OF DRAWINGS; Single figure (Fig 1) in the accompanying drawings show Bimorphs (parallel) on the Aluminum beams of the device according to this invention. A1, A2, A3 and A4 are the metal beams which are centrally joined and are disposed at 90° angle with respect to the adjacent beam. Piezoelectric bimorphs (PZT) are distributed paralelly on one side of the beams. These piezoelectric bimorphs are electrically actuatable. DETAILED DESCRPTION Piezoelectric actuation has already been studied by various researchers on wide gamut of structural systems namely, beams plates and shells by employing shape control on the antenna surface. Some researchers have studied the Polyinlydine Fluoride (PVDF) material and observed the far field radiation pattern. They have also studied the radiation modes with respect to the vibration modes. Other researchers have highlighted the use of Piezo ceramic actuators (PZT) and found them to be more robust in the applications domains of aperture antenna. Experiments have also been conducted in the domains of PZTs and have been highlighted that the, analytical model provides a reasonable prediction of actuator performance at low input voltage but does not account for the nonlinear behaviour of Piezo ceramic and also effects of hysteresis. Experiments have been conducted on number of small structural systems like cantilever beams and shells also. Some of the researches have worked in the domain of Thunder actuators / Power Pack actuators in lieu of Unimorphs / Bimorphs for studying beam shaping in the domain of reflector surfaces. This development work covers the FE (Finite Element) modeling and experimental work on a 700 mm diameter parabolic shell surface (Prime Feed Fed type antenna) with piezoelectric Bimorph actuators using ATILA, a Finite Element software for modeling structures with smart materials and structural systems. For the proof of concept exercise, the nonlinear structural behavior of smart materials and their respective hysteresis issues have been eliminated from the investigations. Constitutive equations: In this investigation, an attempt has been made to simplify & study the complex static shape displacement problems of parabolic antenna reflectors by using limited number of discrete Piezo ceramic actuators by assuming a linear material behaviour. It was noticed that the Unimorph Piezo patches fixed on the beams give deflection towards the patch side when put under electrical field. For getting improved performance from the point of view of tip displacements, Bimorphs have used for the experimental investigation. An attempt has been made to simplify & study the complex static shape displacement problems of parabolic antenna reflectors by using limited number of discreet Piezo ceramic Bimorph actuators of series and parallel type by introducing the concept of Piezo actuated backup beams as mentioned above for parabolic reflectors. Experiments have been conducted on a 700 mm diameter parabolic shell surface made up of polycarbonate skins with backup structure made up of Aluminum beams with bimorphs. Pictorial representation is shown in Fig 2 for the concept proposed. To begin with, an Aluminum beam held in the center has been taken which is of 450 mm length, 30mm width & 0.8mm thickness with Piezo patches (Bimorphs) with wrap around electrodes with lead wires soldered. PZT—SP-.5H (25.4 X 25.4 X 0.7mm) twelve numbers on one side of the beam have been used with approx. 50.96 % area coverage. The beams have on one side provisions for pre-loading the patches during curing stage as shown in Fig 1. For the final configuration, 400 V DC (Forward) has been used per mm thickness of PZT-SP-5H patch to energize the backup beam. When a piezoelectric Bimorph actuator is attached to the beam surface, the converse effect develops a bending moment in the backup structure making the reflector show displacements inward & outward under an electrical field. Maximum tip displacement obtained was to the tune of 4 mm which caused the 700 mm diameter Lexan reflector to bend inwards. The investigations with respect to the tip displacements on beams pinned in the center and with Piezo patches on one side on the backup beams, pave the way as a solution to balance the thermal distortions of the spacecraft reflectors by providing a rigid body movement of the reflector using Piezo stacks. Moreover, the bending of the polycarbonate film reflector skin for RF applications in space, includes metalized skins which can be used with ultra low expansion characteristics applications in antenna beam shaping and beam steering in futuristic re-configurable antennas of space programs. This invention includes a device for making parabolic reflector skins for micro wave antennae. It consists of a plurality of metal beams centrally joined. Each beam is disposed at an angle of 90° with respect to the adjacent beams. One side of each beam has a plurality of antennae table bimorph piezoelectric patches disposed thereon. This invention also includes a method making parabolic microwave antennae reflector skins. The antenna body with the reflector skin is stretched on the device described herein above and the piezoelectric patches provided thereon are actuated electrically till the body including the skin is bent in the desired parabolic shape. Mechanically actives parabolic microwave antenna provided with a reflector skins made according to the above method also forms a part of this invention. Observations: When a Piezoelectric actuator is attached to the reflector surface, the converse effects develops a bending moment in the structure making the reflector show displacements inward or outward under an electrical field. With the usage of Lexan material, the results with respect to the reflector tip displacement are found to be encouraging in both reflector form & discrete beam form. We Claim: 1. A device for making mechanically active parabolic microwave antenna comprising a plurality of centrally joined metal beams, each beam being fixedly disposed at 90° with respect to the adjacent beam, one side of each beam having actuatable multiple piezoelectric bimorphs disposed therein. 2. The device as claimed in claim 1 wherein the said metal beams are aluminum beams. 3. The device as claimed in claims 1 and 2 wherein said piezoelectric bimorphs are parallely disposed on said beams. 4. The device as claimed in claims 1 to 3 wherein said device has means provided for mounting a flat antenna body thereon. 5. The device as claimed in claims 1 to 4 wherein the piezoelectric bimorph patches have a wrap around electrodes with lead wires soldered to enable grouping of electrodes. 6. The device as claimed in claim 5 wherein the beam comprises evenly distributed plurality of piezoelectric bimorph patches to cover the beam. 7. The device as claimed in claims 1, 5 and 6 wherein the positive electrode of piezoelectric bimorph patches are grouped to apply the positive voltage potential and the negative electrodes are grouped to apply negative voltage potential. 8. A method of making parabolic antenna reflector with reflector skins comprising the steps of stretching flat antenna body provided with said reflector skin on the beams of the device as claimed in claims 1 to 7 and electrically actuating said piezoelectric bimorphs till the desired parabolic shape is achieved. 9. The method as claimed in claim 8 wherein said reflector skin is made of poly carbonate which is preferably metalized. 10. A mechanically active parabolic microwave antenna having a reflector skin made by a method as claimed in claims 8 and 9.

Documents:

1464-CHE-2006 EXAMINATION REPORT REPLY RECIEVED 06-11-2009.pdf

1464-CHE-2006 OTHER DOCUMENT 06-11-2009.pdf

1464-CHE-2006 AMANDED CLAIMS 06-11-2009.pdf

1464-CHE-2006 AMANDED PAGES OF SPECIFICATION 06-11-2009.pdf

1464-che-2006-abstract.pdf

1464-che-2006-claims.pdf

1464-che-2006-correspondnece-others.pdf

1464-che-2006-description(complete).pdf

1464-che-2006-drawings.pdf

1464-che-2006-form 1.pdf

1464-che-2006-form 26.pdf

1464-che-2006-form 3.pdf