Satoshi Harada

Key technologies for high-accuracy large mesh antenna reflectors ☆

Abstract Nippon Telephone and Telegram Corporation (NTT) continues to develop the modular mesh-type deployable antenna. Antenna diameter can be changed from 5 m to about 20 m by changing the number of modules used with surface accuracy better than 2.4 mm RMS (including all error factors) with sufficient deployment reliability. Key technologies are the antennas structural design, the deployment mechanism, the design tool, the analysis tool, and modularized testing/evaluation methods. This paper describes our beam steering mechanism. Tests show that it yields a beam pointing accuracy of better than 0.1°. Based on the S-band modular mesh antenna reflector, the surface accuracy degradation factors that must be considered in designing the new antenna are partially identified. The influence of modular connection errors on surface accuracy is quantitatively estimated. Our analysis tool SPADE is extended to include the addition of joint gaps. The addition of gaps allows non-linear vibration characteristics due to gapping in deployment hinges to be calculated. We intend to design a new type of mesh antenna reflector. Our new goal is an antenna for Ku or Ka band satellite communication. For this mission, the surface shape must be 5 times more accurate than is required for an S-band antenna.

AN ULTRA-LIGHT LARGE ANTENNA REFLECTOR FOR COMMUNICATION SATELLITES

To lower the cost and increase the performance of commercial satellite systems, we are developing larger and lighter antenna reflectors than are currently available. To realize this new breed of reflector antennas, we propose a geodesic cable network system whose backbone is a tendon reinforced deployable frame structure. Two issues are fundamental to realizing a successful structure. One is to design a cable network system that keeps its shape even if the support structure is strongly deformed by in-orbit thermal and vibration disturbances. The other is to design an extremely light weight support structure whose structural behavior is non-linear and that can accept high levels of deformation. The results of a preliminary design consideration demonstrate the feasibility of a large deployable mesh antenna reflector whose aperture is 20m and weight is less than 80 kg.

A High Precision Surface Shape Design for Large Deployable Mesh Antenna

We’ve been investigating large deployable mesh antenna. To achieve high surface accuracy for these reflectors, it is required to reduce deformation sensitivity to truss structure displacements. We selected high stiffness for surface cables and low stiffness for supporting cables to reduce the sensitivity. Calculation is performed to clarify its characteristics for real-scale reflector modules. INTRODUCTION We have been developing a modular mesh deployable antenna for S-band mobile communication satellites. Antenna diameter can be varied from 5m to about 20m by changing the number of modules. Key technologies are the antenna structure design (modular structure, mesh-cable system, and deployable support structures)[1][2], the deployment mechanism design, the design tool (OOCD: Object Oriented Coordinate Designer), the analysis tool (SPADE: Simple coordinate Partitioning Algorism based Dynamics of finite Elements)[3] and modularized testing/evaluation methods [4][5][6]. We can obtain surface accuracy of better than 2.4 mm(RMS) (including thermal distortion and elastic vibration due to thruster jetting) with sufficient deployment reliability [7]. In order to expand the application region of modular mesh antennas, we are also examining its application to the Ku-band and/or the realization of much larger antennas. These applications require the reflectors to have even about 5 times lower Fig.1 Modular Mesh Reflector

New Tendon Reinforced Reflector for Large-Scale and Ultra-Lightweight Antenna onboard the Satellite

For a future mobile satellite communication, we’ve been investigating large antenna reflectors. From perspectives of the launch cost, highly lightweight structure is very attractive. In this paper, we investigated the lightweight and large antenna reflector as its aperture is 20m for S-band and its weight is less than 80kg. To realize such a lightweight reflector, it is necessary to reduce the volume or the number of members as possible. Mesh reflectors are composed of support structures and cable networks with metallic mesh. Then, the support structures are deployed and tension the cable networks. We contemplate to reduce the mass of the support structure because it is difficult to reduce mass of cable networks so as to keep its electrical properties. Total mass of the support structure is primary subjected by the size and the number of hinge blocks, that is almost proportional to the volume or the number of members. We propose a new configuration that decreases the members and adopt a slender rib structure with cables (tendon) to reinforce the support structure. The support structure is required to spread the cable network. In other words, the support truss structure has to endure the reactive compressive load caused by cable network tension. Especially, this load is applied at the tip of the rib structure. The compressive load may exceed the buckling load. When the buckling is occurred displacements ascend quickly and support truss couldn’t tension the cable network. To reinforce the support structure, we adopt tendons reinforced structure. In this configuration, tendons constrain ribs each other and suppress the displacement of rib structure. Therefore, tendons reinforce the support structure to endure the compression load and to suppress the deformation of the reflector. To clarify the effect of tendons reinforcement quantitatively, calculations are carried out and experiments are also carried out by using a 3m trial model

Deformed Antenna Pattern Compensation Technique for Multi-Beam Antennas in Broadband and Scalable Mobile Communications Satellites

To create a next-generation mobile satellite communication system that offers large communication capacity, the onboard antenna system must be a multi-beam system consisting of a light weight 20-m class reflector and a light weight 100-beam class antenna feed system. We clarify that the antenna gain decrease created by the reflector surface distortion expected in orbit is relatively large. This paper presents a deformed antenna pattern compensation method that minimizes circuit scale. Validity of the proposed method is confirmed by antenna pattern calculations and experiments on a fabricated array-fed reflector antenna.

Deformed Antenna Pattern Compensation Method for onboard Multi-beam Antennas

To create a next-generation mobile satellite communication system that offers large communication capacity, the onboard antenna system must be a multi-beam system consisting of a light weight 20-m class reflector and a light weight 100-beam class antenna feed system. We clarified that the antenna patterns were deformed by a thermal distortion of the reflector surface and that the antenna gain decrease is relatively large. Our studies confirmed that all of the deformed antenna patterns could be compensated using variable phase-shifters connected to each feed element. This paper proposes a deformed antenna pattern compensation method as an extension of our previous study and describes the results of experiments on a fabricated array-fed reflector antenna that possesses the proposed compensation function.

Buckling Mode Injection Algorithm and its Implementation to Flexible Multibody Analysis Program

Buckling analysis based on the corotational finite element method has been developed for complex flexible multi-body beam structures. This method makes it possible to analyze lightweight deployable beam structures that may be subjected to loads and takes account of geometric nonlinearity. Elastic deformation and buckling during mechanical motion can be handled by the proposed computational algorithm. This algorithm is applied to the deployment analysis of an ultra-light large reflector antenna, which is a geodesic cable network system supported by a tendon-reinforced structure.