paper ijmet iaeme may 2012

International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 6340(Print), ISSN 0976 6359(Online) Volume 3, Issue 2, May-August (2012), IAEME

108

DEVELOPMENT AND REALIZATION OF LIGHT WEIGHT HIGH POWER MULTIPLEXER COMPONENT FOR SPACE PAYLOAD

SYSTEM Prof. Bipin D. Patel#1, A. R. Srinivas*2,Prof. D. A. Patel#3

#1, #3Sankalchand Patel College of Engineering, Mechanical Engineering Department, Gandhinage-Ambaji State Highway Link Road, Visnagar-384315,

Dist. Mahesana, State: Gujarat, India. Telephone: (02765) 220417, Mobile (091) 09909468081.

#1Emai:[email protected] #3Email: [email protected]

*2 Space Application Centre, Scientist/SAC/ISRO, Ahmedabad, India.

Telephone: (079) 26915284, Mobile (091) 9427304333. *2Emai:[email protected]

ABSTRACT

To reach up to the present need development of the high power application multiplexer for satellite communication system which provides stable RF performance over operating temperature range is essential.Thispaper work deals with one of the satellite component, which is called as multiplexer (MUX).The performance of the MUX depends on the dimensions of its components. These filters operate in high temperature environment which are seen in operating life time of the satellite in space. When RF energy is passed inside the cavity heat is dissipated in the cavity. Thermal expansions/contraction occurs due to heat dissipation and material property variation. The presence of thermal gradients will cause stress, strain, and deformation in the components which in turn cause changes in the functional performance of MUX.To eliminate these effects of thermal expansion and provide stable RF performance over the range of operating temperature a technique called temperature compensating mechanism is proposed.Also to reach up to the present need the Conventional MUX made from Invar material has higher cost and heavy weight with lower operating temperature range up to 140 watt power is replaced by light weight Novel multiplexer has operating temperature range as high as 250 watts to 400 watts. The objective of such multiplexer is minimizing the weight and size with handling a very high power than the conventional multiplexer. Thiswork is carried

INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING AND TECHNOLOGY (IJMET)

ISSN 0976 6340 (Print) ISSN 0976 6359 (Online) Volume 3, Issue 2, May-August (2012), pp. 108-119 IAEME: www.iaeme.com/ijmet.html Journal Impact Factor (2011): 1.2083 (Calculated by GISI) www.jifactor.com

IJMET I A E M E


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out by using FEA simulation tools and the same option is tested by experimentally by fabricating the real component is explained in this paper.

Keywords: multiplexer, compensation mechanism, diaphragm, parallel cavity.

INTRODUCTION

Multiplexer is one of the components of the satellite transponder which is used in a communication system according to the power requirement of the filter. It segregates different radio frequencies (RF) of microwave energy to different channels according to the band width allocation [1].

Figure 1: Conventional Multiplexer

The Conventional Multiplexer has six channels connected by single manifold as shown in figure 1. Conventional Multiplexer contains of circular cavity filter, irises, input adapters, output adapters, manifold, rigid bracket, flexible bracket, base plates etc. All these components are assembled to meet a defined functional performance and are joined together in a sequential process. Mostly, all radio frequency devices are subjected to temperature variation. Heating and cooling is caused by factors such as resistive power dissipation, ambient temperature changes, and thermal radiation. During the operating life of such multiplexer in a space, it has to withstand stress due to thermal excursion which can hamper the functional requirement of the multiplexer. Therefore, minimizing or eliminating the effect of temperature excursion on the multiplexers is a major concern for the radio frequency designer and becomes the scope of the present work.

To keep these problems at bay many conventional methods uses materials like Invar, an alloy of Iron, Cobalt and Nickel having almost an invariable Coefficient of Thermal Expansion(CTE) of the order of 1 to 1.5 parts per million. While CTE of invar controls the dimensional stability of the filters but due to certain its high density, poor mach inability, low thermal conductivity and dependence of its CTE on temperature makes Invar based multiplexer as shown in figure 1. This Invar based multiplexers are not only very heavy and cumbersome but consumes larger life cycle development time, reaches very high temperature ultimately rendering them, incapable, of handling high carrier signal powers and thereby forming a highly cost ineffective methodology of producing multiplexers. Combinations of different materials with different linear coefficient of


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thermal expansion , when subjected to predominant thermal excursions tend to develop complex thermal stress fields. Under the influence of such thermo structural stress fields the component will tend to deform and deviate from its tolerance limits, thereby affecting the design functionality and performance of system.

Therefore the new generation multiplexers are looking at light weight, cost effective and high conductive materials for development of filters. Aluminium alloy with many years of proven space heritage has low density, less costly and has good thermal conductivity to form a viable alternative for construction of the filter. Aluminium alloy has a good mach-inability with favorable electrical properties and excellent thermal conductivity. It can handle very high RF powers with marginal temperature rise and thus enables the construction of a low cost and low development cycle time filters for the above said multiplexers. Nevertheless, its high CTE (24ppm) is principal disadvantage causing more frequency drift than conventional Invar filters. To overcome this effect of high CTE of aluminum material a technic called thermal compensating mechanism using a plate and rod is proposed is a potential area of research and form thethrust area for the present work also[3].

Figure 2: Novel Multiplexer To reach up to upcoming requirements need a channel power as high as 250 watts to 400 watts the research has been ongoing by two different ways. Firstly the Invar based multiplexer is built from Aluminum alloy material[5] and secondly the conventional multiplexer is replaced by newly conceptual design i.e. Novel multiplexer as shown in figure 2. The main component of such Novel multiplexer are top cavity, bottom cavity, input/output adaptor, base plate, manifold etc. are built from a lightweight Aluminum alloy material. Also thermal compensating mechanism by plate and rod is used to eliminate the effect of high CTE of aluminum material. The objective of such multiplexer is minimizing the weight and size with handling a very high power than the conventional multiplexer.

COMPENSATION MECHANISM The function of compensation mechanism is bringing back the volume of the resonator cavity to its initial value even at the higher temperature and hence eliminate the effect the high CTE of aluminum based parallel cavity filter. The component of such thermal


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compensating mechanism is the control rods and plate as shown in figure 3. The function of the control rods is to hold the plate at its original position under the thermal excursion. It has threaded and non-threaded portion. Invar is selected to have less or no expansion in control rods. Four control rods are required to hold the plate in place. Control rods are designed to withstand torque, buckling and bending criteria. The shape of plate is rectangular and is made up of invar material. The thickness of plate is decided from the point of view of structural rigidity so that the plate does not deform. Four holes are provided at corners to hold control rods and one hole at the center for tuning screw.

Figure 3: Parts of compensation mechanism Parallel Cavity filter is made up of aluminum 6061 T6 having high co-efficient of thermal expansion (24x10-6 oC-1) these property will cause higher expansion and contraction when subjected to temperature excursion and therefore very severely affect the functional performance of system. Cavity filter carries high power microwave energy and heat is dissipated in the cavity. This heat will cause temperature of cavity to rise and being aluminum cavity, it will expand to 24 parts/million. When cavity is expanded the volume of cavity will increase. This will change microwave frequencies which depend upon volume of cavity. It is required to bring back the volume of the cavity to the initial value and always maintaining at this value even within the temperature excursion. Therefore temperature compensation mechanism will aim to counter the effect of expansion and contraction produced due to temperature excursions. This mechanism will try to compensate change in volume, when cavity expands the diaphragms expands so that plunger expands, which pushes top plate, but top plate being invar and rigid will restrict the expansion and create a counter effect on the diaphragm applying retracting force on the plunger which in turn pushes diaphragm into the cavity and thus changes the volume of cavity to its original volume hence compensating the volume change.

FINITE ELEMENT ANALYSIS Finite Element Method is used for analysis and simulation of the thermo-structural environment to predict the compensation of the various problems under consideration. The Parallel cavity filter assembly experiences complex thermo structural environment. So Finite Element Analysis is carried out by considering the following boundary condition for both steady state thermal and structural analysis.

Boundary Condition: Thermal contact conductance between metal to metal=3000 W/m2C. Heat flow in right side cavity=8 W.


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Heat flow in left side cavity=8 W. Ambient temperature =25 C. All surface exposed to atmosphere are given convection at 25 C with film

coefficient of 10 W/m2.

Simulation under free-free condition: To develop some reference condition simulation of the parallel cavity without any compensation mechanism carried out. The Computer Aided Design model and Mesh model with mesh charecteristics for the parallel cavity is shown in the following figure 4.

Figure 4: CAD and Mesh model of parallel cavitywithout compensation mechanism

Mesh characteristics: Number of nodes = 41690 Number of element = 21134 Steady state thermal analysis carried out by implementing boundary conditions mentioned above and resultant temperature distribution profile is achieved. Thermo structural analysis carried out by considering previously achieved temperature as loading condition and constraining four holes of the bottom cavity. Deformation profiles of system and diaphragm are as shown in figure 5.

Figure 5: Deformation profile of the diaphragm and parallel cavity filter

Table 1 Simulated results of parallel cavity filter without compensation mechanism. Maximum temperature on system 86

oC

Maximum deformation of cavity 134 m

Maximum deformation at the 120 m


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center of diaphragm Compensation 14 m Maximum stress on the diaphragm 3 MPa

Simulation under constrained condition:

The finite element analysis of the parallel cavity with plain diaphragm with integrated plunger is carried out under three different configuration of the plate and rod mechanism.

1. Conventional Plate and rod mechanism 2. Extended plate and rod mechanism 3. Modular plate and rod mechanism

The Computer Aided Design model for the parallel cavity with plain diaphragm under three different configuration of plate and rod mechanism are shown in the following figure 6. The geometry of the diaphragm, cavity and the base plate are assigned with aluminium material. The geometry of the plate and rod are assigned with Invar material to make it more stiff.

Figure 6: CAD model of parallel cavity filter with plain diaphragm under compensation mechanism

The finite element model of parallel cavity with plain diaphragm meshed with FEA software with tetrahedron coupled field solid element is shown in figure 7 with following mesh characteristics.


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Figure 7: Mesh model of parallel cavity with plain diaphragm under compensation mechanism

Table 2 Mesh characteristics of plate and rod mechanism. Plate Type Conven-

tional Extended Modular

Number of elements

25026 23517 23020

Number of nodes

513212 51021 50771

Steady state thermal analysis is carried out by implementing boundary conditions mentioned above and resultant temperature distribution profile is achieved. Thermo structural analysis is carried out by considering previously achieved temperature as loading condition and providing constraints at the four grounding hole of the bottom cavity. Deformation profiles of parallel cavity with plain diaphragm under different configuration of plate and rod mechanism are shown in figure 8.

Figure 8: Deformation profile of the parallel cavity with plain diaphragm under compensation


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The finite element analysis of parallel cavity filter with plain diaphragm with integrated plunger under plate and rod mechanism is carried out by considering three configuration of the plate as listed above and result are listed in table3. By comparing and analyzing the results with each option, the modular plate and rod mechanism find good option for the effective compensation mechanism.

Table 3 Simulated results of parallel cavity filter with plain diaphragm under different configuration of plate and rod mechanism and rod mechanism.

Plate Type Conven-tional Extended Modular

Maximum temperature on system 74 72 78 Maximum deformation of cavity 97 94 106 Maximum deformation at the center of diaphragm 60 42 32

Compensation 37 52 74 Maximum stress on the diaphragm 45 95 80

EXPERIMENTAL TESTING The following figure 9 shows the block diagram of the set up for measuring the deformation with practical thermo structural environment on the system. The experimental assumptions are;

The condition of the thermal loading is assumed to be constant throughout the cycle of operation of the filter whereas in actual environment dissipation of microwave energy in the filter could be random and therefore the generation could be of unsteady nature.

More over in actual environment the heat transfer from the system is through the base plate by conduction. The practical set up consists of supplying heat by means of two heaters having capacity of 5 Watts at 28 Volt and resistance of 157 mounted on the inner circular surface of the cavity.

The temperature sensor is mounted on the top surface of the cavity to measure the temperatures of the system.

Two dial gauges are used on the diaphragm and flange for the purpose of measuring deformation on the diaphragm and flange of the cavity.


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Figure 9: Experimental test setup for parallel cavity Testing of parallel cavity without compensation For comparison and the evaluation of different designs of compensation for parallel cavity, one reference condition has to be set i.e. condition is without any compensation. The figure 10 shows snapshots of the set up for measuring the practical deflection for the parallel cavity filter having diaphragm with integrated plunger made of Aluminum on top of cavity without any compensation mechanism. The configuration is used for reference condition.

Figure 10: Experimental snapshots for parallel cavity without compensation mechanism

Results achieved by experimental measurement of deflection of parallel cavity without compensation are shown in figure11.


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Figure 11: Deformaion & temperature Vs Time graph of experimental results of parallel cavity without compensation mechanism

Testing of parallel cavity under compensation mechanism

Experimentation of the plain diaphragm with integrated plunger under plate and rod mechanism with above said three different configurations of the plate and rod is carried out. The following figure 12 shows the experimental setup for parallel cavity filter under three diffferent plate configuration for mesuring deflection of the diaphragm and cavity to find most effective plate and rod mechanism.

Figure 12: Experimental snapshots for parallel cavity filter with plain diaphragm under compensation mechanism

Experimental results achieved by practical measurement of deflection of parallel cavity with all three plate and rod configuration are listed in table 4 and the same also plotted in separate graphas shown in figure 13.

Table 4 Experimental results for parallel cavity filter with plain diaphragm.

Plate Type Conven-tional Exten-ded Modular Maximum temperature on system 75 76 76 Maximum deformation of cavity 108 109 106 Maximum deformation at diaphragm center 74 68 55

Compensation 34 41 51


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Figure 13: Deformaion & temperature Vs Time graph of experimental results of parallel cavity with plain diaphragm under three different configuration of plate and rod mechanism

The Experimental results of parallel cavity filter of plain diaphragm with plate and rod mechanism under three options of the plate are listed and plotted. By comparing and analyzing the results with each option, the modular plate and rod mechanism find good option for the future experimentation testing under different design parameters for development of effective compensation mechanism.

CONCLUSION

Temperature compensation system is being established as a viable solution for the problems found in the MUX devicessince conventional invar filter being bulky, hard to machine, takes long developmentcycle and is incapable of withstanding high temperature/heat. Various design configuration of the plate and rod mechanism are discussed, simulated and tested and final results are obtained as shown in table5. The modular plate and rod mechanism found to be most effective configuration for realizing required amount of compensation.


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Table 5 Experimental results.

Condition Cavity Temp (oC )

Compensation (m )

Free (without compensation mechanism)

28 145-136= 9 80

29 Under compensation mechanism

27 106-55= 51 76

28

An initial conceptual design of modular plate and rod mechanism is taken as a reference to establish a baseline versionof the mechanism. This baseline design is visualized using CAE tools for modeling and simulation and also the same is tested by experimentation. This work has presented one of the possible solutions to the conventional problems and proposed new techniquescan be implemented in the ongoing activities of space craft development at Space Application Centre (SAC), ISRO. ACKNOWLEDGMENT The authors are thankful to Space Application Center (SAC) for enabling them to work on the project. We deeply acknowledge the knowledge base bestowed on us by SAC official at various levels for generating the solutions proposed.

REFERENCES

[1]C. Kudsia, et.al. (1992) Innovations in microwave filters and multiplexing networks for communications satellite systems,IEEE Digest on Microwave Theory and Techniques, vol. 40, pp. 11331149, June 1992.

[2] D. Rosowsky et. al. (1982), A 450-W output multiplexer for direct broadcasting satellites,IEEE Digest on Microwave Theory and Techniques Symposium, vol. 82, pp. 13171323, September 1982, issue9.

[3]S.Lundquist, M. Yu et. al. (2002), Ku-Band Temperature Compensated high Power Multiplexers,IEEE Digest on Microwave Theory and Techniques, May 15, 2002.

[4]D. J. Small et. al.(2003),"Temperature compensated high power band pass filter," U.S. Patent 6529104, Mar. 4, 2003.

[5]A. R. Srinivas &B. D. Patel, (2011) Validation of light weight thermal compensating mechanism for space craft component, ICESET, Rajkot, India, March-2011.

[6]Fitzpatrick W, (2003) Microwave resonator having an external temperature compensator U.S. Patent 6535087, March 18, 2003.

paper ijmet iaeme may 2012

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