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