Antenna Design Through Mems

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A NTENNA DESIGN

THROUGH MEMSPRESENTED BY:

SWATI CHOUDHARY


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P RESENTATION OUTLINE

Introduction: About MEMSReconfigurable AntennaRF MEMS Switches

Modeling of MEMS SwitchesModeling Of MEMS based AntennaConclusion


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W H AT IS MEMS

Microelectromechanical systems is the technologyof very small mechanical devices driven by theelectricity.

It merges at the nano scale intonanoelectromechanical systems (NEMS) &Nanotechnology.

MEMS are separate and distinct from thehypothetical vision of molecularnanotechnologyoy molecular electronics.


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M ATERIALS FOR MEMS MANUFACTURING

SILICON

POLYMERS

METALS


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MEMS BASIC PROCESSES

BASICPROCESSES

DEPOSITION PATTERNING ETC H ING


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RECONFIGURABLE A NTENNA DESIGNTH ROUG H MEMS

Antennas with capability to change theirradiation characteristics adaptively are generallycalled reconfigurable antennas .

These have been conventionally pursued forsatellite communication applications, where it isoften required to change the broadcast coveragepatterns to suit the traffic change.


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In addition to satellite antennas, reconfigurableantenna systems find applications in collisionavoidance radars. These being of low power

requirements are readily amenable to MEMSbased fabrication technology.

Reconfigurable multi-band antennas areattractive for many military and commercialapplications where it is required to have a singleantenna that can be dynamically reconfigured totransmit or receive on multiple frequency bands.


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Such common aperture antennas result inconsiderable savings in size, weight and coast .

They find application in space-based radar,communication satellites, electronic intelligence,aircraft and many other communications andsensing applications.

MEMS switches are used to connect antennasegments to make antenna reconfigurable.


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Reconfigurable antenna arrays are complexelectromagnetic structures usually comprisingmultilayer planar radiators that are switchedusing a network of MEMS switches.

Significant effort is currently underway todevelop reconfigurable aperture antenna systems(RECAP) in response to the pressing antennabandwidth needs.


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Reconfigurable antennas have received a greatdeal of attention for their applications incommunications, electronic surveillance andcountermeasures by adapting their properties toachieve selectivity in frequency, bandwidth,polarization and gain.

The leading technology for a RECAP system isbased on switchable antenna elements inconjunction with multilayer substrateconfigurations.


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More recently, with the exciting advancements inthe field of microelectromechanical systems(MEMS), miniature micromechanical microwaveswitches with low actuation voltages have beendeveloped that rival the performance of conventional solid-state switching devices.


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RF MEMS S W ITC H ES

Reconfigurable antennas using RF MEMSswitches show unique advantages . The use of MEMS switches has provided a reliablealternative to semiconductor devices. MEMSswitches have higher Q compared tosemiconductor devices.


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These switches plays a vital role while designingan antenna through MEMS technology.

Miniaturized high frequency circuits with highsystem integration and low cost for personal usebecome only possible with the advent of the RF-MEMS technology, which is using MEMStechnology to fabricate the integrated RF circuits.


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RF MEMS switch, in essence, is a miniaturizedversion of the venerable toggle switch.

From a mechanical point of view, MEMSswitches can be a thin metal cantilever, airbridge, or diaphragm; from RF circuitconfiguration point of view, it can be seriesconnected or parallel connected with an RFtransmission line; The contact condition can beeither capacitive (metalinsulatormetal) andresistive (metal-to-metal) and designed to openthe line or shunt it to ground upon actuation of the MEMS switch.


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Such switches have displayed excellent RFcharacteristics, including lower insertion loss,higher isolation, zero power consumption, smallsize.

RF MEMS switches are ideal elements forreconfigurable antennas. One of the goals of antenna design is to minimize the reactance of the device by operating the antenna at itsresonant frequency.


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RF MEMS switches can be used in antennadesign to modify the resonance frequency byphysically changing electrical length (withrespect to wavelength) attributed to capacitiveand inductive reactance.

Reconfigurable antennas using RF MEMSswitches have unique advantages. They offervery low loss switching. This means that biasnetwork for RF MEMS switch, which can beextensive in large antenna arrays, will notinterfere and degrade the antenna radiationpatterns.


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M ODELING OF MEMS S W ITC H ES


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In general, to design a RF MEMS electrostaticactivated switch, the structure of the switchbeam must be chosen so as to produce the lowestpossible insertion loss, the highest possibleisolation, the highest possible switchingfrequency, and lowest possible actuation voltage.


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DESIGN SPECIFICATIONS OF A MEMSS W ITC H

S ignalFrequcy(GHz)

Sw itching freq .(k Hz)

Up- stateca p acitance(fF )

I solation(d B)

I nsertion loss(ohm )

A ctivation Voltage (V )

DC~ 40 30 4 ~6 - 40 0 .2 ~0 .5 2 ~5


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The MEMS design involves:(1 ) design of a coplanar waveguide transmission

line with Z 0 = 50 W characteristic impedance and

short circuit gaps;(2 ) design of a switch beam with optimized

spring constant, materials and beam gap heightto reduce the activation voltage with reasonableisolation


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D IAGRAM O F A RECON F IGURABLE ANTENNA SYSTEM

R adiating E lementsC or p orate Feed N et w ork

MEMS Sw itching N et w orkB ias C ircuitFrequency S electiveS urfaceP hotonic B and -ga pS tructure


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MODELING O F MEMS-BASEDRECON F IGURABLE

ARRAY

A reconfigurable linear slot antenna tuned viacantilever MEMS switches (MEM-antenna) hasbeen modeled using the method of moments.

Switches are represented by a shunt capacitanceof 50 fF in up position and by a 5 shuntresistor in down position.


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The length of the stub is selected to be nearlyquarter-guided wavelength in the upper band.The dimensions of the stub, i.e. the characteristicimpedance of the stub, affect the resonantfrequencies and the separation between thefrequencies.

6 MEMS cantilever type capacitors are placedonto the stub to change the characteristicimpedance of the stub, and to dynamically loadthe antenna


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GENERAL VIE W OF T H E RECTANGULAR SLOT ANTENNA LOADED W IT H 6 MEMS CANTILEVERTYPE CAPACITORS


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The anchors of these cantilevers are attached tothe stub. Two cantilevers supported by theseanchors are suspended over the conductorcarrying the RF signal.

These cantilever type capacitors resemble a T-wing structure which can be actuatedelectrostatically by applying DC voltage betweenthe RF signal line and suspended cantilevers.


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The reflection coefficient characteristic of therectangular slot antenna is measured using CP W RF probes.

It can be seen that the measured antenna has acantilever height of approximately 4 m which isdesigned to be at 2 m. The change in thecantilever height is also verified with SEM andsurface profiler measurement.


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CONCLUSION

At last we can conclude that by using MEMStechnology for designing of Antenna we can havefollowing advantages:

Cost efficiencyLow power consumptionMiniaturizationH igh performance and integration

Functionality can be integrated on the samesilicon or in the same package, which reduces thecomponent count and contributes to overall costsavings.


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Antenna Design Through Mems

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