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RF-MEMS-BASED-SWITCHABLE-LOW-PASS-FILTER

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									 RF MEMS BASED SWITCHABLE LOW PASS FILTER



M.R.VISHNU PRIYA                          S.AARTHY
Vishnupriya_mr@yahoo.co.in      artiswamy@yahoo.com




                       SECOND YEAR

             DEPARTMENT OF ECE
        K.L.N COLLEGE OF ENGINEERING
                POTTAPALAYAM-630 611




ABSTRACT
   Recent developments in Micro Electro Mechanical Systems (MEMS),
   promises to solve several technological limitations that have plagued the
   wireless electronics for decades. This paper reports the applicability of
   MEMS technology in the implementation of RF switches for the realization
   of switch able low pass filter. The switch and filter are designed and
   simulated for 2 GHz, 3 GHz using HPEEs of simulator.




INTRODUCTION
       The rapid growth of wireless and mobile communications in this decade
has catalysed an increasing demand for a high performance filter with a high
selectivity. The present day switchable filter using a microstrip ring resonator
loaded with two p-i-n diodes has low loss performance and inter-modulation
distortion [1]. By replacing p-i-n diodes with varactor diodes electronically
tuneable filter isolation exceeding 20db with 9% tuning bandwidth has been
demonstrated [2].The need for reduced size and weight and low-loss systems has
stimulated the design of RF systems using MEMS technology [3-4].The MEMS
based switchable filter is possibly the best topology to generate wide stop band,
sharp cut – offs, small size and low insertion loss




PROBLEM STATEMENT
      The objective of this paper is to design and characterize a RF MEMS based
switchable low pass filters. A microstrip transmission line structure is chosen to
realise a low pass filter [6]. An alumina substrate (Є r=9.6) with thickness
0.635mm, Cut-off frequencies 2GHz and 3GHz, source and load impedances
both of 50Ω are chosen. A coplanar waveguide transmission structure is chosen
to realize a MEMS switch as the coplanar structure presents better isolation and
insertion loss [7-10].
DESIGN
MICROSTRIP FILTER
       In this paper a low pass filter is designed using a 5-section 1db equi-ripple
Chebyshev approximation prototype as shown in fig 1. The filter section lengths
are initially approximated by means of equivalent circuit model for short
microstrip line sections, at the critical cut-off frequencies specified as 2 GHz and
3 GHz [6]. The distributed element model of stepped impedance microstrip
model is shown in fig. 2.




C1 , C3 ->End capacitances
L2,L4 ->End inductances,l1,l2,l3, l4 inductive lengths



Fig2.General Microstrip Configuration for a 5-section LPF consisting of
cascaded “Low-high-low” impedance lines
A circuit model simulation is performed using an HPEEs of EM simulator to
obtain the insertion and reflection loss characteristics of the microstrip filter. The
parameters are tabulated in Table 1.1 ,1.2 and 1.3.
Table 1.1: Parameters of the simulation model of microstrip filter




Table 1.2: Simulation parameters for 2 GHz microstrip filter




Table 1.3: Simulation parameters for 3 GHz microstrip filter
RF MEMS BASED SWITCHABLE FILTER
Fig 4: shows the building blocks of switchable Microstrip Filter.
      A microstrip filter with source and load impedances of 50 ohms is combined
with the CPW MEMS switch to form a switchable low pass filter. The RF performance is
simulated for the OFF and ON positions to find the reflection loss and insertion loss of
the filters. The simulated layout is shown in fig. 5. Fig.5: Simulated layout of
switchable microstrip filters




RESULTS AND DISCUSSION
The RF performance of the switchable low pass filters is simulated using HPEEs
of. The S-parameters for the filters has been obtained. Fig: 6 show the Isolation
of Switchable Filter for OFF and ON States for the frequencies 2 GHz and 3
GHz. The simulation results in a -22 dB isolation at 2 GHz and -12 dB isolation
at 3 GHz for ON position. Similarly the S11 parameters for both 2 and 3 GHz are
obtained.
CONCLUSION

The design and simulation of RF MEMS based switchable filter is done for the
ON and OFF states of the switch and filter. Research work is in progress to
design and develop a wideband tuneable filter using RF MEMS technology.
    REFERENCES
    1. V.K. Tripathi and I.Wolff, “Perturbation analysis and design equations for
       open and closed-ring microstrip resonators,” IEEE Trans. Microwave
       Theory Tech., Vol. MTT-32, pp.405-409,Apr.1984.
    2. Y.S.Wu and F.J.Rosenbaum,”Mode chart for microstrip ring
       resonators,”IEEE Trans. Microwave Theory Tech., Vol.MTT-21, pp.487-
       489,July 1973.
    3. Lawrence E.Larson, “Microwave MEMS Technology for Next
       Generation Wireless Communication”-Invited paper.


Contact address
M.R.Vishnu priya,                               S.Aarthy,
4/434 a sundara murugan street,       1-1-21A Tempcy colony
 Thasildhar nagar,                          old vilangudi,
  madurai-20.                                            madurai-18.

vishnupriya_mr@yahoo.com                           artiswamy@yahoo.com

								
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