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Wideband Micromachined Patch Antenna

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					International Journal of Scientific Research Engineering &Technology (IJSRET)
 Volume 1 Issue2 pp 016-017 May 2012           www.ijsret.org  ISSN 2278 - 0882




                        Wideband Micromachined Patch Antenna
                                                  Manidipa Nath
                                                       AICTR
                                             manidipa.deoghar@gmil.com



  ABSTRACT                                                  developed can be applied to fabricate many passive
                                                            components and can be used to replace other
  A rectangular patch centered over a cavity and fed
                                                            technologies gradually.
  by a microstrip line on high index Silicon based
  substrate    is investigated using micromachined
  technology. This fabrication technique is used to                II.DESIGN
  laterally remove the material underneath the              The rectangular microstrip patch antenna was
  specified cavity region. It has been observed that        designed      using a standard design procedure, For
  bandwidth increases from 2.9% for the regular             excitation, a centre microstrip feed line was used
  antenna to 5% for Micromachined patch.                    using a relative permittivity of 11.7 for silicon and a
  Keyword- Cavity, substrate, Microstrip line               substrate thickness of 500 micrometer .The antenna
                                                            dimensions were calculated to a resonant length of
    I.    INTRODUCTION                                      l=1.21 mm and width 1.91 mm. The microstrip
  In this work cavity model is used to predict the          feed line is .65 mm wide corresponding to a 50ohm
  effective dielectric constant of the mixed air-silicon    line. A commercial code is used for simulation and
  region. A quasi-static model based on series              to maintain a good accuracy of simulation 15 cells
  capacitance is used to determine the patch                per wavelength at the shortest wavelength is
  capacitance. Effective dielectric constant of 2.2 is      maintained        Antenna parameters are extracted
  achieved for a mixed air-silicon ratio of 1:1.            during post processing.

  Rectangular patch designs are fabricated on Silicon
  substrate (relative permittivity of 11.7) having
  thickness of 500 microns. The patch is fed by a 50
  ohm Microstrip feed line which is fabricated and
  mounted on the test fixture. Initial design has been
  etched into the wafer using a method called bulk
  micromachining. The parametric study gives the
  dimension of the patch and feed line under design
  consideration with a given thickness and resistivity
  of silicon substrate. The dimension of feed line
  circuits has been optimized using software tools. The
  design methodology can be readily applied to
  performance       characterization     and     design
  optimization. The fabrication process involves 3-D
  photoresist mold, which fill both upper and lower
  recess regions with metals and finally the photoresist
  mold is removed. The micromachining technology            Figure1.      Micromachined        patch      antenna
  offers     small    tolerances     and     favourable     configuration
  manufacturing costs. The technology once




                                                   IJSRET @ 2012
International Journal of Scientific Research Engineering &Technology (IJSRET)
 Volume 1 Issue2 pp 016-017 May 2012           www.ijsret.org  ISSN 2278 - 0882


  The antenna was designed for an etch depth of 300       Measurement of the far field radiation pattern has
  micrometer and etch profile with sloping walls was      been done and is shown in figure 3.The 3 dB beam
  maintained at a inclination of 45 degree for the        width is 100 degree in the E & H plane. A scaled
  geometry. The synthesized dielectric constant of the    size model of the antenna at a lower operating
  composite substrate has been determined and             frequency has been fabricated and measured.
  simulations have been performed to obtain
  synthesized permittivity of the composite substrate.
  The comparison of the patch on RT duriod (2.2)
  substrate shows bandwidth of 1GHz compared to
  that on Silicon substrate as 1.48 GHz. Other antenna
  parameters like radiation efficiency and gain also
  improves with micromachined antenna.

     III.FABRICATION
  A cavity was etched under the area of microstrip
  antenna and then filled with lower permittivity
  material such as Silicon dioxide. A metal layer was
  added at the horizontal planar interface between the
  low permittivity material and the silicon dioxide.
  Simulation has been done in FDTD code and
  fabricated antenna radiation pattern has been
  measured. Silicon antenna pattern exhibits many
  ripples, but micromachined antenna pattern is much
  smoother. It was observed that H plane pattern is       Figure 3: E and H plane radiation patterns for (a)
  much smoother and almost same whereas the electric      patch antenna on Silicon substrate at resonance
  fields mounted on metallic holder that served as        frequency 21.5 GHz and (b) scaled model on a
  ground plane significant difference in the radiation    duroid substrate at resonant frequency of 20.2 GHz
  pattern.
                                                                 V. CONCLUSION
      IV.RESULTS
                                                          In this paper a planar antenna structure is presented
  The simulated results of the input match and the        and evaluated in terms of return loss. The SiO2
  measured result from the fabricated patch antenna is    material was used to get better performance in terms
  shown in figure 3.A match better than -20 dB is         of return loss bandwidth and radiation pattern.
  observed with a -10 dB bandwidth of 1.48 GHz.           Antenna performance with different low dielectric
                                                          constant material is under investigation.

                                                              VI. REFERENCES
                                                          [1]   Papapolymerou     I,   Franklin  Drayton
                                                          R,Ketehi,L.P.B., “Micromachined Patch Antenna”
                                                          IEEE Trans Ant & propagation, Vol 46, pp 275-
                                                          283,1998.


  Figure 2 Reflection coefficient of the simulated and
                  measured antenna




                                                 IJSRET @ 2012

				
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Description: A rectangular patch centered over a cavity and fed by a microstrip line on high index Silicon based substrate is investigated using micromachined technology. This fabrication technique is used to laterally remove the material underneath the specified cavity region. It has been observed that bandwidth increases from 2.9% for the regular antenna to 5% for Micromachined patch.