RECONFIGURABLE MICROSTRIP ANTEENA
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PRESENTED BY
UPALI APARAJITA DASH

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RECONFIGURABLE MICROSTRIP ANTEENA
Microstrip Antenna
 A microstrip patch antenna offers a low profile, i.e. thin, and easy manufacturability, which provides a great advantage over traditional antennas.
 The microstrip technique is a planar technique used to produce lines conveying signals and antennas coupling such lines and radiated waves.
 Microstrip array antennas, i.e., microstrip antennas having an array of microstrips, may be used with applications requiring high directivity.
 Microstrip antennas can be designed to produce a wide variety of patterns and polarizations, depending on the mode excited and the particular shape of the radiating element used.
Important Features of Microstrip Antenna
 A patch antenna is a narrowband, wide-beam antenna fabricated by etching the antenna element pattern in metal trace bonded to an insulating dielectric substrate with a continuous metal layer bonded to the opposite side of the substrate which forms a ground plane.
 Because such antennas have a very low profile, are mechanically rugged and can be conformable, they are often mounted on the exterior of aircraft and spacecraft, or are incorporated into mobile radio communications devices.
 Another main feature is, ability to have polarization diversity. Patch antennas can easily be designed to have Vertical, Horizontal, Right Hand Circular (RHCP) or Left Hand Circular (LHCP) Polarizations, using multiple feed points, or a single feed point with asymmetric patch structures. This unique property allows patch antennas to be used in many types of communications links that may have varied requirements.
Rectangular Patch Antenna
 The rectangular patch antenna is approximately a one-half wavelength long section of rectangular [microstrip] transmission line.
 When air is the antenna substrate, the length of the rectangular microstrip antenna is approximately one-half of a free-space wavelength .
 As the antenna is loaded with a dielectric as its substrate, the length of the antenna decreases as the relative dielectric constant of the substrate increases.
 The dielectric loading of a microstrip antenna affects both its radiation pattern and impedance bandwidth. As the dielectric constant of the substrate increases, the antenna bandwidth decreases which increases the Q factor of the antenna and therefore decreases the impedance bandwidth.
Transmission line model of microstrip antenna
 It is the easiest of all but it yields the least accurate results and it lacks the versatility
 Basically transmission line model represents the microstrip line model represents the microstrip antenna by two slots, separated by a low impedance Zc transmission line of length L.
 Gives good physical insight.
Fringing Effect in Transmission Line Model
 Because the dimensions of the patch are fine along the length and width, the fields at the edges of the patch undergo fringing.
 The amount of fringing is a function of the dimensions of the patch and the height of the substrate.
 For the principal E-plane (xy plane) fringing is a function of the ratio of length of the patch L to the height h of the substrate (L/h) and the dielectric constant of the substrate.
 Since for microstrip antennas L/h>>1,fringing is reduced; however it must be taken into account because it influences the resonant frequency of the antenna.
Effective Length and Width
 Due to fringing effect, electrically the patch dimensions will be bigger than its physical dimensions. A formula to calculate the effective length Leff is shown below.
 Where, an approximate relation for the normalized extension of length ΔL is given below:
 For an efficient radiator, a practical width that leads to good radiation efficiencies is,
 A Conductance: Each radiating slot is represented by a parallel equivalent admittance Y(with conductance G and susceptance B). The slots are labeled as Θ1 and Θ2. The equivalent admittance of a slot is given by
Y1 = G1 + B1
 Where for a slot of finite width (W)
 For
 Cavity Model of Microstrip Antenna :
 Microstrip antennas resemble dielectric loaded cavities , and they exhibit higher order resonances.
 The normalized fields within the dielectric substrate ( between the patch and the ground plane) can be found more accurately by treating that region as a cavity bounded by electric conductors (above and below it) and by magnetic walls( to simulate an open circuit) along the perimeter of the patch.
 Charge Distribution and Current Density
 Cavity Model of Rectangular Microstrip Antenna
 E-plane and H-plane of Microstrip Antenna
Gain and Directivity
 The gain of an antenna is the radiation intensity in a given direction divided by the radiation intensity that would be obtained if the antenna radiated all of the power delivered equally to all directions.
 The definition of gain requires the concept of an isotropic radiator; that is, one that radiates the same power in all directions.
 An isotropic antenna, however, is just a concept, because all practical antennas must have some directional properties
 Nevertheless, the isotropic antenna is very important as a reference. It has a gain of unity (g = 1 or G = 0 dB) in all directions, since all of the power delivered to it is radiated equally well in all directions.
Antenna Polarization
 The term polarization has several meanings. In a strict sense, it is the orientation of the electric field vector E at some point in space . linear and either vertical or horizontal .
 At sufficiently large distances from an antenna, beyond 10 wavelengths, the radiated, far-field wave is a plane wave.
 If the E-field vector retains its orientation at each point in space, then the polarization is linear; if it rotates as the wave travels in space, then the polarization is circular or elliptical. In most cases, the radiated-wave polarization is linear and either vertical or horizontal. At sufficiently large distances from an antenna, beyond 10 wavelengths, the radiated, far-field wave is a plane wave.
Input Impedance
 There are three different kinds of impedance relevant to antennas.
 One is the terminal impedance of the antenna.
 characteristic impedance of a transmission line.
 wave impedance .
 Resistance vs frequency
WLAN
 A wireless LAN (or WLAN, for wireless local area network, sometimes referred to as LAWN, for local area wireless network) is one in which a mobile user can connect to a local area network (LAN) through a wireless (radio) connection.
 Wireless LANs have become popular in the home due to ease of installation, and the increasing popularity of laptop computers. Public businesses such as coffee shops and malls have begun to offer wireless access to their customers; sometimes for free. Large wireless network projects are being put up in many major cities: New York City, for instance, has begun a pilot program to cover all five boroughs of the city with wireless Internet access.
 It operates under IEEE 802.11 standard.
 Frequency band of operation is 2.4 Ghz and 5 Ghz.
 Data rate 54 mbps.
 Coverage range -30 mts.
WIMAX
 Wi Max is a Broadband Wireless Access (BWA) technique has its full form as “World wide interoperability for microwave Access
 Wi MAX offers fast broadband connection over long distances.
 The interpretability between different vendor’s product is the most important factor when comparing to other techniques.
 IEEE 802.16 standards
 Wi-MAX stands for World wide Interoperability for microwave Access.
 Coverage range- 30 miles.
 Frequency band – 2 to 11 Ghz.
 Data rate 75 mbps.
 Rectangular Patch Simulated Using IE3D And Optimized Using Genetic Algorithm To Get 3.6 Ghz Resonant Frequency.
 Patch Designed Using IE3D And Using Genetic Algorithm Optimization Toget 2.7 Ghz Resonant Frequency.
WAY AHEAD………………………
01- Improvement on current design
a- The gain of the antenna without slit is very less, suitable optimization is to be done to get high gain for the antenna at 3.6 Ghz.
b- Resonant frequency occurs at 2.7 Ghz after introducing slit, suitable optimization is to be done to shift the resonant frequency to 2.4 Ghz
c-Proximity coupling is to be done to adjust the bandwidth of the antenna according to WLAN and wi-MAX standards
02- Introducing re-configurability in the slit using RFMEMS( Radio frequency micro elecro mechanical switches).
RFMEMS Switches are to be introduced within the slit so as to switch between WLAN and Wi-MAX frequency bands according to choice.
RFMEMS can be simulated in two ways:
a-By introducing small metal tapes in the slit for switch ON conditions and removing the metal tapes for switch OFF conditions.
b-RFMEMS can be modeled as 2-port networks in ANSOFT-HFSS software
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