Matching Network Design For Ultrawideband Antennas
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Matching Network Design For Ultrawideband Antennas

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Matching Network Design For Ultrawideband Antennas Matching Network Design For Ultrawideband Antennas Presentation Transcript

  • MATCHING NETWORK DESIGN FOR ULTRAWIDEBAND ANTENNAS Maria C. Gonzalez MICROWAVE LABORATORY University of California, Davis
  • OVERVIEW
    • PROBLEM STATEMENT
    • ANTENNAS FOR ULTRAWIDEBAND
      • ANTENNA IMPEDANCE
    • BROADBAND IMPEDANCE MATCHING APPROACHES
      • ANALYTICAL
      • REAL FREQUENCY
    • DESIGN CIRCUIT RESULTS
    • CONCLUSIONS
  • 1.INTRODUCTION
    • To obtain MAXIMUM POWER TRANSFER:
    •  the impedance of the generator needs to match the load.
    • LOAD :antennas for ultrawideband (UWB):
    •  Load frequency dependent
    •  the efficiency of the power transmission depends on the impedance matching in the frequency range.
    •  The actual bandwidth performance of the antenna is limited by this factor.
    • TO ENHANCE the bandwidth and efficiency of the antenna, a broadband matching network may be required.
    • THE DIFFICULTY of design of this matching network depends on the antenna and transmitter impedance characteristics.
  • 2.ANTENNAS FOR UWB
    • There are many kinds of antennas proposed for UWB applications.
    • The impedance characteristics of each type differs since the shape, material, and propagation characteristics within the antenna structure are different for each design.
    • Popular proposed Antenna Types :
    • dipole, horn, spiral, bicone, bow-tie, Vivaldi, etc
    • New designs appears in the literature continuously:
  • Source: www.acorde.biz Source: www.ece.vt.edu Source: ece.atilim.edu.tr Source: kom.aau.dk Source: www-mtl.mit.edu
  • ANTENNA IMPEDANCE
    • The impedance of the antenna is in general a complex function. Moreover, the resistance and reactance of the antenna are frequency dependent in a not-linear fashion.
    • EXAMPLE: Measured Impedance of a Vivaldi antenna. From NASA/TM-2004-213057 report
    • R.Q.Lee, 2004
  • 3.BROADBAND IMPEDANCE MATCHING PROBLEM
    •  
    • V 1 + + V 2
    •  
    •  
    • V s Z 11 Z 22
    • S 11 - - S 22
      • Single Matching:
        • Impedance generator: Real
      • Double Matching:
        • Impedance generator: Complex
    • [1] D.C. Youla, “ A new theory of broadband matching”, IEEE Trans. Circuit Theory, vol. CT-11, pp. 30-50, March. 1964
    • DESIGN TECHNIQUES FOR SINGLE MATCHING
    • Analytic Form[1]
      • It requires a load model
      • It requires analytical expression for the transducer power gain
    • Real Frequency Technique[2]
      • It uses measured data
      • No need network topology is assumed
    • [2] H. J. Carlin, “A new approach toGain-Bandwidth Problems”, IEEE Trans. Circuit Theory , vol. CAS-24, N0. 4, April, 1977
    Two-Ports ImpedanceMatching Network Z load (w) R s
  • REAL FREQUENCY TECHNIQUE Measured R Load Matching Network Initial guess R MN Piecewise Linear Approximation R MN = f (q,w) R MN Rational approximation Hilbert Transform X MN Z MN = R MN + jX MN Synthesis Network Actual Gain (q,w) Z Load = R Load + jX Load - Desired Gain Error = g (q,w) Optimization: Find q to minimize Error New q q n w o w 1 w n q o
  • SYNTHESIS CIRCUIT SPECIFICATIONS
    • Software Design Tool: ADVANCE DESIGN SYSTEMS from Agilent
    • Load description is entered in a file
    • Analytical approach:
      • Chebyshev Bandpass filter
      • Order of polynomial :3
      • Low and upper freq.: 27.5-29 GHz
    • Real frequency
      • Same specifications as in the analytical approach
      • Main different: optimization is done in each frequency interval
  • 4.a) CIRCUIT RESULTS:ANALYTICAL
    • Bandpass Network
    • 13 Circuit networks
    • The circuit with the smaller Maximum Passband Error = 0.45640
    Generator Matching Network UWB Antenna Air
  • 4.b) CIRCUIT RESULTS:REAL FREQUENCY
    • 10 Networks
    • The network with smaller Maximum Passband Error = 0.38563
  • COMPARISON
    • Power Reflected = |S 11 | 2
    • Power Transmitted = |S 12 | 2
    • Radiation Efficiency =  =
    Matching Network Antenna Power transmitted = Ploss + Prad Pin G Pref P rad P in ~ P trans P in |S 12 | 2 |S 11 | 2 +|S 12 | 2 Z=50 OHM Zin
  • RADIATION EFFICIENCY
  • CONCLUSIONS
    • To improve performance in UWB communications systems require impedance matching network along the frequency of operation.
    • The design depends on the characteristics of transmitter and antenna
    • To find actual components that realize the impedance transfer function may be difficult
    • The results obtained with the analytical and real technique may not be optimum
    • The real technique give better results than the analytical in the edges, while the analytical gives better result in the center of the band.