Friday, September 17, 2010

Chip Antenna Mounting and Tuning Techniques

Chip Antenna Mounting and Tuning Techniques

  • Chip Antenna an efficient means of "connectivity" to modern portable electronic devices.
  • Miniature portable devices requires small antennas.
  • Can be internalized – i.e. "Concealed" within adevice.

  • Chip antennas are small, cheap and perform well.
  • Bulky external "whip" type antennas are a thing of the past.
  • Must be accounted for during initial circuit design stage
  • Interference, proximity de-tuning & degradation concerns.
Chip Antenna Characteristics - 1
  • Features Ag radiating element encapsulated in ceramic.
  • A quarter-wave ( λ/4 ) monopole system.
  • Works with GND plane to form dipole system.
  • Certain "GND clearance" space necessary.
  • Small form factor, thin profile & light weight

Chip Antenna Characteristics - 2
  • Omni-directional diversity.
  • Linear Polarization.
  • Mounting configuration flexibility.
  • Frequency range supported: 0.75 GHz thru 10 GHz.
  • WiFi, BT, WiMAX, UWB, GSM, CDMA, GPS etc.
  • Suitable for Pick & Place.
Antenna Selection Considerations - 1

  • Size
  • Frequency Band
  • Bandwidth
  • Polarization
  • Peak Gain
  • Ave Gain
  • Radiation Diversity Pattern
Antenna Selection Considerations - 2
  • Successful Antenna design means harmonious interaction of the "seven" parameters.
  • Additional considerations for diversity systems – e.g. MIMO
  • Overall performance is also system dependent.
Circuit Design Constraints
  • Size of the Circuit board.
  • Layout of the other board components.
  • Complexity of circuit.
  • Proper GND/No-GND dimensions.
  • "Tuned" Matching Circuitry
  • Shielding
  • Suitable Enclosure (material)
Layout Tips -1

Layout Tips - 2
  • Don't put any metal plates or batteries above or below the yellow region
  • Keep away any other metals from the GND clearance area.

Layout Tips - 3

  • Further examples of good antenna placement schemes
  • Example of antenna diversity (eliminate low/zero radiation poles)

Layout Tips - 4
  • Antenna placement schemes for Diversity systems

A. Antenna Matching Setup

B. Measuring Steps

  • One port calibration for NA Open-Short-Load
  • Mount probe onto populated PCB and connect to NA
  • Measure S11 of test board without antenna → S11_open → save trace to memory of NA
  • Measure S11 of test board with antenna (with enclosure if applicable) and 0 Ω R mounted → S11_antenna
  • Set NA to data/memory mode (S11_antenna/S11_open) → S11_match
  • Match the trace of S11_match to 50Ω (center of Smith chart at the desired frequency)

Conclusion – How to design

  • Determine the antenna location on board
  • Select the most appropriate antenna model
  • Implement antenna in conformance with design rules

1 comment:

  1. Nice lay out of Antenna mounting and Tunning techniques it is not difficult to understand
    is really great.