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JTI Chip Antenna Mounting and Tuning Techniques

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This technical note is also available in PDF Format: pdfJohanson Technology Antenna Mounting Techniques (336KB)

 

Outline

 
  • Chip Antenna Characteristics
  • Antenna Selection Considerations
  • Circuit Design Constraints
  • Layout Tips


Ultimate Goal → To Maximize Performance

 

Motivation

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

 

Pros

 
  • Chip antennas are small, cheap and performs well.
  • Bulky external “whip” type antennas are thing of the past.

 

Cons

 
  • Must be accounted for during initial circuit design stage
  • Interference, proximity de-tuning & degradation concerns.

 

LTCC Chip Antennas

LTCC Chip Antennas

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 “No-GND” metal-free space necessary.
  • Small form factor, thin profile & light weight

 

Chip Antenna Characteristics - 2

 
  • Omni-directional radiation.
  • Linear Polarization.
  • Mounting configuration flexibility.
  • Frequency range supported: 0.08 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
  • Average Gain
  • Radiation Pattern requirements

 

Antenna Selection Considerations - 2

 
  • Successful Antenna design means harmonious interaction of the “seven” parameters (next page).
  • Additional considerations for diversity systems – e.g. MIMO
  • Overall performance is always system dependent.

 

Circuit Design Constraints

 
  • Size of the Circuit board.
  • Layout of other board components.
  • Complexity of circuit.
  • Proper GND/No-GND dimensions and clearances.
  • “Tuning” Matching Circuitry
  • Shielding
  • Suitable Enclosure (material)

 

Circuit Design Constraints

 
  • Size of the Circuit board.
  • Layout of other board components.
  • Complexity of circuit.
  • Proper GND/No-GND dimensions and clearances.
  • “Tuning” Matching Circuitry
  • Shielding
  • Suitable Enclosure (material)

Layout Tip 1

 

Layout Tips - 2

Layout Tip 2

  • Don’t put any metal objects or batteries (if applicable) above or below the yellow region
  • Keep away any other metals from clearance area.

 

Layout Tips - 3

Layout Tip 3

  • Further examples of good antenna placement schemes

 

Layout Tips - 4

Layout Tip 4 Layout Tip 4
  • Antenna placement schemes for antenna diversity systems

 

Antenna Matching -5

A. Antenna Matching Setup

Test Board matching example

A. Antenna Matching Setup

 

B. Measuring Steps

  1. One-port (S11) calibration for N.A. (Network Analyzer) Open-Short-Load for desired operating bandwidth
  2. Mount probe (semi-rigid RF cable for our example) onto PCB and connect to N.A.
  3. Measure S11 of test board without antenna or any matching components and save as: →S11_open →save trace to memory of N.A.
  4. Measure S11 of test board with antenna and series 0Ω resistor mounted and save as: →S11_antenna
  5. Set N.A. to data/memory mode (S11_antenna/S11_open) and display/save as: →S11_match
  6. Match the trace of S11_match to 50Ω (center of Smith chart at the desired frequency)

 

  1. Probe+Feed Line Smith chart display from 1-4GHz
    (not-normalized)
 
  1. Probe+Feed Line
    (normalized)
Matched Antenna Example   Matched Antenna Example
    Test Board matching example

 

  1. Probe + Feed Line + Antenna Smith chart display from 1-4GHz
    (not-normalized)
 
  1. Probe + Feed Line + Antenna
    (normalized)
Matched Antenna Example   Matched Antenna Example
    Test Board matching example

 

Step 1 in matching:
Ant + shunt 3.9nH (normalized)
Matched Antenna Example
    Test Board matching example

 

Step 2 in matching:
Ant + shunt 3.9nH + series 1.5pF (normalized)
Matched Antenna Example
  Test Board matching example

 

Matched Antenna Example

Matched Antenna Example

 

Conclusion – How to design

  • 1st – Determine the antenna location and space available on board
  • 2nd – Select the most appropriate antenna model
  • 3rd - Implement antenna in conformance with design rules
  • 4th – Match antenna to your system
 
 

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