Chip Antenna Mounting and Tuning Techniques

Chip Antenna Mounting and Tuning Techniques

Motivation

• 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.

Pros

• Chip antennas are small, cheap and perform well.
• Bulky external "whip" type antennas are a thing of the past.

Cons

• 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