Antenna Tuning & Layout Techniques

Outline

Chip Antenna Characteristics
Antenna Selection Considerations
Circuit Design Constraints
Layout Tips

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 & Cons

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.

Ultimate Goal is to Maximize Performance

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

Considerations - 1

Size
Frequency Band
Bandwidth
Polarization
Peak Gain
Average Gain
Radiation Pattern requirements

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)

Layout Tips

The ceramic chip antenna and top RF ground must be on the same plane. Substituting the top layer for an inner layer as a ground plane requirement will not work.

A. Antenna Matching Setup

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)

Part Number	2450AT45A100
Frequency Range	2400 - 2500 Mhz
Peak Gain	3.0 dBi typ. (XZ-V)
Average Gain	1.0 dBi typ. (XZ-V)
Return Loss	9.5 dB min.

JTI P/N for Matching Circuit: Cap (1.5pF): 500R07S1R5BV4T Inductor (3.9nH): L-07C3N9SV6T