LTCC Chip Antennas – How to maximize performance Johanson Technology Inc. Johanson Technology Inc. 4001 Calle Tecate Camarillo, CA 93012 URL: http://johansontechnology.com Outline Chip Antenna Characteristics Antenna Selection Considerations Circuit Design Constraints Layout Tips Ultimate Goal Æ 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 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 1. 2. 3. 4. 5. 6. 7. 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) GND-bottom layer underneath, prohibited c Layout Tips -1 e c GND-top layer c d No ground area (yellow area) Good Placements c Bad Placements d & e Layout Tips -2 Ground 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 GND GND Further examples of good antenna placement schemes Layout Tips -4 ANT 1 ANT 2 Pattern compensation Antenna placement schemes for antenna diversity systems Radiation pattern “Null” Elimination/Compensation Antenna Matching -5 A. Antenna Matching Setup GND Probe or semi-rigid RF cable Test Board matching example 50 Ω Feed line NO GND π-type Matching Pads (scheme) preferred Soldering to: Connect Probe_GND and PCB_GND Calibration Plane of Network Analyzer(NA) 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: ÆS11_open Æsave trace to memory of N.A. 4. Measure S11 of test board with antenna and series 0Ω resistor mounted and save as: ÆS11_antenna 5. Set N.A. to data/memory mode (S11_antenna/S11_open) and display/save as: ÆS11_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 (notnormalized) 2. Probe+Feed Line (normalized) Test Board matching example 1. Probe + Feed Line + Antenna Smith chart display from 1-4GHz (not-normalized) (not normalized) 2. Probe + Feed Line + Antenna (normalized) (normalized) Test Board matching example Step 1 in matching: Ant + shunt 3.9nH (normalized) Test Board matching example Step 2 in matching: Ant + shunt 3.9nH + series 1.5pF (normalized) Test Board matching example Matched Return Loss chart 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