SI4703 查看數據表（PDF） - Silicon Laboratories

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SI4703

Si47XX ANTENNA, SCHEMATIC, LAYOUT, AND DESIGN GUIDELINES

Silicon Laboratories 

AN383

Figure 12. Stub Antenna in Wire Implementation

5.1.1. Embedded Stub Antenna—Wire Implementation

A stub (wire) antenna is typically a floating wire that is approximately 10 cm in length and is embedded inside the

device with FM functionality. The antenna can be longer if the device's industrial design will accommodate it. The

material for a stub (wire) antenna can be an actual wire or a PCB trace. PCB traces can be either in flexible

packaging (flexible PCB trace) or as a trace on the PCB. The 24AWG wire has been experimentally proven to have

optimal performance.

The stub (wire) antenna should be placed such that it is not obstructed by a ground plane or shield. This

requirement can be met by placing the antenna on an extremity of the device (e.g., top or bottom) or on the

perimeter. The antenna can also be embedded in the device plastic or outside the plastic with a protective

covering. The flexible PCB antenna should be between a PCB and the device plastic such that the antenna trace is

not obstructed by a ground plane or shield. The antenna is connected to pin 4 and resonated with the on-chip

variable capacitor.

5.1.1.1. Matching

A 10 cm stub (wire) antenna has a capacitive impedance, typically more than 1~2 pF. The antenna is matched by

resonating it with a shunt inductor and the on-chip shunt variable capacitor. See Appendix B for inductor value

calculation.

26

Rev. 0.8

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