AN768

Rev. 0.2

7

Figure 7. WES0034-01-AWH868M-01

Panic Button ILA (WES0035-01-APF868P-01) and Panic Button IFA (WES0036-01-APL868P-01) along the

circumference: These type of antennas are very low-cost, small monopole type antennas. Typically they fully

surround the small circuitry along the PCB edge, which allows them to have the highest possible radiation

efficiency and make impedance tuning easier.

These antennas are basically the same as the first antenna type (e.g. WES0031-01-APL868M-01).The antenna

trace also runs along the PCB circumference, but the PCB is significantly smaller.

Due to the very small size, the gain is low, especially at low frequency bands, and these solutions are also sensitive

to the hand effect. Typically, these antennas are used in wristband panic buttons applications, where strong hand

effect exists. Here the antenna is parallel with the hand, and, thus, the hand degrades the radiation. Fortunately,

the range requirement is also low in most cases.

The main difference between the ILA and IFA is that the ILA needs a parallel matching capacitor (5.6 pF here) at

the input, while the IFA is inherently matched. However, the post tuning of the ILA is easier. In the upcoming

document “Antenna Design Guide for Single Ended 50

 Antennas,” Silicon Labs will provide a detailed

description of the tuning process, both for the ILA and IFA antennas. The panic button antennas given in this Matrix

are tuned without hand effect, so the range achieved with them is better than what one could see with the hand

effect.

Figure 8. WES0035-01-APF868P-01