Esd Protection By Λ/4 Short Stub - Furuno GN-86F User Manual

ESD Protection by λ/4 Short Stub
2.3
The implementation of λ/4 short stub is the best way to improve the product's robustness against ESD
coming through RF line. λ/4 short stub is structured with the microstrip line, and the input impedance
depends on the electrical length of it. So it is very important to design the electrical length of λ/4 short stub
correctly.
Well-designed λ/4 short stub has features as below.
- High impedance in GPS/GNSS signal frequency band to minimize the insertion loss.
- Low impedance in other frequency band to bypass the ESD energy to ground.
- No additional component required.
MASC is also very useful to design λ/4 short stub correctly and efficiently. Figure 2-7 shows an example of
calculation result .
In case of using 87 series module, which can receive GPS/Galileo and GLONASS, the frequency should be
set to 1,589 MHz as the center frequency of both constellations. In case of using 86 series receiver module,
it should be set to 1575.42 MHz as the center frequency of GPS/Galileo signal.
Figure 2-7 An Example of λ/4 Short Stub Line Length Design by MASC
Figure 2-8 shows an example of the simulation result on Insertion Loss-Frequency characteristics of λ/4
short stub shown in Figure 2-7 by using Agilent ADS
only 0.281 dB at 1.589 GHz, and the variation of insertion loss between 1.234 GHz to 1.830 GHz is less
than 0.1 dB. It means that the λ/4 short stub design is not critical against the in insertion loss.
In case of using active antenna, this loss is compensated by the LNA in the active antenna, and the total
system NF (Noise Figure) won't be changed. Therefore there is no negative impact from inserting λ/4 short
stub in this case.
In case of using passive antenna, it can cause the degradation of receiver sensitivity. However, the loss
itself is very small, and the benefit to implement the λ/4 short stub is significant for protecting the module
from ESD stress. Therefore it is highly recommended to install λ/4 short stub even in the passive antenna
case.
FURUNO ELECTRIC CO., LTD. All rights reserved.
FURUNO GPS/GNSS Receiver 86/87 Series User's Design Guide
TM
software. This result shows the insertion loss will be
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SE13-900-001-06